[Mechanism of action of prolonged-action injectable contraceptives]. / Mecanismo de accion de los contraceptivos inyectables de deposito.

PIP: Several parameters were studied to clarify the mechanisms of action of 2 prolonged-action injectable contraceptives: 17alpha-19-hydroxynorprogesterone caproate (with a contraceptive effectiveness of at least 8 weeks) and 19-norethindrone enanthate (effectiveness over 12 weeks). The generally accepted theory of ovulation inhibition was unconvincing. In 14 ovarian biopsies of patients under treatment, taken in the 2nd phase of the cycle, ovulation was evidenced in 11 cases by the presence of corpora lutea. 245 endometrial biopsies showed that the exogenous gestagen effect lasts only 3 weeks; after such period, most endometria could be correlated with the day of the cycle on which they were taken; 2/3 of them suggested biphasic cycles. An evaluation of 240 colpocytograms also confirmed endogenous cyclic activity. In order to explain the prolonged contraceptive effectiveness of the drugs, the cervical mucus was thoroughly studied in 380 cases. A definite, uniform, and constant effect of the progestogen on the mucus was demonstrated, in contrast to the cyclic changes in the other parameters; such effect begins to decline simultaneously with the loss of contraceptive protection. It is suggested that the effectiveness of the 2 drugs is due to changes in the cervical mucus, which affect sperm penetration.^ieng