Involvement of the adrenal gland in the suckling-induced decrease in LH and FSH secretion and the concomitant increase in prolactin secretion in the rat

The role of the adrenal gland in the regulation of gonadotrophin and prolactin secretion in the lactating rat was investigated. Changes in secretion of LH, FSH, prolactin, ACTH, beta-lipotrophin (beta-LPH), inhibin, corticosterone and progesterone after adrenalectomy were examined during the second half of lactation. Follicular maturation was determined by the ability of the follicles to ovulate in response to 10IU human chorionic gonadotrophin (hCG). Adrenalectomy on day 10 of lactation prevented an increase in plasma concentrations of LH and FSH in response to ovariectomy performed at the same time as adrenalectomy, and markedly stimulated secretion of ACTH, beta-LPH and prolactin. Adrenalectomy reduced the number of follicles capable of ovulating in response to hCG. Concentrations of inhibin and progesterone in the plasma significantly decreased after adrenalectomy, indicating that development of ovulatory follicles and luteal function had been suppressed. Abolishing the increase in plasma concentrations of LH and inducing a decrease in FSH in the plasma by adrenalectomy therefore prevented maturation of a new set of follicles usually seen during the second half of lactation in rats. The decrease in plasma concentrations of LH also inhibited the ability of the corpus luteum to secrete progesterone, although high concentrations of plasma prolactin were maintained in adrenalectomized lactating rats. These results indicate that the pituitary-adrenal system is capable of influencing the maintenance of a normal secretion of gonadotrophin and prolactin as well as the maintenance of ovarian function during lactation in the rat.