Effects of Castration and Hormone Replacement in Fully Adult Male Rhesus Monkeys (<i>Macaca mulatto</i>)*

Abstract

A group of 4 fully adult male rhesus monkeys each paired with 2 female partners, making 8 paired combinations, were studied over a 3-year period during 1135 mating tests each of 1-hr duration. Within 4 weeks of castration there was a significant decline in the mean number of ejaculations and intromissions per test although individual differences were marked and ejaculation persisted for between 5 and 109 weeks in different pairs. In contrast, the effect of castration on the males-mounting behavior was less marked and very gradual. Testosterone replacement (2.0 mg/day) was effective in restoring mounting and intromission but did not fully restore ejaculations to intact levels. In addition to any central effects on motivation, it is thought that testosterone influences peripheral mechanisms responsible for ejaculation. (Endocrinology95: 150, 1974)