Relationship between the pubertal fall in sex hormone binding globulin and insulin-like growth factor binding protein-I. A synchronized approach to pubertal development?

In a cross-sectional study of 69 normal adolescents we have found sex hormone-binding globulin (SHBG) levels to fall in both males and females throughout the pubertal period. Multiple regression analysis revealed a close negative correlation with insulin in both sexes. Weaker correlations were also found between SHBG and circulating androgen concentrations, in both males and females. Similar results were also obtained for a second circulating binding protein of primarily hepatic origin. This low molecular weight insulin-like growth factor (IGF) binding protein I (IBP-I) is one of two distinct classes of IGF binding proteins which bind IGF-I and IGF-II. IGF-I in turn mediates, at least in part, the actions of growth hormone. IBP-I also fell throughout puberty, correlating with the increasing insulin levels. In addition IBP-I correlated with androgen levels in both sexes. These similarities between SHBG and IBP-I, together with a strong correlation across puberty between the levels of the two binding proteins themselves (r = 0.737, P less than 0.001), suggest common mechanisms of control over the circulating levels of these two binding proteins. The association with insulin raises the possibility of a synchronized modulation of the actions of sex steroids and IGFs by nutritional intake. Thus pubertal growth and sexual development may occur over the same time with both modulated according to nutritional intake, linked through pancreatic insulin release, to hepatic production of SHBG and IBP-I.