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.

Somatomedins in pregnancy: a cross-sectional study of insulin-like growth factors I and II and somatomedin peptide content in normal human pregnancies.

To explore the role of the somatomedins (SM) during human pregnancy, we have measured plasma levels of insulin-like growth factor I (IGF-I), IGF-II, and SM peptide content (SMPC) in 79 women in various stages of normal pregnancies. IGF-I and IGF-II were measured by specific RIAs, and SMPC was measured by a radioreceptor assay using human placental membranes. IGF-I and SMPC rose during pregnancy, showing a significant positive correlation with the length of gestation. Plasma levels of IGF-I in the third trimester averaged 324 ng/ml, a 33% increase over the first trimester average of 243 ng/ml (P less than 0.05). Although IGF-II did not correlate with the length of gestation, the third trimester average was significantly higher than the first trimester average (780 vs. 630 ng/ml; P less than 0.05). After delivery, both IGF-I and IGF-II levels rapidly dropped to levels significantly below those seen in the third trimester. The gestational rise in SMPC and plasma levels of both IGF-I and IGF-II supports the hypothesis that SM play a role in the regulation of fetal growth.