Progressive decrease in serum sex hormone-binding globulin from infancy to late prepuberty in boys.

Serum Sex hormone-binding globulin (SHBG) levels and affinity constant (Ka) of SHBG-dihydrotestosterone association were determined in 91 boys, aged 3 months to 15 yr, all at Tanner stage I of pubertal development. A gradual decrease in serum SHBG as a function of age was found in spite of unchanged serum testosterone levels. Ka values at different ages were not significantly different. Since steroids bound to SHBG are not transported into most tissues, particularly brain, a decrease in SHBG will have the effect of increasing tissue entrance of non-SHBG-bound sex hormones despite unchanged plasma concentrations. We speculate that the gradually increasing androgen and estrogen milieu of the brain created by this mechanism might be of physiological significance in triggering the onset of puberty.