The catabolism of arginine and ornithine in the liver

Abstract

The liver is a key organ for the catabolism of amino acids in mammals. However, the processes for the catabolism of arginine and ornithine in liver have not been studied in great detail. Neither the extent to which these amino acids are catabolized, nor the location within the liver of this catabolism is known. With respect 10 the localization of these processes, certain metabolic pathways are restricted to specific regions within the liver. Thus, it is possible that the processes for catabolizing ornithine and arginine are not distributed homogeneously throughout the liver, but are contained within a specific region. Furthermore, the catabolism of amino acids such as glycine and glutamine in liver is known to be regulated by various dietary and hormonal stimuli; the rates of catabolism of arginine and ornithine may also respond to such stimuli. -- It was discovered that the catabolism of both ornithine and arginine could be carried out, in their entirety, in the perivenous cells of the liver (those cells lining the central vein. where blood normally exits the liver). Also, the rates of catabolism of ornithine and arginine are subject to regulation by the amount of dietary protein. Rats fed a high protein diet over a period of days showed increased rates of catabolism of these amino acids, when compared with rats fed a diet with normal protein content. With respect to the effects of hormones, it was demonstrated that the catabolism of arginine, but not of ornithine, is subject to acute stimulation by glucagon, whereas insulin was without effect.