DIFFERENTIAL EFFECTS OF ANTI-ESTROGEN MER-25 AND OF 3 5A-REDUCED ANDROGENS ON MOUNTING AND LORDOSIS BEHAVIOR IN RAT

Four experiments were performed in order to evaluate further the hypothesis that androgen must be aromatized to estrogen for the activation of masculine sexual behavior in the male rat. In experiment 1 the anti-estrogen MER-25 failed to disrupt mounting behavior in castrated males which simultaneously received testosterone propionate (TP). However, in experiment 2 MER-25 as well as 3.beta.-androstanediol effectively activated masculine behavior in castrated males treated simultaneously with dihydrotestosterone propionate. Both MER-25 and 3.beta.-androstanediol had previously been shown to display an affinity for cytoplasmic estradiol-17.beta. receptors present in male rat anterior hypothalamus. In experiments 3 and 4, performed with ovariectomized females, whereas MER-25 antagonized the stimulatory effect of estradiol benzoate (EB) or lordosis behavior, 3.beta.-androstanediol did not. In addition, 5.alpha.-dihydrotestosterone and 3.alpha.-androstanediol, 2 compounds which had previously been shown to have almost no affinity for estradiol-17.beta. receptors in the hypothalamus, both inhibited the stimulatory effect of EB on lordosis. The fact that anti-estrogens suppress lordosis induced in females with either EB or TP, but fail to disrupt TP-induced mounting behavior in male rats does not argue against the aromatization hypothesis for masculine sexual behavior.