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

Abstract

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 (NOx) concentrations were measured by the Griess method. Results:: Median (interquartile range) serum NOx 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) NOx levels. Conclusions:: Nitrate and L-arginine administration had opposite effects on NOx levels in stomach and liver of normal rats. Increase in stomach NOx following nitrate administration may be due to gastric nitrate absorption, while the decrease in tissue NOx 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.