ONO-1714, a new inducible nitric oxide synthase inhibitor, attenuates diaphragmatic dysfunction associated with cerulein-induced pancreatitis in rats

Objectives. Acute experimental pancreatitis (induced by cerulein) recently has been reported to cause marked diaphragmatic dysfunction, which may contribute to respiratory distress in this setting. In cerulein-induced acute pancreatitis, expression of inducible nitric oxide synthase is induced to produce a large amount of nitric oxide. Nitric oxide excessively produced has been implicated in diaphragmatic dysfunction induced by a variety of etiologies. The aims of the current study were, first, to examine whether nitric oxide overproduced through inducible nitric oxide synthase is involved in cerulein-induced impairment of diaphragmatic function, and second, if demonstrated, to assess effects of ONO-1714, an inducible nitric oxide synthase inhibitor, on diaphragmatic dysfunction associated with cerulein-induced acute pancreatitis. Design: Prospective, randomized animal study. Setting: University research laboratory. Subjects: Ninety-one male Sprague-Dawley rats, weighing 200-250 g. Interventions: Rats were randomly divided into seven groups (n = 8 each): CONT-SAL, GAER-SAL, CONT-ONO, GAER-DEX, CAER-AMI, GAER-ONOhigh, and GAER-ONOlow. Groups labeled CAER received two consecutive intraperitoneal doses (50 mug/kg) of cerulein, whereas groups labeled CONT received two consecutive intraperitoneal injections of saline. Groups labeled SAL received intraperitoneal saline before cerulein or saline. The group labeled DEX received 2 mg/kg intraperitoneal dexamethasone, and the group labeled AMI received 100 mg/kg intraperitoneal aminoguanidine. The groups labeled ONO, ONOhigh, and ONOlow received ONO-1714 at 0.1 mg/kg, 0.1 mg/kg, and 0.03 mg/kg, respectively, before cerulein or saline. Measurements and Main Results: Diaphragmatic contractility and fatigability were assessed in vitro by using muscle strips excised from the costal diaphragms 6 hrs after the first dose of cerulein or saline. Expression of inducible nitric oxide synthase protein in the diaphragm was assessed by immunohistochemistry by using anti-inducible nitric oxide synthase antibody. Plasma concentrations of nitrite plus nitrate and diaphragmatic concentrations of malondialdehyde were measured. With another set of rats (n = 5 each group), diaphragmatic inducible nitric oxide synthase activity was determined. Twitch and tetanic tensions and tensions generated during fatigue trial were lower in group CAER-SAL than in group CONT-SAL. Cerulein increased diaphragmatic malondialdehyde and plasma nitrite plus nitrate concentrations. Positive immunostaining for inducible nitric oxide synthase protein was found in group CAER-SAL. Dexamethasone and aminoguanidine attenuated the diaphragmatic mechanical damages. A high dose of ONO-1714 attenuated cerulein-induced impairment of diaphragmatic contractility and endurance capacity, although a low dose of the drug failed to do so. Conclusions: Cerulein-induced diaphragmatic dysfunction was attributable, in part, to nitric oxide overproduced via inducible nitric oxide synthase. Pretreatment with ONO-1714 at a dose of 0.1 mg/kg attenuated diaphragmatic dysfunction associated with cerulein-induced pancreatitis in rats assessed by contractile profiles and endurance capacity. This beneficial effect of ONO-1714 may be attributable, in part, to inhibition of diaphragmatic lipid peroxidation induced by nitric oxide-derived free radicals.