Effects of an estrogen antagonist on behavior and on estrogen retention in neural and peripheral target tissues

Abstract

Sexual receptivity was induced in ovariectomized female rats by a single intravenous injection of 4μg or more of estradiol-17β. Intravenous administration of the estrogen antagonist CI-628 up to 6 hr after the estrogen injection completely inhibited subsequent lordotic responses. A partial inhibition of behavior was observed when the antiestrogen was given 8 or more hr after the estrogen. Parallel analysis of retention of radioactivity following 3H-estradiol administration in neural and peripheral tissues revealed that CI-628 displaced the hormone from uterine and hypothyseal receptor sites. However, radioactivity was not displaced from the anterior and posterior hypothalamus, anterior mesencephalon and cerebral cortex. The results suggest that the inhibitory action of CI-628 on behavioral receptivity was not mediated by displacement of estradiol from neural sites. Thus the model relating estradiol displacement to estrogen antagonism in peripheral tissues was not supported for neural tissues.