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

Abstract

. W. 2010. Plasma amino acid concentrations and mRNA expression of components related to protein degradation in lambs with nutritionally induced metabolic acidosis. Can. J. Anim. Sci. 90: 537Á546. Aspects of amino acid metabolism and proteolysis were examined in lambs with metabolic acidosis. Lambs (n 030; 42.894.1 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'NH 4 Cl-treated DDG (anionic load of (29 mEq 100 g (1 DM), or (3) DDG'NH 4 Cl-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 NH 4 Cl-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 CO 2 and urinary pH were linearly decreased as dietary anionic load increased (P B0.001). Plasma glutamine, glycine, histidine, arginine and asparagine increased linearly (PB0.06) due to acidosis, while renal glutamate dehydrogenase (P 00.02) and hepatic glutamine synthetase (P00.02) mRNA expression were linearly increased. Caspase-3 mRNA expression was linearly decreased in soleus muscle by acidosis (P00.01), 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.

Differential regulation of components of the apoptotic and ubiquitin-mediated proteolytic pathway in slow- and fast- twitch muscle type in lambs receiving increasing amounts of dietary non-structural carbohydrate

“…Hence, soleus and EDL muscle can be considered to be slow-and fast-twitch muscle types in sheep and could demonstrate similar differential muscle responses to disease induction to those observed in the rat. We have also observed some differential regulation of Caspase-3 mRNA expression in these muscle types in metabolically acidotic sheep (Greenwood et al 2010). Perhaps exclusive of its role in muscle proteolysis, Caspase-3 also participates in apoptosis.…”

“…3). The authors have previously demonstrated a lack of response in Caspase-3 mRNA expression after induction of a moderate metabolic acidosis using dietary HCl (Greenwood et al 2009), but have successfully induced downregulation of soleus muscle specific mRNA expression of Caspase-3 using an ammonium chloride induction model of metabolic acidosis (Greenwood et al 2010). However, Caspase-3 serves functions in other cellular activities, such as apoptosis (Jesenberger and Jentsch 2002) and this role should not be overlooked, as this process could be the more dominant regulator of Caspase-3 mRNA expression.…”