Melanocyte stimulating hormone and the inhibition of sexual behaviour in the female rat.

When administered to ovariectomized females, primed with oestradiol benzoate (OB) and progesterone, alpha-MSH increased lordosis behaviour in those rats that showed a low level of receptivity but in rats that were receptive it had an inhibitory effect. alpha-Melanocyte stimulating hormone also inhibited proceptive behaviour in these females. Luteinizing hormone releasing hormone (LHRH), on the other hand, failed to have a similar inhibiting effect although it did stimulate lordosis. While adrenalectomy failed to alter the stimulatory effect of alpha-MSH on lordosis it completely prevented the inhibitory actions of alpha-MSH on both lordosis and proceptive behaviour. Thus, while alpha-MSH may stimulate lordosis through a central action its inhibitory effects on lordosis and proceptive behaviour are probably mediated via the adrenal glands. Although alpha-MSH may stimulate the secretion of an adrenal steroid that blocks the facilitatory action of progesterone on female sexual behaviour the present results suggest that this inhibitory effect could be mediated by a catecholamine.