Progesterone Regulation of the Production and Release of Pituitary Gonadotrophins in the Gonadectomized Sheep

Abstract

One preliminary study and 3 experiments were conducted with gonadectomized male sheep to obtain information on the influence of progesterone administration on the pituitary production and release of gonadotrophic principles. Sequential collections of pituitaries and cavernous sinus blood (pituitary venous blood) were made from progesterone-treated animals, and aliquots of both were bio-assayed in immature, hypophysectomized female rats. The results showed that increased amounts of gonadotrophic hormones were released into the blood stream on the 5th and 6th days of treatment with 20 mg of progesterone daily and again at approximately the same time interval following withdrawal of treatment. Similar increases in the plasma titer were observed on the 6th and 10th day following a single 500 mg injection of progesterone. In some of the experiments in which progesterone was administered daily, smaller increases in the plasma titer were apparent on other days during and following the administration of progesterone. Pituitary FSH activity was significantly increased immediately after treatment, but changes in ICSH were inconclusive. The findings of this study are discussed in relationship to current concepts of progesterone and pituitary interactions. (Endocrinology75: 401, 1964)