PLASMA ARGININE, CITRULLINE, AND ORNITHINE KINETICS IN ADULTS, WITH OBSERVATIONS ON NITRIC-OXIDE SYNTHESIS

The plasma fluxes of ornithine (Orn), arginine (Arg), and citrulline (Cit) and rate of conversion of labeled ornithine-to-citrulline (Q(Orn-->Cit)) were estimated in six healthy adult men receiving an arginine-rich or arginine-free L-amino acid-based diet, each for 6 days. On day 7 an 8-h (3-h fast, 5-h fed) primed continuous intravenous infusion of L-[guanido-N-15,N-15] arginine, L-[ureido-C-13]citrulline, L-[5,5,H-2(2)]ornithine, and L-[5,5,5-H-2(3)]leucine was conducted. Mean citrulline fluxes (mu mol.kg(-1).h(-1)) were 10.4-13.6 for the various conditions and/or diets and remained unchanged (P > 0.05). Arginine flux was lowered (P < 0.01) by 38% for fed state during arginine-free period. Ornithine fluxes for arginine-rich were (P < 0.01) reduced with the arginine-free diet. Rates of Q(Orn-->Cit) declined by 30% (P < .05) during the fed arginine-free period. Short-term restriction in the dietary supply of arginine did not alter the rate of whole body nitric oxide synthesis. One subject showed a very high output of nitrate on arginine-free diet (6 times average for remaining subjects).