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This Article Full Text Full Text (PDF) All Versions of this Article: 558/2/381    most recent jphysiol.2004.066365v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Biolo, G. Articles by Guarnieri, G. Search for Related Content PubMed PubMed Citation Articles by Biolo, G. Articles by Guarnieri, G.

¹ Department of Clinical, Technological and Morphological Sciences, Division of Internal Medicine, University of Trieste, Italy² Institute of Cardiology and Sports Medicine, German Sport University, Cologne, Germany³ DLR-Institute of Aerospace Medicine, Cologne, Germany

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[1-¹³C]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.

(Received 12 April 2004; accepted after revision 29 April 2003; first published online 30 April 2003)
Corresponding author G. Biolo: Clinica Medica, Ospedale di Cattinara, Strada di Fiume 447, Trieste 34149, Italy. Email: biolo{at}units.it

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