Hormonal control of sexual behaviour in the male rat and its implications for other species

Abstract

Renewed interest in the hormonal control of male sexual activity stems from the finding that 5ol-reduced metabolites of testosterone (e.g. dihydrotestosterone) are strongly androgenic in the castrated rat but do not support sexual behaviour. In contrast, androgen/ oestrogen intermediates such as 19-hydroxytestosterone and oestrogen itself maintain the arousal component of sexual behaviour but not intromission performance. This deficit is a consequence of reduced penile sensitivity since oestrogenic steroids fail to maintain penile spines which provide peripheral feedback. If oestrogen-treated castrates additionally receive dihydrotestosterone to restore normal penile morphology, normal sexual behaviour ensues. Hence, oestrogen plus dihydrotestosterone effectively substitute for testosterone in the male rat. Biochemical evidence supports this finding since testosterone is known to undergo aromatization to oestrogen in the hypothalamus of the male rat and Se-reduction peripherally. Whether the aromatization model of testosterone action is applicable to species other than the rat is currently a matter for speculation. In mice, guinea pigs and hamsters evidence is either contradictory or unclear. However, the rabbit appears to be like the rat and oestrogen also supports normal sexual activity in castrated red deer stags. Conversely, in the rhesus monkey dihydrotestosterone alone appears to be effective. Further studies are required to establish the generality of the aromatization hypothesis; this applies particularly to domesticated species. SENSORY ASPECTS OF THE SEXUAL BEHAVIOUR OF MARES . . J. VEECKMAN and F.O. ODBERG Rijksuniversiteit Gent, K.L. Ledeganckstraat 35, B-9000 Gent (Belgium)