ONTOGENY OF THE ESTROGEN INDUCIBILITY OF UTERINE PEROXIDASE

The estrogen inducibility of the enzyme, peroxidase (donor: hydrogen-peroxidase oxidoreductase, EC 1.11.1.7), in the uterus of the 3-22 day old rat was studied and compared to the ability of estrogen to stimulate increases in uterine weight. Neither estradiol nor diethylstilbestrol were able to effect significant increases in uterine weight or peroxidase content in 4 or 7 day old rats. Around 11-13 days of age the uterus becomes sensitive to both estrogens as indicated by both significant estrogen stimulation of uterine weight and induction of uterine peroxidase 20 h after either estrogen. Since diethylstilbestrol, which does not readily bind to α-fetoprotein, is also incapable of stimulating uterine weight or inducing peroxidase in the 4 and 7 day old animal it is likely that the insensitivity of the early postnatal uterus to estrogen is not due to the high circulating levels of a-fetoprotein. At the same age that the uterus becomes sensitive to the effects of estrogen it also becomes sensitive to progesterone inhibition of the estrogen-stimulation. These studies indicate that the inducibility of uterine peroxidase correlates very well with the estrogen stimulation of uterine weight in the postnatal rat and that the ontogeny of hormonal sensitivity of the uterus appears rather abruptly, within a period of several days. © 1979.