Plasma lipoproteins in follicular fluid of human ovaries

Human corpus luteum tissue, maintained in organ culture, is dependent upon low-density lipoprotein (LDL) as a source of cholesterol for maximal progesterone secretion whereas high-density lipoprotein (HDL) does not support progesterone biosynthesis by human corpus luteum tissue. In the present investigation, follicular fluid of human ovaries was found to contain little or no LDL or very low-density lipoprotein. The concentration of HDL in follicular fluid approached that found in plasma. We suggest that one reason that granulosa cells of the preovulatory follicle produce limited quantities of progesterone is because of the absence of LDL-cholesterol in follicular fluid. Following ovulation, vascularization of the corpus luteum provides a means by which LDL is available to the luteinized granulosa cells and thence progesterone biosynthesis can commence.