Arginine (Arg) is generated in the kidney by the conversion of circulating citrulline. The most important source for circulating citrulline is the metabolism of glutamine (Gln) by the gut. In this study, we investigated the influence of an enteral diet enriched with Gln on renal Arg synthesis in the rat.
Rats were fed a 12.5% Gln-enriched diet or an isocaloric, isonitrogenous control diet for 14 days. Kidney plasma flow and arterial and renal venous plasma levels of a number of amino acids were measured, and kidney amino acid fluxes were calculated.
Compared with the control diet, Gln enrichment resulted in significantly higher arterial plasma levels of circulating citrulline (30%, p < .0001) and Arg (31%, p < .0005). The uptake of circulating citrulline and the subsequent production of Arg by the kidneys were significantly higher in the Gln-enriched group (40% and 38%, respectively) and showed an equimolar relationship in both the control (r = .84, p < .0001) and the Gln-enriched group (r = .83, p < .0001).
The findings indicate that enteral Gln supplementation caused significantly increased arterial plasma levels of Arg as a result of increased renal Arg production from circulating citrulline. Considering the multiple important biologic properties of Arg, the reported beneficial effects of Gln in catabolic states might be explained in part by increased renal Arg production.