Endothelial-mediated control of coronary and skeletal muscle blood flow during exercise: introduction.

There is extensive vasodilation of arterial vasculature in heart and active skeletal muscle during exercise. Considerable knowledge concerning mediators of this vasodilation which act directly on vascular smooth muscle has been acquired. Less well-understood is the role that mediators that act via vascular endothelium may play in exercise-induced vasodilation in vivo. Nonetheless, many studies have been conducted, both on blood vessels in vitro and in resting animals in vivo, since the discovery of endothelial-derived relaxing factor (EDRF) in 1980. In fact, several EDRF have been defined, of which nitric oxide (NO) appears to be most important. Release of NO from vascular endothelium can be induced by two general classes of stimuli, pharmacologic and physical. Of the former class, a physiologically relevant example is norepinephrine. In the latter class, elevated shear stress due to increase blood flow associated with exercise could be a stimulus for NO release. This symposium examines the role that endothelium may play in vasodilation of the coronary and skeletal muscle circulations during acute exercise. It also addresses the question of whether exercise training modifies this role of vascular endothelium.