Precipitation of Menstruation in Castrated Monkeys with Progesterone in The Presence of Estrogen. ∗

Abstract

Summary

Two adult castrated monkeys (Macaca mulatta) on a dosage of estradiol-17B (10 μg daily), which with rare exceptions maintains the endometrium without “break-through” bleeding, also were given concurrently small doses of progesterone (0.062 to 0.75 mg daily). A total of thirty experiments were performed over a period of about 4 years. “Break-through” bleeding occurred in a great majority of experiments within approximately 2 to 3 weeks when 0.125 to 0.5 mg progesterone was combined with 10 μg estradiol. Bleeding was not observed when 0.75 mg progesterone was given and occurred in one of 3 experiments with 0.062 mg, thus indicating a general upper and lower limit of dosage for the reaction. It is concluded that small doses of progesterone in some way decrease the effectiveness of a minimal maintenance dose of estradiol resulting in precipitation of “break-through” bleeding.