Effects of morphine, beta-endorphin and naloxone on catecholamine levels and sexual behavior in the male rat.

Intraperitoneal administration of the opiate antagonist naloxone hydrochloride (30 mg/kg) to sexually experienced male rats caused a significant reduction in mount and intromission latencies, number of mounts preceding ejaculation and ejaculation latencies. Intraperitoneal adminstration of naloxone (30 mg/kg) also stimulated persistant non-copulators to begin mating and to ejaculate within a twenty minute test period. Conversely, intraperitoneal administration of morphine sulphate (6 mg/kg) as well as intraventricular injection of the endogenous opiate beta-endorphin (6 micrograms) produced a complete loss of copulatory behavior in male rats. The deficit in sexual behavior induced by beta-endorphin was correlated with a significant increase in hypothalamic norepinephrine levels. It is suggested that the endogenous opiates may be involved in the mediation of sexual behavior via an interaction with central catecholaminergic systems.