[Increase in estradiol level in the male rat hypothalamus at birth].

In the newborn male Rat, hypothalamic estradiol levels suddenly increase during the first hour following birth and decrease between 2 and 24 hr. This surge is absent in the female or in the male gonadectomized at 0 hr. Serum estradiol levels decrease between fetal stage 21 days 8 hr. and 24 hr. post partum, in the rats of both sexes. In the male, the hypothalamic estradiol surge occurs when testosterone levels increase. These results suggest the aromatization of testosterone to estradiol in the hypothalamus of the newborn male Rat.