Effects of eel calcitonin on plasma beta-endorphin-like immunoreactivity levels in rats

The effect of synthetic eel calcitonin (CT) on the level of plasma beta-endorphin-like immunoreactivity (beta-En-LI) and on its content in hypothalamus and anterior pituitary in vivo and on the release of beta-En-LI-from anterior pituitary in vitro was studied. The level of beta-En-LI was increased significantly in a dose-dependent manner after the injection of 1-100 U/kg CT, maximum level being found at 10 min after the injection. After the administration of 50 U/kg CT, the increase was still significant at 40 min. Such an increase was not found in hypophysectomized animals. The content of beta-En-LI in the hypothalamus and anterior pituitary did not change significantly after CT injection. In vitro, the release of beta-En-LI from anterior pituitary was enhanced significantly after CT. It may be concluded that CT acts on the pituitary to increase the release of beta-En-LI which results in increased plasma level.