Hepatic zonation of the catabolism of arginine and ornithine in the perfused rat liver

The metabolism of 14 C-labelled arginine and ornithine was studied in the isolated, nonrecirculating, perfused rat liver. The catabolism of these amino acids required ornithine aminotransferase since treatment of rats with gabaculine, an inhibitor of this enzyme, decreased substantially the production of 14 CO 2 from the 14 C-labelled amino acids. In the liver, ornithine aminotransferase is restricted to a small population of hepatocytes proximal to the terminal hepatic vein [Kuo, F. C., Hwu, W. L., Valle, D. and Darnell Jr., J. E. (1991) Proc. Natl. Acad. Sci. U.S.A. 88 , 9468-9472], i.e. the perivenous subpopulation of hepatocytes. Catabolism of arginine requires arginase to convert arginine to ornithine which can then be catabolized through ornithine aminotransferase. The presence of arginase activity in the perivenous hepatocytes was demonstrated by experiments in which livers were perfused with [ 14 C]arginine in both antegrade and retrograde directions. Identical rates of 14 CO 2 production were obtained in these experiments, a result which could only occur if the process of arginine catabolism through ornithine aminotransferase can be carried out in its entirety in the perivenous cells.