ROLE OF PERIVASCULAR ADIPOSE TISSUE ON VASCULAR FUNCTION

In the last years a paracrine role for perivascular adipose tissue (PVAT) in the regulation of vascular function has been uncovered by several studies. Soltis and Cassis were the first to demonstrate that PVAT significantly attenuates vascular responsiveness of rat aortic rings to norepinephrine. More recent reports have confirmed the inhibitory action of PVAT on the contractile response to a variety of vasoconstrictors on rat aortic and mesenteric arteries, as well as on human thoracic arteries. The anti-contractile action is induced by a still undefined transferable factor released by periadventitial fat, called adipocyte-derived relaxing factor. Its anticontractile effect seems to be mediated by different mechanisms depending on the type of vascular bed and species. In addition, PVAT is a source of leptin, which participates in the regulation of vascular tone. Vascular effects of leptin are the net result of two different actions: a) indirect vasoconstriction through stimulation of sympathetic activity at hypothalamic level, and b) direct vasodilatation that depends on intact and functional endothelium through mechanisms that vary between different vascular beds. Moreover, PVAT also releases several vasoconstrictors. It expresses the components of the renin-angiotensin system and releases angiotensin II. Other factors with vasoactive effects, such as superoxide anion and inflammatory cytokines, have also been described. Changes in the amount of PVAT in different situations such as hypertension and obesity are related to an altered balance of vasoconstrictors and vasodilators, thus contributing to changes in arterial blood pressure.