Attenuating Heat-Induced Acute Lung Inflammation and Injury by Dextromethorphan in Rats

Dextromethorphan (DM) has been shown to protect against endotoxic shock in mice. Heatstroke resembles sepsis in many respects. The objective of this study was to examine the heat-induced acute lung inflammation and injury in rats with or without DM, and for comparison with those of the rats with MK-801 (an N-methyl-D-aspartate receptor antagonist), SA4503 (a sigma-1 receptor agonist), or fluoxetine (a serotonin reuptake inhibitor). Heatstroke was induced by exposing the anesthetized rats to heat stress (438 degrees C for 68 min). At 68 minutes after start of heat stress, animals treated with vehicle medium, DM(10-30 mg/kg of body weight, intramuscular), MK-801 (1 mg/kg of body weight, intraperitoneal), SA4503 (1 mg/kg of body weight, intraperitoneal), or fluoxetine (5 mg/kg of body weight, intraperitoneal) were allowed to recover at room temperature (268 degrees C). As compared with vehicle-treated heatstroke rats (25-31 min; n 8), DM(30 mg/kg)-treated heatstroke rats and MK-801(1 mg/kg)treated heatstroke rats had significantly greater survival time (193209 min [n 7] and 121-133 min [ n 8], respectively). However, the survival times for the SA4503-treated heatstroke rats (28-34 min; n 8) or the fluoxetine-treated heatstroke rats (20-26 min; n 8) were not significantly different from the vehicle-treated heatstroke rats. DM treatment significantly: (1) reduced acute lung injury, including edema, neutrophils infiltration, and hemorrhage scores; (2) decreased acute pleurisy; and (3) decreased bronchoalveolar fluid levels of the proinflammatory cytokines, and ischemia and oxidative damage markers during heatstroke. Our results indicate that DM therapy may improve outcomes of heatstroke in rats by antagonizing the N-methyl-D-aspartate receptors.