Magnesium sulphate attenuates tourniquet-induced hypertension and spinal c-fos mRNA expression: a comparison with ketamine.

Magnesium and ketamine are well-known N-methyl-D-aspartic acid receptor antagonists. The aim of this study was to determine whether magnesium, in comparison with ketamine, attenuates tourniquet-induced hypertension and spinal c-fos mRNA expression. Rats were divided into four treatment groups: normal (baseline for c-fos mRNA expression); control (saline injection); magnesium injection; and ketamine injection. Arterial blood pressure and c-fos mRNA expression at 60 min were higher in the control than in the magnesium and ketamine groups. Human patients under sevoflurane-oxygen/nitrous oxide anaesthesia were also assigned to receive similar treatments. In humans, arterial blood pressure was increased in the control group at 50 min and thereafter compared with the magnesium and ketamine groups; the magnesium and ketamine groups did not differ. Magnesium and ketamine are equally effective in attenuating tourniquet-induced hypertension and spinal c-fos mRNA expression, suggesting that this effect may be due to reduced pain transmission.