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Abstract

Fructose is found naturally in many sources, such as fruits and honey, in relatively small quantities, however it has become an important part of our diet due to its increasing usage in food industry. Emerging evidences suggest a strong link between high fructose consumption and increased prevalence of metabolic syndrome (MetS). Melatonin, which is primarily synthesized by the pineal gland as well as many other tissues, is also known to be a strong antioxidant and cell protectant in addition to its chronobiologic roles. In our study, we aimed to demonstrate a metabolic syndrome model in rats by high-fructose consumption, investigate the alterations of the renal tissue Nitric Oxide-ADMA pathway and search for the effects of melatonin. Thirty-two male adult Sprague-Dawley rats were randomly divided into four groups (n = 8): (i) Control group, (ii) Fructose group, (iii) Melatonin group, (iv) Fructose + Melatonin group. Fructose was given as 20% solution in tap water to drink ad libitum and 20 mg/kg/day melatonin was administered by oral gavage. Systolic blood pressures were measured at the beginning, at the end of the 4th and 8th weeks. After the experimental period of 8 weeks, rats were sacrificed under anaesthesia and to test for the metabolic syndrome criteria, serum glucose, lipid profile and insulin were determined. Renal nitratenitrite (NOx), ADMA, Arginine concentrations and endothelial (eNOS) and inducible (iNOS) nitric oxide synthase protein levels were investigated. Our results showed that fructose consumption significantly increased systolic blood pressure, serum triglyceride and insulin levels and caused insulin resistance (metabolic syndrome criteria). Renal NOx levels were found to be non-significantly decreased only in fructose group compared to control group. NOx concentrations of fructose + melatonin group were significantly higher than fructose group. While ADMA and Arginine contents of the kidney tissues of fructose group did not change compared to control group, they were significantly higher in fructose + melatonin group compared to both control and fructose groups. eNOS protein levels were the same among all groups and iNOS protein was not detected in any of the groups.