Effect of iron on rat serum melatonin levels under different light/dark cycle patterns

Exposure to constant light or darkness for long periods has diverse effects on circadian physiology. Iron (Fe) overloading promotes oxidative stress and causes alterations in cellular structure and function in animals and humans. The aim of this study is to evaluate the interactions among serum melatonin (ML), photoperiod manipulation, and Fe overloading in rats. The results showed that constant darkness exposure for 15 days significantly increased serum ML levels (up to 22%) while the constant light exposure failed to reduce the serum ML level compared to the normal light/dark cycle treated rats. The lost serum ML level usually from the pineal gland under the long term of constant light exposure may be compensated by ML generated by other organs which adapted to the situation. Also, Fe overloading decreased ML production due to this molecule being consumed to scavenge the free radicals induced by the Fe overloading. In addition, we observed interactions among constant light or darkness exposure, Fe overloading and serum ML level. Overall, our results support the hypothesis of ML as scavenging molecule; it may be an effective therapeutic tool in iron-induced oxidative stress.