Regulation of Lipid Metabolism and Progesterone Production in Rat Corpora Lutea and Ovarian Interstitial Elements by Prolactin and Luteinizing Hormone

The effects of prolactin in vivo and LH in vitro on synthesis of progesterone and 20α-hydroxypregn-4-en-3-one in isolated, 3-dayold corpora lutea and remaining ovarian elements (interstitial tissue and follicles) of intact rats have been examined. Prolactin (200 μg administered sc twice daily) increased in vitro synthesis of progesterone approximately 4-fold in corpora lutea, and decreased synthesis of 20α-hydroxypregn-4-en-3-one to the same extent; “total progestin” accumulation in vitro was not altered by prolactin treatment. A slight inhibition of synthesis of both steroids in interstitial elements resulted from prolactin treatment. LH (2 μg/ml) added to incubation media significantly increased (by about 50 %) the synthesis of total progestin in corpora lutea only from prolactin-treated rats, the increase being predominantly due to progesterone. Synthesis of both steroids was much lower in interstitial elements than in corpora lutea in the absence of LH; addition of LH caused 7-to 9-fold increases in synthesis of progesterone, but not of 20α-hydroxypregn-4-en-3-one. Prolactin treatment resulted in 2-fold increases and 4-fold decreases in peripheral erum levels of progesterone and 20αhydroxypregn-4-en-3-one, respectively. Incorporation of acetate-l-14C into free cholesterol, esterified sterols, triglyceride fatty acids and progestins was markedly increased by prolactin treatment in corpora lutea, but not in interstitial elements. LH, in vitro, decreased acetate-l-14C incorporation in free cholesterol, and in both the fatty acid and sterol moieties of cholesterol esters in corpora lutea and interstitial elements f both control and prolactin-treated rats. Tissue concentrations of both free and esterified sterols were considerably lower in corpora lutea of prolactin-treated than of control rats. Esterified sterol concentrations decreased further upon in vitro incubation of corpora from prolactintreated, but not from control, rats. Comparable increases in free cholesterol were not observed, indicating increased conversion of esterified sterol to products (e.g., progesterone) upon incubation. Prolactin treatment did not influence concentrations of either free or esterified sterols observed in interstitial elements either before or after incubation. Triglyceride fatty acid levels decreased considerably upon incubation of both corpora lutea and interstitial elements, an effect which was not influenced by either hormone. (Endocrinology85: 393, 1969)