ROLE OF MELATONIN IN THE REGULATION OF TH E INTERDIGESTIVE ILEO-CECO-COLIC ELECTROMYOGRAM IN THE RAT

In the interdigestive period, intestinal motility displays myoelectric al complexes occurring cyclically at a constant rhythm. Since it is es tablished that the pineal gland plays an important role in the control of circadian rhythms via its melatonin secretion, we decided to study the effects of pinealectomy and melatonin on the organization of the ileo-ceco-colic electromyogram of the rat. Pinealectomy resulted in th e disappearance of ileal myoelectrical complexes and, concurrently, an excitomotor effect on the cecocolic tract. In pinealectomized rats a single intravenous injection of melatonin during lighting period induc ed an immediate recovery of the ileal myoelectrical complexes and a pr ogressive return to the control electromyographic pattern of the ceco- colic tract. The melatonin action was definitive.