QUANTITATIVE ASPECTS OF INTERORGAN RELATIONSHIPS AMONG ARGININE AND CITRULLINE METABOLISM

The quantitative roles of the splanchnic region and the kidneys in who le body (WB) arginine and citrulline metabolism were assessed in posta bsorptive mongrel dogs with primed constant intravenous infusions of [ N-15(2)-guanidino, 5,5-H-2(2)]arginine and [C-13-ureido] citrulline or [C-13-guanidino]arginine and [N-15]urea tracers. Isotope and metaboli te concentration balances of arginine and citrulline were measured acr oss the gut, liver, splanchnic region, and kidneys, together with WB a rginine and citrulline fluxes and urea production rate. The WB citrull ine flux and rate of citrulline to arginine (C-A) conversion were 16 a nd 9.4 mu mol . kg(-1) . h(-1), respectively. Concentration balance of citrulline across kidneys was +8.2 mu mol . kg(-1) . h(-1), and metab olism of citrulline by kidneys was 8.7 mu mol kg(-1) . h(-1), which wa s derived about equally from intestine and liver. The appearance rate of citrulline-derived arginine in renal vein was 6.8 mu mol . kg(-1) . h(-1). These three separate estimates of C-A conversion within the ki dneys were in good agreement, indicating 40% of blood C-A conversion o ccurring outside kidneys. These findings of interorgan metabolism are discussed in reference to the current knowledge derived largely from s tudies in laboratory rodents.