Interruption of early pregnancy in the monkey with mestranol and 5-oxa-17-phenyl-18,19,20-trinor prostaglandin F1 alpha methyl ester.

Prior work has shown that 5-oxa-17-phenyl-18,19,20- trinor prostaglandin F1 alpha methyl ester (PGF-analog) inhibits luteal progesterone secretion, but does not shorten menstrual cycles in human chorionic gonadotropin (hCG)-treated, nonpregnant monkeys. This report demonstrates that a combination treatment of PGF-analog and mestranol not only reduces blood progesterone concentrations in the hCG-treated monkey, but also results in a significant shortening of menstrual cycles. The corpus luteum-inhibiting activity of PGF-analog in hCG-treated, nonpregnant monkeys was not enhanced by simultaneous administration of nonestrogenic steroids (norethisterone, oxymetholone, azastene , 17 alpha-allyl-3-methoxy-1,3,5(10)- estratrien-17 beta-ol). Most importantly, pregnancy was interrupted in 11 or 12 monkeys when PGF-analog and mestranol were administered on Day 28 of fertile menstrual cycles; this abortifacient activity of the prostaglandin-estrogen treatment was not prevented by concomitant administration of progesterone. Administration of PGF-analog and mestranol in the third trimester terminated pregnancy in only 1 of 3 monkeys. The data indicate that a combination treatment of PGF-analog and mestranol is highly effective for the termination of early pregnancy in the monkey. Although PGF-analog and mestranol clearly inhibit the monkey corpus luteum, it is unlikely that this activity is essential for the abortifacient activity of the prostaglandin-estrogen treatment.