Wolfe R R, Goodenough R D, Wolfe M H
Adv Shock Res. 1983;9:81-98.
Determination of the protein requirement of the severely burned patient has been hampered by the lack of an appropriate means of evaluating the effects of various levels of intake. We have used two new isotopic techniques in an attempt to assess the effects of two levels of protein intake in six severely burned adult patients. A crossover experimental design enabled us to study each patient at the end of two 3-day dietary regimens. All diets were isocaloric and provided approximately 25% more calories than the measured energy expenditure (means = 40 Kcal/kg X day). In one regimen, each patient received 2.2 g protein/kg X day; during the other treatment period they received 1.4 g protein/kg X day. The patients were studied in the fed state and after 10-12 h of fasting. Leucine kinetics were determined by means of the primed-constant infusion of (1-13C)-leucine. We were able to distinguish the oxidation of plasma leucine from the oxidation of leucine derived from intracellular protein at the site of the deamination of leucine (predominantly muscle) by simultaneously determining both leucine and alpha-ketoisocaproic acid enrichment. Also, rates of whole-body protein synthesis and catabolism were calculated by means of another stable-isotope technique involving the infusion of (15N2)-urea. Finally, a third means of estimating net protein catabolism based on urinary N-excretion data was used at the same time that the isotopic studies were performed. The 13C-leucine data and the N-excretion data indicated that a balance between protein synthesis and catabolism could be achieved with a protein intake of 1.4 protein/kg X day. When protein intake was increased to 2.2 g protein/kg X day, neither isotopic method indicated a further beneficial effect on net protein synthesis, although the absolute rates of protein synthesis and catabolism were stimulated. The N-excretion data, however, indicated a significant improvement in net protein synthesis with higher protein intake. Regardless of the level of protein intake, the underlying alterations in protein metabolism that occurred as a response to burn injury persisted.
由于缺乏评估不同摄入水平影响的合适方法，严重烧伤患者蛋白质需求量的测定一直受到阻碍。我们采用了两种新的同位素技术，试图评估六名严重烧伤成年患者两种蛋白质摄入水平的影响。交叉实验设计使我们能够在两种为期3天的饮食方案结束时对每位患者进行研究。所有饮食的热量均相等，且提供的热量比测得的能量消耗多约25%（平均值 = 40千卡/千克×天）。在一种方案中，每位患者每天每千克体重摄入2.2克蛋白质；在另一个治疗阶段，他们每天每千克体重摄入1.4克蛋白质。在进食状态和禁食10 - 12小时后对患者进行研究。通过对(1 - 13C)-亮氨酸进行预充恒定输注来测定亮氨酸动力学。通过同时测定亮氨酸和α-酮异己酸的富集情况，我们能够在亮氨酸脱氨基部位（主要是肌肉）区分血浆亮氨酸的氧化与细胞内蛋白质衍生亮氨酸的氧化。此外，通过另一种涉及输注(15N2)-尿素的稳定同位素技术计算全身蛋白质合成和分解代谢的速率。最后，在进行同位素研究的同时，使用了基于尿氮排泄数据估算净蛋白质分解代谢的第三种方法。13C-亮氨酸数据和氮排泄数据表明，每天每千克体重摄入1.4克蛋白质时可实现蛋白质合成与分解代谢的平衡。当蛋白质摄入量增加到每天每千克体重2.2克时，尽管蛋白质合成和分解代谢的绝对速率受到刺激，但两种同位素方法均未显示对净蛋白质合成有进一步的有益影响。然而，氮排泄数据表明，较高的蛋白质摄入量可使净蛋白质合成有显著改善。无论蛋白质摄入水平如何，因烧伤损伤而发生的蛋白质代谢潜在改变仍然存在。
