A LONGITUDINAL ASSESSMENT OF HORMONAL AND PHYSICAL ALTERATIONS DURINGNORMAL PUBERTY IN BOYS .2. ESTROGEN-LEVELS AS DETERMINED BY AN ULTRASENSITIVE BIOASSAY

A limited number of reports of estrogen levels in prepubertal and earl y pubertal boys have been published because previous estrogen assays h ave lacked adequate sensitivity to quantitate circulating estrogen con centrations. Development of a new ultrasensitive assay has permitted m easurement of estrogen levels in 23 normally growing boys progressing through puberty. Concentrations were measured at approximately 4-month intervals over a 5- to 8-yr period. The levels increased with maturat ion in all and correlated directly with chronological age, bone age, w eight, height, pubertal stage, and testosterone and insulin-like growt h factor-I levels. Of these factors, the level of testosterone had the greatest influence on the estrogen concentration. The time hom peak. growth velocity also significantly correlated with estrogen level. The estrogen level correlated positively with growth velocity before the time of peak growth velocity and negatively after peak growth velocity . The estrogen levels first increased significantly an average of 3 yr after pubertal onset and reached a peak by 5 yr after pubertal onset. Peak growth velocity was attained an average of 3 yr after pubertal o nset. The greatest increase in the rate of rise of the estrogen level was an 11-fold rise during the year in which puberty began. The next m ost significant increase was a 4.8-fold rise 3 yr after pubertal onset . With respect to pubertal stage, the greatest absolute change occurre d from stage 4 to stage 5 and the greatest fold change occurred from s tage 1 to stage 2. The estrogen level did not significantly correlate with the 24-h GH level. In conclusion, circulating estrogen levels are very low in all boys prepubertally and rise steadily during adolescen t development. The estrogen level is closely related to testosterone c oncentration and to the time of peak growth velocity. These findings a re consistent with the hypothesis that estrogen at low levels augments skeletal growth and maturation in boys (as well as girls). They are a lso consistent with the hypothesis that continued exposure to estrogen leads to epiphyseal fusion. Further studies are required to define th e separate and combined roles of estrogen, GH, and testosterone, as we ll as other factors, on growth and sexual development at puberty.