DIFFERENTIAL EFFECTS ON BEHAVIOUR OF THE SUBCUTANEOUS AND INTRAVAGINAL ADMINISTRATION OF OESTROGEN IN THE RHESUS MONKEY (MACACA MULATTA)
The behavioural interactions between pairs of oppositely sexed, adult rhesus monkeys were studied during 1307 mating tests, each of 1 hr. duration. Females were ovariectomized and the effects of administering oestrogen subcutaneously, intravaginally, and directly to the sexual skin at different daily dose rates were compared. The subcutaneous route resulted in a greater enhancement of the overall sexual activity of the pair, and in a greater stimulation of the females' sexual invitations. In contrast, the intravaginal route of administration resulted in a greater stimulation of the males' sexual interest and of the males' mounting attempts: this occurred without a corresponding increase in female sexual receptivity and, in two pairs, resulted in increased aggression. It is concluded that communication between these primates was influenced by oestrogen-dependent changes in the vagina, and the findings point to the existence of a substance with a pheromone-like action.