Postnatal development of estradiol receptor in female and male rats.

The concentration of available cytoplasmic estradiol receptor was quantified in the postnatal hypothalamus and pituitary of male and female rats, aged from 4 to 28 days. The uterine receptor was measured in female rats. The method used was designed to avoid non-specific contamination of cytosol from very young animals by plasma proteins, especially alpha-feto-protein (AFP). In the hypothalamus, the concentration of estradiol binding sites was maximal 6 days after birth, and declined until day 28 to low constant level. In the pituitary, the estradiol receptor concentration increased from day 4 and reached a plateau at 13--14 days, whereas in the uterus, the concentration of cytoplasmic binding sites rose up to day 10--12, and then markedly decreased.