Castellino P, Luzi L, Del Prato S, DeFronzo R A
Diabetes Division, University of Texas Health Science Center, San Antonio 78284.
Am J Physiol. 1990 Jan;258(1 Pt 1):E117-25. doi: 10.1152/ajpendo.1990.258.1.E117.
The separate and combined effects of insulin and epinephrine on leucine metabolism were examined in healthy young volunteers. Subjects participated in four experimental protocols: 1) euglycemic insulin clamp (+80 microU/ml), 2) epinephrine infusion (50 ng.kg-1.min-1) plus somatostatin with basal replacement of insulin and glucagon, 3) combined epinephrine (50 ng.kg-1.min-1) plus insulin (+80 microU/ml) infusion, and 4) epinephrine and somatostatin as in study 2 plus basal amino acid replacement. Studies were performed with a prime-continuous infusion of [1-14C]leucine and indirect calorimetry. Our results indicate that 1) hyperinsulinemia causes a generalized decrease in plasma amino acid concentrations, including leucine; 2) the reduction in plasma leucine concentration is primarily due to an inhibition of endogenous leucine flux; nonoxidative leucine disposal decreases after insulin infusion; 3) epinephrine, without change in plasma insulin concentration, reduces plasma amino acid levels; 4) combined epinephrine-insulin infusion causes a greater decrease in plasma amino levels than observed with either hormone alone; this is because of a greater inhibition of endogenous leucine flux; and 5) when basal amino acid concentrations are maintained constant with a balanced amino acid infusion, epinephrine inhibits the endogenous leucine flux. In conclusion, the present results do not provide support for the concept that epinephrine is a catabolic hormone with respect to amino acid-protein metabolism. In contrast, epinephrine markedly inhibits insulin-mediated glucose metabolism.
在健康年轻志愿者中研究了胰岛素和肾上腺素对亮氨酸代谢的单独及联合作用。受试者参与了四个实验方案：1）正常血糖胰岛素钳夹（+80微单位/毫升）；2）肾上腺素输注（50纳克·千克⁻¹·分钟⁻¹）加生长抑素，并基础补充胰岛素和胰高血糖素；3）联合输注肾上腺素（50纳克·千克⁻¹·分钟⁻¹）加胰岛素（+80微单位/毫升）；4）同研究2中的肾上腺素和生长抑素加基础氨基酸补充。研究采用[1-¹⁴C]亮氨酸的首剂-持续输注和间接测热法进行。我们的结果表明：1）高胰岛素血症导致血浆氨基酸浓度普遍降低，包括亮氨酸；2）血浆亮氨酸浓度降低主要是由于内源性亮氨酸通量受到抑制；胰岛素输注后非氧化型亮氨酸处置减少；3）肾上腺素在血浆胰岛素浓度无变化的情况下降低血浆氨基酸水平；4）联合输注肾上腺素和胰岛素导致血浆氨基酸水平的降低幅度大于单独使用任何一种激素时观察到的情况；这是因为对内源性亮氨酸通量的抑制作用更强；5）当通过平衡氨基酸输注使基础氨基酸浓度保持恒定时，肾上腺素抑制内源性亮氨酸通量。总之，目前的结果不支持肾上腺素在氨基酸-蛋白质代谢方面是一种分解代谢激素这一概念。相反，肾上腺素显著抑制胰岛素介导的葡萄糖代谢。
