CHRONIC TREATMENT WITH NITRIC-OXIDE SYNTHASE (NOS) INHIBITOR PROFOUNDLY REDUCES CEREBELLAR NOS ACTIVITY AND CYCLIC GUANOSINE-MONOPHOSPHATE BUT DOES NOT MODIFY MINIMUM ALVEOLAR ANESTHETIC CONCENTRATION

We previously found that acute administration of: a nitric oxide synth ase (NOS) inhibitor (N-omega-nitro-L-arginine methyl ester [L-NAME]) d oes not reduce the minimum alveolar anesthetic concentration (MAC) of halothane in rats. However, a recent study has suggested that brain NO S activity could not be inhibited by more than approximate to 50% by a cute administration of L-NAME. To investigate the effect of marked inh ibition of NOS activity on the MAC of halothane, we measured cerebella r NOS activity, cerebellar cyclic guanosine monophosphate (cGMP) level s, and halothane MAC in rats chronically treated with L-NAME and compa red the results to those of the saline-treated control group. Although the cerebellar NOS activity and cGMP levels were significantly decrea sed (14% and 2.7% of control, respectively) by L-NAME, the value of th e halothane MAC was not significantly affected. These results suggest that the anesthetic action of halothane, as measured by its MAC in rat s, is not related to NOS activity or cGMP levels in the brain.