Plasma amino acid concentrations and mRNA expression of components related to protein degradation in lambs with nutritionally induced metabolic acidosis

Abstract

Aspects of amino acid metabolism and proteolysis were examined in lambs with metabolic acidosis. Lambs (n = 30; 42.8 ± 4.1 kg BW) were randomly assigned to treatment groups, receiving a topdress of either (1) dried distiller’s grain (DDG; anion load of 7 mEq 100 g-1 DM, (2) DDG + NH4Cl-treated DDG (anionic load of -29 mEq 100 g-1 DM), or (3) DDG + NH4Cl-treated DDG (anionic load of -42 mEq 100 g-1 DM). Lambs were maintained on DDG topdress for 9 d, after which increasing amounts of DDG were substituted with NH4Cl-treated DDG in the treatment group diets from day 10 to day 21. Blood gas, blood acid-base, urine pH and plasma amino acid concentrations were determined on day 9 and day 21. On day 22, lambs were slaughtered and kidney, liver, extensor digitorum longus muscle (EDL), and soleus muscle samples were collected. Blood pH, bicarbonate, base excess of blood and extracellular fluid, total CO2 and urinary pH were linearly decreased as dietary anionic load increased (P < 0.001). Plasma glutamine, glycine, histidine, arginine and asparagine increased linearly (P < 0.06) due to acidosis, while renal glutamate dehydrogenase (P = 0.02) and hepatic glutamine synthetase (P = 0.02) mRNA expression were linearly increased. Caspase-3 mRNA expression was linearly decreased in soleus muscle by acidosis (P = 0.01), but not in EDL muscle. No change in mRNA expression of components of the ubiquitin-mediated proteolytic pathway was observed in either muscle. These results suggest muscle-specific regulation of caspase-3 mRNA expression during metabolic acidosis in sheep.