ESTROGENS REGULATE ANGIOTENSIN-CONVERTING ENZYME AND ANGIOTENSIN RECEPTORS IN FEMALE RAT ANTERIOR-PITUITARY

We studied the effects of the estrous cycle, ovariectomy and estrogen replacement on angiotensin-converting enzyme (ACE) (kininase II, EC 3. 4.15.1) and angiotensin II (AT) receptors in the pituitary gland of th e female rat. Quantitative autoradiography, with the use of consecutiv e pituitary sections, allowed for simultaneous determination of change s in binding and in the potential AT synthetic ability of individual p ituitaries, and for a correlation between these two phenomena. In the anterior pituitary, ACE activity and binding of the ACE inhibitor [I-1 25]-351A were not changed during the estrous cycle. Ovariectomy produc ed a significant increase in ACE activity and binding, and both of the se parameters returned to normal after estrogen replacement. There wer e no changes in ACE activity or binding in the posterior pituitary dur ing the estrous cycle or after ovariectomy or hormone replacement. AT receptors were characterized as of the AT1 type, since they were displ aced by the selective AT1 antagonist DuP 753 and not by the AT2 compet itor PD 123177. There were marked changes in the concentration of AT1 receptors during the estrous cycle, with highest numbers in metestrus, lower in estrus and diestrus, and lowest during proestrus. Estrogen r eplacement in ovariectomized rats decreased AT1 receptor number in the anterior pituitary. Our results indicate a dual effect of estrogen on anterior pituitary AT, physiologically on AT receptor expression and pharmacologically on ACE activity.