INSULIN-LIKE GROWTH-FACTORS (IGFS) AND IGF BINDING PROTEIN-1, PROTEIN-2, AND PROTEIN-3 IN NEWBORN SERUM - RELATIONSHIPS TO FETOPLACENTAL GROWTH AT TERM

Cord sera were obtained from term, Chilean newborns exhibiting various patterns of intrauterine growth and assayed for IGF-1, IGF-2, IGFBP-1 , IGFBP-2, and IGFBP-3 by specific radioimmunoassays (RIA). Serum leve ls of each peptide were correlated with birth weight (BW), ponderal in dex (PI), and placental weight (PW). Total IGF-1 levels correlated wit h BW (r = 0.665, P = 0.0001), PI (r = 0.527, P = 0.004), and PW (r = 0 .596, P = 0.0017). In contrast, IGF-2 failed to correlate with any gro wth parameter. Of the three binding proteins, IGFBP-3 exhibited the st rongest relationship to each growth parameter. IGFBP-3 correlated sign ificantly with BW (r = 0.71, P < 0.0001), PI (r = 0.782, P < 0.0001), and PW (r = 0.57, P = 0.0029). In addition IGFBP-3 levels positively c orrelated to IGF-I levels (r = 0.614, P = 0.0005). By contrast, circul ating IGFBP-1 and IGFBP-2 were inversely related to IGF-1 levels. All five peptides were subjected to multiple regression analysis and relat ed to BW. Significant relationships between the predicted BW and the a ctual BW were observed in these infants (r = 0.802, P = 0.0006). The B Ws of a cohort of unrelated North American infants were also predicted using the Chilean-derived equation and found to be significantly rela ted to their actual BWs (r = 0.453, P = 0.0033). These relationships w ere strengthened by the inclusion of estimated gestational age (EGA) a s an independent variable. These data point to particularly important roles for IGF-1 and IGFBP-3 in regulating fetal growth at term, and su ggest that they are regulated in a coordinated manner during the latte r stage of gestation. Furthermore, they suggest that IGFBPs play multi ple, and potentially opposing, regulatory roles in modulating IGF acti on. Lastly, an integrated expression of IGF activity derived from one population significantly correlated with newborn BW in a geographicall y and culturally distinct population.