Peroxidase as a marker enzyme in estrogen-responsive tissues

Abstract

Peroxidase, an enzyme that can be induced readily in immature rat uteri by physiological doses of estrogen and is also present in some DMBA-induced mammary tumors, has proved to be a useful marker for the study of estrogen action. The induction of peroxidase in the rat uterus under various endocrine conditions has been investigated together with the effect of progesterone and a number of estrogens and related compounds. The nature of the steroids present in the uteri of immature rats and in those of animals pretreated with estrogen which contain peroxidase was examined after the in vivo administration of [ 3H]estradiol. Only unchanged estradiol and some estrone were detected in the uteri of both groups of rats and most of the radioactivity was released into the medium after incubation with p-hydroxymercuribenzoate or diethylstilbestrol, indicating an absence of covalent binding. Peroxidase is therefore unlikely to limit the duration of estrogen action in the intact animal as had been suggested earlier. In DMBA-induced mammary tumors, a moderate correlation was obtained between peroxidase activity and the concentration of nuclear estrogen receptors. It is proposed that the enzyme peroxidase which is dependent on estrogen for its biosynthesis provides a better indication of the hormone responsiveness of tumors than the concentration of estrogen receptor.