Tissue and plasma somatomedin-C/insulin-like growth factor I concentrations in the human fetus during the first half of gestation.

To investigate the possible role of somatomedin-C/insulin-like growth factor I (Sm-C/IGF I) in early human development, we measured this peptide by radioimmunoassay in extracts of multiple tissues and in plasma from fetuses during the first half of gestation (9-19 wk). All tissues contained Sm-C/IGF I far in excess of that which could be accounted for by Sm-C/IGF I derived from blood entrapment. Lung and intestine had the highest concentrations (166 +/- 35 mU/g, n = 25 and 160 +/- 20 mU/g, n = 19, respectively; mean +/- SEM) and liver the lowest (67 +/- 16 mU/g, n = 26). Plasma concentrations were 270 +/- 20 mU/ml (n = 20). Neither fetal weight (6-258 g) nor gestational age correlated with Sm-C/IGF I concentrations in any tissue or in plasma. These findings suggest that Sm-C/IGF I is synthesized in many human fetal tissues from as early as the 1st trimester. They also provide further evidence for an autocrine/paracrine role of this peptide growth factor.