Facilitation by opiate antagonists of sexual performance in the male rat.

Intraperitoneal administration of increasing doses (5 mg/kg or 20 mg/kg) of the opiate antagonists naloxone hydrochloride or naltrexone hydrochloride to sexually experienced male rats caused a significant reduction in the number of intromissions prior to ejaculation and ejaculation latency. Mount and intromission latencies were significantly reduced following treatment with only the lower dose of each antagonist. Ways are suggested whereby endorphins may modulate masculine sexual performance and thereby contribute to successful fertilization of female conspecifics.