ARGININE METABOLISM IN CAT KIDNEY

1. Arginine is essential for growth in the kitten and, because of the resulting hyperammonaemia, in the adult cat an arginine-free diet is l ife threatening.2. The kidney is the main site of arginine synthesis. 3. This study was performed to determine whether the cat kidney synthe sizes arginine and to establish which factors, such as low citrullinae mia, defects of argininosuccinate synthase and lyase activities or hig h renal arginase activity, might limit renal arginine production. 4. I dentified nephron segments were isolated by microdissection from colla genase-treated cat kidney. 5. Arginine metabolism was studied by incub ating the nephron segments with either physiological concentrations of L-[ureido-C-14]citrulline (anabolism) or L-[guanido-C-14]arginine (ca tabolism). Arginine and urea were measured by a micro-enzymatic method . Amino acids were measured by HPLC. 6. In cat blood, the citrulline, but not the arginine, concentration was very loss by comparison with o ther species. 7. Arginine synthesis occurred almost entirely in the pr oximal tubule, the highest rate occurring in the proximal convoluted t ubule and the lowest in the medullary straight proximal tubule. 8. Arg inase activity was restricted to the proximal tubule. Urea production increased from the convoluted towards the medullary straight tubule. 9 . The limited capacity of the cat kidney to produce arginine in vivo m ay result from the low blood concentration of citrulline and from the high arginase activity in the various proximal cells with the ability to synthesize arginine.