IGF-1 has insulin-like effects and is thought to be important in fetal development. We have demonstrated that IGF-1 infusion decreases amino acid rate of appearance (Ra) (AJP 271:E177, 1996). The present study was designed to determine the dose-response of rhIGF1 on ovine fetal amino acid kinetics. Chronically catheterized fetal lambs were studied at 122-127 days gestation. Ra Leu was determined by infusion of 1-13C-Leu. Leu oxidation was determined by 1-14C-leu infusion, and measurement of 14CO2 excretion. SRIF was infused throughout the study to minimize IGF induced changes in fetal Ins. After isotopic steady state was achieved, basal samples were obtained. rhIGF-1 was infused into the fetal inferior vena cava at low, medium, or high rates (75, 150, or 300 μg/hr), followed by identical sample determinations. Results, mean±SEM. N=6 Table A stepwise increase in serum IGF-1 was achieved. Ins concentrations were decreased equally at all IGF doses. Leu Ra was decreased at the highest infusion rate while Leu Ox was decreased at both medium and high infusion rates. These results indicate that inhibition of amino acid oxidation may be more sensitive to changes in circulating IGF-1 than is amino acid appearance from protein breakdown.

Table 1
Full size table