Effects of Epidural Ketamine on Blood Pressure and Renal Sympathetic Nerve Activity in Rabbits

Abstract

The aim of this study was to evaluate the effects of epidural ketamine, an N-methyl-D-aspartic acid (NMDA) antagonist, on haemodynamic responses and renal sympathetic nerve activity (RSNA). Mean arterial blood pressure (MAP), heart rate (HR), RSNA, and integrated RSNA (IRSNA) were recorded in anaesthetized and artificially-ventilated Japanese white rabbits. Epidural ketamine (2 mg kg−1), decreased MAP and IRSNA (P < 0.05), and increased HR (P < 0.05) in intact rabbits (n = 6). Epidural MK-801 (0.024 mg kg−1), another NMDA-receptor antagonist, increased IRSNA, but did not significantly change HR or MAP (n = 6). Pretreatment with epidural naloxone (0.2 mg) did not affect the changes of MAP, HR, and IRSNA induced by ketamine (n = 4), suggesting that opiate receptors were not involved. In sino-aortic denervated rabbits (n = 6), epidural ketamine decreased MAP and IRSNA, but did not significantly change HR, indicating that the ketamine-induced increase in HR occurred via a baroreflex in the neuraxis-intact rabbits. These results indicate that the effects of epidural ketamine on MAP, HR, and RSNA are different from those of MK-801, and suggest that the decrease in sympathetic nerve outflow induced by epidural ketamine is not mediated by NMDA receptors.