Regulation of anterior pituitary and brain beta-adrenergic receptors by ovarian steroids

Ovariectomy of adult female rats (200-230g) resulted in an increase in beta-adrenergic receptors in the cerebral cortex, hypothalamus and anterior pituitary. The anterior pituitary had the largest overall increase as well as the most rapid increase in beta-adrenergic receptor density of the tissues examined. The increase in hypothalamic or cerebral cortical beta-adrenergic receptors became apparent only long after ovariectomy (7-14 days). Fourteen days after ovariectomy, the density of beta-adrenergic receptors was 79%, 40%, and 24% in excess of control values in crude membranes prepared from anterior pituitary, hypothalamus and cerebral cortex, respectively. Over the same interval, the plasma concentration of luteinizing hormone (LH) increased 28-fold, while the concentration of follicle-stimulating hormone (FSH) rose 5-fold compared to control levels. Estradiol replacement (20 micrograms/kg/day) in these animals for four days before sacrifice concomitantly reduced plasma levels of the gonadotropins as well as the density of beta-adrenergic receptors in both the anterior pituitary and the hypothalamus. Long-term steroid replacement during the fifth and sixth week after ovariectomy, with implants of estradiol and progesterone which released the steroids in approximately physiological concentrations, significantly reduced beta-adrenergic density in anterior pituitary, but not in the hypothalamic membranes. This treatment significantly reduced plasma LH, but not FSH. Beta-adrenergic receptor density was also found to fluctuate significantly during the 4-day estrous cycle. The highest values were found on proestrus, and the lowest on diestrus 1. These studies indicate that changes in plasma concentrations of gonadal steroids (e.g. during the estrous cycle) influence the density of beta-adrenergic receptors in tissues involved in the control and release of anterior pituitary gonadotropins.