Suppression of ovulation by a synthetic progestin in the capuchin monkey

From the limited research in New World monkeys it is not clear whether they are as sensitive to the antiovulatory effects of synthetic progestins as noted in human beings. We examined whether levonorgestrel prevented ovulation in the capuchin monkey.

Cebus apella monkeys were treated orally with two doses of 2 mg of levonorgestrel, 8-9 hours apart, in four periovulatory stages assessed by laparoscopy.

Levonorgestrel-induced luteinization of the follicle prevented oocyte release up to 8 hours before ovulation. Unhealthy oocytes were recovered from 46% of unruptured follicles. Luteal progesterone was reduced by 55%, 35%, and 25% according to when levonorgestrel was given -2, -1, and 0 day from estradiol peak respectively.

The capuchin monkey, a neotropical primate in which progesterone circulates at levels much higher than in Old World primates and human beings, is sensitive to the antiovulatory effects of synthetic progestins.