Regulation of prostaglandin production in carrageenan-induced pleurisy by melatonin

The aim of the present study was to investigate the effect of melatonin on the production of the inflammatory mediator prostaglandins in a model of ac ute inflammation, carrageenan-induced pleurisy, where prostaglandins are kn own to play a crucial role. The results show that melatonin (12.5, 25, and 50 mg/kg, intraperitoneally, 15 min before the carrageenan) inhibits the in flammatory response (pleural exudate formation, polymorphonuclear cell infi ltration, and prostaglandin production) in a dose-dependent manner. Immunoh istochemical examination demonstrated a marked increase in the immunoreacti vity to cyclooxygenase-2 (COX-2) in the lungs of carrageenan-treated rats. Pretreatment of carrageenan-treated rats with melatonin (50 mg/kg, intraper itoneally, 15 min before the carrageenan) prevented COX-2 expression. The p resent results demonstrate that melatonin exerts potent anti-inflammatory e ffects. Part of these anti-inflammatory effects may be related to a reducti on of prostaglandin production during the inflammatory process.