Comparison of the effects of inhalational anaesthetic agents on sympathetic activity in rabbits

The effects of inhalational anaesthetic agents on renal sympathetic nerve a ctivity (RSNA) were compared in anaesthetized rabbits. Concentrations of 6% desflurane, 1.2% isoflurane, and 2.4% enflurane increased mean RSNA up to 32, 36 and 44% while higher concentrations, of 12, 2.4 and 3.2% depressed i t by 42, 83 and 5%, respectively. For halothane RSNA was unchanged up to 0. 8% and decreased by 36% at 1.6% concentration. Nitrous oxide increased RSNA up to 28% at 50% concentration. Maximum reductions in mean arterial pressu re (MAP) were 60% for both 2.4% isoflurane and 3.2% enflurane, 50% for 12% desflurane and 1.6% halothane, while 70% nitrous oxide increased MAP by 22% . In conclusion, unlike the entirely depressive effects of halothane, the e ffects of desflurane, isoflurane and enflurane were biphasic involving exci tation at lower concentrations and depression of RSNA and a reduction in MA P at higher concentrations. Nitrous oxide caused increases in both RSNA and MAP.