Changes in Pituitary Prolactin Release and Hypothalamic PIF Content During the Estrous Cycle of Rats.

Abstract

Comparisons were made of pituitary prolactin content, pituitary pro-lactin release in vitro and hypothalamic PIF [prolactin inhibitory factor] content at different stages of the estrous cycle of the rat. The anterior pituitaries of proestrous and estrous rats contained significantly more prolactin than anterior pituitaries of diestrous rats; the former released significantly more prolactin when incubated in vitro than the latter, and proestrous and estrous rats had significantly less PIF in the hypothalamus than diestrous rats. Ovarian estrogen secreted during proestrous and estrous is believed to increase prolactin release by depressing hypothalamic PIF production and by directly stimulating the pituitary.