The effect of orally supplemented melatonin (MT) at 1 mg/kg bw for 4 weeks on feeding behavior of non-diabetic and diabetic male Wistar rats has been studied by computerized meal pattern analysis. Exogenous MT has a satiating effect in non-diabetic rats, but not in diabetic animals. The changes in feeding behavior induced by MT in non-diabetic animals are related to changes in meal frequency, size and duration leading to lower total food intake during the scotophase. MT administration to diabetic rats resulted in lower drinking time and higher faecal output, without further behavioral effects. We conclude that the notorious metabolic changes ocurring in the streptozotocin-diabetic rat can overcome most of the underlying effects of MT supplementation. The possible MT usage for therapeutical purposes could benefit from the lack of behavioral alterations in diabetic animals.<br>Varias líneas de evidencia señalan a la melatonina (MT) como un importante factor en el complejo entramado de la regulación de la ingestión de alimento. Puesto que la secreción de MT aumenta en la rata con diabetes tipo I, y dada la importancia de MT en el tracto gastrointestinal, es interesante comprobar los efectos de MT sobre el alterado comportamiento ingestivo de estos animales. Se ha estudiado el efecto de la suplementación oral de MT (1 mg por kg de peso corporal y día) en la escotofase sobre el comportamiento ingestivo de ratas Wistar macho diabéticas y no diabéticas durante cuatro semanas mediante análisis de pautas de ingestión asistido por ordenador. La administración de MT exógena indujo un efecto de saciación en ratas no diabéticas, pero no en animales diabéticos. Los cambios en comportamiento ingestivo inducidos por MT en animales no diabéticos están relacionados con cambios en frecuencia, tamaño y duración de las comidas, con el resultado de una disminución de la ingestión total de alimento durante la escotofase. La administración de MT en ratas diabéticas originó una disminución del tiempo total de actividad dípsica y aumento de la masa fecal durante la escotofase, sin otros cambios comportamentales significativos. Se concluye que los notables cambios metabólicos que tienen lugar en la rata con diabetes experimental inducida por estreptozotocina provocan cambios comportamentales más potentes que los ejercidos por la suplementación oral con MT. El posible uso terapéutico de MT podría beneficiarse de la falta de alteraciones comportamentales en animales diabéticos.

Background: Diabetic neuropathy is one of the serious problems due to microvessel vasculopathy in diabetes. It has been reported that hyperglycemia and hypertriglyceridemia are the underlying mechanisms in inducing and progression of diabetic neuropathy. The aim of the present study was to investigate the effects of melatonin on serum glucose and lipid levels, as well as food consumption and water intake in streptozotocin-induced diabetic rats. Materials and Methods: Eighty male Wistar rats were randomly assigned to six groups including; normal control group, diabetic control group and 4 diabetic experimental groups that received melatonin intraperitoneally at doses of 2.5, 5, 10, and 20 mg/kg at the end of sixth week after verification of neuropathy by means of evaluation of sciatic nerve conduction velocity (MNCV), for two weeks. Blood glucose and lipid levels, body weight, the amounts of food consumption, and water intake were determined in all groups at weeks 0 (before diabetes induction), 3, 6, and at the end of eighth week. Results: Treatment with melatonin reduced significantly the serum glucose (P < 0.001) and triglyceride (P < 0.05) levels, food consumption (P < 0.001), and water intake (P < 0.001) in diabetic rats at the end of eighth week. However, melatonin had no significant effect on body weight of diabetic animals. Conclusions: Treatment with melatonin could improve several signs of diabetes, including hyperglycemia, hypertriglyceridemia, polyphagia, and polydipsia. Therefore, melatonin may be used as an adjunct therapy in the treatment of diabetes.