VERSATILE MELATONIN - A PERVASIVE MOLECULE SERVES VARIOUS FUNCTIONS IN SIGNALING AND PROTECTION

Melatonin, which is able to enter all tissues and all compartments of the cell, acts in a highly pleiotropic fashion. Some melatonin effects are mediated by membrane receptors, others are receptor independent. Melatonin is produced in the pineal gland and various extrapineal organs of vertebrates, but is also found in invertebrates, angiosperms, and unicells. In mammals, melatonin elicits various secondary humoral responses, e.g., in the immune system via interleukin-4 and other cytokines and in the brain by modulation of NO formation. Melatonin is also a powerful radical scavenger, terminating free radical reaction chains initiated by photooxidants, hydroxyl or peroxyl radicals. The protective potency of this indoleamine is demonstrated by various experiments.