RESUMO
To evaluate the competitive molecular phenomenon of Ethynyl-Estradiol (EE-2) from contraceptive formulations against the endogenous Estradiol (E-2) at the intra and the extracellular compartments, plasma and endometrial samples were simultaneously obtained on different days of the pseudomenstrual cycle from oral contraceptive users under EE-2+ Norgestrel (30 micrograms/+ 500 micrograms) and EE-2+ Norethindrone (50 micrograms + 1.0 mg) in order to quantify EE-2 & E-2. When measuring both molecules it was shown that the chronic administration of steroids regardless of the pharmacological action of the progestin component the lower content of EE-2 (30 micrograms) does not compete substantially at the circulating level permitting the cyclic fashion of the natural estradiol while at the endometrial compartment such phenomenon is not seen thus, a local infertility effect should be reconsidered to anticipate a different approach in the future of contraception.
PIP: 27 women participated in a study of systemic and endometrial estradiol concentrations in oral contraceptive (OC) users. 13 women aged 15-22 used OCs containing ethinyl estradiol 30 mcg and norgestrel 500 mg for 4-24 months, and 14 women aged 18-28 used OCs containing 50 mcg ethinyl estradiol and 1.0 mg norethindrone for 1-28 months. A peripheral blood sample and an endometrial biopsy were obtained at random from each woman on different cycle days to measure the concentration of endogenous estradiol. The ovarian response defined by endogenous plasma and endometrial estrogen levels differed greatly in the two groups. In the 30 mcg group, plasma estrogen levels were similar to those described in an ovulatory menstrual cycle, while this profile was not observed in the 50 mcg group. The endometrial estrogen profile described for women not using hormonal contraception was not observed in either of the two dose groups.