Effect of melatonin on NF-kappa-B DNA-binding activity in the rat spleen.

It was recently demonstrated that the pineal neurohormone melatonin is a hydroxyl radical scavenger and antioxidant, and that it plays an important role in the immune system. In studies reported herein, we have investigated the relationship of the melatonin level and the NF-kB DNA binding activity in the spleen of Sprague. Dawley rats. These in vivo results indicate that NF-kB DNA binding activity in the spleen is lower at night, when endogenous melatonin levels are elevated, than during the day, when endogenous melatonin levels are lower. Furthermore, exogenously administered melatonin (10 mg/kg) was shown to cause a significant decrease in NF-kB DNA binding activity in the spleen at 60 min after intraperitoneal injection (as compared with vehicle-treated rats). These new findings suggest that the normal night time rise which can be expected for melatonin may be associated with increased NF-kB DNA binding activity in the spleen. The melatonin, therefore, could potentially act to modulate spleen function and/or the immune system by regulating the NF-kB DNA binding activity in the spleen.