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The frequency of lipid droplets in the parathyroid glands of young, adult and senile golden hamsters after treatment with isoproterenol was investigated. In the parathyroid glands of the young and senile animals the number of lipid droplets increased gradually by 1 h, and thereafter it remained almost unchanged at 3 h after administration. In the glands of adult animals it increased, at first rapidly and then gradually, by 3 h after administration. It is considered that in the parathyroid glands of the golden hamsters stimulated by isoproterenol there is a relationship between the number of lipid droplets and aging.

Immunocytochemical localization of parathyroid hormone was examined in the rabbit parathyroid gland by means of protein A-gold technique. Protein A-gold particles were observed on the secretory granules and the large secretory granules thought to be storage granules. No protein A-gold particles were observed on cisternae of the endoplasmic reticulum and the Golgi apparatus.

The ultrastructural characteristics of parathyroid in fresh-water turtles (Pseudemys scripta) are studied during the four seasons of the year. The gland parenchyma consists of chief cells organized in solid cordons. No oxifil cell is seen in turtle parathyroid. The chief cells present seasonal variations in cytoplasmatic organization. These are essentially represented by: the presence of secretory granules, cilia with centriolar apparatus and microfilaments in autumn; middle and wide lipid vacuoles and glycogen particles in winter; light and dark chief cells in spring. The dates, described above, suggest that seasonal variations of parathyroid in fresh-water turtles can be correlated with ultrastructural parathyroid aspects of hibernant animals.

Electron-microscopic immunocytochemistry for the demonstration of parathormone in parathyroid chief cells was performed in adult male rats, gerbils, mice, and dogs, using the protein A-gold technique. Protein A-gold particles were detected over both large and small secretory granules in all the animals examined. In the former, they were concentrated not only over type-I granules with a large core, but also over type-II granules with a small core. They were also located over atypical granules, including heterogeneously dense granules, granules having vesicles in a finely particulate core, and distorted granules. All labelled secretory granules were characterized by the presence of a clear halo of varying width around the core. Occasionally, Golgi cisternae as well as Golgi vacuoles with a finely particular content were also labelled. The labelling of the secretory granules was strong in dogs, moderate in rats and gerbils, and weak in mice. In addition, it was more intense in the non-osmicated preparations than in the osmicated preparations. The frequency of both types of large granules showed species differences. The possible factors involved in these differences are discussed.

Ultrastructural features of the rat parathyroid (PT) glands have been studied under 3 different glutaraldehyde fixation methods. Cell differences caused by fixation or due to functional conditions were evaluated. The changes of organelles and relationship of plasma membranes of chief dark-light cells, as well the pericapillary and intercellular spaces were used for this evaluation. Light cells were observed in all PT glands studied. PT glands adequately perfused presented light chief cells as transitional secretory form. Incompletely-perfused and immersion-fixed glands presented most of light chief cells as a fixation artifact. The same interpretation was given to intercellular spaces which appeared only in glands fixed by immersion. In adequately perfused glands interdigitated and straight plasma membranes of neighbour chief cells were tightly continuous with frequent desmosomes. Distended mitochondria, RER and Golgi cisternae as well vacuolizations of chief cell cytoplasm and connective tissue were characteristics of unadequately perfused glands. The best fixation method for a homogeneous preservation of all components of rat PT glands, which decreased the possibility of a wrong interpretation of normal variations, was perfusion through the left ventricle. Fixative with pH and osmolarity carefully controlled were injected after saline washing of the vascular bed.

To determine both a threshold value of calcium concentration (CC) for the release of storage granules and that for the acceleration of degradation of these granules, the rat parathyroid glands were perfused in situ with HEPES-Ringer solutions containing different concentration of Ca2+ for 10 min. With perfusates containing 0.83-1.21 mM Ca2+ (equivalent to 8-11 mg/dl serum calcium), the number of type-I storage granules (large core) [NSG-I] and that of type-II storage granules (small core) [NSG-II] remained unchanged. With perfusates containing 0.83 mM Ca2+ (7.5 mg/dl) or less, however, both NSG-I and NSG-II decreased remarkably and the former was larger than the latter. On the contrary, with perfusates containing 1.27 mM Ca2+ (11.5 mg/dl) or more, NSG-II increased and the ratio of NSG-I to NSG-II was changed reversely. We concluded that a threshold value of CC required for the release of storage granules may be present between 0.88 and 0.83 mM Ca2+ (8 and 7.5 mg/dl) and that a threshold value of CC for accelerating the transformation of type-I granules into type-II, the degradation of storage granules, may be situated at about 1.27 mM Ca2+ (11.5 mg/dl). Additionally, it was suggested that both pro-secretory and storage granules are not only formed at the innermost Golgi cisterna but also at the trans-Golgi network.

Aggregates of bovine parathyroid cells (organoids) were cultured with or without 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and examined for effects on the synthesis, cellular content, and release of parathyroid hormone (PTH) and secretory protein I. Organoids cultured with 120 pM 1,25(OH)2D3 at 1.35 mM calcium contained 27 +/- 2% (mean +/- SE) less and released 26 +/- 7% less PTH and contained 21 +/- 2% more and released 49 +/- 16% more secretory protein I than untreated organoids. After 15-min incubations with radioactive leucine, treated organoids incorporated 25 +/- 2% less radioactivity into precipitable cellular proteins than did untreated organoids, indicating that the overall synthetic rate of proteins was decreased by 1,25(OH)2D3 at 1.35 mM calcium. After separation of cellular proteins by gel electrophoresis, analysis of individual protein bands indicated that the mean treated-control ratio for proparathyroid hormone radioactivity was 0.88 +/- 0.06 (P less than 0.10) while that for secretory protein I was 1.56 +/- 0.17 (P less than 0.01), respectively. Experiments were performed at 1.2, 12, 120, and 1,200 pM 1,25(OH)2D3 and both 1.4 and 1.8 mM calcium. In both cases, increasing levels of 1,25(OH)2D3 progressively decreased PTH synthesis and release and progressively increased that of secretory protein I, significant effects being observed at 1.2 pM 1,25(OH)2D3. We conclude that at physiological calcium levels, 1.2-1,200 pM 1,25(OH)2D3 suppresses the synthesis and secretion of PTH, increases that of secretory protein I, and at similar concentrations decreases the overall protein synthetic rate compared with untreated controls.

Parathyroid glands from 50 cases of primary hyperparathyroidism were examined by light and electron microscopy in an attempt to elucidate the diagnostic role of electron microscopy in this disease. In the cases in which only one gland was removed at surgery, a final diagnosis by light microscopy was not possible. The electron microscopic findings for some of these single glands (e.g., ribosomal-lamellar complexes and groups of centrioles) suggested that they were adenomas. In cases in which two or more enlarged glands were removed, a correct final diagnosis could be made on the basis of the light microscopic findings alone, and electron microscopy provided no further significant information. Where one enlarged gland and one normally sized gland were removed, electron microscopy disclosed important findings in the normally sized glands. Specifically, light microscopic examination of normally sized glands suggested endocrine suppression, while electron microscopy showed chief cell activity, thereby changing the final diagnosis from adenoma to hyperplasia. The clinical follow-up assessment in some of these patients confirmed the electron microscopic findings. Therefore, the incidence of adenoma in patients with primary hyperparathyroidism should be critically re-evaluated by ultrastructural studies of the normal glands that should be removed with the enlarged ones.

A number of studies concerning the effects of hypergravity on bone have shown increases in bone mass or bone dimensions. Correlative studies, which could provide clues to the mechanism for such a response, have been lacking. The purpose of the present study was to evaluate the ultrastructure of parathyroid glands of Mongolian gerbils exposed to a continuous 2 X gravity force for 60 d. It was found that the experimental animals had parathyroid glands which had a greater percentage of cheif cells in the active stage of their secretory cycle when compared with control animals. This result was interpreted to indicate an increase in parathyroid gland secretory activity and, hence, and increase in parathyroid hormone release. It was suggested that increased parathyroid secretory activity was necessary to maintain serum calcium levels of hypergravity animals within normal limits. Cellular forms resembling water clear cells and highly compact, degenerating cells were described in experimental animals but not in controls. Areas suggestive of cellular dissolution and disorganization were also reported in experimental parathyroids

Effects of pilocarpine treatment and of electrical vagal stimulation on the rat parathyroid were studied ultrastructurally. The number of type I storage granules with a narrow halo (NSG-I) and that of type II storage granules having a wide halo (NSG-II) were calculated. After pilocarpine treatment, NSG-I gradually decreased and reached a minimum at 30 min; in contrast, NSG-II gradually increased and reached a maximum at 20 min, but thereafter it slightly decreased and instead vacuolar bodies increased. Excluding these alterations, the ultrastructure of parenchymal cells showed no remarkable changes. Electrical vagal stimulation furthermore confirmed these results. Acid phosphatase activity was occasionally found in storage granules of both types in control and experimental rats. It was concluded that storage granules normally may be transformed from type I into type II and finally into vacuolar bodies as a result of hydrolysis, and that these processes may be accelerated by parasympathetic stimulation.

The effects of hypocalcemic and hypercalcemic substance on activity of the parathyroid and plasma calcium and phosphorus levels in the lizard, Uromastix hardwickii are described. The cellular hypertrophy and degranulation of cytoplasm in the parathyroid cells along with decrease in plasma calcium level appeared after sodium citrate and ethylenediaminetetraacetate (EDTA) treatment. On the other hand, degenerative changes are observed after calcium chloride treatment. It is suggested that the secretion of parathyroid is regulated by the circulating blood calcium level.

Parathyroid follicle formation was studied in Mongolian gerbils subjected to different concentrations of calcium in vivo and in vitro, using light and electron microscopic methods, including the potassium pyroantimonate technique and x-ray microanalysis for identification of cations. Follicles were frequent at high calcium concentration, but sparse at intermediate and low levels of calcium. Two main types of follicle were differentiated: "degenerative follicles" containing cellular debris and lined by smooth-surfaced epithelium which occasionally showed degenerative changes; and "secretory follicles" characterized by amorphous and granular contents, and an epithelium possessing microvilli and cytoplasmic projections. Amorphous masses were also seen in dilated intercellular spaces and in dilated cisterns of rough endoplasmic reticulum in the follicle epithelium. Calcium-containing precipitates were found in degenerating chief cells, and between degenerating cells and follicles. Parathyroid follicles are believed to be formed by degeneration of suppressed chief cells (degenerative follicles), and by secretion of hormonal and/or other substances into dilated intercellular spaces which progressively increase in size to form follicular cavities (secretory follicles), thereby possibly reducing the level of metabolically active parathyroid hormone. Functional suppression is believed to underlie the development of parathyroid follicles.

The ultrastructure of the chief cells of the parathroid gland and thyroid parafollicular (C) cells and the morphology of bone in calcium depletion and subsequent repletion were examined in young growing pigs. A low calcium diet resulted in osteopenia, increased removal of the cartilaginous core, osteoclasia and osteocytic osteolysis. Subsequent repletion quickly returned bone to normal. In pigs fed the low calcium diet, there was a marked depletion of secretory granules but a striking increase in the number of microtubules in chief cells. Increasing the calcium content of the diet to normal quickly returned the ultrastructural appearance of chief cells to apparent normal. In the initial response to calcium repletion, chief cells exhibited large number of lysosomes and occasionally prominent paracrystalloid bodies. Electron microscopic examination of parafollicular (C) cells of the thyroid gland failed to reveal differences in ultrastructure between test and control pigs. These findings support the view that bone resorption following calcium deficiency may be the result of a secondary hyperparathyroidism rather than of calcium deficiency per se.

Cilia were found in intracellular localizations or on the surface of certain cells of frog thymus and chicken parathyroid gland and ultimobranchial body. The experimental observations suggest that ciliogenesis is probably a general property of branchiogenic epithelium, which either persists, or can be activated by certain influences after the functional differentiation of endocrine organs arising from the foregut.

Parathyroid glands from patients in chronic haemodialysis and with secondary hyperparathyroidism have been studied by electron probe X ray microanalysis and analytical ion microscopy. Aluminium associated with phosphorus has been detected in phagolysosomes of parathyroid cells (chief cells and oxyphil cells).

Multinucleated syncytial cells consisting of clusters of closely apposed, darkly staining nuclei and densely eosinophilic cytoplasm were present in parathyroid glands from 25 of 36 dogs (69%). They were most often located either peripherally in the parathyroid gland or adjacent to blood vessels. The numbers of nuclei per syncytial cell ranged from two to greater than 30. Syncytial cells had degenerative changes as suggested by vacuolated mitochondria, dilated rough endoplasmic reticulum, irregular nuclear outlines, and condensed nuclear chromatin. These ultrastructural changes contrasted sharply with adjacent chief cells that had well-preserved organelles. The presence of desmosomes and fragments of cell membranes between nuclei suggested that syncytial cells were derived from fusion of adjacent chief cells rather than nuclear division without cytokinesis. Syncytial cells were present in normal, hyperplastic, and inactive parathyroid glands from dogs. There were no significant correlations between the presence of multinucleated cells and age of dog, parathyroid histology, and changes in the concentrations of serum calcium, phosphorus, creatinine, or plasma parathyroid hormone. Syncytial cells occurred frequently in canine parathyroid glands regardless of the state of activity of the gland or the concentration of plasma parathyroid hormone or serum calcium.

The ultrastructure of the parathyroid glands of hamsters subjected to 5 g environment after an intraperitoneal injection of isoproterenol was studied. In the isoproterenol-treated hamsters exposed to hypergravity environment, the Golgi complexes, cisternae of the granular endoplasmic reticulum and lipid droplets were significantly increased and secretory granules were significantly decreased compared with those of the control group. In addition, many chief cells contained numerous prosecretory granules in the Golgi areas and several secretory granules were situated close to the plasma membrane of the chief cells. These results suggest that the synthesis and release of parathyroid hormone may be markedly stimulated in the parathyroid glands of the isoproterenol-treated hamsters exposed to hypergravity environment.

The fine structure of the parathyroid glands of propranolol-treated hamsters subjected to 5 x gravity environment was studied. In the parathyroid glands of the propranolol-treated hamsters exposed to hypergravity environment, the volume density occupied by the Golgi complexes and cisternae of the granular endoplasmic reticulum was increased as compared to that of propranolol-treated hamsters and was decreased as compared to that of hamsters exposed to a hypergravity environment but was almost similar to that of control hamsters. In addition, many chief cells contained rich free ribosomes, abundant mitochondria and some secretory granules located in the peripheral cytoplasm. These findings suggest that the parathyroid gland which may be suppressed by treatment of propranolol and stimulated in response to a hypergravity environment indicates the secretory activity of the control parathyroid gland.

Light and electron microscopic morphometry was performed on the parathyroid (PT) glands of the SHC rats with naturally occurring chronic renal failure. Macroscopically, the PT glands were distinctively hypertrophied in 24-week-old male SHC rats when compared with the corresponding controls, Sprague Dawley (SD) rats. Light microscopic morphometry on consecutive sections of the PT glands showed that the volume was about 3 times greater in the SHC rats, whereas there was no difference in the size of the chief cells. Mitoses were often found in the PT glands of the SHC rats. The total number of mitoses was about 8.5 times greater in the SHC rats, and was closely related to the volume of the PT glands. Ultrastructural morphometry of the chief cells revealed an increase in the cell surface area by the interdigitation of the plasma membrane and increases in the volume of mitochondria and Golgi complex. Secretory granules sometimes existed close to the cell surface in the SHC rats, but not in the SD rats. These results suggest that the PT glands of the SHC rats are hyperplastic mainly because of the proliferation of the chief cells. Concurrently, an increase in volume of the cell organelles suggests enhanced secretion activity in the chief cells.

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.

Nuclear diameter was measured in 55 parathyroid chief-cell adenomas to determine its value in histological diagnosis and to assess its relationship to other features of primary hyperparathyroidism. Mean nuclear diameter for the whole group of adenomas was significantly greater than that for the accompanying normal glands. Mean nuclear diameter in individual adenomas was significantly greater than that in the accompanying normal gland in 27 out of 34 cases. Nuclear diameter was correlated with tumour weight and with plasma calcium but was not correlated with duration of history. It was significantly greater in the group of patients with overt bone disease than in those with kidney stones and in those with neither kidney stones nor overt bone disease. Assessment of nuclear diameter is of value in histological diagnosis of parathyroid adenoma. The rate of growth of the adenoma may be a factor determining nuclear diameter.

Definitive chief cells, characterized by the presence of specific secretory granules and typical membrane configurations, were present in the developing parathyroid glands of sheep embryos from 26 days of gestation (term = 150 days). During earlier stages of gestation developing chief cells contained lysosomal systems which appeared to be concerned with the autophagy of retained secretion product. The EM evidence suggests that physiologic release of the hormone does not occur until at least 30 days of gestation, which correlates well with the experimentally established time of onset of functional capacity in the parathyroid gland in the sheep. 'Bark cells' were found in the parathyroid primordia of embryos between 20 and 27 days of gestation. The significance of these "dark cells" is discussed with respect to glutaraldehyde fixation and to their possible relationship to chief cells.

Rickets can be induced by oral administration of metals. A depressive effect exerted by metal ions on the parathyroid gland has previously been suggested to be a pathogenetic factor in strontium-induced rickets. In the present investigation, rickets was induced in young rats by oral administration of strontium and manganese, respectively. The parathyroids were fixed by perfusion and the total volume of the parathyroid glands was determined by serial sectioning. Conventional stereological techniques were applied on the ultrastructural level and the densities obtained could be related to the total mass of parathyroid tissue. In both rachitic groups the volume of the parathyroid glands as well as the absolute amounts of all cellular components studied, were reduced. All these changes were, however, correlated to the decreased body weight of the experimental animals. This is well in line with the finding of unaltered serum concentrations of calcium and immunoreactive parathyroid hormone. Therefore, it is concluded that the parathyroids do not play an important role in the pathogenesis of metal rickets.

Ultrastructural changes of the parathyroid glands of 18-day-old mouse fetuses after administration of calcium chloride (calcium) or ethylenediaminetetraacetic acid (EDTA) were examined. Many chief cells in the parathyroid glans of the calcium-treated mouse fetuses contained poorly developed Golgi complexes and cisternae of the granular endoplasmic reticulum and many secretory granules as compared with those of the control fetuses. Many chief cells in the glands of the EDTA-treated mouse fetuses contained well-developed Golgi complexes and cisternae of the granular endoplasmic reticulum and many prosecretory granules as compared with those of the control fetuses. These findings suggest that calcium or EDTA affects the secretory activity of the parathyroid gland of the mouse fetus.

Ultrastructural aspects of the parathyroid glands of acetazolamide-treated mice were examined. Many chief cells of the treated mice are deficient in free ribosomes compared with the control mice. Most Golgi complexes are poorly developed and associated with a few prosecretory granules. However, relatively numerous secretory granules are observed in the cytoplasm, and a few secretory granules are present in the peripheral cytoplasm. Large secretory granules (storage granules), homogeneously dense bodies with a low electron density, heterogeneously dense bodies containing osmiophilic substance and/or lipid-like material, multivesicular bodies and lipid droplets have apparently increased in number in many chief cells of the experimental mice. Many transitional forms are recognized between each of the large secretory granules and the bodies mentioned above. These ultrastructural features suggest that parathyroid gland cellular activity is suppressed in response to acetazolamide treatment. In addition, correlations of the occurrence of large secretory granules and various bodies are discussed.

The ultrastructure of the human parathyroid chief cell has been studied by comparing thin section with freeze-fracture findings in close consideration of functional activity. Assessment of function was based on the careful analysis of normal and pathological conditions of the parathyroids in patients with various entities of hyperparathyroidism including clinical data. In contrast to the atrophic glands contralateral to an actively secreting adenoma, stimulated chief cells especially in cases with acute hyperparathyroidism (hypercalcemic crisis), display several remarkable findings: an enlargement of the nucleus with an increase in pores, an abundant amount of rough endoplasmic reticulum, many mitochondria and conspicuous interdigitations of the plasma membrane and an extensively developed Golgi apparatus with budding of numerous vesicular structures and dense lysosomal bodies as well as secretory granules. The fine structure of these alterations was assumed to reflect different states of function in consideration of clinical and laboratory parameters. The process of extrusion of secretory granules and the retrieval of membrane material by endocytosis was particularly investigated by comparison of images obtained by thin sections and freeze-fracture replicas. Our results demonstrate that the human parathyroid chief cell may serve as an ideal model for the study of a polypeptide hormone synthesizing cell with a well known feedback mechanism expressed by the various pathological conditions in patients with the clinical picture of primary and secondary hyperparathyroidism.

Hypercalcemia, which occurs 4 hr after bilateral nephrectomy in normal rats, is not seen 4 hr after either bilateral ureterotomy or sham surgery. These results indicate that it is loss of renal mass per se, not the uremic syndrome, which is responsible for the hypercalcemia. Citric acid levels also increase 4 hr after nephrectomy, and a degree of hypercalcemia and hypercitricemia comparable to that which follows nephrectomy can be produced by administration of citric acid to normal rats. In an attempt to evaluate the role of the parathyroid gland in the development of hypercalcemia in these two situations, the microtubule content of parathyroid gland chief cells was determined by ultrastructural sterologic techniques 4 hr after either bilateral nephrectomy or citric acid administration. The results of these measurements indicate that parathyroid gland chief cell microtubule content increases after citric acid administration but not following bilateral nephrectomy. The significance of these results is not clear. However, since a previous study has suggested a correlation between increased microtubule content and increased secretory status in the chief cell, one may speculate that increased microtubule content resulting from citric acid administration may also be associated with increased parathyroid hormone secretion. By this formulation, citric acid-induced hypercalcemia would be secondary to increased parathyroid hormone secretion, but the transient hypercalcemia that occurs after nephrectomy would take place in the absence of an increase in parathyroid hormone secretion. In this latter instance, it is possible that loss of the kidney, a major site of parathyroid hormone removal from plasma, leads to an increase in circulating parathyroid hormone level, and hypercalcemia, in the absence of an increase in hormone secretion rate.

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.

Freeze-fracture images of the parenchymal cells in the parathyroid gland of rats were observed after vitamin D2 plus calcium chloride-suppression and EGTA-activation of secretion. In cells of the suppressed glands, large bulges protruded from the Golgi cisternae, and large granules with a stalk, which are identified as storage granules, suggest that, during maturation, some storage granules may be connected by long tubules with the Golgi cisternae and supplied with secretory products from the Golgi cisternae via these tubules. In the activated glands, presumptive exocytotic and endocytotic specializations of intramembranous particles of the parenchymal cell plasma membrane were frequently observed. In addition, elevations and complementary shallow depressions of various shape and extent were occasionally encountered in the intercellular space. From their morphological characteristics it was concluded that these originated from secretory granule cores, which are discharged from the parenchymal cells into the intercellular space by exocytosis, and it was suggested that discharged granule cores may retain their spherical shape until they fuse to form a flat conglomerate.

Isolated parathyroid glands from gerbils incubated at low (0.5 mM), normal (1.25 mM) or high (3 mM) calcium concentration for 1 or 6 h were studied with regard to the following stereological parameters: the volume densities of the nucleus, mitochondria, endoplasmic reticulum, Golgi zone, lipid bodies, lysosomes, secretory granules and storage granules, and the surface densities of the cell membrane and endoplasmic reticulum. In glands incubated for 1 h no significant differences were seen between the experimental groups in any of the parameters investigated, however, the volume density of the Golgi zone and the surface density of the cell membrane were significantly increased in glands incubated for 6 h at low calcium concentration, compared with those incubated at high calcium concentration. The enlargement of the Golgi zone in stimulated glands was also evident when the two glands from the same animal incubated at different calcium concentrations were compared. The data suggest that the early response of parathyroid glands to altered concentration of extracellular calcium includes functional activities associated with the Golgi zone.

Isolated parathyroid glands from normal adult Mongolian gerbils were incubated for 10 minutes to 16 1/2 hours at high, medium or low concentrations of Ca2+, with or without added 1,25-dihydroxycholecalciferol (1.25-DHCC) or 25-hydroxycholecalciferol (25-HCC), after which they were studied electron microscopically. 1,25-DHCC appeared to potentiate the inhibitory action of high calcium on parathyroid activity, whereas 25-HCC had no structurally detectable effect.

The fine structure of the intercellular junctions of the hen parathyroid gland was studied using freeze-fracture replicas and thin sections. In the conventional thin sections, desmosomes, intermediate junctions (maculae adherentes) and gap junctions were observed, and in the lanthanum-fixed sections, tight junctions (maculae occludentes) were demonstrated as well. In the freeze-fracture replicas, desmosomes, gap junctions, tight junctions and combination forms of gap and tight junctions occurred, but intermediate junctions were not identified. Junctional complexes (zonulae occludentes) were not encountered in any preparations. The gap junctions varied in size and shape; they ranged from irregularly shaped, minute assemblages of particles to large aggregations of a round or elliptic outline. Both the tight junctions and the combination forms of gap and tight junctions also exhibited a variety of shape and dimension, and, depending on the form of the tight junctional strands, they were classified into three types: type I consisted of a simple line of strands; type II consisted of a closed network of strands; and type III consisted of an open network of strands. The combination forms were more numerous than the typical tight junctions. The possible significance of these junctions is discussed in relation to the function of the parathyroid parenchymal cell.

We have performed a submicroscopic analysis of the parathyroid glands removed from 2 patients with tertiary hyperparathyroidism. In both cases an RER-associated structure was found, which has never been described in normal or pathologic conditions in protein-secreting cells. This finding was present in only one of the glands of each patient. Their morphologic features are described. The significance of this structure is also discussed.

From July 1973 to July 1984, 50 patients underwent parathyroidectomy because of secondary hyperparathyroidism due to chronic renal failure. One hundred fifty-eight excised parathyroid glands in 41 of these patients were submitted to the histopathological examinations in the relations to their clinical features which revealed the following findings. Inspite of secondary hyperparathyroidism, eleven of 41 patients showed four unevenly enlarged parathyroid glands with one or two glands weighing less than 100mg. The glands were divided into three adenomas, 101 diffusely and 54 nodulary hyperplastic glands. The nodular type hyperplasia, which had a greater proportion of clear chief cells, vacuolated chief cells, transitional oxyphil cells and oxyphil cells, was more hyperplastic than the diffuse type. The patients with the nodular type showed more advanced clinical features in the secondary hyperparathyroidism.

The parathyroid glands were studied ultrastructurally in two groups of rats: one control group and one group with an immobilized hindleg. The aim was to see whether immobilization has any effect on the fine structural appearance of the parathyroid glands. No morphological differences were recorded between the two groups. Nor were any signs of increased functional activity observed. The results denote that no increased parathyroid activity occurs after immobilization of an extremity in rats.

Ultrastructural changes of the parathyroid glands of starved mice were examined. The parathyroid glands of the starved mice showed a decrease in the volume of Golgi complexes and storage granules and an increase in the volume of lipid droplets, and contained more heterogeneously dense bodies and multivesicular bodies compared with that of the control mice. In addition, the volume of mitochondria, cisternae of granular endoplasmic reticulum and secretory granules and the number of prosecretory granules appeared to be decreased compared to those of the control mice. Myelin-like structures were observed in the parathyroid glands of the starved mice. The results of our study provide support for the hypothesis that starvation exerts an inhibitory influence not only on the synthesis but also on release of parathyroid hormone.

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.

Two groups of weanling pigs, injected with 45Ca, were fed diets containing optimal calcium and phosphorus, and vitamin D3 at 1320 IU/kg feed in the control group, and 825,000 IU/kg feed in the test group. The groups were further subdivided with 2 pigs in each subgroup, with survival times of 1, 2, 3, 4, 7, and 14 days. Pigs fed the high level of vitamin D3 lost weight and anorexia, weakness, rough hair coat and labored breathing were observed. Hypercalcemia began at 12 hours and progressed rapidly after 2 days. Radioisotope sutdies interpreted in the light of histopathologic findings indicated that bone was the primary source of increased plasma calcium. Calcium was released at a rapid rate into blood from prelabeled bone which was undergoing necrosis; it was also removed from blood and deposited into bone at a slower rate due to decreased apposition. Histopathologic examination of bones from test pigs showed regressive changes in the osteocytes, chondrocytes and osteoblasts which bean within 1 day of treatment and resulted in evidence osteopenia within 7 days. Arrested osteocytic osteolysis led to the appearance of cementing lines and to chondroid core retention. Further regressive changes in the osteocytes resulted in osteocytic death and osteonecrosis with subsequent osteoclasia and osteopenia. Retardation and arrest of cartilage maturation as well as osteoblastic deficiency contributed to the osteopenia. The osteopenia was further evidenced by decreased specific gravity and ash content per unit volume of humerus. The initial negative effect on the osteocytes, chondrocytes and osteoblasts is attributed to a direct toxic effect of excessive dietary vitamin D3 since hypoparathyroidism and hypercalcitoninism, which occur secondarily to hypercalcemia, could not account for the rapid appearance of this effect, nor are they known to induce osteocytic death. The release of bone calcium and the resulting hypercalcemia in vitamin D3 toxicosis is therefore due to a direct toxic effect of the vitamin, or its metabolites, on the osteocyte resulting in osteonecrosis. It is not due to increased resorption as has been reported previously from both in vivo and in vitro investigations. Degeneration, with subsequent inflammation, but without calcification, was observed in the kidneys and in the lungs. Epithelial cells, basement membranes, and smooth muscle were affected. This conclusively demonstrates that degeneration is the primary soft tissue lesion in vitamin D3 toxicosis, and that the subsequent calcification is therefore dystrophic. Degenerative changes occurred in the parathyroid glands within 1 day of treatment resulting in necrosis, inflammation and atrophy within 4 days. Relative fibrosis was seen as the parenchyma receded. The parathyroid gland changes were considered a direct effect of vitamin D3 toxicity since they occurred with only mild hypercalcemia and since necrosis of parathyroid cells has not been demonstrated with hypercalcemia either in vivo or in vitro.

The behavior of membranes concerned with parathyroid hormone secretion was studied by electron microscopic morphometry in parathyroid cells of rats with temporarily reduced serum calcium concentration resulting from phosphate ion application and in rats with elevated serum calcium concentration following vitamin D3 administration. The phosphate ion application resulted in an increase of the cell surface area and a concomitant decrease of the surface area of the Golgi complex and secretory granules within 3 hours. After 3 hours, the cell surface area decreased, whereas the surface area of the Golgi complex and the secretory granules increased, and after 12 hours, the surface area of the rough endoplasmic reticulum also increased. In the vitamin D3-treated rats the surface area of the secretory granules increased, but the cell surface area had decreased by 24, 48, and 72 hours after application. These data suggest that parathyroid cells respond to a transient depression of the serum calcium concentration by an initial centrifugal membrane shift indicating enhanced exocytosis, followed by a centripedal membrane shift indicating enhanced endocytic retrieval of the plasma membrane. Later, membrane synthesis led to an increase of the membrane compartments concerned with parathyroid hormone secretion. Elevation of the serum calcium concentration following vitamin D3 treatment resulted in reduced release of parathyroid hormone by exocytosis and enhanced retrieval of plasma membranes by endocytosis. The fate of the retrieval plasma membrane remains unclear.