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Enzymes and Metabolites of Intermediary Metabolism in Urea-fed Sheep¹

Department of Animal Science, Cornell University, Ithaca, New York 14850

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 -ketoglutarate concentrations were higher in the urea-fed lambs but blood ammonia and hematocrit were lower. Liver concentrations of pyruvate, -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.

² Present address: Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Mass.

Manuscript received 14 November 1969.