Therapeutic Perspectives of Gastrointestinal Melatonin (pp. 233-252)
Authors: (George A. Bubenik, Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada)*
Abstract: Melatonin is present in a variety of living organisms ranging from bacteria and plants to invertebrates and vertebrates. Some 30 years ago, melatonin was also found in the gastrointestinal tract (GIT) of several vertebrate species. Later melatonin was also localized in digestive glands and the hepatobiliary system. More recently, the presence of melatonin-synthesizing enzymes as well as the production of melatonin in GIT tissues has been reported in vitro. It has been calculated, that at any time of the day, there is at least 400 times more melatonin in the GIT than in the pineal gland. The mode of secretion and the physiological functions of GIT melatonin differ substantially from melatonin produced in the pineal gland. GIT melatonin can act not only as an endocrine but also as paracrine, autocrine and luminal hormone. Melatonin increases mucosal blood flow by alleviating spastic action of melatonin precursor serotonin. Melatonin also stimulates the immune system and fosters reepithelization of mucous membranes. Furthermore, melatonin is secreted in response to food intake or food withdrawal. Finally, melatonin is a potent antioxidant molecule and a scavenger of hydroxyl free radicals. It has been concluded, that because of these special properties, melatonin was effective in animals experiments either as a preventive or therapeutic remedy in numerous pathological conditions of the GIT, such as gastric ulcers, ulcerative colitis, children’s colic, irritable bowel disease and colon cancer. Anecdotal evidence as well as most recent research studies indicates that melatonin might be useful for treatment of various diseases of the human GIT.