Plasma sex hormone binding globulin concentration and binding capacity in children before and during puberty

The steroid binding capacity and concentration of plasma sex hormone binding globulin have been compared in 116 children aged between 2 and 14 years. Concentration was measured by electroimmunodiffusion standardised with reference to the mass of the pure protein and binding capacity by quantitating the binding of radiolabelled 5 alpha-dihydrotestosterone. Binding capacity correlated highly with concentration in all subjects and neither differed significantly between the sexes before or during puberty. However, both were significantly lower in pubertal than in pre-pubertal children. These findings suggest the metabolism of the protein is similar in boys and girls and that the fall in its steroid binding capacity at puberty in fact is due to a fall in its concentration rather than to changes in its physicochemical properties.