Wolfe R R, Goodenough R D, Burke J F, Wolfe M H
Ann Surg. 1983 Feb;197(2):163-71. doi: 10.1097/00000658-198302000-00007.
The effects of two levels of protein intake on protein metabolism in six severely burned adult patients were studied (means of 70% BSA burned). A crossover experimental design enabled the authors to study each patient at the end of two three-day dietary regimens. All diets were isocaloric and provided approximately 25% more calories than the measured energy expenditure (means = 40.8 Kcal/kg X day). In one regimen, each patient received 2.2 g protein/kg X day, while 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 to 12 hours of fasting. Leucine kinetics were determined by means of the primed-constant infusion of [1--13C]--leucine. The authors 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 from the leucine flux and oxidation data. Net protein synthesis was also 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, on the other hand, 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.
研究了两种蛋白质摄入量水平对6名严重烧伤成年患者（平均烧伤面积达70%体表面积）蛋白质代谢的影响。交叉实验设计使作者能够在两种为期三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约多25%（平均 = 40.8千卡/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，而在另一个治疗阶段，他们每天每千克体重摄入1.4克蛋白质。在进食状态以及禁食10至12小时后对患者进行研究。通过[1--13C] - 亮氨酸的预充恒速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，作者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，根据亮氨酸通量和氧化数据计算全身蛋白质合成和分解代谢的速率。净蛋白质合成也通过另一种稳定同位素技术进行计算，该技术涉及输注[15N2] - 尿素。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。另一方面，氮排泄数据表明，较高的蛋白质摄入量使净蛋白质合成有显著改善。无论蛋白质摄入量水平如何，因烧伤损伤而发生的蛋白质代谢潜在改变仍然存在。
