Enzymes and Metabolites of Intermediary Metabolism in Urea-fed Sheep

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Abstract
Purified diets containing isolated soybean protein or urea as the only source of nitrogen were fed to eight lambs for 55 days. Blood pyruvate and α-ketoglutarate concentrations were higher in the urea-fed lambs but blood ammonia and hematocrit were lower. Liver concentrations of pyruvate, α-ketoglutarate, ammonia, urea and protein did not show statistically significant treatment differences. Liver NAD was elevated while NADH and NADPH concentrations were decreased, thereby greatly increasing the NAD/NADH ratio. Liver NADP-ICD activities were 57% lower in the urea-fed lambs. Activities of liver LDH, G-6-PDH, cytoplasmic NADPH oxidase and NADH oxidase were not altered by dietary treatment. Liver NADPH oxidase activity was lower in the urea-fed lambs. These observations are discussed in relation to the known effects of ammonia on cellular energy metabolism.