Gastrointestinal melatonin: cellular identification and biological role.

Melatonin, a pineal hormone, because of its wide activity spectrum, is a subject of much current interest for biologists and physicians. It has been demonstrated that pineal gland is not an exclusive source of melatonin synthesis. Melatonin synthesis has been found in different sites of the organism, and a major source of extrapineal melatonin is the gastrointestinal tract. The role of melatonin in gastrointestinal functions is considered in the present review.