Role of Prolactin in the Lactational Amenorrhea of the Rhesus Monkey (Macaca mulatta)1

The role of prolactin in suckling-induced suppression of gonadotropin secretion was investigated in postpartum rhesus monkeys treated with bromocriptine, some of which were allowed to suckle their young while others were not. Serum prolactin (PRL) was suppressed in all animals. The postpartum rise in the basal levels of luteinizing hormone (LH) and the response to the positive feedback action of estradiol were delayed in the suckled monkeys when compared with their nonsuckled controls. The inhibition of LH secretion was more pronounced than that of follicle stimulating hormone (FSH). These findings permit the conclusion that hyperprolactinemia may not entirely account for the inhibition of gonadotropin secretion during lactation and that sensory inputs associated with suckling may affect the hypothalamic control of gonadotropin secretion by some other mechanism.