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- ¹⁵N,¹⁵N] arginine, L-[ureido-¹³C]citrulline, L-[5,5,²H₂]ornithine, and L-[5,5,5-²H₂]leucine was conducted. Mean citrulline fluxes (μmol · 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).