Ethinylestradiol from contraceptive formulations and the ovarian response: an estrogen dose-dependency on natural...

To evaluate the competitive molecular phenomenon of ethinylestradiol from contraceptive formulations vs. endogenous 17 beta-estradiol in the intra- and extracellular compartments, a descriptive analysis was performed. Plasma and endometrial samples were simultaneously obtained on different days of the pseudomenstrual cycle from oral contraceptive users taking ethinylestradiol/norgestrel (30 micrograms/500 micrograms; n = 13) and ethinylestradiol/norethindrone (50 micrograms/1.0 mg; n = 14) in order to quantify the 17 beta-estradiol concentrations. From our results the chronic administration of these combined oral contraceptives demonstrated that the lower component ethinyl-estradiol (30 micrograms) does not compete substantially at the circulating level, permitting concentrations of natural estradiol such as those seen during follicular maturation in the ovulatory cycle. However, in the endometrium such a cyclicity is not seen, thus the possibility of a local infertility effect should be reconsidered to enable the investigation of a different approach in future methods of contraception.