NITRIC-OXIDE SYNTHASE INHIBITOR DOES NOT REDUCE MINIMUM ALVEOLAR ANESTHETIC CONCENTRATION OF HALOTHANE IN RATS

Nitric oxide (NO) synthase inhibitor (N-omega-nitro-L-arginine methyl ester [L-NAME]) has been reported to reduce minimum alveolar anestheti c concentration (MAC) of halothane when administered intravenously (IV ) and to reduce thermal hyperalgesia, or produce antinociception in th e formalin test, when administered intracerebroventricularly (ICV) or intrathecally (IT). This study attempts to identify the site(s) in the central nervous system (CNS) where L-NAME acts to reduce the halothan e MAC. For this purpose, we examined the effects of IV, ICV, and IT ad ministration of L-NAME on the halothane MAC in rats. In contrast to an earlier study, we did not observe any decrease in the halothane MAC a fter IV (10-30 mg/kg) administration of L-NAME. ICV (100 mu g) and IT (100 mu g and 1 mg) administration of L-NAME also did not alter the ha lothane MAC. These findings indicate that the L-arginine-NO pathway is not involved in the mechanism of action of halothane to suppress mech anical nociceptive response or in the nociceptive neural mechanism of mechanical stimulation.