ABSTRACT
Arginine is considered intermediate between a dietary indispensable and dispensable amino acid since it is typically required for optimum growth in immature animals. Dietary requirements for arginine depend upon a variety of factors including: species, age, dietary habits, and physiological state. Differences in requirements among species probably relate to the biosynthesis of urea-cycle intermediates within the intestine and kidney. Hyperammonemia and associated metabolic complications are reduced, or prevented, by the inclusion of the urea-cycle intermediates arginine, citrulline, or ornithine. However, growth is optimized only by the inclusion of arginine or citrulline. Studies with liver slices and isolated hepatocytes revealed that excessive intramitochondrial production of carbamyl phosphate is responsible for the enhanced orotic-acid formation. A diet devoid of arginine is a useful model for studying chronic hyperammonemia and is a valuable model for examining the dynamic relationship that exists between the urea cycle and pyrimidine biosynthesis.
