Relationship of somatomedin-C concentrations to pubertal changes.

The plasma somatomedin-C concentration increases above adult values during the teenage years. We studied the relationship of pubertal variables and the adolescent growth spurt to the changes in plasma total Sm-C concentration in normal volunteers and in boys with delayed puberty. The rise in plasma Sm-C concentrations was gradual and correlated positively with pubertal variables rather than with age. By midpuberty, plasma Sm-C had usually risen twofold. The Sm-C level in midpubertal girls (3.1 +/- 1.1, SD, U/ml) was greater than that in midpubertal boys (1.9 +/- 0.50, P less than 0.05). The Sm-C concentration in sexually mature teenagers was two to three times greater than that of adults. Both estrogens and androgens correlated independently with the plasma Sm-C concentration. The data are compatible with the hypothesis that pubertal estrogen or testosterone levels cause an increase in Sm-C, an effect possibly mediated by stimulation of growth hormone secretion, whereas greater estrogen exposure inhibits Sm-C generation, possibly by a direct effect. Plasma Sm-C concentrations correlated significantly with linear growth velocity until the age of peak pubertal growth velocity. Maximum Sm-C values were observed after the peak pubertal growth velocity was achieved, as height velocity was decelerating, and remained above adult levels for at least two to six years, at which time linear growth had virtually ceased. In boys with delayed puberty, Sm-C values resembled those of boys of like pubertal stage more closely than those of boys of similar age. Depressed plasma Sm-C values were found in some boys with delayed puberty; however, these did not preclude subsequent normal linear growth during sexual maturation.