Localization of melatonin in the digestive tract of the rat. Effect of maturation, diurnal variation, melatonin treatment and pinealectomy.

Using highly specific antibodies, melatonin was identified in the gastrointestinal tract of the rat as early as several hours of postnatal life. Its amount progressively increased and reached the adult levels around day 21. Exogenously administered melatonin concentrates in all parts of the gastrointestinal tract with most pronounced accumulation in the colon and the rectum. Diurnal variations were not clearly demonstrated in any part of the alimentary canal. Pinealectomy had no visible effect on the levels of melatonin in the tissues investigated. A hypothesis of ontogenic as well as phylogenic development of production of N-acetylated indolealkylamines in the pineal and the extrapineal tissues and their physiological role is presented.