[Significance of endothelial cells for the regulation of the tone of smooth muscle--formation of an endothelial, relaxing factor].

Vascular endothelium is not only a mechanical, non-thrombogenetic barrier in the blood vessel wall, but probably plays a substantial role in the regulation of vascular smooth muscle tone. Besides the ability to metabolize vasoactive compounds like catecholamines and angiotensins, endothelial cells possess an active biochemical machinery for the production of vasoactive compounds (e.g. prostacyclin). During recent years it has become apparent that a large variety of vasodilator compounds require intact endothelial cells to exert their relaxing action. These endothelium-dependent relaxations are not mediated by prostacyclin of endothelial origin, but by an unknown substance that is referred to as endothelium-derived relaxing factor (EDRF). EDRF is a chemically unstable humoral substance and has a biological half-life in the range of seconds. Although EDRF is not a prostaglandin or leukotriene, several findings suggest possible relationships of its production with the eicosanoid system. Both stimulation of phospholipase A2 and inhibition of lysolecithin acyltransferase induce the production of EDRF. This suggests that cleavage of phospholipids may be an important step in the formation of EDRF. EDRF-mediated vascular relaxations (like relaxations induced by nitrovasodilators) were found to be associated with increases in cyclic GMP in vascular smooth muscle. Endothelial cells produce a factor that directly stimulates the enzymatic activity of soluble guanylate cyclase. Several points of evidence indicate that this factor may be identical with EDRF. Thus the mechanism of action of the EDRF formed endogenously may be similar to that of nitrovasodilators.(ABSTRACT TRUNCATED AT 250 WORDS)