Histochemical and Electron Microscopical Studies on the Parathyroid Gland in Experimental Hens Producing Soft-Shelled Eggs.

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The parathyroid gland was examined morphologically in experimental hens producing soft-shelled eggs in which the secretion of egg shell calcium was inhibited by ligation of the shell gland of the oviduct with the loop of a string. Histological observation of medullary bone and measurement of plasma calcium levels were carried out.The chief cells of parathyroid glands in experimental hens had poorly developed cell organelles compared to those in normal hens. Although secretory granules were comparatively numerous in the cytoplasm, secretion of the granules was not observed at the plasma membrane. Acid phosphatase, succinate and lactate dehydrogenase activity in the chief cells of experimental hens did not differ from those of normal hens. However, alkaline phosphatase activity was weaker than that of normal hens.In the experimental hens, thickened medullary bones occupied the marrow cavity. Their surfaces were covered with a small number of osteoblasts and osteoclasts. Most of the cells showed atrophic figures.Plasma calcium levels in experimental hens were somewhat higher than those in normal hens.These results suggest that the egg shell calcium is not secreted and the secretion of parathyroid hormone in chief cells is suppressed by ligation of the shell gland of the oviduct, so that osteoclastic bone resorption is not activated in experimental hens.
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