Regulation of inhibin production by bovine ovarian cells in vitro

Abstract

The regulation of ovarian inhibin production was investigated using a rat pituitary cell culture system as a bioassay for inhibin activity. Bovine follicular granulosa cells produced inhibin in vitro provided that the culture medium contained serum. The stimulatory factor(s) present in serum is unlikely to be gonadotrophins, because bovine LH and/or FSH failed to stimulate inhibin production when added to medium devoid of serum. Luteinization of granulosa cells in culture was accompanied by a reduction in their inhibin production and an inverse relationship existed between inhibin and progesterone production by granulosa cells. Bovine corpus luteum cells in culture failed to produce detectable amounts of inhibin. Androgens stimulated granulosa cell inhibin production with testosterone and 5α-dihydrotestosterone being more potent than androstenedione. The androgens did not stimulate inhibin production by luteal cells. Progesterone inhibited granulosa cell inhibin production but oestrogens had no effect. Measurement of steroids and inhibin in fluid from individual follicles indicated that as follicle size increased, concentrations of oestradiol-17β increased, testosterone and inhibin decreased and progesterone remained unchanged. The stimulatory effect of testosterone on inhibin production in vitro together with the parallel changes in follicular fluid concentrations of testosterone and inhibin suggest that ovarian inhibin production in vivo may be controlled, at least in part, through androgens modifying granulosa cell inhibin production. The inhibitory effect of progesterone on granulosa cell inhibin production may be more important in regulating ovarian inhibin production at the time of granulosa cell luteinization and CL formation. The stimulatory effect of androgens on granulosa cell inhibin production might also be a means by which androgens promote follicular atresia.