Luteinizing hormone/human chorionic gonadotropin stimulates progesterone biosynthesis in the corpus luteum by activating cyclic adenosine monophosphate/protein kinase A cascade. Recent studies have shown that cyclic adenosine monophosphate-mediated activation of protein kinase A interacts with the mammalian target of rapamycin signaling pathways. Furthermore, the use of mammalian target of rapamycin inhibitors for immunosuppression in transplant patients has shown adverse effects in reproductive functions. This study examined whether the mammalian target of rapamycin pathway plays any role in luteinizing hormone-mediated regulation of progesterone production. Human granulosa lutein cells were isolated from follicular aspirates of women undergoing in vitro fertilization. Cells were cultured for 72 h and treated with human chorionic gonadotropin (50 ng/ml) for different time periods with or without pretreatment with mammalian target of rapamycin complex 1 inhibitor, rapamycin, (20 nM) for 1 h. Expression of steroidogenic enzymes, including steroidogenic acute regulatory protein, cholesterol side chain cleavage enzyme, and 3 beta-hydroxysteroid dehydrogenase type 1 messenger RNA, were examined by real-time polymerase chain reaction after 6 h of human chorionic gonadotropin treatment. Expressions of phospho-ribosomal protein S6 kinase and cholesterol side chain cleavage enzyme were analyzed after 15 min and 24 h of human chorionic gonadotropin treatment, respectively. Progesterone production was analyzed by an enzyme immunoassay kit after human chorionic gonadotropin (50 ng/ml) or forskolin (10 mu M) treatment for 24 h. Treatment with human chorionic gonadotropin increased the expression of downstream targets of mammalian target of rapamycin complex 1, as well as cholesterol side chain cleavage enzyme, 3 beta-hydroxysteroid dehydrogenase type 1 and steroidogenic acute regulatory protein messenger RNAs. These increases were inhibited by rapamycin pretreatment. Increased progesterone production in response to treatment with human chorionic gonadotropin or forskolin was also blocked by rapamycin pretreatment. Our findings support a role for mammalian target of rapamycin complex 1 in regulating steroidogenesis in human granulosa lutein cells.