Induction of uterine ornithine decarboxylase (ODC) by antiestrogens. Inhibition of estradiol-mediated induction of ODC: a possible mechanism of action of antiestrogens.

The ability of antiestrogens (tamoxifen and nafoxidine) to affect uterine ornithine decarboxylase (ODC) in the ovariectomized rat was determined. Tamoxifen citrate (1 mg or 10 mg/kg) and nafoxidine (0.5 mg/kg) markedly elevated ODC levels. Tamoxifen (1 mg/kg) given for 4 days totally inhibited the E2 (0.5 mug/kg)-mediated induction of ODC. Similarly nafoxidine (0.5 mug/kg) given once a day for 2 days inhibited the E2-mediated induction of ODC. The relation of the inhibition of ODC induction by antiestrogens to their mechanism of action as antiestrogens is discussed.