The Relative Expressed Estrogenicity of Oral Contraceptives

Abstract

Total effective estrogenicity of several human oral contraceptives was investigated through a method determining uterine weight in immature rats. The preparations, normally given to human females in tablet, form were Norinyl-1 (.05 mg mestranol, 1mg norethindrone), Norinyl-2 (.10 mg mestranol, 2 mg norethindrone), Ovulen (.10 mg mestranol, 1mg ethynodiol diacetate), Enovid-E (.10 mg mestranol, 2.5 mg norethynodrel), and Enovid-5 (.075 mg mestranol, 5mg norethynodrel). Each products was administered in total doses of .0025, .005, and .01 of a tablet. Each dose had 3 trials, approximately 10 mice to a trial. Each mouse was given the compound in .2 ml aqueous vehicle orally, daily for a 3-day period so that the sum of the daily doses equaled 1 of the tablet fractions above. Autopsy, on Day 4, discovered the ratio of mg uterus/gm body weight. A .0025 fraction of a tablet of Norinyl-1 produced a mean uterine ratio of 1.79, while control (untreated) mice had a mean ratio of 1.06. Norinyl-2, Ovulen, Enovid-5 and Enovid-E, judging from the corresponding increases in ratios from the control ratio, were found to be 2.1, 2.7, 6, and 8 times, respectively, more estrogenic than Norinyl-1. The relatively high estrogenicity of the Enovids is probably due to the conversion of norethynodrel to estrogenic compounds.