The effects of Medroxyprogesterone acetate (MPA) on suppressive of menstrual cycles and sexual behavior were studied in female macaque monkeys. In Experiment 1, 8 female cynomolgus monkeys (Macaca fascicularis) were used. Five monkeys received a single s.c. injection of 15 mg/kg of MPA, whereas the remaining 3 monkeys received vehicle (water) as controls. Blood samples were collected three times a week, and changes in plasma concentrations of estradiol, progesterone, and LH were monitored as an indicator of ovulatory cyclicity. Before treatments, all monkeys exhibited normal menstrual cycles with mid-cycle increase in plasma estradiol and LH, followed by luteal increase in plasma progesterone and onset of menses. After MPA-treatments, menstrual cycles completely disappeared and anovulation persisted for 161 ± 17 days, followed by the spontaneous recovery of normal menstrual cycles. Control monkeys did not show any change after treatment. In Experiment 2, 39 multiparae female Japanese monkeys (Macaca fuscata) of the provisioned free-ranging Arashiyama E troop at the Iwatayama Monkey Park were used for behavioral and contraceptive studies. Fifteen monkeys received a single s.c. injection of 7.5 mg/kg of MPA in early autumn, just before the onset of breeding season, whereas the remaining 24 monkeys served as intact controls. Both groups of monkeys exhibited copulatory behaviors during the ensuing breeding season, and delivered live babies during the subsequent birth season. In Experiment 3, 19.4 mg/kg of MPA was injected to five monkeys of the same troop in the following year. These monkeys did not show copulation or delivery. These results showed that a single s.c. injection of MPA suppressed ovulatory cycles in dose-dependent and reversible manners. Thus, MPA appears one of the most effective means for fertility control in macaque monkeys and possibly in other wild mammals.
