Despite a large first‐pass extraction for urea synthesis, the systemic bioavailability of meal arginine is high and dose‐dependent in men

Dietary Arginine is supposed to be largely extracted by the liver for ureagenesis but favourable effects of dietary Arginine are mainly ascribed to a systemic utilization for NO synthesis. Using [ 15 N 2 ‐(guanido)]‐Arginine, we traced the fate of L‐Arginine at two nutritional levels in a complete amino acid meal given to healthy men. We monitored the postprandial appearance of meal arginine (mArg) in the plasma, body and urinary urea derived from mArg, and plasma citrulline and urinary nitrate derived from mArg[FM1]. The relative urea production from mArg was high but similar whatever the mArg level (49±2% of mArg) and completed early after ingestion. With the lower level of mArg, intact mArg accounted for 56±4% of the marked postprandial increase in plasma arginine. In contrast, plasma concentrations of mArg‐derived citrulline were very low. After the 2.7‐fold higher mArg intake, plasma mArg AUC was 3.2±0.2‐fold higher, and plasma mArg‐derived citrulline AUC and urinary mArg‐derived nitrate excretion were 1.8±0.3 and 2.2±0.3‐fold higher, respectively. Because its relative splanchnic extraction for urea synthesis stays steady, mArg exhibits a high incremental systemic bioavailability. However, our data suggests that the utilization of mArg for NO synthesis, although modulated by the systemic availability of mArg, stays very low in these healthy men. Supported by a grant of the French ministry of research [FM1] OU, pour gagner un peu de place," mArg‐derived body and urinary urea, and mArg‐derived plasma citrulline and urinary nitrate"