Plasma amino acid profile and expression of the ubiquitin-mediated proteolytic pathway in lambs with induced metabolic acidosis

Metabolic acidosis is a condition often induced by ruminal acidosis. Identification of the specific proteolytic pathways affected by metabolic acidosis and characterization of AA concentration changes induced by metabolic acidosis in ruminants has yet to be confirmed. The objective of this study was to examine the effect of nutritionally induced metabolic acidosis on lamb plasma AA and tissue variables, including mRNA and protein expression of components of the ubiquitin-mediated proteolytic pathway. Lambs (n = 10) were divided evenly into treatment groups receiving alfalfa pellets supplemented with 1) a control canola meal supplement, or 2) HCl-treated canola meal supplement for a 10-d treatment period. On d 11, lambs were slaughtered and liver, muscle, and kidney samples were collected to determine mRNA expression of components of the ubiquitin-mediated proteolytic pathway and ubiquitin protein expression. Plasma concentrations of serine (P = 0.06), glycine (P = 0.002), and glutamine (P = 0.04) were greater in acidotic lambs compared with control animals, indicating that protein catabolism may be occurring. However, no alteration (P > 0.1) in messenger RNA expression of the proteasome subunit C8, ubiquitin-conjugating enzyme E2, or ubiquitin or in ubiquitin protein expression were observed. These results suggest that ubiquitin-mediated proteolysis is not the primary pathway of protein degradation in lambs afflicted with metabolic acidosis.