Resumption of estrogen-induced gonadotropin surges in postpartum monkeys.

Abstract

To evaluate the functional integrity of the hypothalamic-pituitary (H-P) system in postgestational monkeys, peripheral serum concentrations of LH and FSH were determined in postpartum (nursing and nonnursing) and postabortion (midpregnancy) females challenged with estradiol benzoate (EB) at a dose known to be effective in eliciting gonadotropin surges in cycling monkeys. In a longitudinal study of nursing and nonnursing postpartum mothers and postabortion females, EB was administered serially during weeks 1, 3, 5, 7, 9, and 11 post delivery. Some nursing monkeys were challenged with EB up to 6 months post partum. In a cross-sectional study of nursing mothers, this response to EB was evaluated during weeks 1, 3, 5, 7, and 9 postpartum. H-P responsivity to EB was impaired in nursing monkeys through 180 days post partum, in that FSH or LH surges were not induced by estrogen therapy. In contrast, nonnursing postpartum mothers and postabortion females regained their sensitivity to this positive feedback action of estrogen within 35-49 days. Our findings indicate that during gestation a transient lesion develops in the H-P system and persists into the puerperium. It blocks the positive feedback response of surge gonadotropin secretion induced by estradiol. However, this H-P failure is not sufficient by itself to explain postpartum infertility in these primates, since in nonnursing monkeys, spontaneous resumption of ovulatory menstrual cycles seldom occurs until 2-4 months after delivery at term.