[Copulatory behavior after ectopic pituitary grafting in male rats]

It is known that suppression of copulatory behavior observed in aged male animals is due to elevate prolactin levels, the so-called hyperprolactinemia, found in these animals. The present study was done to determine whether hyperprolactinemia can modify the copulatory behavior of young adult male rats. Hyperprolactinemia was induced by grafting one or two pituitary glands of adult males of the same strain under the kidney capsules of each sexually experienced male. Grafted animals exhibited suppressed copulatory behavior patterns when tested one month after pituitary transplantation. The animals given two pituitary grafts differed from the sham-operated controls in latency to intromit (P < 0.05), as well as in the numbers of intromission (P < 0.05) and ejaculation (P < 0.01). After tests of copulatory behavior, serum concentrations of LH, FSH, prolactin and testosterone were measured by radioimmunoassay. Serum levels of prolactin were significantly increased (P < 0.05) in the animals given 2 grafts, compared with sham-operated controls. From these results, suppression of copulatory behavior in the young adult animals grafted was similar to that in aged adults. The findings suggest that decline of copulatory behavior with increasing age results from chronic elevation of prolactin.