Biochemical changes during experimental carcinogenesis. III. The production of urea from aspartic acid, arginine, or ammonia in the perfused rat liver.

In the earlier papers in this series (3, 4) data have been presented which indicate tha t the isolated perfused liver from a ra t fed 8'-methyldimethylaminoazobenzene 1 has a decreased ability to oxidatively catabolize amino acids. Such livers, however, show an increased capacity for incorporation of C14-1abeled amino acid into both liver and plasma proteins. A biochemical block or impairment in the chemical reaction sequence from amino acid nitrogen to urea nitrogen was thought to develop during the process of azo dye carcinogenesis. To a t t empt to demonstrate definitively the locus of this metabolic impairment, we have studied the ability of the perfused livers from 3'-Me-DABfed rats to produce urea from ammonia, aspartic acid, or arginine added to the blood perfusate.