Inhibition of progestin accumulation by activin-A in human granulosa cells

The effects of activin and inhibin on steroidogenesis in the human ovary were investigated. Granulosa cells harvested from follicles of women undergoing oocyte recovery for in vitro fertilization were maintained in culture for 4 days before treatment in serum-free medium. Human recombinant inhibin-A and activin-A at concentrations of 100 ng/mL did not affect basal progesterone secretion (P greater than 0.05). Progesterone concentrations were increased 2- to 6-fold by hCG or FSH. Activin-A inhibited the progesterone response to hCG compared with that of cells treated with hCG alone (P less than 0.01). The effect of activin-A was dose dependent and significant at 16-18 h of treatment (P less than 0.01). Inhibin-A at the same concentrations as activin-A had no effect on the progesterone responses to hCG and FSH. The hCG-induced accumulation of 20 alpha-hydroxyprogesterone was also attenuated by simultaneous activin-A treatment compared to that in cells treated with hCG alone (P less than 0.01). To investigate the mechanism of action of activin-A, cells were treated with a cAMP analog (8-bromo-cAMP) or an activator of adenylate cyclase (forskolin), with or without activin-A. Activin-A had no effect on 8-bromo-cAMP-stimulated progesterone accumulation. Likewise, forskolin-stimulated progesterone accumulation was not affected by activin-A. The hCG-induced increase in intracellular cAMP was decreased by activin-A in the presence of a phosphodiesterase inhibitor, isobutylmethylxanthine (P less than 0.01). Thus, activin-A may inhibit progesterone production by suppression of gonadotropin-induced cAMP production. These results support an autocrine role of activin-A in the steroidogenic capacity of human ovarian cells.