ABSTRACT-The effects of NG-nitro-L-arginine methyl ester (L-NAME), the nitric oxide (NO) syn thase inhibitor, on gastric HC03 secretion were examined in anesthetized rats. Intravenous adminis tration of L-NAME (1, 2.5, 5 mg/kg) increased HC03 secretion in a dose-related manner. This effect of L-NAME was mimicked by NG-mono-methyl-L-arginine (50 mg/kg, i.v.) and was antagonized signifi cantly by concurrent administration of L-arginine but not D-arginine (200 mg/kg, i.v.). These results in dicate that gastric HC03 secretion is stimulated by inhibition of NO biosynthesis.Keywords: Nitric oxide synthase inhibitor, HC03 secretion, StomachNitric oxide (NO), synthesized from the semi-essen tial amino acid L-arginine by NO synthase in the vascu lar endothelium is now established to mediate various biological actions under physiological conditions (1). Recent studies have shown that NO also plays an im portant role in the modulation of the gastric mucosal integrity by interacting with other protective mediators (2, 3). Regulation of gastric mucosal blood flow is con sidered to be the major mechanism responsible for the mucosal protective action of NO (2, 4), yet the influ ences of the inhibition of NO biosynthesis on other de fensive factors such as HC03 secretion has not been studied. In the present study, we thus examined the effects of the NO synthase inhibitor on HC03 secre tion in the rat stomach using NG-nitro-L-arginine as the methyl ester (L-NAME) and characterized these effects in relation to endogenous NO.Male Sprague Dawley rats (230 250 g), kept in indi vidual cages with raised mesh bottoms, were deprived of food but allowed free access to tap water for 18 hr before the experiments. The animals were anesthetized with urethane (1.25 g/kg, i.p.; Tokyo Kasei); and then the stomach was exposed, mounted on a chamber (ex posed area: 3.14 cm2), and perfused with saline that was gassed with 100% 02. HC03 secretion was deter mined at pH 7.0 by continuous titration of the perfusate with 10 mM HCl under acid inhibition by omeprazole (60 mg/kg, i.p.). In some cases, the stomach was per fused with acidified saline (pH 4.5) at the rate of 1 ml/min, and the pH of the perfusate and transmucosal potential difference (PD) were monitored simultaneous ly with arterial blood pressure (BP). The pH was meas ured by a flow type glass electrode (Horiba, Model 6901-25T), while PD was determined by using two agar bridges, one positioned in the chamber and the other in the abdominal cavity (5). BP was monitored via the femoral artery by a pressure transducer and amplifier system (Nihon Kohden). NG-nitro-L-arginine methyl ester (L-NAME: Sigma), NG-monomethyl-L-arginine (L-NMMA: Sigma) and prostaglandin E2 (PGE2, Funa koshi) were given i.v. after basal secretion had stabi lized. In some cases, L or D-arginine (Wako) was given i.v. 5 min before administration of L-NAME. Data are presented as the mean ± S.E. from 5-6 rats. Statistical analyses were performed by the two-tailed Dunnett's multiple comparison test, and values of P < 0.05 were r...
