[Effect of isoflurane anesthesia on norepinephrine metabolism in rat brain]

The author studied the effect of isoflurane anesthesia on norepinephrine (NE) metabolism in rat brain to elucidate a mechanism of anesthesia by measuring NE and its metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG). Male Wistar rats weighing 230-270 g were anesthetized in a cage (42 x 27 x 19 cm3) with 2% isoflurane in air for 20 minutes. Rats were allocated to one of three groups randomly: unanesthetized control group (8 rats), anesthesia group (8 rats) and recovery group (8 rats). The rats were decapitated after only staying in the cage for 20 minutes in the control group, immediately after isoflurane anesthesia for 20 minutes in the anesthesia group and 20 minutes after recovery from anesthesia in the recovery group. Immediately after decapitation, their brains were rapidly dissected on the ice into the locus coeruleus, pons plus medulla oblongata, hypothalamus, thalamus, corpus striatum, midbrain, hippocampus, amygdala and cerebral cortex. NE and MHPG contents were determined by high pressure liquid chromatography. The NE contents of the pons plus medulla oblongata, hippocampus, and cerebral cortex increased significantly in the anesthesia group as compared with those of the control group. A significantly lower NE content was observed in the amygdala, and cerebral cortex of the recovery group as compared with that of the anesthesia group. The MHPG contents of the locus coeruleus, pons plus medulla oblongata, hypothalamus, and thalamus increased significantly in the recovery group as compared with those of the anesthesia group. The MHPG/NE ratio was calculated to determine NE turnover. The ratios of the locus coeruleus, pons plus medulla oblongata, thalamus, corpus striatum, and cerebral cortex decreased significantly in the anesthesia group as compared with the control group, while those of the locus coeruleus, pons plus medulla oblongata, hypothalamus, thalamus, and amygdala increased significantly in the recovery group as compared with the anesthesia group. The results obtained in the study suggest that a possible mechanism of isoflurane anesthesia in rat might be associated with decreased NE release in the locus coeruleus, pons, medulla oblongata and thalamus.