BACKGROUND & AIMS: Metabolic acidosis is a common finding in critical illness. The aim of the present study was to evaluate acute acidosis as a signal that induces changes in protein metabolism. METHODS: In the first study, Wistar rats were infused for 6h with HCl or saline resulting in blood pH7.30+/-0.03 and 7.46+/-0.02, respectively. The whole body protein metabolism was evaluated using L-[1-(14)C]leucine. In the second study, soleus and extensor digitorum longus muscles from normal rats were incubated in medium, pH7.4, 7.3 or 7.0. Protein metabolism was evaluated using L-[1-(14)C]leucine and tyrosine release. RESULTS: In the in vivo study we observed increased protein turnover-protein synthesis, proteolysis and leucine oxidation and more negative protein balance in rats with acidosis. There was no change in protein synthesis in gastrocnemius muscle. We observed an increase in plasma levels of most amino acids including branched-chain amino acids and a decrease in intracellular amino acid pool in skeletal muscle. In vitro decrease in pH of 0.1 had no effect on protein metabolism, decrease of 0.4 decreased protein turnover and leucine oxidation. CONCLUSION: Acute metabolic acidosis is a protein wasting condition. Direct effect of acidosis on skeletal muscle is under condition in vivo modified by neurohumoral regulations.

Department of Physiology Charles University Hradec Králové Czech Republic

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