Suppression of male rhesus testicular function and sexual behavior by a gonadotropin-releasing-hormone agonist

Maryann Davis, University of Massachusetts Medical School
Kim Wallen, Yerkes Regional Primate Research Center

At the time of publication, Maryann Davis was not yet affiliated with the University of Massachusetts Medical School.


Castrated rhesus monkeys tested in pair tests in small areas mate up to 6 yr after castration, though there is high individual variability (22,23). The generalizability of these findings to social groups in larger areas is unknown. The sexual behavior of 4 adult rhesus males tested singly with a group of 9 intact adult females was examined during short-term, counterbalanced, gonadotropin-releasing-hormone(GnRH)-agonist-induced testicular suppression and control treatment. GnRH-agonist treatment suppressed testosterone to less than 0.6 ng/ml within 16 days. Ten days later (e.g., after 26 days of GnRH-agonist treatment) males were observed for 7 days. The frequency of hiptouches, mounts, intromissons and ejaculations were significantly reduced by testicular suppression. This behavioral reduction was more marked than previously reported in pair-tested castrates during a similar time-period, suggesting testicular suppression more profoundly affects behavior in multifemale groups in larger areas. Males differed in the extent that testicular suppression reduced their sexual behavior. Male ejaculations were completely unaffected in one male and completely eliminated in another. Sexual behavior was reduced less in males with high control levels of testosterone and behavior. Behavioral suppression was unrelated to differences in female behavior and appeared to result from reduced male sexual responsiveness or motivation.