[The negative and positive phases of the reaction of the hypothalamo-hypophyseal-gonadal system in female rats to the administration of sex hormones].

: I.m. administration of estradiol benzoat in physiological doses decreased 3-fold the lutropin secretion and follitropin secretion by one third, in ovariectomised rats. The same dose in intact rats decreases the lutropin level in the blood and gonadoliberin contents in the medial eminence by the negative feedback mechanism. In 4-6 hrs after injection the positive effect of estradiol is at its highest level, the lutropin level in the blood increases by 80-100 times, the follitropin--by 2-3 times. Therefore, estradiol plays a decisive role in positive as well as negative effects on the lutropin secretion, whereas its effect upon follitropin secretion is less obvious. The gonadoliberin transport in negative phase of estradiol effect is mainly performed through the medial eminence whereas the positive effect of estradiol needs a participation of organum vasculosum of the lamina terminalis too.