Serum levels of growth hormone binding protein in children with normal andprecocious puberty: relation to age, gender, body composition and gonadal steroids

AIM To study the regulation of GHBP serum levels by gonadal steroids in nor mal and precocious puberty. STUDY PROTOCOL We studied GHBP levels in relation to age, sex, pubertal mat uration, body composition as well as to circulating IGF-I and gonadal stero id levels in 320 healthy children. Furthermore, we studied the regulation o f circulating GHBP in 33 girls with central precocious puberty before and d uring gonadal suppression with GnRH agonist. METHODS GHBP was determined by a time-resolved fluoroimmunoassay (GHBP TR-F IA) based on a commercially available immunoassay for GH, the DELFIA GH ass ay. RESULTS In healthy children GHBP levels were significantly higher in normal girls compared with boys, and there was no significant increase in GHBP in puberty in both sexes. GHBP levels did not correlate with height (SDS), ag e, pubertal stage, IGF-I or testosterone/oestradiol levels in boys and girl s, respectively. There were significant correlations between BMI and GHBP i n boys and girls (R-2 = 0.14 and R-2 = 0.12, both P < 0.0001). Furthermore, GHBP correlated highly significantly with the percentage body fat, determi ned by BIA in 43 healthy girls (R-2 = 0.40, P < 0.0001). GHBP levels were s ignificantly higher in girls with central precocious puberty (CPP) (1.31 SD S (1.26), mean (SD)) compared to prepubertal controls (P < 0.0001), and abo ve +2 SD in 10 out of 33 patients. In girls with CPP, GHBP correlated inver sely with oestradiol before treatment (R-2 = 0.26, P < 0.01) and there was a tendency towards a positive correlation with BMI (R-2 = 0.13, P = 0.078). By contrast, there were no signficant correlations between GHBP and IGF-I or height SDS. Gonadal suppression with GnRH agonist treatment caused a tra nsient significant increase of 0.57 SD after 2 months of treatment (P < 0.0 01), but decreased to baseline levels hereafter. CONCLUSION We conclude that in children, as in adults, body fat is the prim ary determinant for the circulating level of GHBP, and that the difference in body fat is probably the main factor for the higher levels of serum GHBP in girls compared with boys, as well as for the negative influence of test osterone levels in boys and of oestrogen levels in girls. The elevation in GHBP levels observed in girls with central precocious puberty is probably d ue their higher body fat content.