Control of microvascular resistance in physiological conditions and reperfusion

Regulation of coronary microvascular resistance is not distributed uniforml y, but varies across different segments of the vasculature. Differences in regulatory mechanisms, including metabolic, myogenic, ol-adrenergic and end othelial cell mediated, help define a series of coronary vascular microdoma ins. Generally, small arterioles, those less than 100 mu m in diameter, res pond differently than large arterioles or small arteries. This segmental di stribution suggests an integrative hypothesis of regulation whereby a varie ty of mechanisms play a role in the overall response. One pathology that di sturbs these control mechanisms in the microcirculation of the heart is rep erfusion injury. Reperfusion injury of the microcirculation has as its prim ary target the vascular endothelium, The mechanisms responsible for reduced endothelium-dependent relaxation, likely include a reduction in the levels of tetrahydrobiopterin, a co-factor of nitric oxide synthase. Manipulation of levels of tetrahydrobiopterin in endothelial cells may be beneficial in the prevention of the pathophysiological sequelae of reperfusion injury in the coronary microcirculation. (C) 1998 Academic Press.