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The ultrastructure of the parathyroid glands of phosphate-treated golden hamsters exposed to a 5-G environment was studied. In the phosphate-treated animals exposed to a hypergravity environment, the Golgi complexes associated with numerous prosecretory granules, and the enlarged intercellular spaces containing floccular or finely particulate material showed a significant increase compared to those of the control, centrifuged, and phosphate-treated groups, and the cisternae of the granular endoplasmic reticulum showed a significant increase compared to those of the control and phosphate-treated groups. In addition, numerous secretory granules were situated close to the plasma membrane of chief cells in the phosphate-treated animals exposed to a hypergravity environment. These findings suggest that the synthesis, and to a greater extent the release of secretory granules may be markedly stimulated, in the parathyroid glands of phosphate-treated animals exposed to a hypergravity environment.

The ultrastructure of the parathyroid glands of fetal and pregnant golden hamsters exposed to 5-gravity environment was studied. In the centrifuged fetal animals the Golgi complexes associated with some prosecretory granules were significantly increased compared with those of the control fetal animals, and several secretory granules were located in a peripheral position just beneath the plasma membrane. In the centrifuged pregnant animals the Golgi complexes associated with numerous prosecretory granules were significantly increased, cisternae of the granular endoplasmic reticulum appeared to be increased compared with those of the control pregnant animals, many secretory granules were located in the peripheral cytoplasm and several granules were situated close to the plasma membrane. These findings suggest that in the parathyroid glands of the fetal golden hamsters as well as the pregnant animals the synthesis and release of parathyroid hormone may be stimulated in response to a hypergravity environment.

Effects of 5-gravity environment on the ultrastructure of the parathyroid glands of norepinephrine-treated golden hamsters were studied. In the centrifuged animals treated with norepinephrine, the volume density occupied by the Golgi complexes associated with numerous prosecretory granules was significantly increased compared with that of the control, centrifuged and norepinephrine-treated animals, as well as the volume density occupied by the cisternae of the granular endoplasmic reticulum compared with that of the control and centrifuged animals. In addition, in the centrifuged animals treated with norepinephrine, numerous secretory granules were situated close to the plasma membrane. It is suggested that the synthesis and release of secretory granules may be markedly stimulated in the parathyroid glands of the norepinephrine-treated golden hamsters subjected to a hypergravity environment.

The effects of different ages on large vacuolar bodies in the parathyroid glands of golden hamsters after short-term treatment with calcium were investigated. In the parathyroid glands of the young and adult animals 15 min and the senile animals 15 and 60 min after administration of calcium, the percent area occupied by large vacuolar bodies was significantly increased as compared to that of the young, adult and senile control animals, respectively. These findings suggest that the percent area occupied by large vacuolar bodies is increased in response to acute hypercalcemia. It is thought that in the parathyroid glands suppressed by hypercalcemia there is a relationship between the percent area occupied by large vacuolar bodies and aging.

The ultrastructure of the parathyroid glands of golden hamsters subjected to 5-gravity environment after administration of epinephrine was studied. In the epinephrine-treated animals exposed to a hypergravity environment, the Golgi complexes associated with numerous prosecretory granules were significantly increased compared with those of the control, centrifuged and epinephrine-treated animals, as well as the cisternae of the granular endoplasmic reticulum compared with those of the control and centrifuged animals. In addition, many secretory granules were situated close to the the plasma membrane of the chief cells in the epinephrine-treated animals exposed to a hypergravity environment. Those observations suggest that the secretory activity of the parathyroid gland may be markedly stimulated in the epinephrine-treated animals exposed to a hypergravity environment.

The ultrastructure of the parathyroid glands of infantile, young, adult and senile golden hamsters subjected to a hypergravity environment was studied. In the parathyroid glands of 5-, 10- and 20-day-old, and 1- and 3-month-old golden hamsters exposed to a hypergravity environment, the Golgi complexes were significantly increased, and in 5-, 10- and 20-day-old, and 1- and 8-month-old animals exposed to a hypergravity environment, the cisternae of the granular endoplasmic reticulum appeared to be increased as compared to those of each control group. In addition, in centrifuged animals numerous prosecretory granules were observed in the Golgi areas, and many secretory granules were located in the peripheral cytoplasm. The ultrastructure of the parathyroid glands of 14-month-old centrifuged animals resembled that of 14-month-old control animals. These results suggest that the secretory activity of the parathyroid gland may be stimulated in infantile, young and adult golden hamsters subjected to a hypergravity environment and may not be stimulated in senile animals subjected to a hypergravity environment.

Water-clear cells and transitional forms between the chief cells and water-clear cells were observed in the parathyroid gland of the golden hamster. Their ultrastructure is described, and the origin of the water-clear cell is discussed.

Ultrastructural changes of the parathyroid glands of ovariectomized golden hamsters were investigated. In the parathyroid glands there is a decrease in the area of each cell occupied by the Golgi complex, in the number of prosecretory granules and in the tortuosity of plasma membrane as compared with those of the control golden hamsters. In addition, the area occupied by lipid droplets appears to be increased and the number of secretory granules in the peripheral cytoplasm and large vacuolar body appears to be decreased compared to those of the control animals. These features suggest that the synthesis and release of parathyroid hormone may be suppressed in many chief cells of the ovariectomized golden hamsters.

Intraperitoneal horseradish peroxidase was found to penetrate directly into the vagal preganglionic neural elements. After intraperitoneal administration of horseradish peroxidase, the bilateral dorsal nucleus of vagus nerve was labelled retrogradely with the enzyme. Other regions of medulla oblongata and sacral spinal cord were free from labelling. The significance of these findings was considered in relation to studies of autonomic nerve supply of abdominal viscera using retrograde transport of horseradish peroxidase.

Ultrastructural changes of the parathyroid glands of vagotomized rabbits were examined. Many chief cells at 6, 12, 18 and 24 h after vagotomy are rich in free ribosomes compared to control rabbits. The main changes in the parathyroid glands of rabbits at 12, 18 and 24 h after vagotomy as compared with the control animals are a proliferation of the Golgi complexes, an increased number of secretory granules in the peripheral cytoplasm, and a frequent occurrence of enlarged intercellular spaces containing finely particulate substance. Large secretory granules, heterogeneously dense bodies, multivesicular bodies and lipid droplets apparently decrease in number in many chief cells at 12, 18 and 24 h after the operation. These alterations suggest that synthesis and release of parathyroid hormone are stimulated in many chief cells of the vagotomized rabbits. In addition, correlations of the occurrence of large secretory granules and various bodies are discussed.

The frequency of lipid droplets in the parathyroid glands of young, adult and senile golden hamsters after starvation was investigated. In the parathyroid glands of the young and senile golden hamsters, the number of lipid droplets increased to reach a peak by 2 days, then decreased slowly by 5 days after starvation, and decreased rapidly after refeeding. In the glands of adult animals it increased to reach a peak by 5 days after starvation and decreased rapidly after refeeding. These findings suggest that in the fasting condition there is a relationship between the number of lipid droplets and aging.

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.

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.

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.

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.

The immunocytochemical localization of parathyroid hormone was examined in the hamster parathyroid gland by using the protein A-gold technique. Protein A-gold particles were concentrated over secretory granules, large secretory granules thought to be storage granules and Golgi vacuoles. No protein A-gold particles were detected over large vacuolar bodies and cisternae of the granular endoplasmic reticulum.

The fine structure of the parathyroid glands of golden hamsters exposed to 2, 5 or 10 g environment for 5 h was studied. In the centrifuged hamsters, many secretory granules are located in a peripheral position just beneath the plasma membrane of chief cells, and the Golgi complexes and cisternae of the granular endoplasmic reticulum are significantly increased compared with those of control animals. There are no significant differences between the control and centrifuged animals with regard to secretory granules, large secretory granules, lysosomes, vacuolar bodies and lipid droplets. These findings suggest that the secretory activity of the parathyroid gland may be stimulated in response to hypergravity environment.

The cells of origin of nerve fibers innervating the parathyroid gland were studied in the rabbit using the HRP-retrograde transport method. Numerous labeled neurons were observed in the caudal half of the ipsilateral superior cervical ganglion following HRP injection into the parathyroid gland. Furthermore, in the medulla oblongata, labeled neurons were found in the dorsal nucleus of the vagus and many of them were distributed caudal to the level of the obex.

Electron-microscopic studies were made on the parathyroid gland of cadmium-treated mice. Most chief cells in treated mice were rich in free ribosomes and secretory granules compared to the control mice. In the parathyroid gland after 3 and 4 weeks of administration of cadmium, interdigitations between adjacent chief cells became more complex than in the control mice. In most chief cells of the parathyroid gland after 2, 3 and 4 weeks of administration of cadmium, the Golgi complexes associated with numerous prosecretory granules were better developed than in the control mice. These ultrastructural appearances suggest that parathyroid gland cellular activity was stimulated in response to cadmium treatment.