Perivascular adipose tissue (PVAT) is a type of adipose tissue that surrounds large arteries and veins. In addition, to provide mechanical support to the blood vessels, PVAT also functions as a paracrine and endocrine organ. PVAT secretes several bioactive substances that exert an anti-contractile effect thus modulating the vascular response to different vasoactive agents. In obesity, there is an increase in the amount and structural modification of PVAT along the vasculature. These changes include increased reactive oxygen species (ROS) via NAD(P)H oxidase and reduced antioxidant capacity. Together these responses lead to increased oxidative stress, reduced anti-contractile action of PVAT and vascular dysfunction. Melatonin (5-methoxy-N-acetyltryptamine) is a hormone produced centrally by the endocrine cells of the pineal gland. This hormone has been used to protect against oxidative damage and modulation of the anti-inflammatory response in the cardiovascular system. Melatonin is also able to prevent oxidative damage in the aorta of diabetic and septic rats. In obese mice aorta, melatonin restores the levels of superoxide dismutase (SOD) 2 and catalase. In addition, in mesenteric arteries, melatonin prevents the loss of the anti-contractile function of PVAT in a model of senescence. Melatonin has been used in several animal models of obesity as a pharmacological tool for weight reduction and obesity-induced changes. However, there are no studies in the literature that describe the effect of melatonin on the maintenance of oxidative stress and its role in the loss of the anti-contractile function of PVAT during obesity. The hypothesis of this work is that the increase of oxidative stress observed during obesity is associated with the loss of the anti-contractile function of PVAT and that the treatment with melatonin acts directly in the reduction of oxidative stress as a scavenger of free radicals and, indirectly, stimulating the activity and expression of antioxidant enzymes. Thus, the present project was designed with the objective of investigating whether melatonin could reverse the increase of oxidative stress in PVAT induced by obesity.
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