Abstract

Previous studies have shown that bromocriptine interacts with cytosolic estrogen receptors in the rat uterus. We have now investigated the possible agonistic or antagonistic action of bromocriptine on various responses to estrogen in the rat uterus. Immature rats were intravenously injected with bromocriptine (1 mg/kg b.wt), estradiol-17? (300 ?g/kg b.wt) and/or their vehicle(s) and several responses to estrogen were monitored 6 or 24 h later. In the absence of estrogen, bromocriptine induced a slight uterine eosinophililia and endometrial oedema. Bromocriptine inhibited estrogen-induced hypertrophy of uterine luminal and glandular epithelium and myometrium, the uterine mitotic response in most cell-types and deep endometrial oedema. Bromocriptine potentiated estrogen-induced uterine eosinophilia at 6 h after treatment, but antagonized the response at 24 h. The dissociation between responses to estrogen is in agreement with a previous finding of differences between estrogen receptors in various uterine cell types and the existence of independent mechanisms of estrogen action in the uterus.