Hyperprolactinemia Suppresses Copulatory Behavior in Male Rats and Mice

Male rats and sexually inexperienced male mice, each with chronic hyperprolactinemia induced by ectopic pituitary grafts, exhibited reduced levels of copulatory behavior. Grafted male rats exhibited significantly longer latencies to mount, intromit and ejaculate and significantly fewer mounts and intromissions than did control animals. The proportion of grafted male rats and mice that ejaculated was significantly lower than was that of control animals. Sexual experience eliminated the deficits seen in the copulatory behavior of grafted male mice. In contrast, grafted male rats after additional copulatory exposure continued to show deficits in behavior which were more severe than those seen on earlier tests. Plasma testosterone levels and fertility were unaffected in grafted animals whereas plasma prolactin and corticosterone were significantly elevated and plasma gonadotropins were significantly depressed. The hyperprolactinemic rodent may be a useful model for understanding the mechanisms underlying impaired libido in men with pathological hyperprolactinemia.