Ovarian Cholesterol Levels During the Reproductive Cycle of the Rat. ∗

Abstract

Evidence that ovarian cholesterol may be a precursor of the ovarian hormones, particularly progesterone, has been by inference, both positive and negative. Comparison of results from previous studies on cholesterol variations during the ovarian cycle is difficult because of the lack of uniformity in presenting data, i.e., some report the free cholesterol and others only the cholesterol esters. By histochemical methods, no changes were observed in ovarian cholesterol during the reproductive cycle in humans 1 although chemical analysis of human corpora lutea indicated a significant decrease in cholesterol esters only in the actively functioning corpus luteum of pregnancy. 2 In the pig, the cholesterol ester content of the corpora lutea was found to vary inversely with the activity of the gland. 3 Boyd4 found that in the whole ovary of the rabbit, there was an increase in the free cholesterol during the first half of pregnancy followed by a decline while the cholesterol esters increased only during the last half of pregnancy. These results were interpreted as indicating that the rabbit corpora lutea reach a peak of activity about the middle of gestation. No change in free cholesterol was observed in the ovaries of guinea pigs during the course of gestation. 5 Based on histochemical studies of the corpora lutea of diestrum in the rat, Everett 6 strongly suggested that cholesterol serves as a precursor of progesterone.

A systematic examination of cholesterol in the ovary of the rat has been undertaken in this laboratory, and this report will show the changes in cholesterol level of the ovary in diestrum, pseudopregnancy, and at several intervals during pregnancy and lactation.

Methods. Total cholesterol was determined by the method of Chamberlain 7 which consists essentially in saponification of the lipids in alkaline alcohol, extraction of the lipids with ether, and determination of the cholesterol directly on the washed ether-extract residue by the Liebermann-Burchard reaction.