USE OF INSULIN-LIKE-GROWTH-FACTOR-I (IGF-I) AND IGF-BINDING PROTEIN MEASUREMENTS TO MONITOR FEEDING OF PREMATURE-INFANTS

To determine whether peptides of the insulin-like growth factor (IGF) system might be useful indicators of nutritional adequacy in premature infants, we studied 50 premature (25-34 weeks gestation) infants pros pectively to define the relationship between nutrient intake and serum concentrations of IGF-I, IGF-binding protein-2 (IGFBP-2), and IGFBP-3 . Each infant was monitored for at least 2 weeks. Nutrient intake was quantified from daily logs; weight was determined daily, and measureme nts of IGF-I, IGFBP-2, and IGFBP-3 in serum were made twice weekly. Se rum IGF-I correlated strongly with length of gestation, increasing 4.0 3 +/- 0.95 ng/mL for each additional week of gestation (P < 0.0001) an d 0.36 +/- 0.07 ng/mL.day each day since birth (P < 0.0001). A higher intake of calories increased IGF-I by 0.07 +/- 0.01 ng/mL for each cal orie per kg ingested over the previous 3 days (P < 0.0001). IGF-I incr eased quadratically as protein intake increased. For each change of 1% in calories as protein squared, IGF-I increased 0.36 +/- 0.11 ng/mL ( P < 0.0001). Serum IGFBP-3 concentrations also correlated with length of gestation, increasing 25.06 +/- 11.83 mu g/L.wk (P = 0.035) and 4.1 4 +/- 1.33 mu g/.day since birth (P = 0.003). Unlike IGF-I, variation in the amount of protein supplied did not change IGFBP-3. As calorie i ntake increased, IGFBP-3 increased by 0.54 +/- 0.17 mu g/L for each ca lorie per kg consumed over the previous 3 days (P = 0.0015). In contra st to IGF-I and IGFBP-3, IGFBP-2 declined as the length of gestation i ncreased (56.12 +/- 16.92 ng/mL.week; P = 0.001) and with each additio nal day of life (7.57 +/- 2.44 ng/mL.day; P = 0.003). Dietary protein, the predominant regulator of IGFBP-2, caused a decrease of 33.22 +/- 9.00 ng/mL with each percent increase in dietary calories as protein ( P < 0.0003). Calorie intake had less effect on IGFBP-2 than protein in take. These results indicate that each of the three peptides studied i s regulated in premature infants by nutritional intake, and that their regulatory patterns are qualitatively similar to those observed in ol der individuals. Measurements of these peptides in premature infants m ay be useful indicators of nutritional status and adequacy of nutrient intake.