Melatonin reduces acute lung inflammation, edema, and hemorrhage in heatstroke rats

Abstract

Aim: To assess the therapeutic effect of melatonin on heat-induced acute lung inflammation and injury in rats.

Methods: Heatstroke was induced by exposing anesthetized rats to heat stress (36 °C, 100 min). Rats were treated with vehicle or melatonin (0.2, 1, 5 mg/kg) by intravenous administration 100 min after the initiatioin of heatstroke and were allowed to recover at room temperature (26 °C). The acute lung injury was quantified by morphological examination and by determination of the volume of pleural exudates, the number of polymorphonuclear (PMN) cells, and the myeloperoxidase (MPO) activity. The concentrations of tumor necrosis factor, interleukin (IL)-1β, IL-6, and IL-10 in bronchoalveolar fluid (BALF) were measured by ELISA. Nitric oxide (NO) level was determined by Griess method. The levels of glutamate and lactate-to-pyruvate ratio were analyzed by CMA600 microdialysis analyzer. The concentrations of hydroxyl radicals were measured by a procedure based on the hydroxylation of sodium salicylates leading to the production of 2,3-dihydroxybenzoic acid (DHBA).

Results: Melatonin (1 and 5 mg/kg) significantly (i) prolonged the survival time of heartstroke rats (117 and 186 min vs 59 min); (ii) attenuated heatstroke-induced hyperthermia and hypotension; (iii) attenuated acute lung injury, including edema, neutrophil infiltration, and hemorrhage scores; (iv) down-regulated exudate volume, BALF PMN cell number, and MPO activity; (v) decreased the BALF levels of lung inflammation response cytokines like TNF-alpha, interleukin (IL)-1β, and IL-6 but further increased the level of an anti-inflammatory cytokine IL-10; (vi) reduced BALF levels of glutamate, lactate-to-pyruvate ratio, NO, 2,3-DHBA, and lactate dehydrogenase.

Conclusion: Melatonin may improve the outcome of heatstroke in rats by attenuating acute lung inflammation and injury.

Figures

Figure 1

Core temperature (Tco, A) and mean arterial pressure (MAP, B) values for normothermic controls, vehicle-treated heatstroke rats, melatonin (0.2 mg/kg)-treated heatstroke rats, melatonin (1 mg/kg)-treated heatstroke rats, and melatonin (5 mg/kg)-treated heatstroke rats. The values were obtained at 0, 100, or 140 min after the initiation of heat exposure in heatstroke rats or the equivalent times in normothermic controls. All heatstroke groups had heat exposure (36 °C) withdrawn at exactly 100 min and were then allowed to recover at room temperature (26 °C). Bars are the mean±SD of 6 rats for each group. bP<0.05 compared with normothermic controls; eP<0.05 compared with vehicle-treated heatstroke rats.

Figure 2

Histological examination of lung tissue from normothermic controls (NC), vehicle-treated heatstroke rats (HS+Sal), melatonin (0.2 mg/kg)-treated heatstroke rats (HS+Mel-0.2 mg/kg), melatonin (1 mg/kg)-treated heatstroke rats (HS+Mel-1 mg/kg), and melatonin (5 mg/kg)-treated heatstroke rats (HS+Mel-5 mg/kg). (A) Representative lung microscopic image from an NC rat (a), an HS+Sal rat (b), and an HS+Mel-5 mg/kg rat (c). The HS+Sal rats had interstitial edema, neutrophil accumulation and hemorrhage. The lung pathological changes that occurred during heatstroke were significantly attenuated by melatonin (1–5 mg/kg) (P<0.05). (B) The level of edema, neutrophils infiltration, and hemorrhage score. Data are expressed as the mean±SD. n=6. bP<0.05 compared with the NC group; eP<0.05 compared with the vehicle-treated heatstroke group (HS+Sal).

Figure 3

Exudate volume, number of PMN cells and MPO activity in lung tissues from NC, HS+Sal, HS+Mel (0.2 mg/kg), HS+Mel (1 mg/kg), and HS+Mel (5 mg/kg) rats. Data are expressed as mean±SD. n=6. bP<0.05 compared with the NC group; eP<0.05 compared with the HS+Sal group.

Figure 4

Interleukin-10, tumor necrosis factor-alpha, interleukin-1β, and interleukin-6 levels in BALF from the NC, HS+Sal, HS+Mel (0.2 mg/kg), HS+Mel (1 mg/kg), and HS+Mel (5 mg/kg) rat. Data are expressed as the mean±SD. n=6. bP<0.05 compared with the NC group; eP<0.05 compared with the HS+Sal group.

Figure 5

Glutamate, lactate-to-pyruvate ratio, lactate dehydrogenase (LDH), nitric oxide metabolites (NO), and 2,3-dihydroxybenzoic acid (2,3-DHBA) levels in BALF from the NC, HS+Sal, HS+Mel (0.2 mg/kg), HS+Mel (1 mg/kg), and HS+Mel (5 mg/kg) rats. Data are expressed the meanSD. n=6. bP<0.05 compared with the NC group; eP<0.05 compared with the HS+Sal group.