Effect of several androgens, cyproterone acetate or estrogen-progesterone on the prolactin-releasing activity of arginine vasotocin in castrated male rats.

Intravenous (iv) administration of 5 microgram of arginine vasotocin (AVT) into urethane-anesthetized, castrated male rats had no effect on plasma prolactin titers as compared to the rise in prolactin levels observed in intact AVT-treated rats. However, when castrated rats were first treated for two days with 2.5 mg/day of testosterone propionate and then challenged with a 5-microgram dose of AVT, the prolactin surge values obtained were comparable to those seen in intact AVT-treated rats. Conversely, treatment of intact rats for two days with 25 mg/day of the anti-androgen, cyproterone acetate, blocked the prolactin-releasing activity of AVT. In a separate experiment, treatment of castrated rats for two days with 2.5 mg/day of testosterone, androsterone or 50 microgram of estradiol benzoate and 25 mg progesterone, completely restored the prolactin-releasing activity of AVT. Similar treatment with 2.5 mg/day of androstenedione or dihydrotestosterone was without effect in restoring this response to AVT. It is concluded that the presence of gonadal steroids is essential to the action of AVT in provoking the release of prolactin in urethane-anesthetized male rats.