Effect of Prolactin on Progestin Release and Cholesterol Storage by Rabbit Ovarian Interstitium

Abstract

Previous studies have shown that pituitary luteinizing hormone (LH) accelerates the synthesis and release of 20 alpha]-hydroxy-pregn-4-en-3-one (20[alpha] -OH) from rabbit ovarian interstitial tissue (IST) concomitant with a loss of IST cholesterol. When ovarian cholesterol is depleted by a large dose of exogenous LH, steroido-genesis is depressed and less steroid is released. Chronic prolactin treatment promotes cholesterol storage, restores the basal output of 20[alpha]-OH and enhances the sensitivity of the ovary to LH in the intact animal. When rabbits are hypophysectomized 24 hr. after an iv injection of 250 [mu]g LH, both the IST and the new corpora lutea (CL) become atrophic, cholesterol levels remain low, and no basal release of either 20[alpha]-OH or progesterone is detectable. In such animals, chronic prolactin treatment causes hypertrophy of the IST and elevates cholesterol stores but does not induce progestin release in the absence of estrogen or LH. On the other hand, when the CL are maintained with estrogen, the IST remains atrophic and the basal release of progesterone exceeds that of 20[alpha] -OH. It prolactin and estrogen are administered together, both IST and CL hypertrophy and the amount of 20[alpha]-OH released is greater than that of progesterone. It can be concluded, therefore, that prolactin acts specifically on the rabbit ovary to maintain the steroid producing capacity as well as the morphology of the IST.