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MELATONIN DECREASES BLOOD PRESSURE VIA INCREASED BRAIN NITRIC OXIDE SYNTHASE ACTIVITY IN RATS WITH METABOLIC SYNDROME: PP.34.415

Objective: Melatonin, a multitasking indolamine, seems to be involved in a variety of physiologic and metabolic processes via both receptor-mediated and receptor-independent mechanisms. Design and Method: The aim of this study was to determine whether melatonin can affect blood pressure and nitric oxide synthase (NOS) activity in the model of metabolic syndrome (MS) represented by obese, spontaneously hypertensive rats [SHR/ND mcr-cp (cp/cp)]. Animals were divided into two groups: male 6-week-old MS rats treated with melatonin (10 mg/kg/day) for 3 weeks and age-matched MS controls. Blood pressure was measured by tail-cuff plethysmography once a week. NOS activity was determined by measuring the formation of L-[3H] citrulline from L-[3H] arginine in the aorta, heart, kidney, cerebellum, brain cortex and brain steam. Results: Blood pressure was decreased by 10% already after the second week of melatonin treatment and this decrease persisted till the end of the treatment in comparison with age-matched untreated MS rats. While melatonin treatment faild to affect NOS activity in the aorta, heart and kidney, it was able to increase total NOS activity in all brain parts investigated. As no changes in NOS activity in peripheral organs were found, we hypothetised that nitric oxide produced in brain may be responsible for blood pressure decrease after 3 weeks of melatonin treatment in rats with metabolic syndrome. Conclusion: These data suggest that melatonin might play an important role in blood pressure decrease via increasing brain NOS activity in rats with metabolic syndrome.