Stimulation of progesterone synthesis in luteinized human granulosa cells by human chorionic gonadotropin and 8-bromo-adenosine 3',5'-monophosphate: the effect of low density lipoprotein.

Primary cultures of luteinized human granulosa cells reduced progestin secretion when taken from serum- and gonadotropin-containing medium into serum- and hormone-free medium. When added individually hCG, 8-bromo-cAMP and low density lipoprotein (LDL) stimulated progestin secretion by the cells after they spent 48 h in serum- and hormone-free medium. However, combinations of hCG or 8-bromo-cAMP and LDL were most effective in increasing steroidogenesis. The effects of hCG in enhancing steroidogenesis in the presence of LDL were first detectable after 3 h, but were most marked after 20 h of culture. hCG and 8-bromo-cAMP increased the conversion of [3H]cholesteryl linoleate, which had been incorporated into the core of LDL, into [3H]progesterone. hCG also stimulated cellular accumulation of LDL cholesterol, as assessed by incorporation of [1-14C]oleic acid into sterol esters or by measurement of total cellular cholesterol in the presence of amino-glutethimide to block steroidogenesis. In contrast to progesterone secretion, estradiol secretion was not affected by the addition of LDL in the absence or presence of 8-bromo-cAMP. We conclude that LDL cholesterol is required for maximal rates of progestin synthesis by human luteinized granulosa cells. When granulosa cells are stimulated by hCG, uptake of LDL cholesterol is promoted, and there is increased utilization of LDL cholesterol for steroid synthesis.