Diabetes induces changes in melatonin concentrations in peripheral tissues of rat.

OBJECTIVE: Exogenous melatonin was found to protect target organs under conditions of diabetes mellitus, however, concentrations of the hormone in peripheral tissues have not been determined. Therefore the aim of the present study was to measure the daily profile of melatonin levels in the pineal gland, plasma, pancreas, kidney, spleen, duodenum and colon of control and diabetic rats.

MATERIAL & METHODS: Diabetes was induced by a single injection of streptozotocin (STZ, 65 mg/kg of body weight) and samples were collected over a 24 hr cycle on day 17 after STZ treatment. Melatonin and corticosterone levels were measured directly in plasma and after extraction in the pineal gland and peripheral organs (pancreas, kidney, spleen, duodenum and colon).

RESULTS: A significant daily rhythm of melatonin concentrations was found not only in the pineal gland and plasma but also in the pancreas, kidney, spleen and duodenum. The daily pattern of melatonin levels in the colon was arrhythmic without a characteristic night-time increase of hormone concentration. Experimentally induced diabetes resulted in lower melatonin levels in the pancreas, kidney and duodenum as compared to control. No differences between STZ-treated and control rats were found in the spleen and colon. Plasma corticosterone levels were enhanced in diabetic rats in comparison with controls and the daily profile was not rhythmic.

CONCLUSION: Our data suggest that the lower amplitude of melatonin rhythm in target organs induced by experimental diabetes can contribute to desynchronization of daily rhythms and can lower the antioxidative capacity of tissues.