[Increase in endogenous testosterone in the hypothalamus of the male rat at birth].

The evolution of serum and hypothalamic concentrations of endogenous testosterone was measured in newborn male and female Rats, from 0 up to 6 hrs. after birth. The serum testosterone surge observed in males between 0 and 2 hrs. was not found in the females. During this period, the hypothalamic concentration of testosterone increased in males but decreased in the females.