Parenteral amino acid intake alters the anabolic actions of insulin-like growth factor I in rats

The anabolic properties of insulin-like growth factor (IGF) I are attenuate d by oral diets that are low in protein. However, it is not known whether p arenteral nutrition (PN) providing a low amino acid (AA) input will influen ce IGF-I action. With the use of a rat model, this study examined the inter action between AA input (1.27 and 0.62 g N . kg body wt(-1) . 24 h(-1), AA. and 1/2 AA groups, respectively) and recombinant human IGF-I (rhIGF-I, 2.5 mg . kg body wt(-1) . 24 h(-1)) infusion on the composition of the carcass and organs and on plasma insulin, IGF-I, IGF-binding protein 1 (IGFBP-1), and acid-labile subunit (ALS) concentrations. Carcass protein deposition on ly occurred in the AA groups (P < 0.003) and was not influenced by administ ration of rhIGF-I. However, visceral protein loss persisted in the AA group but was prevented by rhIGF-I infusion. The changes in water content of the carcass and the organs were generally in the expected proportion of normal lean tissue. The accumulation of lipid that follows the infusion of the AA -deficient PN was prevented by rhIGF-I infusion, which may indicate an impr oved energy utilization. Neither serum insulin nor ALS concentrations were influenced by the level of AA infusion but were reduced by rhIGF-I administ ration. However, plasma IGF-I levels were elevated by higher AA infusion an d by IGF-I administration. Also, IGFBP-1 concentrations were reduced by the higher AA infusion and increased with rhIGF-I administration. Interestingl y, there was a significant interaction effect between both of these influen ces. It is concluded that free IGF-I concentration, which may be regulated by IGFBP-1 through a direct effect of AAs on the liver, may have an importa nt role in regulating anabolism in visceral and possibly skeletal tissue du ring PN.