Prolactin Control of Receptor for Estradiol in Corpora Lutea of Pregnant Rats

Abstract

Both prolactin and a prolactin-like hormone from the placenta, rat placental lactogen, appear to be required for the luteotropic effect of estrogen in corpora lutea of pregnant rats (1–3). However, the specific synergistic role of these two hormones with estrogen has not been defined. Because receptors for both estradiol and prolactin have been identified and characterized in corpora lutea of pregnant rats, the luteotropic effects of these two hormones are presumed to be direct (4,5). The following studies were designed to determine if the synergistic role of prolactin in maintaining luteal cell progesterone production might involve, at least in part, maintenance of luteal cell receptors for estradiol. To examine the roles of pituitary and placental hormones during early pregnancy two approaches were taken. In the first, pituitary prolactin surges (6) were selectively inhibited by the administration of 2-bromo-α-ergocryptine (ECO; CB-154; 7–10). In the second, both the pituitary and placenta were surgically removed.