Urea cycle enzymes in tissues (liver, rumen epithelium, heart, kidney, lung and spleen) of sheep ( Ovis aries)

Abstract

1. 1. The enzymes of urea cycle were studied in the tissues (liver, rumen epithelium, heart, kidney, lung and spleen) of sheep ( Ovis aries). 2. 2. The complete urea cycle was functional in significant quantities only in the liver. 3. 3. Activities of urea cycle enzymes (carbamyl phosphate synthetase, ornithine transcarbamylase, arginine synthetase and arginase) were much higher in the liver than in other tissues; the enzymic pattern in other tissues tested was the same. 4. 4. It is concluded that the rumen epithelium disposes very little ammonia through the urea cycle. Other mechanisms in addition to glutamate dehydrogenase and glutamine synthetase are expected to exist in this tissue to avoid ammonia toxicity. The rumen epithelium is exposed to very high concentrations of ammonia (5–55 mg NH 3-N/100 ml rumen contents).