DIETARY ARGININE UPTAKE BY THE SPLANCHNIC REGION IN ADULT HUMANS

To determine the uptake of dietary arginine and leucine by the splanch nic region, two experiments were carried out, each involving four heal thy young adult men who received a diet supplying 1 g1 protein . kg-1 . day-1 for 7 and 10 days before conducting a primed constant tracer i nfusion protocol. In study 1, subjects received for 8 h (3-h fast; 5-h fed state, achieved by a constant intragastric infusion of the diet f ormula) L-[5,5-H-2(2); guanidino-N-15(2)]arginine ([M4]Arg), L-[guanid ino-C-13]arginine ([C-13]Arg), and L-[5,5,5-H-2(3)]leucine ([H-2(3)]Le u) simultaneously by an intragastric infusion on day 7 and a repeat of this protocol on day 10 except with tracer administration given by ve in. Plasma arginine fluxes were essentially the same for the two argin ine tracers but differed significantly with route of administration. I n study 2 the subjects received on day 7 a constant intravenous infusi on of [C-13]Arg and [H-2(3)]Leu and a simultaneous intragastric infusi on of [M4]Arg and [1-C-13]eucine. On day 10 the routes of administrati on of these tracer pairs were reversed. During the fed state in study 1, splanchnic uptake of dietary arginine was 31 +/- 10 and 34 +/- 8%, based on the [C-13]Arg and [M4]Arg tracers, respectively, and it was s ignificantly higher (P < 0.01) than for leucine, which was 10 +/- 6%. In study 2, splanchnic uptake of dietary arginine, estimated from a se ries of tracer-protocol combinations for the fed state, was approximat ely 38% compared with a lower (P < 0.01) value of approximately 15% fo r leucine.