Reversible inhibition of ovulation in the rhesus monkey by polydimethylsiloxane subdermal capsules of megestrol acetate.

The effect of megestrol acetate in polydimethylsiloxane subcutaneous implants on menstrual cycle, ovarian function, and uterine histology of adult parous rhesus monkeys was studied. Release rates of 129.6 and 64.8 mug/day inhibited ovulation and produced amenorrhea in all of the treated monkeys. The plasma progesterone level was 0 ng/ml during the initial part of the study (8 months). Endometrial biopsies obtained at different times showed a suppressed endometrium. Approximately 30 days after removal of all of the polydimethylsiloxane implants, the monkeys menstruated normally and the plasma progesterone levels subsequently were between 3 and 19 ng/ml. Histologic studies showed secretory endometria and corpora lutea, thus confirming resumption of ovulation.