Effect of melatonin on lipid peroxidation, glutathione and glutathione-dependent enzyme activities in experimental otitis media with effusion in guinea pigs

: Melatonin plays a role in the prevention of oxidative damage. In the present study, we investigated whether the increased oxidative stress in experimental otitis media with effusion (OME) induced by histamine is reflected in erythrocytes and middle ear effusion fluid. Lipid peroxidation in effusion fluid was measured to determine the effects of melatonin on oxidative stress. Erythrocyte and middle ear effusion malondialdehyde (MDA) levels, erythrocyte glutathione (GSH) levels and glutathione peroxidase (GPx), glutathione reductase (GRd) and glutathione‐S‐transferase (GST) activities were measured in three groups of six guinea pigs each at 3 hr after the injection of 0.1 mL of histamine (or saline) into the middle ear. In erythrocyte and middle ear effusion samples, MDA levels showed a significant increase in guinea pigs with experimental OME group when compared with the control animals. Erythrocyte GPx, GST, GRd activities and GSH levels significantly reduced in experimental OME guinea pigs when compared with the control and melatonin‐treated animals. Erythrocyte GPx activity also significantly increased after melatonin treatment when compared with the control group. These findings suggest that reactive oxygen species play a role in histamine‐induced OME. Pretreatment with melatonin increases antioxidant enzyme activities and reduced formation of MDA, an indicator of lipid peroxidation, in histamine‐induced OME.