Increased somatomedin receptor sites in newborn circulating mononuclear cells

To evaluate the potential role of somatomedin as a growth factor in fetal development, we studied somatomedin receptors on circulating mononuclear cells from placental cord blood from 13 normal term newborns. Twelve healthy young adults served as controls. By radioreceptor assay of acid-chromatographed plasma, total somatomedin peptide content of cord blood was 0.30 +/- 0.02 U/ml (mean +/- SEM) compared to 1.12 +/- 0.08 U/ml for adults. Specific binding of [125I]somatomedin C to 50 X 10(6) mononuclear cells was 11.38 +/- 0.74% for newborns and 6.67 +/- 0.51% for adults. This increase in specific binding appears to be due to an increased number of receptor sites per cell. These data support a hypothesis of increased fetal sensitivity to somatomedin.