Insulin-like growth factor-I (IGF-I) responses in rats maintained with intravenous or intragastric infusion of total parenteral nutrition solutions containing medium- or long-chain triglyceride emulsions

Our objective was to determine how intravenous or intragastric feeding affects serum concentrations of insulin-like growth factor (IGF)-I and -II and IGF binding proteins (IGFBP), and hepatic abundance of IGF-I mRNA. Male Fischer 344 rats (235-246 g) were fed for 14 d by intravenous or intragastric infusion with total parenteral nutrition (TPN) solutions providing 65% of energy from long-chain triglyceride (LCT) or a 3:1 admixture of medium-chain triglyceride (MCT) and LCT emulsions (MCT/LCT). Twice as much TPN solution was required per gram of weight gain with MCT/LCT compared with LCT infusion (P < 0.0003). Serum IGF-I and -II concentrations and hepatic IGF-I mRNA abundance were not significantly different. Circulating concentrations of IGFBPs with molecular weights of 38,000-43,000 (IGFBP-3) were significantly greater with intravenous MCT/LCT than with intravenous LCT infusion. Our data demonstrate that reduced growth in rats given TPN containing MCT/LCT compared with LCT emulsions is not associated with reduced serum IGF-I concentrations or hepatic abundance of IGF-I mRNA, although serum IGFBPs are elevated.