Plasma testosterone-binding proteins in the developing rat

Blood plasma of male rats aged 3 weeks contained two testosterone-binding proteins which differed in apparent molecular weight on Sephadex G-200 column. The binding characteristics of both proteins were similar. They had high affinity for androgens, but little or no affinity for estrogens and corticoids. Blood concentrations of both proteins began to increase markedly 15 days after birth, reached a peak at about 20 days, and then decreased. The higher molecular weight form disappeared by 5 weeks of age, whereas the lower molecular weight form was reduced to much lower levels that remained relatively unchanged until the end of the experimental period, i.e., 63 days of age.