Kee A J, Baxter R C, Carlsson A R, Smith R C
Department of Surgery, University of Sydney, Australia.
Am J Physiol. 1999 Jul;277(1):E63-72. doi: 10.1152/ajpendo.1999.277.1.E63.
The anabolic properties of insulin-like growth factor (IGF) I are attenuated by oral diets that are low in protein. However, it is not known whether parenteral nutrition (PN) providing a low amino acid (AA) input will influence IGF-I action. With the use of a rat model, this study examined the interaction between AA input (1.27 and 0.62 g N. kg body wt(-1). 24 h(-1), AA and 1/2AA 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 only occurred in the AA groups (P < 0.003) and was not influenced by administration 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 improved energy utilization. Neither serum insulin nor ALS concentrations were influenced by the level of AA infusion but were reduced by rhIGF-I administration. However, plasma IGF-I levels were elevated by higher AA infusion and by IGF-I administration. Also, IGFBP-1 concentrations were reduced by the higher AA infusion and increased with rhIGF-I administration. Interestingly, there was a significant interaction effect between both of these influences. 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 important role in regulating anabolism in visceral and possibly skeletal tissue during PN.
蛋白质含量低的口服饮食会削弱胰岛素样生长因子（IGF）I的合成代谢特性。然而，尚不清楚提供低氨基酸（AA）输入的肠外营养（PN）是否会影响IGF-I的作用。本研究利用大鼠模型，考察了AA输入量（分别为1.27和0.62 g氮·kg体重⁻¹·24 h⁻¹，AA组和1/2AA组）与重组人生长激素（rhIGF-I，2.5 mg·kg体重⁻¹·24 h⁻¹）输注对胴体和器官组成以及血浆胰岛素、IGF-I、IGF结合蛋白1（IGFBP-1）和酸不稳定亚基（ALS）浓度的影响。胴体蛋白质沉积仅发生在AA组（P < 0.003），且不受rhIGF-I给药的影响。然而，AA组内脏蛋白质持续流失，但rhIGF-I输注可预防这种情况。胴体和器官水分含量的变化通常符合正常瘦组织的预期比例。rhIGF-I输注可预防输注缺乏AA的PN后脂质的积累，这可能表明能量利用得到改善。血清胰岛素和ALS浓度均不受AA输注水平的影响，但rhIGF-I给药可使其降低。然而，较高的AA输注和IGF-I给药可提高血浆IGF-I水平。此外，较高的AA输注可降低IGFBP-1浓度，而rhIGF-I给药则使其升高。有趣的是，这两种影响之间存在显著的交互作用。研究得出结论，游离IGF-I浓度可能受IGFBP-1调节，而AA对肝脏有直接作用，其在PN期间调节内脏和可能的骨骼组织合成代谢中可能起重要作用。
