Influence of NG‐nitro‐L‐arginine methyl ester and L‐arginine on gastric mucosal tolerant cytoprotection under stress

OBJECTIVE: To determine the role of endogenous nitric oxide (NO) in gastric mucosal tolerant cytoprotection under stress and its possible mechanism. METHODS: Sprague–Dawley rats were exposed to repeated water immersion and restraint stress (WRS), during which NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor, and L-arginine (L-Arg), a substrate for NO synthesis, were administered to inhibit or promote the synthesis of endogenous NO, respectively. Gastric mucosal blood flow (GMBF) was measured with an LDF-3 Flowmeter (Electronic Instrument Factory of Nankai University, Tianjin, China), the NO level in the gastric mucosa was monitored by the Griess reaction and gastric mucosal lesions were evaluated using the ulcer index (UI). The relationships between changes in GMBF, UI and NO content in the gastric mucosa were analyzed by linear correlation analysis. RESULTS: Repeated WRS induced gastric mucosal tolerant cytoprotection and this was accompanied by increased GMBF and NO levels in the gastric mucosa. Inhibition of endogenous NO synthesis by L-NAME worsened mucosal lesions induced by single WRS and, after repeated WRS, the adaptive incremence in GMBF was abolished and the NO content in the gastric mucosa was significantly reduced. In contrast, enhancement of endogenous NO synthesis by L-Arg attenuated mucosal erosions caused by single WRS. After repeated WRS, GMBF and the NO content in the mucosa increased gradually. Mucosal lesions were negligible after rats were exposed to the fourth WRS. CONCLUSIONS: During the tolerant cytoprotection, GMBF, UI and the NO content showed regular changes and there were good relationships between them. L-NAME and L-Arg changed the levels of endogenous NO, which, accordingly, affected GMBF and the gastric tolerance. By regulating GMBF, endogenous NO may play an important role in the gastric mucosal tolerant cytoprotection under stress. Inhibition of the synthesis of NO delayed the induction of tolerant cytoprotection, whereas increased NO synthesis promoted cytoprotection.