Endogenous opiate systems and primate reproduction: inability of naloxone to induce sexual activity in rhesus males

The opiate antagonist naloxone was tested for its effectiveness in inducing sexual behavior in sexually inactive male rhesus macaques (Macaca mulatta). Naloxone was administered to males directly into the carotid artery via a T-tube implant. Naloxone-treated males and sexually receptive females were pair tested for sexual behavior. Despite the positive behavioral cues of the females, the males failed to initiate heterosexual interactions at any level of naloxone therapy. The implications of this finding for the role of the endogenous opiate system in primate reproduction are discussed in relation to the homeostatic nature of the system.