Nitrate/L-arginine Therapy and Nitric Oxide Levels in the Stomach and Liver of Rats

Background: The L-arginine/nitric oxide (NO) pathway is a major defensive system in gastric mucosa. Nitrate can restore NO homeostasis when enzymatic NO production becomes dysfunctional. Objectives: The aim of this study was to investigate the effects of nitrate/L-arginine administration on NO levels in the stomach and liver of rats. Materials and Methods: In this interventional study, adult male Wistar rats were divided into 3 groups of control, nitrate and L-arginine (n = 8). Rats in the nitrate and L-arginine groups were administered sodium nitrate (500 mg/L) or L-arginine (2%) for one week in drinking water while those in control group consumed tap water. At the end, serum, stomach and liver NO metabolite (NO x ) concentrations were measured by the Griess method. Results: Median (interquartile range) serum NO x concentrations in the control group [28.2 (19.6 - 37.8) μmol/L] were significantly (P < 0.05) different to those of the nitrate [152.4 (111.4 - 180.2) μmol/L] and L-arginine [14.5 (11.2 - 21.5) μmol/L] groups. Nitrate administration increased and L-arginine administration decreased stomach and liver NOx levels respectively. A positive correlation was observed between serum concentrations and stomach (r = 0.847, P < 0.001) and liver (r = 0.650, P = 0.006) NO x levels. Conclusions: Nitrate and L-arginine administration had opposite effects on NO x levels in stomach and liver of normal rats. Increase in stomach NO x following nitrate administration may be due to gastric nitrate absorption, while the decrease in tissue NO x following L-arginine administration may be due to increase in arginase activity. These findings may be important considering current data on the protective roles of dietary nitrate/nitrite.