CULTURED HUMAN GRANULOSA-CELLS SECRETE A FOLLICLE-STIMULATING-HORMONERECEPTOR-BINDING INHIBITOR

We previously reported that human follicular fluid contained a protein that inhibits binding of I-125-human FSH to its membrane receptor (FS H-BI) and demonstrates FSH-like agonist activity in vitro, The cellula r origin of FSK-BI was unknown, although ovarian granulosa cells seeme d a likely source, To address this question, human granulosa cells wer e collected from patients during routine in-vitro fertilization (IVF) or gamete intra-Fallopian transfer (GIFT) procedures. Cells from 98 pa tients were cultured and then examined for their ability to secrete FS H receptor-binding inhibitory activity into the culture medium, The fu nction of the cultured cells was confirmed by their ability to respond to added FSH with conversion of exogenous androstenedione to oestradi ol. Radioreceptor assays were performed individually on cell culture m edium obtained from granulosa ceh cultures from these 98 patients. Cul tured granulosa cells, under basal conditions (in the absence of FSH s timulation), secreted significant FSH-BI activity into the culture med ium, In order to accumulate enough material for further study, this cu lture medium was pooled and lyophilized, The lyophilized medium retain ed FSH-BI activity, and also demonstrated FSH agonist activity by stim ulating oestradiol synthesis in cultured rat Sertoli cells, A fraction showing a single component after purification by polyacrylamide gel e lectrophoresis had an estimated molecular weight of 25 000, and inhibi ted I-125-human FSH binding to receptor by 50% at 2.5 mu g/ml. The res ults indicate that human granulosa cells secrete a protein with FSH-li ke activity having potential significance as a local regulator of FSH action in the ovary.