4-Hydroxyestradiol-17 beta and 4-hydroxyestradiol-17 alpha: comparative studies on central and peripheral effects of two epimeric catecholestrogens

4-Hydroxyestradiol-17 beta and 4-hydroxyestradiol-17 alpha (5 or 20 microgram/d) were continuously s.c. infused for 3 days into ovariectomized adult rats. The serum levels of either epimer were virtually identical when the same dose was administered. 4-Hydroxyestradiol-17 beta significantly altered body and uterus weight and LH serum levels (negative and positive effects) at both doses tested. 4-Hydroxyestradiol-17 alpha showed no effects even at the 20 microgram/d dose. As both epimers have similar affinities for catechol O-methyltransferase, but their potencies regarding effects on lH serum levels differ markedly, it is concluded that the interaction of catecholestrogens with this enzyme is not essential for their effects on LH release.