Effect of the neuronal nitric oxide synthase inhibitor 7-nitroindazole on the righting reflex ED50 and minimum alveolar concentration during sevoflurane anaesthesia in rats

Abstract

Background and objective: The aim was to determine the effect of acute and chronic administration of 7-nitroindazole, a selective neuronal nitric oxide synthase inhibitor, on the righting reflex ED50 and the minimum alveolar concentration during sevoflurane anaesthesia in rats. Methods: 7-Nitroindazole was acutely (0, 50 and 100 mg kg−1) and chronically (0 and 150 mg kg−1 day−1, 4 days) administered to rats. After the preparation, the minimum alveolar concentration and the righting reflex ED50 were measured. The concentration of cGMP in the brain, cerebellum and spinal cord was also measured. Results: Acute administration reduced the minimum alveolar concentration (50 mg kg−1, 58.8% (95% CI: 50.3-67.3%) of the baseline value, P < 0.01; 100 mg kg−1, 55.8 (46.9-64.7), P < 0.01) and the righting reflex ED50 (50 mg kg−1, 27.2 (17.2-37.2), P < 0.01; 100 mg kg−1, 14.3 (6.6-22.0), P < 0.01). Chronic administration did not reduce the minimum alveolar concentration; however, it reduced the righting reflex ED50 (65.3 (52.9-77.7), P < 0.01). Overall, the reduction in minimum alveolar concentration in the acute and chronic protocol did not correlate with that of the righting reflex ED50. 7-Nitroindazole (100 mg kg−1, acute) reduced the cGMP concentration within the cerebellum by 55.4%; however, it did not decrease concentrations in the brain or spinal cord. Conclusions: Different mechanisms are responsible for the observed alterations to the minimum alveolar concentration and the righting reflex ED50 following treatment with 7-nitroindazole. The nitric oxide-cGMP pathway might play a less important role in the determination of minimum alveolar concentration than the righting reflex ED50.