Somatomedins in adolescence: a cross-sectional study of the effect of puberty on plasma insulin-like growth factor I and II levels.

To explore the effect of puberty on the somatomedins (SMs), a group of insulin-like peptides which mediate the action of GH on skeletal tissue, we measured SM-C/insulin-like growth factor-I (SM-C/IGF-I) and IGF-II by specific RIAs in 110 adolescents between the ages of 10 and 18 yr. All subjects were in good health and between the 5th and 95th percentiles for height. In both females and males, SM-C/IGF-I levels rose during puberty to a peak approximately 3-fold higher than the average adult level. The rise in SM-C/IGF-I levels corresponded better with the Tanner stage of the adolescents than with their chronological age. IGF-II levels did not rise during puberty and were slightly below adult levels. The dramatic rise in SM-C/IGF-I levels during puberty suggests a role for this SM peptide in the adolescent growth spurt. Furthermore, these data indicate that proper interpretation of SM-C/IGF-I levels during adolescence must include a knowledge of the patient's pubertal development.