Characterization of a factor from human ovarian follicular fluid which stimulates Leydig cell testosterone production

A factor from human ovarian follicular fluid (hFF) has been characterized which stimulates testosterone production of human, rat, mouse and hamster Leydig cells. hFF was obtained from women participating in an in vitro fertilization programme. Basal and hCG stimulated testosterone production of rat interstitial cells, and Percoll purified Leydig cells were significantly stimulated by hFF. The steroidogenic response of the cells was 3-5 fold higher than that obtained after stimulation with maximal doses of hCG. A serum pool from the same patients was found to be about 30 times less potent than hFF in stimulating steroidogenesis. The stimulatory activity was retained after precipitation with ammonium sulphate and dialysis. Precipitation with ethanol, ether and acetone resulted in a partial loss of activity, whereas extraction with charcoal or heating at 100 degrees C for 10 min resulted in significant loss of activity. When hFF was fractionated by gel chromatography, the stimulatory activity was eluted in a molecular weight region between 30 and 50 kD. The stimulatory factor was further purified by chromatofocusing and was eluted as a homogeneous peak with an isoelectric point between 8.8 and 9.5. The SDS-PAGE analysis of these fractions, however, revealed that the active substance was not homogeneous. The purified factor was immunologically distinct from hCG and hLH. These studies demonstrate for the first time the presence of a factor in the hFF which may potentiate the action of LH in the ovary.