Effect of Estrogen on Thyrotropin-Releasing HormoneInduced Release of Prolactin in Intact, Ovariectomized, and Stalk-Sectioned Female Rhesus Monkeys*

The effects of estrogen treatment on basal and TRH-induced serum PRL concentrations were studied in three groups of four female rhesus monkeys; intact monkeys, ovariectomized animals, and monkeys in which the pituitary gland had been isolated from direct hypothalamic influences by pituitary stalk section. The TRH tests (50 microgram, iv) were performed before and 7 and 21 days after the sc implantation of one or two 3-cm long silastic capsules containing 17 beta-estradiol. Treatment with estradiol significantly increased the PRL response to TRH in the three groups of animals. The highest PRL response to TRH was observed after stalk section. The estrogen treatment also increased basal PRL concentrations in stalk-sectioned monkeys but no statistically significant increase was observed in intact or ovariectomized animals. These results indicate that physiological amounts of estradiol increase the magnitude of TRH-induced PRL release in rhesus monkeys, and that this estrogen effect is probably enacted directly at the level of the anterior pituitary gland.