Effects of medroxyprogesterone acetate on plasma testosterone and sexual behavior in male cynomolgus monkeys (Macaca fascicularis).

Medroxyprogesterone acetate (MPA), a synthetic progestin with androgen-depleting activity, is used to treat the deviant sexual behavior of men. To investigate the effects of MPA in another anthropoid primate, 16 oppositely-sexed pairs of cynomolgus monkeys were observed in one-hour behavior tests during 15 successive 4-week periods conducted before, during and after administering to males weekly IM injections of first 20 mg and then 40 mg MPA. The doses used were comparable on a body weight basis to those employed clinically. Blood samples were collected weekly and assayed for plasma testosterone. During MPA treatment both plasma testosterone and ejaculatory behavior were significantly decreased, but the changes in behavior were less marked than the changes in hormone levels. There were clear differences between individual males in the effects of treatment, and the identity and hormonal status of the female partners also influenced the results. During the 6 month withdrawal period, effects were only partially reversible, and the data suggested that the behavioral changes depended on the hormonal changes rather than the opposite. However, a direct central action of MPA on behavioral mechanisms could not be excluded.