CEREBELLAR NITRIC-OXIDE IS INCREASED DURING ISOFLURANE ANESTHESIA COMPARED TO HALOTHANE ANESTHESIA - A MICRODIALYSIS STUDY IN RATS

Background: This study examined the influences of isoflurane versus ha lothane anesthesia on basal and agonist-stimulated nitric oxide in the cerebellum of intact rats. Nitric oxide was measured using the hemogl obin-trapping method in an in vivo microdialysis technique. This metho d uses the stoichiometric reaction of nitric oxide with oxyhemoglobin to produce methemoglobin and nitrate; the change in methemoglobin conc entration is measured spectrophotometrically to estimate nitric oxide concentration. Methods: Male Wistar rats were anesthetized with isoflu rane (1.4%) or halothane (1.2%), mechanically ventilated and paralyzed (intravenous pancuronium, 1 mg/kg). Microdialysis probes were implant ed into the cerebellum Bovine oxyhemoglobin dissolved in artificial ce rebrospinal fluid was pumped through the probe (2 mu l/ min) and assay ed at 15-min intervals. The glutamatergic agonist, kainic acid (KA, 5 mg/kg, intraarterially), was used to stimulate nitric oxide production . NG-nitro L-arginine methylester (L-NAME, 40 mg/kg, intravenously) wa s used to inhibit nitric oxide synthase. Results: Unstimulated cerebel lar nitric oxide concentrations were stable and greater during anesthe sia with isoflurane (532 +/- 31 nM; mean +/- SEM) than with halothane (303 +/- 23 nM). L-NAME pretreatment reduced nitric oxide concentratio ns during isoflurane, but not halothane, anesthesia Infusion of KA inc reased nitric oxide in both groups; however, the increase in nitric ox ide was significantly greater during isoflurane anesthesia. Pretreatme nt with L-NAME inhibited the response to KA in both groups. Conclusion s: Nitric oxide production in the cerebellum, monitored by microdialys is, was greater during isoflurane anesthesia than during halothane ane sthesia Increased nitric oxide production during isoflurane anesthesia mould be expected to impact central neuronal function and cerebral bl ood flow and vascular resistance.