Catechol estrogen formation in mouse uterus.

Estrogen 2/4-hydroxylase (ESH) and catechol-O-methyltransferase (COMT) activities in mouse liver and uterus were studied. While 2-hydroxyestradiol (2-OHE2) was the predominant product in the liver, equal amounts of 2- and 4-hydroxyestradiol were produced in the uterus. Two-hydroxyestradiol was the preferred substrate for COMT in both tissues, but the level of this enzyme activity was much less in the mouse uterus (17-fold less). Thus, preferential production of 4-hydroxyestradiol (4-OHE2) in the presence of relatively less deactivation provides a mechanism for the local formation of a more chemically active form of estrogen by uterine tissue.