[Endometrial interference of synthetic estrogens in fertility regulation.Is it necessary to interfere with the antiovulatory mechanism at the central nervous system level in order to obtain contraception?]. / Interferencia endometrial de los estrógenos sintéticos en la regulación de la fertilidad. Es necesario el mecanismo antiovulatorio a nivel del sistema nervioso central, para obtener la anticoncepción?

For some time the anti-ovulatory activity of certain estrogen/progestagen preparations was the main approach in fertility control. Up to date a drastic dosage reduction of both steroid hormones has been accomplished ameliorating the side effects on the one hand, and being active compounds as contraceptives, in the other. Currently, there are a wide variety of oral contraceptives available with a variety of estrogen doses combined with different progestagens. The estrogen content is a high as 80 micrograms and as low as 20 micrograms, moreover, such formulations are prescribed beginning the 1st or the 5th day of the menstrual cycle. By studying plasma and endometrial samples simultaneously obtained from chronic oral contraceptive users taking either 30 micrograms or 50 in such pills; a 17-beta-estradiol pattern was attained as that seen during follicular maturation in the ovulatory cycle only women under the lower dose of synthetic estrogen. However, in the endometrium such a cyclicity did not take place; in parallel circulating progesterone in both groups never reach levels greater than 5.0 ng/ml. Results offer to find a local critical period during the ovulatory menstrual cycle to achieve with much lower hormonal dosages a different approach in future methods of contraception.