Protective effect of melatonin in carrageenan-induced acute local inflammation

The aim of the present study was to investigate the protective effect of the pineal hormone melatonin in a model of acute local inflammation (carrageenan-induced paw oedema). Inflammation was assessed by measurement of nitric oxide (NO), Malondialdehyde (MDA) and glutathione levels in the paw tissue in rats. The intraplantar injection of carrageenan elicited an inflammatory response that was characterised by a time-dependent increase in paw oedema, increased level of nitrite/nitrate and MDA, a lipid peroxidation product and decreased glutathione levels in the paw tissue. The maximal increase in paw volume was observed at 4h after administration (maximal in paw volume 160+/-3.34 ml). In addition, NO level and MDA were markedly increased in the carrageenan-treated paw (59.96+/-6.58 and 19.33+/-3.35 micromol g(-1), respectively), versus in the control paw glutathione level decreased in paw tissue (3.24+/-0.24 micromol g(-1)). However, carrageenan-induced paw oedema was significantly reduced in a dose-dependent manner by treatment with melatonin (given at 5 and 10 mg kg(-1)) at 1, 2, 3, 4, 5 and 6h after injection of carrageenan. Melatonin treatment also caused a significant reduction of the NO and MDA levels, while increasing glutathione level in the paw tissue. Our findings support the view that melatonin exerts anti-inflammatory effects. Part of these anti-inflammatory effect may be related to an inhibition of the NO and MDA production, while another part may be related to increase of the glutathione level in the paw tissue.