Steroid contraceptives in non-human primates (II). Metabolic fate of synthetic estrogens in the baboon after exposure to oral contraceptives.

ABSTRACT

PIP The metabolism of isotopically labeled ethinyl estradiol (EE) and mestranol (ME) was studied in 3 baboons before and after the simultaneous injection of a norethindrone-mestranol contraceptive formulation. 6 days after the administration of tritiated-EE and carbon-14-ME, the mean urinary excretion of labeled-EE was 38.3-40.8% of the dose, while the excretion of labeled-ME was 17.8-19.8% of the dose. Plasma levels of tritiated-EE did not differ markedly between the follicular and luteal phases of the cycle. 24 hours after injection, plasma levels of tritiated-EE remained at levels more than 7% of the dose, which was considerably higher than recorded before administration of norethindrone-mestranol. In contrast, carbon-14-ME levels 24 hours after injection did not differ markedly from those found before treatment with norethindrone-mestranol. The results suggest that orally administered ME is demethylated to EE in primates.^ieng