Detoxication of Ammonia in Sheep Fed Soy Protein or Urea

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Abstract
Urea-fed sheep were able to detoxify additional ammonia absorbed from the digestive tract by a mechanism involving increased concentrations of liver ornithine. Feeding urea as the sole nitrogen source caused decreases in activities of carbamyl phosphate synthetase, ornithine transcarbamylase and arginase while no differences were noted in activities of arginine synthetase and argininosuccinase. Decreases in these enzyme systems were concluded to be the result of ammonia causing derangements in cellular energy metabolism or a suboptimum amino acid nutriture in urea-fed animals, both of which could cause decreases in enzyme synthesis. Although activity of the rate-limiting enzyme system, arginine synthetase, was sufficient over a 24-hour period to account for the quantity of urea excreted, reserve capacity was minimal. It was suggested that for several hours after feeding a urea diet, liver ammonia detoxication mechanisms may be exceeded. In view of the effects of ammonia on cellular energy metabolism, part of the lowered productive capacities obtained when urea diets are fed may be due to ammonia-producing biochemical derangements in liver and other tissues.