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Levels of insulin-like growth factors I and II (IGF-I and IGF-II) and somatomedin peptide content (SMPC) were measured in 32 normal term and 11 preterm infants. After acid chromatography to remove somatomedin-binding protein, SMPC was measured by placental membrane radioreceptor assay, while plasma IGF-I and II concentrations were measured by specific RIAs. SMPC levels in term infants were significantly below normal adult levels 0.49 +/- 0.13 (+/- SD) U/ml for infants compared to 1.30 +/- 0.25 U/ml for adult males. IGF-I levels in term infants were also low, averaging 113 +/- 35 ng/ml for infants; the normal adult levels is 184 +/- 32 ng/ml. The IGF-II level was 282 +/- 84 ng/ml for infants and 687 +/- 169 ng/ml for adults. Both IGF-I and II levels in preterm infants were lower than those in term infants. IGF-I, and IGF-II, and SMPC levels showed a positive correlation with birth weight in term infants. Both IGF-I and IGF-II levels showed a strong positive correlation with gestational age in all infants.
Bennett et al. (Thu,) studied this question.