Brief Review Endothelium-Derived Relaxing Factors A Perspective From In Vivo Data

We review below published studies of endothelium-dependent vasodilation in vivo. Endothelium-dependent vasodilation has been demonstrated in conduit arteries in vivo and in the cerebral, coronary, mesenteric, and femoral vascular beds as well as in the microcirculation of the brain and the microcirculation of cremaster muscle. The available evidence, although not complete, strongly suggests that the endothellum-derived relaxing factor generated by acetyl-choline in the cerebral microcirculation is a nitrosothiol. The endothelium-derived relaxing factor generated by bradykinin in this vascular bed is an oxygen radical generated in association with enhanced arachidonate metabolism via cyclooxygenase. In the microcircula-tion of skeletal muscle, on the other hand, the vasodilation from bradykinin is mediated partly by prostacycline and partly by an endothelium-derived relaxing factor similar to that generated by acetylcholine. Basal secretion of endothelium-derived relaxing factor is controversial in vivo but is usually present in vitro. On the other hand, it appears that endothelium-derived relaxing factor mediates flow-dependent vasodilation in both large vessels and in the microcirculation in vivo. The generation and release of endothelium-derived relaxing factor from endothelium may be abnormal in a variety of conditions including acute and chronic hypertension