Sexual behaviour of neonatally castrated rats injected during infancy with oestrogen and dihydrotestosterone

Abstract

Male rats were castrated on the day of birth (day 1) and injected with either testosterone, dihydrotestosterone, a synthetic oestrogen (RU 2858 + dihydrotestosterone, or oil from days 1 to 5. The aromatizable androgen, testosterone, and RU 2858 suppressed both cyclic gonadotrophin secretion, indicated by the absence of corpora lutea from implanted ovarian grafts, and the behavioural response to oestradiol benzoate + progesterone injections in adulthood. The 5alpha-reduced androgen, dihydrotestosterone alone did not affect gonadotrophin secretion or female receptive behaviour, but like testosterone, it increased penis development in response to testosterone propionate, and this was positively correlated with copulatory efficiency, i.e. the ratio of intromission to mount frequencies. Nevertheless, ejaculation only occurred among animals that had received testosterone or RU 2858 + dihydrotestosterone. The results support the concept that during the preinatal period, neural conversion of androgens to oestrogens is important both for the suppression of female gonadotrophin secretion and behaviour patterns as well as for the organization of male behaviour patterns. The 5alpha-reduction of unsaturated C19-steriods to dihydrotestosterone in peripheral tissues is also required to complete the development of the male genital tract.

PIP: Experiments were carried out to compare the masculine sexual behavior of male rats castrated on the day of birth (Day 1) and injected with testosterone (an aromatizable androgen), dihydrotestosterone (a nonaromatizable androgen), or an estrogen. Litters of Sprague-Dawlet rats were castrated under cryoanesthesia on Day 1 and assigned to 1 of 5 treatment groups: Group 1 received 50 mcg testosterone, Group 2 received 50 mcg dihydrotestosterone, Group 3 received RU 2858, Group 4 received 50 mcg dihydrotestosterone plus 1 mcg RU 2858, and Group 5 was given .05 ml oil. During Week 5 an ovary from a prepubertal female rat was transplanted under the left kidney capsule of each rat. Each rat was given 20 mcg estradiol benzoate per kg followed by .5 mg progesterone. Sexual receptivity was assessed. The aromatizable androgen, testosterone, and RU 2858 suppressed both cyclic gonadotropin secretion and the behavioral response to estradiol benzoate plus progesterone injections. Gonadotropin secretion or female receptive behavior was unaffected by dihydrotestosterone, but it increased penis development in response to testosterone propionate which was positively correlated with copulatory efficiency. Ejaculation only occurred in those animals that had recived testosterone or RU 2858 plus dihydrotestosteorne. During the perinatal period natural conversion of androgens to estrogens is needed for the suppression of gonadotropin secretion and behavior and for the development of male behavior patterns.