Search

The basic fibroblast growth factor-like mitogen detected in the plasma of patients with the multiple endocrine neoplasia type 1 (MEN-1) syndrome was found to have a specific mitogenic effect on parathyroid endothelial cells in vitro. To investigate its pathogenic role in humans, the endothelial component of parathyroid glands was evaluated by ultrastructural morphometry in six MEN-1 patients. The results were compared with those found in six patients with uremic hyperparathyroidism (UHPT) and in three subjects with histologically normal glands. Plasma mitogenic activity was found in all MEN-1 patients but not in those with UHPT or in normal subjects. All morphometric parameters investigated (fractional volume and nuclear density of capillary endothelial cells, volume fraction and number per unit area of capillaries) showed 1.5- to 2-fold higher values in patients with MEN-1 than in those with UHPT (P < 0.05). In contrast, no difference was found between MEN-1 cases and normal subjects. Quantitative evaluation of parathyroid pericytes yielded results similar to those of endothelial cells. These data indicate that the proliferation of parathyroid cells in MEN-1 patients is accompanied by parallel increase in the associated endothelial component that does not occur in patients with UHPT and may support the hypothesis of an in vivo role of the MEN-1 mitogen factor on the endothelial component of parathyroid glands in MEN-1 patients.

The administration of 4 mg/kg/day of dichloromethane diphosphonate (Cl2MDP) subcutaneously to pregnant cows fed a low-calcium diet significantly reduced bone resorption as indicated by microradiographic evaluation of endosteal surfaces of cross sections of ribs. Plasma parathyroid hormone levels were similar between Cl2MDP-treated and control cows prepartum, during EDTA infusions, and near parturition. Ultrastructurally, chief cells of the parathyroid glands of both groups of cows were in the active stage of the secretory cycle. The chronically stimulated chief cell from cows administered Cl2MDP had a large cytoplasmic area containing many lipofuscin granules and lysosomal bodies and a few secretory granules near the large Golgi apparatus or aligned along the plasma membrane. Uptake of calcium 45 by the duodenal mucosa incubated in vitro was greater in Cl2MDP-treated cows compared to control cows. The administration of Cl2MDP significantly reduced rapidly mobilization calcium reserves. Following an intravenous EDTA infusion and the spontaneous calcium drain associated with parturition and the beginning of lactation, Cl2MDP-treated cows developed severe hypocalcemia. The rapid mobilization of calcium reserves in cows administered Cl2MDP prepartum was impaired mainly because of diminished resorption of bone despite adequate parathyroid hormone secretion in response to severe postpartal or EDTA-induced hypocalcemia.

Light and electron microscopic localization of parathyroid hormone (PTH) in human and bovine parathyroid tissue has been achieved using an indirect peroxidase labeled antibody method. Granular deposition of the reaction product was found throughout the chief cell cytoplasm. There was no nuclear staining. At the ultrastructural level, parathyroid hormone localized by this method appeared to be largely confined to the secretory granules in the cytoplasm of cells. Mitochondria and nuclei were free of reaction product. Aggregated sacs of granular endoplasmic reticulum were minimally reactive, and Golgi apparatuses did not show reaction product.

A comparative study of ultrastructural and biochemical effects of Tris and ionophores X537A and A23187 on bovine parathyroid tissue is presented. When parathyroid slices were incubated with 3H-leucine and 3H-lysine for 10 minutes alone or with Tris (50 mM), A23187 (9.5-19 microM) or X537A (8.5-17 microM), the incorporation of the amino acids into radioactive proparathormone (proPTH) was similar, indicating that biosynthesis of the hormone was not affected. After 120 minutes of incubation, however, Tris inhibited the conversion of proPTH to parathormone (PTH), judged by a decrease in cellular and secreted radioactive PTH and a corresponding increase in radioactive cellular proPTH. These changes were accompanied by marked dilatation of Golgi membranes. With both concentrations of A23187 and the low concentration of X537A there were no changes in amounts of radioactive proPTH, moderate decreases in cellular and secreted radioactive PTH, and little discernible distension of the Golgi membranes. At 17 microM X537A there was moderate increase in amount of radioactive proPTH, a marked decrease in amount of radioactive PTH and swelling of the Golgi membranes. Taken together, these findings suggest that Tris inhibited conversion of proPTH to PTH by disrupting the Golgi zone-the site of conversion of proPTH to PTH; that A23187 and the low concentration of X537A decreased production of PTH by enhancing its degradation; and that X537A at the higher concentration acted both by inhibiting conversion of proPTH to PTH and by enhancing the degradation of PTH.

Staining of frozen sections of small parathyroid biopsies from patients with primary hyperparathyroidism with Sudan II or IV revealed the almost uniform presence of numerous prominent intracellular sudanophilic bodies in the chief cells of suppressed "normal" parathyroid glands. These sudanophilic bodies were generally absent from the abnormal chief cells of parathyroid adenomas and chief cell hyperplasias. This difference in intracellular lipid provides a rapid, reliable, and easy method for distinguishing at the time of parathyroid exploration between an adenoma which is always accompanied by "normal" parathyroid glands and a chief cell hyperplasia in which all of the glands are abnormal.

Histologic, ultrastructural, and immunofluorescent changes in the parathyroid glands of rabbits have been studied after 48 hours of ozone inhalation at a dosage of 0.75 ppm. The frequent changes observed included hyperplastic parathyroiditis followed by capillary proliferation and leukocytic infiltration. The progressive cytologic events consisted of the presence of eosinophilic leukocytes, reticuloendothelial and lymphocytic infiltration, disaggregation of the parenchyma, and interstitial edema. The ultrastructural changes consisted of degeneration of nuclei, atrophy of the mitochondria, dilatation and atrophy of the endoplasmic reticulum of the chief cells of the parathyroid gland, proliferation of the venous limb of the capillary network, and the prominent interstitial elements. The immunofluorescent techniques revealed positive immunologic response. These data suggest that ozone inhalation perhaps triggers an immune reaction which causes inflammatory injury to the parathyroid gland. The possibility that the modified functional chemical groups of the parathyroid gland act as autoantigen is discussed.

Tris(hydroxymethyl)aminomethane (Tris, Tromethamine, THAM) and other non-amphoteric amines were previously reported to inhibit the conversion of proparathyroid hormone to parathyroid hormone in bovine parathyroid glands incubated in vitro. This inhibition correlated with a striking dilation of the Golgi complex. This work has now been extended to normal, hyperplastic, and adenomatous parathyroid glands from human subjects. The tissues were incubated for up to 3 hours with 3H-leucine in physiologic solutions (control) or in the same solutions containing 50 mM Tris. In one case, diethylamine also was tested. Electron microscopy revealed that the amines produced a dilation of the Golgi complex and swelling of vesicles, predominantly in the region of the Golgi zone. Other organelles were normal in appearance. During the same period, Tris reduced by sixfold the ratio of the parathyroid hormone to proparathyroid hormone, from a control value of 2:1 to 1:3. It was apparent that Tris exerted the same biochemical and morphologic actions in human parathyroid tissues as it was previously shown to do in bovine glands. These studies support the concept that the Golgi zone is that region in the parathyroid gland in which proparathyroid hormone to parathyroid hormone conversion is initiated and that Tris inhibits this conversion through disruption of the converting site.

Oxyphil cells and oxyphil cell adenomas of parathyroid glands are, in most instances, regarded to be nonfunctioning. Although 21 cases of hyperparathyroidism associated with parathyroid oxyphil cell adenoma have been reported, secretion of hormone by these tumors has not been conclusively demonstrated. A parathyroid adenoma, diagnosed by light microscopy as oxyphil type, together with the results from ultrastructural and biochemical studies of the patient's adenomatous tissue, are reported here. The patient, a 64-year-old male, was found to have elevated serum calcium, low serum phosphorus, and elevated serum immunoreactive parathormone: findings consistent with hyperparathyroidism. After excision of two small normal-appearing glands and one greatly enlarged (1.9 g) parathyroid gland, those laboratory values returned to normal. Light microscopy of the enlarged parathyroid indicated that it consisted almost entirely of an oxyphil adenoma. Electron microscopy revealed that the adenoma was composed mainly of mitochondria-rich oxyphil cells but also of interspersed transitional oxyphil cells and rare scattered chief cells. Golgi zones, rough endoplasmic reticulum, and prosecretory and secretory-like granules were observed in some oxyphil cells, in most transitional oxyphil cells, and in the infrequent chief cells. Thus, many of these cells appear to contribute to the production and secretion of parathormone. Biochemical studies performed directly on the adenomatous tissue demonstrated that it was able to synthesize proparathormone and parathormone, although the proportion of hormonal peptide synthesis relative to that of the total protein synthesis in this tissue was much smaller (0.9%) than that found in normal parathyroid tissue (5.7%). There was a small increase in immunoreactive parathormone when the adenoma tissue was incubated in a low-calcium medium. These findings indicate that this oxyphil adenoma of the parathyroid gland synthesized and secreted parathormone, apparently to some extent autonomously, but suggest that its capacity to do so was largely dependent on its component of cells other than fully developed oxyphil cells, such as transitional oxyphil cells.

Sequential development of electron miscrosopic changes in the rabbit parathyroid gland was monitered during induction of parathyroiditis by 48 hours of ozone 0.75 ppm dosage regimen. By 4 to 7 days, electron microscopy revealed prominence of polyribosomes, rough endoplasmic reticulum, Golgi complex, secretory granules, microtubules, and frequent infoldings of the plasma membrane. Presumable this was the stage of parathyroid hormone synthesis. Between 14 to 18 days, ultrastructural observations showed dilatation of rough endoplasmic reticulum with continuity with annulate lamellae, disaggregation of polyribosome attached to the rough endoplasmic reticulum, and accumulation of numerous solitary free ribosomes in the cytoplasm. The dilated portion of endoplasmic reticulum contained medium electron-dense granular material, which also appeared between the intercellular spaces. The medium electron-dense material assumed to condensed appearance of basal lamina bordering the intercellular matrix. On the basis of the present observation it was concluded that the second set of ultrastructural changes signify the stage of basal lamina reconstruction. The significance of these changes as reparative responses to the inflammatory stimuli was discussed.

Fine structural alterations of thyroid C cells and parathyroid chief cells were evaluated after feeding dried leaves of the calcinogenic plant, Solanum malacoxylon, to cattle for 1, 6 and 32 days. Thyroid C cells initially were degranulated in response to the hypercalcemia, and parathyroid chief cells accumulated secretory granules. There was hypertrophy of thyroid C cells with well-developed secretory organelles but few secretory granules in the cytoplasm after 6 days of feeding S. malacoxylon. Inactive chief cells with dispersed profiles of endoplasmic reticulum and increased lysosomal bodies predominated in the parathyroid glands. Multiple foci of soft tissue mineralization were present in the heart, lung, and kidney. Thyroid C cells underwent hypertrophy and hyperplasia after 32 days of S. malacoxylon, and parathyroid chief cells were inactive or atrophic in response to the long-term hypercalcemia. Severe soft tissue mineralization was present throughout the cardiovascular system, lung, kidney, and spleen. These ultrastructural changes in thyroid C cells and parathyroid chief cells plus the widespread soft tissue mineralization observed after feeding cattle small amounts of S. malacoxylon are consistent with the recent evidence that leaves of this plant are a potent source of the active metabolite, 1,25-dihydroxycholecalciferol, of vitamin D.

Cows fed a balanced diet with the required amounts of calcium and phosphorus developed acute hypocalcemia and hypophosphatemia shortly after parturition, even in the presence of the a responsive parathyroid gland, when bone resorption was selectively inhibited by the prepartal administration of disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP). When serum total and ionized calcium levels declined below 6.0 and 1.0 mg/100 ml, respectively, cows developed clinical signs similar to naturally occurring parturient paresis. The plasma immunoreactive parathroid hormone levels were similar prepartum, at parturition, and 1 day postpartum in cows administered EHDP as in control cows. Parathyroid chief cells were predominately in the actively synthesizing phase of the secretory cycle with a prominent Golgi apparatus and lamellar arrays of rough endoplasmic reticulum. Many chief cells were degranulated of mature secretory gransules. Calcitonin activity in thyroid extracts, determined by bioassay, and the numbers of secretory granules in thyroid C-cells were similar in both groups of cows. EDTA infusion after 60 days of the experiment demonstrated that the immediately available calcium reserves were reduced in EHDP-treated cows. The serum calcium remained significantly lower and did not return to preinfusion levels by 24 hours. Serum calcium in control cows returned to within the normal range by 6 hours after EDTA infusion. The urinary excretion of hydroxyproline was consistently reduced prepartum and following EDTA infusion in cows receiving EHDP. The experimental induction of parturient of parturient hypocalcemia by the prepartal administration of EHDP provides a valuable model for studies to investigate the mechanisms in bone responsible for the development of severe hypocalcemia that occurs in response to the increased calcium demand imposed by parturition and the initiation of lactation.