短期間の床上安静はアミノ酸が誘導する蛋白同化を障害する

今日は、短期間の床上安静はアミノ酸が誘導する蛋白同化を障害するという論文を紹介します。先日の第2回神奈川NST合宿の特別講演で大村健二先生が使用された論文です。

Biolo G, et al: Short-term bed rest impairs amino acid-induced protein anabolism in humans. J Physiol. 2004 Jul 15;558(Pt 2):381-8.

下記のHPで全文見ることができます。

http://jp.physoc.org/content/558/2/381.full.pdf+html

9人の健康若年ボランティアを対象に、14日間の床上安静（筋肉の不活動、廃用）が蛋白代謝に及ぼす影響を実験しました。食事は蛋白も含め十分摂取しています。今回の研究では床上安静と安静でない時と比較して、蛋白異化に統計学的有意差はありませんでしたが、蛋白同化に有意差がありました。

私は廃用による筋萎縮は筋蛋白同化の低下よりも筋蛋白異化の亢進によるものだと思っていたのですが、両方の要素がありそうです。そうすると、床上安静、廃用のみでは栄養障害が生じないとは言えません。筋蛋白同化の低下は栄養障害の1つといえますので、不要な安静、廃用を避けること自体が栄養悪化の予防につながる可能性があります。

Abstract
Diminished muscular activity is associated with alterations of protein metabolism. The aim of this study was to evaluate the effect of short-term muscle inactivity on regulation of whole-body protein deposition during amino acid infusion to simulate an experimental postprandial state. We studied nine healthy young volunteers at the end of 14 day periods of strict bed rest and of controlled ambulation using a cross-over design. Subjects received a weight-maintaining diet containing 1 g protein kg(-1) day(-1). l[1-(13)C]leucine was used as a marker of whole-body protein kinetics in the postabsorptive state and during a 3 h infusion of an amino acid mixture (0.13 g amino acid (kg lean body mass)(-1) h(-1)). In the postabsorptive state, bed rest decreased (P < 0.05) the rate of leucine disposal (R(d)) to protein synthesis and tended to decrease leucine rate of appearance (R(a)) from proteolysis, whereas the rate of leucine oxidation did not change significantly. Amino acid infusion increased leucine R(d) to protein synthesis and oxidation and decreased leucine R(a) from proteolysis in both the bed rest and ambulatory conditions. Changes from basal in leucine R(d) to protein synthesis were lower (P < 0.05) during bed rest than those in the ambulatory period, whereas changes in leucine R(a) from proteolysis and oxidation were not significantly different. During amino acid infusion, net leucine deposition into body protein was 8 +/- 3% lower during bed rest than during the ambulatory phase. In conclusion, short-term bed rest leads to reduced stimulation of whole-body protein synthesis by amino acid administration. Results of this study were, in part, presented at the meeting, Experimental Biology, 2004, Washington DC.