Plasma Testosterone, Sex Hormone Binding Globulin Binding Capacity and Per Cent Binding of Testosterone and 5α-Dihydrotestosterone in Prepubertal, Pubertal and Adult Males*

Abstract

Prepubertal and adolescent boys without endocrine disturbances between 0.5 and 18 years (n = 98) were investigated and compared to normal men between 22 and 59 years (n = 95). Plasma testosterone levels were measured using a specific radioimmunoassay including Celite column chromatography. The binding capacity of sex hormone binding globulin (SHBG) was determined using a combined technique utilizing both ammonium sulfate precipitation and differential dissociation. Per cent specifically bound testosterone and 5α-dihydrotestosterone (5α-DHT) was measured by differential dissociation. Mean plasma testosterone levels were almost invariably low (x = 0.20–0.24 ng/ml) between 0.5 and 7 years. From 8 to 15 years of age a rapid increase was measuredwhile constant high values, which corresponded to normal adults, appeared after the age of 16. SHBG binding capacity was extremely high in young children up to the 9th year of life with a maximum at 6. It declined sharply between 9 and 15 years, followed by a slower decrease between 16 and 18, an age at which adult levels were found. The per cent binding of testosterone and 5α DHT to SHBG followed the same basicpattern seen in the SHBG binding capacity, i.e., high percentages between 0.5 and 8 yearsand a steady decrease until the 18th year of life. The SHBG binding capacity did not correlate significantly with total testosterone in boys younger than 12 years and with per cent SHBG bound testosterone or 5α-DHT in boys younger than 6 years old. From 13–18 years a highly significant negative correlation between total plasma testosterone and SHBG binding capacity, and from 7–18 years a positive correlation betweenSHBG binding capacity and per cent SHBG bound testosterone and 5α-DHT was found.