Dardevet D, Manin M, Balage M, Sornet C, Grizard J
INRA Theix, Laboratoire d'Etude du Métabolisme Azoté, Ceyrat, France.
Br J Nutr. 1991 Jan;65(1):47-60. doi: 10.1079/bjn19910065.
The influence of protein content of the diet on the plasma concentrations and binding to skeletal muscle and liver of insulin and insulin-like growth factor-1 (IGF-1), was studied in growing rats. Animals with a starting body-weight of 80 g received for an 11 d period isoenergetic diets containing (g/kg dry matter) 155 protein as controls (MP), or 55 (LP) or 300 (HP) protein. Food was offered as six equal meals/d. Daily food intakes provided adequate amounts of energy. Total plasma IGF-1 increased linearly as a function of dietary protein intake. Plasma insulin was lower in the LP than in the MP and HP groups. Hormone binding was studied in wheat-germ agglutinin (WGA) partially purified skeletal muscle receptor preparations. Each 125I-labelled hormone binding was competed for by increasing amounts of homologous and heterologous unlabelled hormone; this displacement needed lower concentrations of homologous than heterologous hormone. When compared with MP-diet feeding, the LP diet resulted in an increased ligand concentration for half-maximal binding. In addition the specific 125I-labelled insulin and 125I-labelled IGF-1 binding increased at all hormone concentrations and, as revealed by Scatchard analysis, the hormone binding capacity also rose (only significant for low-affinity insulin receptors and high-affinity IGF-1 receptors). The HP diet had little effect on hormone binding, except to increase insulin binding at very low insulin concentrations. Hormone binding was further studied in WGA partially purified liver receptor preparations. Those preparations did not exhibit any detectable specific 125I-labelled IGF-1 binding. The specific 125I-labelled insulin binding was not altered by dietary protein level. It is concluded that the increase in skeletal muscle insulin and IGF-1 binding along with a decrease in insulin and IGF-1 in the blood from rats fed on the LP diet, is consistent with the concept of an inverse relationship between plasma hormone and hormone binding. The physiological significance with respect to metabolic adaptation of muscle remains to be established.
研究了日粮蛋白质含量对生长大鼠血浆中胰岛素和胰岛素样生长因子-1（IGF-1）浓度以及它们与骨骼肌和肝脏结合的影响。初始体重为80 g的动物接受为期11天的等能量日粮，日粮中蛋白质含量（g/kg干物质）分别为155（作为对照，MP）、55（LP）或300（HP）。每天提供六顿等量的食物。每日食物摄入量提供了足够的能量。血浆总IGF-1随日粮蛋白质摄入量呈线性增加。LP组的血浆胰岛素水平低于MP组和HP组。在小麦胚芽凝集素（WGA）部分纯化的骨骼肌受体制剂中研究了激素结合情况。随着未标记同源和异源激素量的增加，每种125I标记激素的结合均受到竞争；这种置换所需的同源激素浓度低于异源激素。与MP日粮喂养相比，LP日粮导致半数最大结合时的配体浓度增加。此外，在所有激素浓度下，特异性125I标记胰岛素和125I标记IGF-1的结合均增加，并且如Scatchard分析所示，激素结合能力也有所提高（仅对低亲和力胰岛素受体和高亲和力IGF-1受体有显著意义）。HP日粮对激素结合影响不大，只是在极低胰岛素浓度下会增加胰岛素结合。在WGA部分纯化的肝脏受体制剂中进一步研究了激素结合情况。这些制剂未表现出任何可检测到的特异性125I标记IGF-1结合。特异性125I标记胰岛素结合不受日粮蛋白质水平的影响。得出的结论是，LP日粮喂养的大鼠血液中胰岛素和IGF-1减少，同时骨骼肌中胰岛素和IGF-1结合增加，这与血浆激素和激素结合之间呈反比关系的概念一致。关于肌肉代谢适应的生理意义仍有待确定。
