Role of estrogens in androgen-induced spontaneous activity in male rats.

Three experiments tested the hypothesis that testosterone may be aromatized to an estrogen to stimulate running-wheel activity in rats. Aromatizable (testosterone propionate: TP) and nonaromatizable (dihydrotestosterone propionate; DHTP) androgens were compared with estradiol benzoate (EB) for the ability to induce running in castrated male rats. The DHTP had no effect on running. The TP increased running, but EB was more than 100 times as effective. A relatively small dose of a specific estrogen antagonist, MER-25, was shown to attenuate the effects of both EB and TP on male running. The MER-25 did not affect the running of castrated, oil-treated male rats and did not inhibit the running induced by food deprivation.