Antagonism of estrogeninduced prolactin release by dihydrotestosterone

Previous work from our laboratory has demonstrated that progesterone can inhibit estrogen-induced prolactin release in female rats. Since androgens have been reported to mimic progesterone actions in certain systems, and to antagonize estrogen action in rat uteri, the purpose of this study was to determine whether androgens, like progestins, can inhibit estrogen-induced prolactin release. The ovariectomized (26 days of age) immature rat was used as the model for analysis of this question. Dihydrotestosterone (DHT) was chosen to be used throughout the study since it does not undergo aromatization to estrogens. In response to estradiol exposure (2 tg/rat), prolactin release reached peak values at 12 h and returned to control levels by 24 h. A second injection of estradiol 13 h after its initial injection stimulated a second increase in serum prolactin at 25 h. A single injection of DHT (0.8 mg/kg BW) I h before the second estradiol injection blocked the increase in serum prolactin. DHT had no effect on basal serum prolactin levels. The DHT inhibition of estrogen-induced prolactin release required estrogen priming. A dose dependency for the DHT effect was demonstrated, with low doses effective and high doses ineffective, in inhibiting estrogen action. This effect of DHT seemed to be androgen receptor-mediated, since flutamide blocked the effect. However, the possibility of progestin receptor mediation could not be ruled out since RU486 also blocked DHT’s effect. Flutamide was also effective in blocking progesterone’s inhibition of estrogen-induced action. This is perhaps consistent with an overlap of activities in androgens and pro gestins reported by several investigators. These observations indicate that the role of androgens in a variety of experimental as well as clinically relevant situations needs to be explored not only in terms of direct action but also as modifying estrogen action