Previous work has documented an acceleration of proteolysis and
branched-chain amino acid oxidation when muscles from rats with chronic
metabolic acidosis were incubated in vitro. The present study examines the impact of chronic
metabolic acidosis on whole body
amino acid turnover and oxidation in chronically catheterized awake male Sprague-Dawley rats using stochastic modeling and a primed continuous infusion of L-[1-14C]
leucine. Whole body
protein turnover was accelerated by
acidosis as reflected in a 70% increase in proteolysis and a 55% increase in
protein synthesis.
Amino acid oxidation was increased 145% in rats with chronic
metabolic acidosis relative to control rats receiving diets identical in
protein and calories based on a reciprocal pool model and plasma
alpha-ketoisocaproate specific radioactivity. These changes were accompanied by a 104% increase in liver
branched-chain ketoacid dehydrogenase (BCKAD) activity in rats with
acidosis, similar to previously documented increases in skeletal muscle BCKAD activity caused by
acidosis. In contrast, kidney BCKAD activity was decreased 38% by
acidosis, illustrating the tissue-specificity of the changes that were present. We conclude that chronic
metabolic acidosis accelerates whole body
protein turnover and affects the reincorporation of
amino acid into body
proteins by accelerating
amino acid oxidation.