Hormonal and behavioral response of male chimpanzees to a long-acting analogue of gonadotropin-releasing hormone.

A long-acting preparation of gonadotropin-releasing hormone (GnRH) was administered to three adult male chimpanzees living in a socially integrated group. Hormonal changes and behavioral responses were monitored for 8 days. Blood serum levels of luteinizing hormone peaked at about 8 hr and returned to baseline at 48 hr. Total serum testosterone reached the highest levels of 140% above baseline at 24 hr and returned to baseline after 48 hr. Out of a wide variety of behaviors observed in detail, only one cluster of three related behaviors showed even a suggestion of response: The two measures of activity, lone travel (p < 0.05) and distance traveled (p < 0.1), decreased on the day of hormone administration followed by an increase on the 2 subsequent days, and idle time (p < 0.1) revealed the reciprocal pattern. In view of various reports of behavioral effects of GnRH in other species, it is particularly noteworthly that parameters of sexual and agonistic behavior of male chimpanzees definitely did not change.