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We sought to determine if any protective effect of dietary calcium (Ca) or Ca supplements on bone could be at least partially mediated by increased calcitonin (CT) secretion. First we studied 10 healthy premenopausal women (median age, 35.5 years) who were randomized to high or low dietary Ca intake (1752 versus 391 mg elemental Ca per day) for 2 weeks and then crossed over. At the end of each dietary period, blood was drawn on 1 day at 0800, 1200, 1700, and 2000 h to assess diurnal variation of plasma CT levels. CT secretory reserve was assessed on the next day by Ca infusion (2 mg Ca per kg body weight over 5 minutes). Next, we studied 10 healthy premenopausal women who took a low-Ca diet (∼ 400 mg Ca per day) for a 2 week control period. The women were then randomized to high- or low-Ca intake [400 mg dietary Ca ± 1500 mg Ca per day (as supplemental CaCO3)] and then crossed over. At the end of each study period, the diurnal variation in CT was tested on day 1; the CT secretory reserve was assessed on day 3 by an oral Ca load (500 mg as CaCO3)] and on day 5 by Ca infusion. Plasma immunoreactive CT was measured in whole plasma (iCT) and after silica extraction (exCT), predominantly monomeric CT. Neither increased dietary Ca nor Ca supplements affected the diurnal levels of iCT or exCT or augmented plasma CT responses to an oral Ca load. Furthermore, there was no change in secretory reserve for iCT or exCT after Ca infusion. We conclude that short-term Ca administration, in the form of dietary Ca or Ca salts, at the extremes of normal dietary intake and in doses normally used to treat osteoporosis, respectively, does not affect CT secretion in healthy premenopausal women. It seems unlikely that any potential beneficial effects of ingested Ca on the skeleton in women are mediated by CT.

Antiresorptive treatments for postmenopausal osteoporosis have been studied extensively, but due to the volume of published data and lack of head-to-head trials, it is difficult to evaluate and compare their fracture reduction efficacy. The objective of this review is to summarize the results from clinical trials that have fracture as an endpoint and to discuss the factors in study design and populations that can affect the interpretation of the results. Although there are numerous observational studies suggesting that estrogen and hormone replacement therapies may reduce the risk of vertebral and nonvertebral fractures, there is no large, prospective, randomized, placebo-controlled, double-blind clinical trial demonstrating fracture efficacy. The effects of raloxifene, alendronate, risedronate, and salmon calcitonin on increasing bone mineral density (BMD) and decreasing fracture risk have been shown in randomized, placebo-controlled, double-blind clinical trials of postmenopausal women with osteoporosis. Although the increases in lumbar spine BMD vary greatly in these trials, the decrease in relative risk of vertebral fractures is similar among therapies. However, nonvertebral fracture efficacy has not been consistently demonstrated. Combined administration of two antiresorptive therapies results in greater BMD increases, but the effects on fracture risk are unknown. Direct comparisons of clinical trial results should be considered carefully, given the differences in study design and populations. Differences in study design that may influence the efficacy of fracture risk reduction include calcium and vitamin D supplementation, primary fracture endpoints, definition of vertebral deformity or fracture, discontinuation rates, and statistical power. Factors in the study population that may influence fracture efficacy include the age of the population and the proportion of subjects with prevalent fractures. The use of surrogate endpoints such as BMD to predict fracture risk should be approached with caution, as the relationship between BMD changes and fracture risk reduction with antiresorptive therapies is uncertain. Consideration of these results from clinical trials can contribute to clinical judgment in selecting the best treatment option for postmenopausal osteoporosis.

Hereditary hyperparathyroidism-jaw tumor syndrome (HPT-JT) is an autosomal dominant disease (OMIM 145001) that has recently been mapped to chromosomal region 1q21-q32 (HRPT2). Here we report two families with HPT-JT syndrome in which adult renal hamartomas or cystic kidney disease were prominent associated features, possibly representing a new phenotypic variant of the HPT-JT syndrome. In the first family, renal lesions were present in five out of six affected individuals, whereas HPT and JT were seen in four and two cases, respectively. In the second family, JT was found in three of the five affected individuals and two affected members also exhibited polycystic kidney disease. The possibility of the latter cosegregating as a separate autosomal dominant gene can not be ruled out. A sex-dependent penetrance of primary HPT, resulting in predominantly male-affected cases was evident in the two families. Twenty microsatellite markers in the HRPT2 region were typed, in addition to markers in the multiple endocrine neoplasia (MEN) types 1 and 2 regions at 11q13 and 10q11. The disease in these two kindreds was linked to five markers in the 1q21-q32 region (logarithm-of-odds scores: 3.2-4.2), whereas linkage to the MEN1 and MEN2 regions was excluded. Meiotic recombinations detected in affected individuals placed the locus telomeric of D1S215, thus narrowing the HRPT2 region from > 60 to approximately 34 centimorgans. Loss of heterozygosity was studied in seven renal hamartomas from two affected individuals in the first family, as well as in a jaw tumor and a parathyroid tumor from the second family. All renal hamartomas showed loss of heterozygosity at the 1q21-q32 region. The losses invariably involved the wild type allele derived from the unaffected parent, suggesting the inactivation of a tumor suppressor gene in this region.

Existing radioimmunoassays for parathyroid hormone (PTH) in rat plasma are based on cross-reactivity of rat PTH (rPTH) with heterologous antisera. We used the synthetic NH2-terminal fragment of rPTH [rPTH-(1-34)] to develop a homologous radioimmunoassay for circulating PTH. An antiserum to rPTH-(1-34) was raised in a goat (G-813), and the same peptide was used as radioligand (125I) and standard. Purification of the label by high-performance liquid chromatography (HPLC) increased specific binding greater than twofold and sensitivity by 50-100%. With a final antiserum dilution of 1:70,000, maximum specific binding of 30-33%, nonspecific binding of 1-5%, and 50-microliters sample additions, the assay detection limit was 1.8-2.5 pmol/l. A midregional fragment of human PTH did not displace 125I-labeled rPTH-(1-34). HPLC of extracts of rat parathyroid glands and hyperparathyroid plasma showed only a single peak of immunoreactivity that eluted 2 min after rPTH-(1-34). Dose dilution curves for rat parathyroid gland extracts, rPTH-(1-34) added to rat plasma, and endogenous rat plasma PTH all paralleled the standard curve. Immunoreactive PTH (irPTH) was detectable in greater than 90% of fasting normal rat plasma and changed appropriately in response to hyper- and hypocalcemia induced by low-calcium and vitamin D-deficient diets, injections of calcium and EDTA, and after thyroparathyroidectomy. The normal range for rat plasma irPTH was less than 2.0-12 pmol/l, in general agreement with bioassay results of others. Thus rPTH-(1-34) is an excellent immunogen for raising antisera to rPTH, and assays incorporating it may be of great value in studying rat parathyroid physiology.

Plasma concentrations of PTH are much lower for a given calcium or phosphorus level in patients with familial benign hypercalcemia (FBH, or familial hypocalciuric hypercalcemia) than in those with primary hyperparathyroidism; these and other data suggest that there might be tissue hypersensitivity to PTH in FBH. To test this hypothesis, we have used cultured dermal fibroblasts from abdominal skin biopsies of six patients with FBH and six age- and sex-matched controls as surrogate PTH-responsive tissues. Cells in 24-well plastic plates were exposed to vehicle, human PTH-(1-34) (10(-10)-10(-7) M), prostaglandin E2 (10(-6) M), or isoproterenol (10(-4) M) for 10 min in the presence of isobutylmethylxanthine, and cellular cAMP was determined by RIA. All cells responded to PTH with dose-dependent increases in cAMP, and all responded strongly to prostaglandin E2 and isoproterenol. There were no consistent or significant differences between control and FBH fibroblasts in maximal responses to the three agonists, and half-maximal stimulation was achieved with about 10(-9) M PTH in both normal and FBH cells. These data are not consistent with increased tissue sensitivity to PTH in FBH.

We have investigated the effects of PTH-induced desensitization on second messenger interactions in the rat osteosarcoma cell line ROS 17/2.8. Adenylate cyclase activation was assessed by accumulation of immunoassayable cAMP, and cytosolic calcium ion ([Ca2+]i) concentrations were measured in adherent perifused cells loaded with the Ca2(+)-sensitive bioluminescent protein aequorin. Preexposure to rat PTH-(1-34) [rPTH-(1-34); 10(-8) M for 48 h, then 10(-7) M for 24 h] dramatically reduced (by 85%) the cAMP response to fresh challenge [2 min; 10(-9)-10(-7) M rPTH-(1-34)], but the peak PTH-induced rise of [Ca2+]i was not diminished significantly (0-20%). Nevertheless, we did observe other changes in the PTH-induced [Ca2+]i response. Exposure of treated cells to (Bu)2cAMP nearly abolished the [Ca2+]i response to PTH (greater than 80% reduction), but had much less effect on the PTH-stimulated [Ca2+]i increment of the naive cells (less than 35% reduction). Treated cells also had a blunted [Ca2+]i response to PTH in the presence of low extracellular calcium (greater than 60% reduction), but in the naive cells, low extracellular Ca2+ did not significantly diminish the peak PTH-induced [Ca2+]i rise, although low extracellular Ca2+ dramatically reduced the area under this [Ca2+]i transient (greater than 50%). Low extracellular Ca2+ had no influence on the peak [Ca2+]i responses of treated cells to bradykinin or prostaglandin F2 alpha. Although the peak PTH-stimulated [Ca2+]i rise of treated cells in normal Ca2+ medium was not significantly attenuated, the time to half-maximum [Ca2+]i concentration was significantly increased (greater than 100%), and the area under the [Ca2+]i transient was diminished. These alterations in the [Ca2+]i response of treated cells were not observed upon challenge with bradykinin or prostaglandin F2 alpha. Thus, 1) the cAMP and [Ca2+]i responses of ROS 17/2.8 cells to rPTH-(1-34) are not obligatorily coupled; 2) the response of naive cells to PTH includes both the release of Ca2+ from intracellular stores and the entry of extracellular Ca2+; and 3) pretreatment of these cells with rPTH-(1-34) augments the dependence on Ca2+ entry during hormone rechallenge. We propose that the preserved PTH-stimulated [Ca2+]i rise in treated cells results partly from loss of cAMP-mediated inhibition of extracellular Ca2+ entry.

We developed and validated a radioimmunoassay for circulating human parathyroid hormone-related peptide (PTHrP), based on a commercial antiserum to the synthetic 1-34 fragment of PTHrP, 125I-Tyr degrees-PTHrP(1-34) as radioligand, and prior extraction of the native peptide from plasma with C-2 cartridges. We determined immunoreactive PTHrP concentrations in plasma samples from 48 healthy persons (mean +/- SD, 3.1 +/- 1.0 pmol/liter; range, less than 2 to 5 pmol/liter), 8 patients with primary hyperparathyroidism, 36 patients with hypercalcemia and a concurrent malignant lesion, and 9 normocalcemic patients with cancer and increased serum levels of carcinoembryonic antigen or prostate-specific antigen. PTHrP was normal in samples from patients with primary hyperparathyroidism (3.2 +/- 1.1 pmol/liter), secondary hyperparathyroidism (2.5 +/- 1.3 pmol/liter), and cancer without hypercalcemia (2.4 +/- 1.0 pmol/liter). In contrast, plasma immunoreactive PTHrP levels were increased (6.0 to 85.0 pmol/liter) in 47% of patients with hypercalcemia and cancer of various types, with or without bone metastatic lesions. Large amounts of PTHrP were also found in conditioned medium from cultured human prostatic carcinoma cells. Thus, PTHrP may be a causative factor for hypercalcemia associated with a malignant lesion in at least half of the cases. Measurement of circulating PTHrP may be of differential diagnostic help in hypercalcemic states.

In an earlier 8-day study, we showed increased immunoreactive PTH (iPTH) levels in young adults fed high phosphorus (P), low calcium (Ca) diets assembled from common grocery foods, a dietary pattern characteristic of teens and young adults. Because animals fed high P, low Ca diets developed secondary hyperparathyroidism and, ultimately, osteopenia, perhaps the typical teen diet may reduce peak bone mass and contribute to osteoporotic fracture later in life. To determine if the elevation in iPTH levels and action persists with chronic intake of this typical diet, we studied the 24-h mineral and hormone responses of 15 young women (18-25 yr of age) to either high P, low Ca or control diets. Each subject served as her own control, first consuming a basal diet (800 mg Ca, 900 mg P) for 28 days; 10 women were then switched to the high P, low Ca test diet (400 mg Ca, 1700 mg P) for 28 days, while the remaining 5 women in the control group continued eating the basal diet. On days 28 and 56, all subjects were studied as inpatients for 24 h, with blood drawn every 4 h and collection of fasting and 24-h urine. Serum iPTH (midregion) and serum intact PTH (2-site immunoradiometric assay) increased significantly [maximal increases of 26% (P less than 0.002) and 36% (P less than 0.004), respectively] after 4 weeks of consuming the test diet, and there was no change in the control group. In contrast to our 8-day study, plasma levels of 1,25-dihydroxyvitamin D did not change in either group. Our findings suggest that this common dietary pattern in young adult women causes persistent alterations in calcium-regulating hormones that could be unfavorable to achieving maximal positive bone balance.

Publisher Summary This chapter discusses familial benign hypocalciuric hypercalcemia (FBHH) and Neonatal Primary Hyperparathyroidism. The FBHH syndrome is inherited in an autosomal dominant fashion and is usually characterized by lifelong asymptomatic hypercalcemia, relative hypocalciuria, and the lack of the classical complications of hypercalcemia, including bone disease and renal stone disease. Some observers have also suggested that FBHH increases the risk of acute pancreatitis. The skeleton in patients with FBHH generally appears to be normal histologically, radiographically, and by mineral densitometry. While FBHH does not appear to threaten skeletal integrity, it does not confer immunity to osteoporosis. The relatively low urinary excretion of calcium in FBHH results from avid renal tubular reabsorption of calcium, and the urinary excretion of magnesium is unexpectedly low given that the serum level is in the upper part of the normal range or, in some cases, mildly elevated. Studies of the FBHH syndrome have almost uniformly suggested a genetic disorder of calcium sensing by the parathyroid gland paired with enhanced renal tubular reabsorption of calcium. PTH secretion persists at normal or slightly elevated values in the face of hypercalcemia, but without obvious disturbances of other calcium-regulating hormone concentrations. These pathophysiologic abnormalities would be most parsimoniously explained by dominant mutations of a single calcium sensing receptor expressed both in parathyroid glands and in kidneys. Neonatal primary hyperparathyroidism can be a mild syndrome representing the neonatal expression of FBHH, or it can present as a much more dramatic disease with high morbidity and even mortality if untreated, which is known as neonatal severe primary hyperparathyroidism (NSHPT).

Publisher Summary This chapter discusses familial benign hypocalciuric hypercalcemia (FBHH) and Neonatal Primary Hyperparathyroidism. The FBHH syndrome is inherited in an autosomal dominant fashion and is usually characterized by lifelong asymptomatic hypercalcemia, relative hypocalciuria, and the lack of the classical complications of hypercalcemia, including bone disease and renal stone disease. Some observers have also suggested that FBHH increases the risk of acute pancreatitis. The skeleton in patients with FBHH generally appears to be normal histologically, radiographically, and by mineral densitometry. While FBHH does not appear to threaten skeletal integrity, it does not confer immunity to osteoporosis. The relatively low urinary excretion of calcium in FBHH results from avid renal tubular reabsorption of calcium, and the urinary excretion of magnesium is unexpectedly low given that the serum level is in the upper part of the normal range or, in some cases, mildly elevated. Studies of the FBHH syndrome have almost uniformly suggested a genetic disorder of calcium sensing by the parathyroid gland paired with enhanced renal tubular reabsorption of calcium. PTH secretion persists at normal or slightly elevated values in the face of hypercalcemia, but without obvious disturbances of other calcium-regulating hormone concentrations. These pathophysiologic abnormalities would be most parsimoniously explained by dominant mutations of a single calcium sensing receptor expressed both in parathyroid glands and in kidneys. Neonatal primary hyperparathyroidism can be a mild syndrome representing the neonatal expression of FBHH, or it can present as a much more dramatic disease with high morbidity and even mortality if untreated, which is known as neonatal severe primary hyperparathyroidism (NSHPT).

Background In postmenopausal women, raloxifene hydrochloride has favorable effects on bone and lipid metabolism and does not stimulate reproductive tissues. The studies reported herein evaluated the long-term (3-year) effects of raloxifene treatment on bone mineral density (BMD), serum lipid levels, and drug tolerability in healthy postmenopausal women. Methods A total of 1145 healthy European and North American postmenopausal women aged 45 through 60 years were enrolled in 2 parallel, double-blind, randomized, placebo-controlled trials of identical design and randomly assigned to receive raloxifene hydrochloride, 30, 60, or 150 mg, or placebo daily; all groups received 400 to 600 mg of elemental calcium. Assessments included measurements for BMD by dual-energy x-ray absorptiometry, markers of bone turnover, and serum lipid levels. Results Lumbar spine BMD changed from baseline to 36 months as follows: placebo (mean percentage change + SE), −1.32% +0.22%; raloxifene, 30 mg, 0.71% +0.23%; raloxifene, 60 mg, 1.28% +0.23%; and raloxifene, 150 mg, 1.20% +0.24%. Comparable BMD changes were observed in the hip and total body. Biochemical markers of bone turnover were suppressed by raloxifene to normal premenopausal ranges through 3 years. Serum low-density lipoprotein cholesterol was reduced 7% to 12% below baseline through 3 years. Study withdrawals due to any reason (37%) and withdrawals due to adverse events (14%) were not different among groups. The only significant adverse effect of therapy was hot flashes (25% in the 60-mg raloxifene group vs 18% in the placebo group); hot flashes were typically reported as mild and were not associated with study withdrawal (1.7% for 60-mg raloxifene vs 2.4% for placebo). Conclusions Raloxifene preserves BMD at important skeletal sites, lowers serum low-density lipoprotein cholesterol levels, and has a tolerability profile comparable to placebo. These results indicate a favorable benefit-risk profile of raloxifene for long-term use in healthy postmenopausal women.

Publisher Summary This chapter elucidates that the laboratory analyses is useful in the diagnosis of bone and calcium metabolic disorders. It elaborates upon serum that plays an important role in the diagnosis of bone and calcium metabolic disorders. Serum Calcium is measured to detect hypercalcemia or hypocalcemia and is not directly related to bone turnover rates. Serum Phosphorous is measured to detect effects of poor phosphorus intake, or phosphate retention in renal failure. Serum Parathyroid Hormone (PTH) is measured to detect hyper or hyposecretion of PTH for pathophysiologic diagnosis of hypercalcemia and hypocalcemia. Serum vitamin D metabolites are useful in the measurement of 25-hydroxyvitamin D, predominant circulating metabolite, and the best reflection of either nutritional vitamin D deficiency or vitamin D excess. Serum Parathyroid Hormone Related Protein (PTHrP) is measured to diagnose humoral hypercalcemia of malignancy resulting from hypersecretion of PTHrP by neoplasm, only after determining serum PTH suppressed. The excretion of calcium and phosphorus in urine varies with diet and is measured to evaluate suspected renal calcium leak in osteoporosis, and intestinal malabsorption. The strategy for pathophysiologic diagnosis of hypercalcemia and hypocalcemia are discussed here. The guidelines to interpret the serum chemistry panel in hyper calcemia and hypocalcemia in the context to calcium, phosphorous, creatinine, albumin, globulins, chloride, and cholesterol are summarized.

The predominant variety of familial benign hypocalciuric hypercalcemia (FBHH) is FBHH(3q), which is associated with presumed inactivating mutations of the cell surface calcium receptor (CaR) gene on chromosome 3q13.3-q21. We sought mutations of the CaR gene in FBHH by direct sequencing of PCR-amplified genomic DNA from 14 affected families: 8 mapped to 3q13, 1 mapped to chromosome 19p, and 5 unmapped. We sequenced the entire coding region of the gene (exons 2-7) in one or two affected members of each family and found six point mutations that altered one amino acid, cosegregated with hypercalcemia, and were absent in more than 100 unaffected persons. Four mutations were unique (S53P, D215G, S657Y, and P748R), and two had been reported previously (P55L and R185Q). Of four mutant CaR proteins expressed in Xenopus oocytes, three were deficient in extracellular Ca2+-induced signaling. No CaR mutations were found in eight families, including the one mapped to chromosome 19p. Three benign polymorphisms occurred in the COOH-terminal region of the CaR protein in 10%, 15%, and 30% of more than 100 unaffected persons. Thus, FBHH-causing CaR mutations were clustered in the NH2-terminal extracellular and membrane-spanning regions of the receptor protein. We suggest that these are important functional domains, probably for calcium binding and signal transduction, respectively. Finally, mutations in regulatory or intronic regions of the CaR gene may also underlie many cases of FBHH.

Inactivating mutations of the parathyroid cell calcium receptor (CaR) gene cause one form of familial benign/hypocalciuric hypercalcemia, and in homozygous form, cause neonatal severe primary hyperparathyroidism with parathyroid hyperplasia. Thus, we postulated that partial or total loss of CaR function might contribute to calcium insensitivity or even stimulate cell proliferation in sporadic parathyroid adenomas (PAds). To examine this possibility, we sought loss of heterozygosity (LOH) for markers flanking the CaR locus (3cen-3q21) in 35 PAds. We used 16 highly-polymorphic PCR-based markers in paired normal and tumor DNA, extracted from slices of archived surgical specimens. Nineteen to 24 of the DNA pairs were informative with at least one marker. In two informative pairs, we found LOH for markers D3S1303, D3S1267, or D3S1269, which are tightly-linked with and flank the CaR locus. In one tumor, deletion mapping confined the lost area between D3S1271 and D3S1238 (41.7 centimorgans, cM). In the other tumor, LOH spanned most of chromosome 3, ranging at least from D3S1307 to D3S1311 (271.4 cM). LOH was confirmed by repetition of the experiments and quantified by phosphorimaging. Thus, we found LOH encompassing the CaR locus in approximately 10% of sporadic PAds. These data are consistent with the hypothesis that loss of CaR function may occur in PAds, with functional consequences for calcium sensitivity and cell proliferation.

The human PTH/PTH-related peptide (PTH/PTHrP) receptor could be involved in hereditary disorders of PTH or PTHrP action. Knowledge of the gene's chromosomal location would allow studies linking it to specific disease traits. Therefore, we mapped the human PTH/PTHrP receptor gene by polymerase chain reaction of human/rodent somatic cell hybrid panels using oligonucleotide primers designed to amplify a portion of the gene from genomic DNA. The PTH/PTHrP gene was unambiguously assigned to the short arm of human chromosome 3, in the region designated 3p21.1-p24.2. Analysis of a second chromosome 3-specific mapping panel suggests that the gene is located near the 3p21.2-p21.3 boundary. The availability of highly polymorphic markers located in this region will permit exploration of the PTH/PTHrP receptor locus in genetic linkage searches for the causes of bone, calcium, and other potential disorders.

Humoral hypercalcemia of malignancy (HHM) is at least partly caused by tumor secretion of PTH-related peptide (PTHrP), but there is growing evidence for cosecretion with PTHrP of other bone-resorbing peptides, such as the cytokine interleukin-1 alpha (IL-1 alpha). Administration of PTHrP in vivo and in vitro generally mimics the actions of PTH itself, with increases in both resorption and formation of bone. However, bone in HHM is characterized by uncoupling of bone turnover, with increased resorption and decreased formation. We performed experiments to determine whether IL-1 alpha might alter the effects of PTHrP and produce uncoupling. Thus, we administered to 100-g male rats by sc osmotic minipumps synthetic PTHrP-(1-34) alone (2 micrograms/100 g/day), recombinant IL-1 alpha alone (1.5 micrograms/100 g/day), both peptides together at the previous doses, or vehicle only. We infused 5 groups of 12 rats each (PTHrP, IL-1 alpha, PTHrP plus IL-1 alpha, ad libitum fed control, and controls pair-fed to the PTHrP plus IL-1 alpha group) for 14 days. At the end of the study, blood and urine were taken for chemical measurements, and tibias and femurs were harvested for histomorphometry and extraction of RNA from periosteal cells. As expected, PTHrP induced hypercalcemia, relative hypophosphatemia, phosphaturia, and reduced bone mass. Osteoblast number was increased, but osteoclast number was not. Indices of bone formation were unchanged or reduced. The dose of IL-1 alpha chosen had no statistically significant effect, except for reduced longitudinal bone growth, but when combined with PTHrP, IL-1 alpha reduced hypercalcemia, hypophosphatemia, and phosphaturia. In contrast to the blood and urine effects, IL-1 alpha did not interact significantly with PTHrP's effect on bone measurements. Northern analysis of periosteal cell mRNA showed that PTHrP reduced expression of osteocalcin, but not glyceraldehyde-3-phosphate dehydrogenase; IL-1 alpha had no additional effect. These data suggest that 1) continuously administered PTHrP alone may induce uncoupled bone turnover with decreased cortical bone formation; 2) IL-1 alpha appears to inhibit strongly the renal effects of PTHrP and weakly (if at all) its actions on bone and, thus, to decrease its hypercalcemic, phosphaturic, and hypophosphatemic actions; and 3) cosecretion of IL-1 alpha, and possibly other peptide cytokines, with PTHrP may modify the clinical expression of HHM.

The cause of hypercalcemia in familial benign hypercalcemia (FBH; also called familial hypocalciuric hypercalcemia) is unclear, although it is PTH dependent. It is also uncertain how plasma PTH levels are related to the severity of biochemical abnormalities in FBH. Because the PTH-related peptide (PTHrP) has many PTH-like actions, it might have a role in the hypercalcemia of FBH. Thus, we studied 29 patients with FBH from 11 families, 29 age- and sex-matched controls, and 42 patients with primary hyperparathyroidism (1 degree HPT), measuring PTH with a highly sensitive two-site immunochemiluminometric assay and the hypercalcemic tumor factor PTH-related peptide (PTHrP) with an extraction/concentration RIA. Plasma PTH values were elevated in 86% of 1 degree HPT patients (36 of 42), but in only 20% of FBH patients, (6 of 29). Plasma PTHrP was elevated in 1 FBH patient, and the group mean value was normal. Plasma PTH was positively correlated with calcium (Ca) in 1 degree HPT (r = 0.66; P less than 0.0001) and in FBH (r = 0.53; P less than 0.004), but the slopes of the regressions were markedly different: 1 degree HPT, 6.72; FBH, 1.61 (P less than 0.0001). There was a negative correlation between PTH and phosphorus (P) in 1 degree HPT (r = -0.39; P less than 0.01) and in FBH (r = -0.41; P less than 0.03), but, again, the slopes differed greatly: 1 degree HPT, -6.57; FBH, -1.95 (P less than 0.0001). There were no correlations between PTHrP and Ca or between PTH and PTHrP. The sums and products of PTH and PTHrP were not better correlated with Ca than PTH alone. Thus, PTH values are lower at given Ca and P levels in patients with FBH than in those with 1 degree HPT, suggesting that PTH is more effective in raising Ca and lowering P in FBH than in 1 degree HPT. The enigma of FBH remains: what molecular defect can simultaneously cause parathyroid cell insensitivity to Ca, enhanced renal tubular reabsorption of Ca, increased renal rejection of P, and enhanced or retained sensitivity to PTH?

The roles of parathyroid hormone (PTH) and calcitonin (CT) in the pathogenesis of familial benign hypercalcemia (FBH, or hypocalciuric hypercalcemia) are uncertain. Thus we performed studies in 26 patients with FBH, 12 patients with primary hyperparathyroidism (HPT), and 20 normal volunteers, to answer these questions: are plasma levels of intact or biologically active PTH frequently elevated in FBH? Is plasma intact PTH nonsuppressible during calcium infusion? Is there blunting of the C cell CT response to calcium infusion as occurs in primary HPT? We used three methods for measurement of PTH: a mid region-specific radioimmunoassay (iPTH, antiserum GP-1M), an extraction-concentration bioassay (bioPTH, stimulation of cAMP generation in osteoblastlike cells), and a two-site immunoradiometric assay (IRMA) for intact PTH. PTH levels were significantly elevated in primary HPT by all three methods, but mean PTH was normal in FBH and 85–92% of values overlapped the normal range. During 5 minute calcium infusions (2 mg Ca2+ per kg) iPTH values fell little, but bioPTH and intact PTH fell sharply in all three groups. Mean calcium-induced decreases of intact and bioPTH were indistinguishable from normal in FBH, but PTH levels generally remained elevated at 5 minutes in primary HPT. In FBH basal and postinfusion CT levels were normal. The data show that, in the majority of patients with FBH, PTH concentrations and bioactivity in blood are within the normal range and are suppressed rapidly to very low levels with further increases of calcium. The data suggest that the abnormality of parathyroid function in FBH differs from that in primary HPT. There was no deficiency of CT or C cell responsiveness in FBH, another difference from primary HPT. Nonetheless, in 8–15% of cases, measurement of PTH could not discriminate FBH from primary HPT.

There is doubt about concentrations of circulating calcitonin gene-related peptide (CGRP) and the value of plasma CGRP measurements in the detection and follow-up of medullary thyroid carcinoma (MTC). Thus, we developed an immunochemiluminometric sandwich assay for CGRP using antibodies purified from a polyclonal antiserum against human CGRP. The assay was sensitive (limit of detection, 0.4 pmol/L; multiply by 3.7892 to derive nanograms per L) and highly specific [no cross-reaction with human calcitonin (CT)]. Normal plasma CGRP values ranged from less than 0.4 to 4.5 pmol/L (median, 0.8; n = 31), with 61% having detectable levels. Values in samples from patients with MTC were elevated: unoperated patients (n = 10), 4.7-137 pmol/L (median, 7.1); and operated patients with gross persistent or recurrent tumor (n = 14), 4.7-171 pmol/L (median, 23.2). In contrast, CGRP values were normal in 78% of nine postoperative patients with elevated CT, but no detectable tumor (range, less than 0.4 to 6.3 pmol/L; median, 1.6). CGRP levels increased after pentagastrin injection in MTC patients, but less than did CT values. Cultured MTC cells in vitro secreted large amounts of CGRP, and rat nerve root ganglia, human osteoblasts, and microvessel endothelial cells secreted lesser amounts. We conclude that CGRP circulates in normal plasma, but at very low levels. Plasma CGRP concentrations are frequently high in patients with MTC, but primarily in those with gross tumor or metastases. Plasma CT assay is the preferable test for MTC, but CGRP assay deserves prospective study for a possible role in predicting gross metastasis.

Specific insulin-like growth factor-binding proteins (IGFBPs) that may enhance or inhibit insulin-like growth factor (IGF) action are produced in various tissues. In the present study we demonstrated that IGFBPs are synthesized and secreted by rat osteoblast-like cells (UMR 106-01). PTH and PTH-related peptide (PTHrP) were potent stimuli for IGFBP production by UMR cells, whereas GH, IGF-I, insulin, epidermal growth factor, and T3 had little or no effect. A maximal 8- to 30-fold increase in IGFBP production was attained at 10(-7)-10(-6) M PTH and PTHrP, with a half-maximal effect at approximately 10(-9) M. By Western blot analysis, PTH and PTHrP markedly and selectively increased the production of 29,000 mol wt (Mr) and, to a lesser extent, 24,000 Mr IGFBPs. Agents that elevate intracellular cAMP by different mechanisms [(Bu)2cAMP, forskolin, and isobutylmethylxanthine] mimicked the effect of PTH and PTHrP on IGFBP synthesis. In comparison, PTH did not stimulate IGFBP production in fibroblasts and ROS 17/2.8 cells, which secrete IGFBPs of 42,000, 38,000, 34,000, 28,000, and 24,000 Mr, but not of 29,000 Mr. The PTH-responsive IGFBPs from UMR cells were nonglycosylated proteins with preferential affinity for IGF-I over IGF-II. These IGFBPs were not immunoprecipitated with antisera against rat IGFBP-2 or human IGFBP-1. Thus, PTH and PTHrP increase the production in UMR 106-01 cells of discrete IGFBP forms with Mr of 29,000 and 24,000 through a cAMP-mediated mechanism, independent of IGF-I synthesis. Taken with the known effects of PTH on IGF production in bone cells, the data suggest that PTH and PTHrP may modulate local IGF action in bone through the regulation of specific IGFBP availability.

Calcitonin assays are essential tools for research into calcitonin (CT) and C-cell physiology and pathophysiology. Several existing radio immunoassays for CT, based on polyclonal antisera, are generally reliable for detection and follow-up of patients having medullary thyroid carcinoma. Occasionally, however, these assays suffer from problems of specificity and sensitivity. Two-site immunometric techniques for CT offer potential for great improvement in sensitivity, specificity, and turnaround time over those based on classical competitive-binding radioimmunoassays.

PTH-related peptide (PTHrP) may be a major cause of the humoral hypercalcemia of malignancy. The circulating form of PTHrP is unknown, but mRNA analysis of tumor tissue suggests that multiple forms of PTHrP may exist. Therefore, we examined the ability of the full 141-amino acid protein as well as 2 amino-terminal fragments, PTHrP-(1-34) and PTHrP-(1-74), to increase cytosolic calcium ion concentrations ([Ca2+]i; assessed by aequorin luminescence) and stimulate cAMP accumulation in osteoblast-like rat osteosarcoma cells (ROS 17/2.8). PTH and all PTH-related peptides examined increased [Ca2+]i and cAMP in a concentration-dependent manner. The [Ca2+]i response to PTHrP-(1-34) closely resembled that to rat PTH-(1-34); both peptides produced biphasic responses. However, the responses to the longer PTHrP fragments generally were not biphasic. There were no significant differences among the three PTHrP forms in increasing [Ca2+]i or stimulating cAMP accumulation, although PTHrP-(1-74) was consistently weaker than the other two PTHrP peptides. PTHrP-(1-34) was more potent than rPTH-(1-34), which, in turn, was more potent than human PTH-(1-34) in increasing [Ca2+]i. However, PTHrP-(1-34) was not consistently more potent than either human PTH-(1-34) or rat PTH-(1-34) in stimulating cAMP accumulation. The inhibitory PTH analog bovine PTH-(3-34) attenuated both cAMP and [Ca2+]i responses to PTHrP-(1-34), but bovine PTH-(7-34) only reduced the [Ca2+]i response. Our data are generally consistent with PTHrP's acting through the PTH receptor, but differences in the effects of inhibitory PTH analogs on PTH and PTHrP action suggest as yet unexplained complexities, such as the existence of a PTH/PTHrP receptor family.

Lymphosarcoma of domestic dogs is often accompanied by hypercalcemia. We have carried out studies to determine the usefulness of this common canine neoplasm as a model for paraneoplastic hypercalcemia. The study population consisted of 27 healthy control dogs, 13 with hypercalcemic lymphosarcoma, and 28 normocalcemic dogs with lymphosarcoma. Studies included measurement of circulating calcium, phosphorus, creatinine, immunoreactive parathyroid hormone (iPTH) and prostaglandin E2 (iPGE2) concentrations, and determination of in vitro bone-resorbing activity in supernatant culture media from normal and neoplastic lymphoid tissue. Hypercalcemia was severe in the affected group (mean ± SE, 14.9±0.5 mg/dl, normals 10.1±0.1 mg/dl) and associated with decreased renal function (serum creatinine 2.0±0.4 mg/dl, normal 0.8±0.1 mg/dl,P

We sought to determine whether cultured human dermal fibroblasts respond to parathyroid hormone (PTH) with accumulation of cyclic 3',5'-adenosine monophosphate (cAMP) reproducibly enough for such cells to be useful in characterizing states of altered end-organ response to PTH. Thus, we cultured fibroblasts from 15 human neonatal foreskins and tested fibroblast cAMP responses to addition of synthetic human PTH-(1-34), bovine PTH-(1-34), and native bovine PTH-(1-84) at concentrations of 10(-6) to 10(-10) M. Accumulation of cAMP (cells plus medium) was significantly enhanced by PTH in only 10 of 37 experiments. In cells that had a significant cAMP response to PTH, the ratio of treated to control cAMP values ranged only from 1.27 to 2.18. No study showed a clear-cut dose-response relationship. In six of six experiments, the cells responded to prostaglandin E2 (1 microgram/ml) with markedly increased accumulation of cAMP (9.7 to 110.9-fold the basal value). We conclude that cultured human dermal fibroblast cAMP responses to PTH with use of the current methods are too small and inconsistent for that tissue to be useful in studies of reduced end-organ responsiveness to PTH such as pseudohypoparathyroidism. Nevertheless, states of hyperresponsiveness to PTH might still be detectable by this method.

Available evidence in vitro and in vivo suggests that pharmacologic doses of isoproterenol stimulate the secretion of parathyroid hormone (PTH) and calcitonin (CT) and propranolol inhibits secretion. However, the findings in man are either quite modest or inconsistent. In view of this controversy, we examined the effects of isoproterenol, 0.15 micrograms intradermally (i.d.), dopamine, 5 micrograms/kg body weight over 60 min intravenously (i.v.), and propranolol, 1 mg over 5 min followed by 60 micrograms per min for 2 i.v. in normal human subjects. It was found that these agents did not alter serum calcium, serum immunoreactive PTH, or plasma immunoreactive CT. The findings do not support a physiologic role for biogenic amines in the control and regulation of PTH or CT secretion in normal man.

Cimetidine, an antagonist to histamine H2-receptors, reportedly lowers serum calcium and/or serum immunoreactive parathyroid hormone (iPTH) concentrations in some patients with primary and secondary (azotemic) hyperparathyroidism. We administered the drug orally (300 mg every 6 h) to five normal volunteers and four azotemic patients with secondary hyperparathyroidism who were not undergoing chronic hemodialysis. The normal persons and one azotemic patient took the drug for 5 weeks, and the remaining azotemic patients took it for 1 week. Before treatment, all patients had elevated levels of serum iPTH (two different assay systems), with or without elevated serum calcium concentrations, and increased urinary excretion of cAMP (per 100 ml glomerular filtrate). Cimetidine treatment caused no changes in serum calcium, phosphorus, or iPTH or in urinary cAMP (expressed as nanomoles per g creatinine). Serum creatinine, however, increased significantly in patients (P less than 0.02) and control subjects (P less than 0.025), which yielded statistically significant but spurious increases of urinary cAMP when expressed per 100 ml glomerular filtrate. We conclude that short term cimetidine administration has no effect on parathyroid function in normal persons or those with azotemic hyperparathyroidism. Because of its confusing effect on serum creatinine and a possible (albeit rare) adverse effect on renal function, the drug should be used with caution in azotemic patients not yet requiring chronic dialysis.

We studied in vitro the presence of histamine and the effect of histamine and its antagonists on cAMP accumulation in parathyroid tissue (parathyroid adenoma or hyperplasia) from patients with primary hyperparathyroidism. Parathyroid adenomatous tissue contained 11.2 +/- 2.9 ng histamine/g wet weight (approximately 2 X 10(-5) M), as determined by a specific radioenzyme assay. Histamine caused a prominent increase in cAMP accumulation in parathyroid tissue slices in a dose-dependent manner, with half-maximal stimulation being achieved at 5 X 10(-6) M and maximal stimulation occurring at 10(-4) M histamine. The histamine H2 receptor antagonists, cimetidine and metiamide, caused profound inhibition of histamine-stimulated cAMP accumulation in the parathyroid tissue. Pyrilamine, an H1 antagonist, also inhibited histamine-stimulated cAMP accumulation. Isoproterenol, a beta-adrenergic agonist, elicited marked elevation of cAMP, and its stimulatory effect was blocked by propranolol, but the effects of histamine on cAMP levels in parathyroid tissue were not blocked by propranolol. Histamine significantly stimulated (an increase of 50%) the release of immunoreactive parathyroid hormone. The present observations demonstrate that parathyroid adenomatous tissue has a relatively high content of histamine, and the release of immunoreactive parathyroid hormone from this tissue. The effects of antagonists suggest that histamine stimulates cAMP accumulation in the parathyroid adenomatous tissue by an action on both H2 and H1 histamine receptors.

β-Adrenergic agonists stimulate PTH release in vitro. The present studies were designed to test the hypothesis that norepinephrine released from sympathetic nerve terminals in the parathyroid glands might be a physiological regulator of PTH secretion. In 22 dogs, electrical stimulation (20 Hz, 1 msec, 50 V nominal) of the right cervical vagosympathetic trunk had no significant effect on release of PTH into the precava, whether the animals were normocalcemic or hypocalcemic, and whether or not they were pretreated with the a-adrenergic antagonist phenoxybenzamine. In 4 other dogs, stimulating release of endogenous nerve terminal norepinephrine by iv injection of tyramine (200 μg/kg) also failed to raise precaval plasma immunoreactive PTH concentrations. In all studies, induction of mild hypocalcemia raised immunoreactive PTH levels. From these and other studies, we conclude that β-adrenergic agonists of neural origin are not important regulators of canine PTH release in vivo. (Endocrinology 116: 1977–1982,...

PDN-21, the carboxyl-terminal flanking peptide encoded by the calcitonin (CT) gene, has been found in plasma of patients with medullary thyroid carcinoma and reportedly is cosecreted with CT. To test whether PDN-21 and CT are cosecreted in normal subjects, we developed a RIA for PDN-21 and measured immunoreactive CT and PDN-21 in whole plasma and silica or C18 cartridge extracts of plasma (exCT, exPDN-21) before and after calcium (Ca) infusion (2 mg Ca/kg over 5 min) in nine normal men and nine normal women. Plasma CT and immunoreactive PDN-21 levels were often below the assay detection limits. In contrast, basal exCT and exPDN-21 were detectable in all plasma samples, and the concentrations of both were significantly higher in men than in women [basal exCT (mean +/- SE): men, 4.8 +/- 0.3 ng/L; women, 2.4 +/- 0.3 (P less than 0.001); basal exPDN-21: men, 4.7 +/- 0.3 ng/L; women, 3.3 +/- 0.3 (P less than 0.01)]. Ca infusion sharply increased CT and PDN-21 concentrations in both sexes, but the increments were greatest in men [mean (+/-SE) increment of exCT: men, 37.2 +/- 3.9 ng/L; women, 15.7 +/- 4.3 (P less than 0.002); mean increment of exPDN-21: men, 29.7 +/- 4.7 ng/L; women, 11.0 +/- 3.1 (P less than 0.005)]. The molar concentrations of exCT and exPDN-21 were closely correlated (r = 0.97; P less than 0.001). With our antiserum, the extraction-concentration technique for measurement of PDN-21 had increased sensitivity and decreased nonspecific interference compared to the whole plasma assay. We conclude that CT and PDN-21 are cosecreted from normal thyroid C-cells under the control of extracellular fluid Ca, and that men have greater secretory capacity for both peptides than women. Plasma PDN-21 may serve alternatively to CT as a marker for C-cell activity.

To determine whether familial benign hypercalcemia, or familial hypocalciuric hypercalcemia (FHH), has adverse effects on the skeleton, we measured bone mineral density (BMD) in 31 affected persons from 14 families (16 women and 15 men), ranging in age from 19 to 68 years. Forearm BMD was measured by single-photon absorptiometry, and spinal BMD was measured by dual-photon absorptiometry. In addition, we systematically queried 82 hypercalcemic and 52 normocalcemic family members about skeletal fractures. Both men and women with FHH had normal BMD (expressed as grams per square centimeter) in the lumbar spine, distal radius, and midradius. Osteoporotic-type fractures (vertebrae, hip, and distal radius) were virtually absent in both affected and unaffected family members. Detailed evaluation of larger numbers of of older affected persons may be necessary to resolve this issue definitively, but we conclude provisionally that FHH has no important adverse effects on skeletal health.

Whether calcitonin deficiency causes and calcitonin excess prevents bone loss is controversial. We therefore measured plasma calcitonin levels and bone mineral density at the radius (by single photon absorptiometry) and lumbar spine (dual photon absorptiometry) in patients with an excess or deficiency of calcitonin. We studied 21 patients who had undergone subtotal thyroidectomy 6.8 to 29 years previously and had no calcitonin secretory reserve, and 11 patients who had received a diagnosis of medullary thyroid carcinoma 6.8 to 23 years previously and had chronic hypercalcitoninemia. Bone-density values, expressed as Z-scores (i.e., as the number of standard deviations above or below the normal means adjusted for age and sex), were indistinguishable from normal in the patients who had undergone thyroidectomy (means +/- SE: radius, 0.36 +/- 0.15; spine, 0.27 +/- 0.17). In the patients with medullary thyroid cancer, radial bone-density values were normal (-0.26 +/- 0.39), but spinal density was significantly reduced (-0.75 +/- 0.17, P less than 0.01). There were no significant correlations between the duration of calcitonin excess or deficiency and the bone density at either site. Bone mineral density was not affected by whether or not thyroxine replacement therapy was given. We conclude that skeletal mass is not affected by endogenous plasma calcitonin in adults.

An acute increase in serum calcium stimulates calcitonin (CT) secretion, but the effects of chronic hypercalcemia are controversial. Histopathological studies have shown C-cell hyperplasia in primary hyperparathyroidism (1 degree HPT), although circulating levels of CT have been variously reported to be normal, elevated, or depressed. We reexamined this relationship using CT RIA in conjunction with a silica extraction technique that conveys improved sensitivity and specificity for monomeric CT. Nine men and seven women with surgically documented 1 degree HPT were studied preoperatively before and after a short calcium infusion (2 mg Ca/kg, for 5 min), as were 72 normal men and 76 normal women. Basal whole plasma immunoreactive CT and silica-extractable CT concentrations in 1 degree HPT were indistinguishable from normal, regardless of sex. In addition, the whole plasma and silica-extractable CT responses to calcium stimulation were normal or blunted in patients with 1 degree HPT. We conclude that hypercalcemia resulting from 1 degree HPT is not associated with augmented CT secretion in response to an iv calcium infusion.

The histologic characteristics of the parathyroid glands in familial benign hypercalcemia (familial hypocalciuric hypercalcemia) are disputed, some finding parathyroid hyperplasia and others finding no abnormalities. To further investigate this issue, the histologic appearance of 82 parathyroid glands from 47 control patients (surgical and autopsy) were compared with those of 28 glands from 23 patients with familial hypocalciuric hypercalcemia who had undergone surgery for suspected primary hyperparathyroidism. Median and mean weights of 23 parathyroid glands from 12 patients with familial hypocalciuric hypercalcemia were 50 mg and 60 mg, respectively, with a range from 5 to 181 mg. Eighty-three percent of individual glands were within extreme normal limits for weight (less than 75 mg). Percent parenchymal area in familial hypocalciuric hypercalcemia was slightly but significantly less than control values (62 +/- 2 versus 71 +/- 2 percent, respectively; (p = 0.009). Conversely, percent fat was higher in familial hypocalciuric hypercalcemia than control values (30 +/- 3 versus 21 +/- 2 percent, respectively; p = 0.015). Stromal area was 8 +/- 1 percent in each group. Although 15 to 20 percent of parathyroid glands in familial hypocalciuric hypercalcemia exceeded normal size, most were indistinguishable from normal by size, weight, and microscopic appearance. The significantly reduced percent parenchyma in glands from patients with familial hypocalciuric hypercalcemia further suggests that the condition is not uniformly accompanied by typical parathyroid hyperplasia and should not be thought of as merely a variant of the latter.

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We compared the effects of exogenous pentagastrin and meal-stimulated gastrin on plasma immunoreactive calcitonin (iCT) in various studies of 13 normal adult men. Bolus intravenous injection of pentagastrin (0.5 microgram/kg) produced increases of iCT in 8 of 9 men. There was a linearly increasing response of iCT concentrations to increasing doses of pentagastrin (0.0625, 0.125, 0.25, and 0.5 microgram/kg) and to achieved serum immunoreactive pentagastrin concentrations (r = 0.72, P less than 0.01). To determine the effects of endogenous gastrin upon peripheral iCT concentrations, we measured serum immunoreactive gastrin (iG) and plasma iCT in four men at frequent intervals for 240 min after ingestion of low- (100 mg) and high- (400 mg) calcium meals. Serum iG increased in all subjects, with a peak at approximately 30 min. However, plasma iCT levels were unchanged from basal throughout the study. The increase of pentagastrin (0.3 pmol/ml) which caused a barely detectable increase of iCT was five- to tenfold greater than the mean maximal increases of gastrin after low- and high-calcium meals (0.04 and 0.06 pmol/ml, respectively). These results suggest that increases of plasma iCT concentrations after administration of pentagastrin in man reflect pharmacologic phenomena and that postprandial gastrin secretion may be insufficient to affect peripheral iCT concentrations.

To examine the relative importance of calcium and gastrin in regulation of calcitonin secretion, we administered graded oral doses of calcium to 10 normal men, ages 23-29 yr. Each subject had previously shown an appropriate increase in calcitonin secretion in response to a pharmacologic (0.5 μg/kg) pentagastrin injection. On separate days and in random order, each man drank 250 ml of distilled water containing 0.0, 0.5, 1.5, and 3.0 g of elemental calcium as the gluconate salt. Blood samples were drawn before and at 30, 60, 90, 120, 180, and 240 min after the oral calcium dose. The samples were analyzed for calcium by atomic absorption spectroscopy, and for gastrin and calcitonin by radioimmunoassays of established sensitivity and specificity. Ingestion of water (control) caused no change in any of the three variables. Calcium ingestion resulted in dose-related increases, within the normal range, of all three variables. Immunoreactive gastrin rose promptly, peaking at 30 min, and returning to basal levels or below by 120 min. In contrast, calcium and immunoreactive calcitonin levels rose slowly and in parallel, peaking at 120-240 min. Changes in calcitonin and changes in calcium were strongly and positively correlated, r = 0.73, when all data were pooled. Furthermore, individual linear regressions for changes in calcitonin and calcium levels (calculated separately for the three oral calcium doses in each subject) had positive slopes in 28 out of 30 sets (P < 0.01). The changes in calcitonin concentrations were much more poorly correlated with the corresponding changes in serum gastrin levels; in fact, the regression coefficient was weakly negative, r = −0.20. These results show that, at least in young adult men, changes of ambient calcium concentration within the normal range may be of major importance in physiologic regulation of calcitonin secretion. The findings are consistent with the hypothesis that calcitonin functions to prevent excessive postprandial hypercalcemia.

I. Introduction Ionic and nonionic control of parathyroid hormone and calcitonin secretion There is general agreement that the plasma concentration of calcium is the dominant regulator of parathyroid hormone (PTH) secretion (1–4) and probably also of calcitonin (CT) release (5, 6). Calcium stimulates CT secretion but inhibits PTH release; hypocalcemia has the opposite effects. Under certain conditions, other divalent cations, especially magnesium, can influence PTH and CT secretion in a fashion parallel to that of calcium, but there is little evidence that these relationships are of importance within the physiological range (3, 4). Normal secretion of PTH does, however, require the presence of magnesium (8, 9). Absence of the chloride and hydroxyl anions impairs PTH release in vitro (10), but it seems unlikely that levels of those anions have a specific regulatory function in calcium homeostasis. Phosphate infusion stimulates PTH secretion only by lowering plasma ionic calcium levels (2, 11), and an early...

We compared serum concentrations of immunoreactive PTH and plasma levels of vitamin D metabolites in 11 patients with adenomatous primary hyperparathyroidism and 32 individuals with the syndrome of familial benign hypercalcemia or familial hypocalciuric hypercalcemia (FHH). Serum immunoreactive PTH was elevated in the hyperparathyroid group but indistinguishable from control in FHH, despite comparable degrees of hypercalcemia. Plasma 25-hydroxyvitamin D concentrations were normal in both groups, but plasma 1,25-dihydroxyvitamin D levels in FHH were significantly lower than control (P less than 0.0025) or hyperparathyroid (P less than 0.01) values. FHH is pathogenetically distinct from primary hyperparathyroidism and should not be thought of simply as a variant of that condition.

Familial benign hypercalcemia, or hypocalciuric hypercalcemia, may be defined as a dominantly inherited disorder of calcium and magnesium metabolism, characterized by lifelong hypercalcemia and hypermagnesemia (both of variable degree), that usually is not associated with any symptoms, physical signs, reduced vitality, or ill health. Chondrocalcinosis, pancreatitis, gallstones, and neonatal primary hyperparathyroidism are possible rare associations, but findings differ among various studies. The biochemical findings are bland, with "normal" values for serum PTH by many techniques, modest hypophosphatemia, and other findings usually normal. A low calcium:creatinine clearance ratio is suggestive of, but not diagnostic for, FBH; urinary calcium excretion less than 100 mg per day may be just as helpful. The diagnosis should not be made casually or without family screening, because the findings in a given patient may be identical to those in mild primary hyperparathyroidism. The major rationale for careful evaluation is to diagnose the syndrome of FBH and to help affected family members avoid needless expense and the risk of further evaluation and treatment.

We measured plasma calcitonin concentrations in healthy volunteers (20 men, ages 23-45 yr, mean, 30 yr; 25 women, ages 21-46 yr, mean, 30 yr) with a radioimmunoassay capable of detecting 5 pg of calcitonin/500 mul incubation volume, or 25 pg/ml of unextracted plasma. All subjects had 4-h calcium infusion (15 mg Ca/kg), and 24 subjects had intravenous pentagastrin injection (0.5 mug/kg) on separate days. Men had higher basal plasma immunoreactive calcitonin concentrations than women (P 30 pg/ml, compared with such a response in only 1 of 14 women (7%). These differences of plasma immunoreactive calcitonin responses between the sexes were statistically significant (calcium infusion, P < 0.02; pentagastrin, P < 0.001). The physiologic importance of these observations is unknown, but we speculate that a lifelong, relative deficiency of calcitonin in some women could play a role in age- and sex-related bone loss, particularly during the estrogen-deficient postmenopausal years.

We examined the incidence and clinical and economic consequences of primary hyperparathyroidism in residents of Rochester, Minn, from 1965 through 1976; 90 cases were found. From January 1, 1965, to June 31, 1974, the average annual incidence was 7.8 +/- 1.2 (mean +/- S.D.) cases per 100,000 population. However, after the introduction of routine measurement of serum calcium, the average annual incidence rose to 51.1 +/- 9.6 cases per 100,000. Even after availability of routine measurement of serum calcium, the annual incidence of primary hyperparathyroidism among persons 39 years of age or younger remained below 10 cases per 100,000. However, the annual incidence increased sharply in persons 40 or more years of age, reaching 188 cases per 100,000 among women 60 years of age and over and 92 cases per 100,000 among men 60 and over. For the last 1.5 years of the study, the average annual age-adjusted incidence of primary hyperparathyroidism was 27.7 +/- 5.8 per 100,000. The frequency of urolithiasis fell from 51 to 4 per cent (P less than 0.001), and the proportion of cases without symptoms or complications of primary hyperparathyroidism rose from 18 to 51 per cent (P less than 0.005). The median charge in 1977 for diagnosis and treatment of primary hyperparathyroidism was $1700. (N Engl J Med 302:189-193, 1980).

To determine the relative importance of parathyroid gland enlargement and alterations in calcium sensing (set-point changes) in the pathogenesis of uremic secondary hyperparathyroidism (2 degrees HPT), we investigated the relationship between estimates of parathyroid gland size and calcium-mediated parathyroid hormone (PTH) suppression in 19 normocalcemic 2 degrees HPT patients on chronic maintenance hemodialysis. We compared our results to calcium-mediated PTH suppression in 12 normal volunteers, 12 patients with familial benign hypocalciuric hypercalcemia (FBHH), a disorder of abnormal calcium sensing, and 9 subjects with primary hyperparathyroidism (1 degree HPT), which is characterized by both calcium set-point abnormalities and parathyroid gland enlargement. We found that the 2 degrees HPT group displayed a distinctive pattern of calcium-mediated PTH suppression characterized by a failure to normally suppress PTH at supraphysiologic ionized calcium concentrations, similar to 1 degree HPT, but without the rightward shift of the calcium-PTH suppression curve that characterizes calcium sensing abnormalities in FBHH and 1 degree HPT. In the patients with 2 degrees HPT, hypercalcemic suppression resulted in an ending PTH (as a percent of baseline) that was significantly higher (39.8 +/- 4.47%), and a slope of the calcium-PTH suppression curve that was significantly less negative (-4.8 +/- 0.53), compared to respective values of 19.4 +/- 1.81% (P = 0.0009) and -9.0 +/- 1.02 (P = 0.001) in normals and 19.1 +/- 2.49% (P = 0.001) and -9.6 +/- 1.11 (P = 0.0006) in FBHH. Values of ending PTH and slope in 2 degrees HPT patients, however, were similar to those found in 1 degree HPT (49.8 +/- 6.35%, P = 0.21 and -4.5 +/- 0.74, P = 0.72). The ionized calcium concentration required to attain half maximal PTH suppression (EC50) in 2 degrees HPT (1.20 +/- 0.02 mmol/liter) was not significantly different from normals (1.25 +/- 0.01 mmol/liter, P = 0.12) but was significantly less than in 1 degree HPT (1.52 +/- 0.02 mmol/liter, P0.0001) and in FBHH (1.44 +/- 0.02 mmol/liter, P0.0001). More importantly, we found a significant linear correlation between the natural logarithm of gland size and ending PTH suppression (r = 0.71, P0.001) and slope of the calcium-PTH curve (r = 0.67, P = 0.002) in 2 degrees HPT. Thus, calcium non-suppressible PTH secretion in 2 degrees HPT does not represent a simple set-point error, but rather correlates with the degree of parathyroid gland enlargement.

The reported effects of PTH on urinary excretion of cations are highly variable. We investigated dose and time relationships for urinary clearance of calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K) after infusions of synthetic bovine PTH fragment 1-34 [bPTH-(1-34)] in seven normal subjects. The bPTH-(1-34) was given over 15 min on widely separated days at doses of 10, 30, 75, 150, and 300 U/70 kg. The 75, 150, and 300 U/70 kg doses produced a biphasic excretory pattern for all four ions, with increased clearance from 0-30 min and enhanced reabsorption at 60-120 min. Lower doses produced only retention of Ca, Mg, and Na, but even 10 U bPTH-(1-34)/70 kg caused a marked biphasic excretory pattern of K. These data explain why in previous studies PTH increased, decreased, or had no effect on the excretion of divalent and monovalent cations and emphasize the importance of short, clearly defined urine collection intervals for in vivo studies of PTH action of the kidney.

Recent reports that cimetidine, a blocker of histamine H2 receptors, lowered serum calcium and/or immunoreactive parathyroid hormone (PTH) concentrations in primary or secondary hyperparathyroidism prompted us to administer the drug (300 mg, orally, every 6 h) to two patients with hyperparathyroidism accompanying familial multiple endocrine neoplasia type 1. The patients were hypercalcemic (10.9--11.2 mg/dl), hypophosphatemic (2.0--2.4 mg/dl), and hypercalciuric (greater than or equal to 410 mg/24 h), with elevated urinary cAMP and phosphate clearance and inappropriately high serum immunoreactive PTH levels. Multiple observations of these variables over 5 weeks of cimetidine treatment showed no systematic changes; in particular, serum and urinary calcium did not change, and there was no evidence of a decreased PTH effect on the kidneys. The data offer no support for the treatment of familial hyperparathyroidism with cimetidine.

In hyperphosphatemic tumoral calcinosis, plasma 1,25-dihydroxyvitamin D [1,25(OH)2D] levels are inappropriately elevated, suggesting an abnormality in vitamin D metabolism. To define this abnormality further, we measured vitamin D metabolites in two patients and four controls before and after phosphate depletion. The patients showed elevated plasma levels of 1,25(OH)2D in the basal state. Phosphate depletion reduced serum phosphate in patients from a mean of 6.1 to 2.6 mg/dl; this was accompanied by a rise in plasma 25-hydroxyvitamin D from 33.6 to 41.9 ng/dl, and in 1,25(OH)2D from 67.7 to 93.2 pg/ml. The absolute rise in 1,25(OH)2D was similar to that of controls. EDTA infusion produced a normal increase of serum immunoreactive PTH levels and urinary cAMP excretion. In this form of tumoral calcinosis, 1,25(OH)2D levels are elevated despite hyperphosphatemia, normal immunoreactive PTH, and normal serum calcium concentrations, suggesting an abnormality in the regulation of 1,25(OH)2D synthesis or metabolism, or alternatively, another undefined stimulus for 1,25(OH)2D synthesis. These patients appear to have concurrent abnormalities of renal tubular phosphate transport and vitamin D metabolism.

To avoid the limitations of present human calcitonin (hCT) assays, we have developed a silica extraction and concentration method for plasma hCT that lowers the detection limit of the assay 40-fold (to 0.5-1.0 pg/ml), and markedly improves specificity of the assay for the CT monomer (hCT-M). Extraction recoveries of radioiodinated and unlabeled synthetic hCT-M added to 20 ml plasma were, respectively, 90 +/- 1% and 99 +/- 4% (mean +/- SE). Gel filtration chromatography of plasma from patients with medullary thyroid carcinoma demonstrated that the extract was markedly enriched in hCT-M. Basal plasma immunoreactive hCT was measured before (iCT) and after extraction (exCT) in 60 normal individuals; basal exCT levels were higher in young men than in young women [8.0 +/- 0.8 (+/- SE) vs. 4.6 +/- 0.5 pg/ml; P less than 0.001] and higher in elderly men than in elderly women (9.4 +/- 0.8 vs. 4.7 +/- 0.6 pg/ml; P less than 0.05), but not different with age. Calcium infusions (2 mg Ca/kg over 5 min) in 36 subjects showed a significantly greater secretory capacity for exCT in men than in women, but showed no decline of exCT response with age. There was no correlation between basal iCT and exCT concentrations, but there was a good correlation between peak Ca-stimulated iCT and peak Ca-stimulated exCT levels (r = 0.94; P less than 0.001), suggesting that hCT-M was the main form released by acute stimulation. The mean extractable CT level in 6 totally thyroidectomized individuals was 2.7 +/- 0.3 pg/ml and did not increase after Ca challenge. We found no significant differences in basal or Ca-stimulated exCT levels measured in 5 women on 3 different occasions over the span of 1 menstrual cycle. After a meal, exCT levels did not change in women, but there was a consistent increase in the men (28 +/- 7% over baseline at 3 h; P less than 0.01). In summary, plasma concentrations of exCT and, most likely, hCT-M were very low (less than 10 pg/ml in most healthy adults) and always increased after calcium infusion. The measurement of plasma exCT is a useful technique that provides new sensitivity and specificity for the study of hCT physiology., Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S., SCOPUS: ar.j, info:eu-repo/semantics/published