The binding of steroids by serum proteins of maturing male and female rats

Abstract

The amount of steroid bound by serum from maturing male and female rats was measured by equilibrium dialysis against 1 nanogram of estradiol-17-beta-7.7- 3H, testosterone-4- 14C, corticosterone-1, 2- 3H or progesterone-4- 14C. The amount of estradiol and testosterone bound in males and females did not change during maturation, while males consistently bound less steroid than females. At six weeks of age there was a transient fall in estradiol binding in males and females and a fall in testosterone binding in males. Only slight changes in combining affinity were noted during maturation. The binding of corticosterone and progesterone was similar in adult males and females and the binding of corticosterone gradually increased during maturation in both sexes. More progesterone was bound in young males than in young females. Estradiol was bound by the alpha and beta globulin fractions and by the albumin fraction of 27-day-old and 55-day-old female serum. No steroid was bound by gamma globulin. It seems unlikely that changes in the binding of steroid by blood proteins are important in the onset of puberty.