EFFECTS OF INSULIN-LIKE GROWTH-FACTOR-I (IGF-I), INSULIN AND COMBINEDIGF-I-INSULIN INFUSIONS ON PROTEIN-METABOLISM IN DOGS

The effect of infusions of recombinant insulin-like growth factor-I (I GF-I) (34, 103 or 688 pmol min(-1) kg(-1)), insulin (3.4, 10.3 or 68.8 pmol min(-1) kg(-1)) or combined infusions (34 pmol IGF-I + 3.4 pmol min(-1) kg(-1) insulin or 103 pmol IGF-I + 3.4 pmol min(-1) kg(-1) ins ulin) on protein metabolism, using an infusion of[1-C-14] leucine was investigated in anaesthetized fasted dogs. Leucine concentration, prod uction rate (measure of protein degradation), oxidation rate and non-o xidative disappearance rate (measure of protein synthesis) were decrea sed in a similar dose dependent manner by the IGF-I and insulin infusi ons (P<0.01). The decrease in these measurements of leucine metabolism were greater following 34 pmol IGF-I + 3.4 pmol insulin than with eit her component infused alone (P<0.05). Free fatty acid concentrations w ere decreased by all insulin doses (P<0.01) but only by 103 and 688 pm ol min(-1) kg(-1) insulin-like growth factor (P<0.05, P<0.01). These d ata demonstrate that IGF-I, like insulin, has a dose dependent effect on protein metabolism and that combined insulin and IGF-I infusions ha ve additive effects on protein metabolism.