Testosterone production and metabolism in laboratory-maintained male rhesus monkeys

Plasma production rates (PR), metabolic clearance rates (MCR) and plasma levels of testosterone were determined in 10 male, laboratory-maintained rhesus monkeys on two occasions out-of-season (April and August) and once in-season (October). Plasma testosterone levels in October were higher than those in April and August. The plasma PR was unchanged in August, but markedly increased in October, as compared to April. The MCR showed a parallel increase betueen August and October. Thus changes in testosterone production and metabolism can be observed between in- and out-of-season male rhesus monkeys, maintained under strict laboratory conditions. These changes must be taken into consideration when the male rhesus minkey is used as an experimental model for human reproductive endocrinology.