Effects of dietary salt intake on plasma arginine

Because L-arginine is degraded by hepatic arginase to ornithine and urea an d is transported by the regulated 2A cationic amino acid y(+) transporter ( CAT2A), hepatic transport may regulate plasma arginine concentration. Group s of rats (n = 6) were fed a diet of either low salt (LS) or high salt (HS) for 7 days to test the hypothesis that dietary salt intake regulates plasm a arginine concentration and renal nitric oxide (NO) generation by measurin g plasma arginine and ornithine concentrations, renal NO excretion, and exp ression of hepatic CAT2A, and arginase. LS rats had lower excretion of NO m etabolites and cGMP, lower plasma arginine concentration (LS: 83 +/- 7 vs. HS: 165 +/- 10 mu mol/1, P < 0.001), but higher plasma ornithine concentrat ion (LS: 82 6 6 vs. HS: 66 +/- 4 <mu>mol/1, P < 0.05) and urea excretion. H owever, neither the in vitro hepatic arginase activity nor the mRNA for hep atic arginase I was different between groups. In contrast, LS rats had twic e the abundance of mRNA for hepatic CAT2A (LS: 3.4 +/- 0.4 vs. HS: 1.6 +/- 0.5, P < 0.05). The reduced plasma arginine concentration with increased pl asma ornithine concentration and urea excretion during LS indicates increas ed arginine metabolism by arginase. This cannot be ascribed to changes in h epatic arginase expression but may be a consequence of increased hepatic ar ginine uptake via CAT2A.