Medroxyprogesterone acetate (MPA), a widely used synthetic steroid, was studied to determine both its effects on steroid receptors and steroidogenesis in the well-characterized rat ovarian granulosa cell model. Initial receptor binding studies showed MPA was as potent as progesterone and 10-fold less potent than R-5020 (an active synthetic progestin) in binding to progesterone cytosolic receptors in rat ovarian granulosa cells. MPA was 20-fold less potent than testosterone, and 10-fold less potent than dexamethasone in binding to the androgen and glucocorticoid cytosolic receptors, respectively. The binding of MPA to progestrone, androgen and glucocorticoid receptors predicted direct effects of MPA on FSH-stimulated estrogen (E), progesterone (P), and 20 alpha-dihydroprogesterone (DHP) production by cultured rat ovarian granulosa cells. MPA at 10(-7) to 10(-6) M significantly augmented FSH-stimulated P and DHP production (a previously documented progestin, androgen and glucocorticoid effect). This augmentation was blocked by the concurrent addition to cell culture of 10-fold excess RU-486 (a potent anti-progestin and anti-glucocorticoid). At concentrations greater than 10(-6) M, MPA inhibited the production of P and DHP (a progestin effect), and the production of E (a progestin and glucocorticoid effect). MPA, structurally a progestin, has complex steroid hormone effects predicted by its interaction with progesterone, androgen and glucocorticoid receptors.