Prolactin inhibition of estrogen production by cultured rat granulosa cells.

The effect of prolactin (PRL) treatment on estrogen production by rat granulosa cells was investigated in vitro. Immature, hypophysectomized, DES-treated rats were injected for 2 days with FSH to induce aromatase enzymes and receptors for PRL and LH. After FSH priming, the granulosa cells were cultured for 4 days in serum-free medium containing 10(-7) M androstenedione and purified FSH, LH and/or PRL. A dose-related inhibition of estrogen production from control cells was observed following PRL treatment in which 1 micrograms/ml of PRL inhibited estrogen formation by > 90%. In these same cultures, PRL caused a dose-related increase in progesterone and 20 alpha-dihydroprogesterone secretion. Treatment with purified FSH or LH stimulated estrogen synthesis by 3-10-fold. Concomitant treatment with PRL suppressed the FSH- and LH-induced increases in estrogen production in a dose-dependent manner; 1 micrograms/ml PRL suppressed estrogen production by > 80% during days 2-4 of culture. In these same cultures, PRL did not alter the stimulatory effects of FSH and LH on progesterone and 20 alpha-dihydroprogesterone production. These experiments demonstrate that PRL acts directly on rat granulosa cells in vitro to suppress basal and gonadotropin-induced increases in estrogen production.