Inhibition of human chorionic gonadotropin production by prolactin from term human trophoblast

In vivo suppression of prolactin concentrations by bromocriptine near term, in a pregnant woman with a prolactinoma, was followed by augmentation of human chorionic gonadotropin levels. Suspension of drug therapy at 38 weeks of gestation was followed by a reversal of this sequence of events. In vitro, both ovine prolactin and human prolactin added to explants of term placental trophoblast significantly inhibited human chorionic gonadotropin production from this tissue. Although, with ovine prolactin, this inhibitory effect was demonstrable up to 5 micrograms/ml of ovine prolactin in the culture medium, only doses of 0.1 to 0.2 micrograms/ml of human prolactin significantly suppressed human chorionic gonadotropin production. Overall, 0.1 and 0.2 micrograms/ml of ovine prolactin and human prolactin most consistently suppressed human chorionic gonadotropin production to a statistically significant extent. In general, the concentrations in the culture medium of both ovine prolactin and human prolactin that inhibited human chorionic gonadotropin production in vitro were comparable to the concentrations of prolactin present in the mother and fetus. These in vivo and in vitro observations suggest that prolactin inhibits human chorionic gonadotropin production from term human trophoblast.