Influence of endothelial mediators on the vascular smooth muscle and circulating platelets and blood cells

The vascular endothelium regulates the tone of the underlying smooth muscle and the reactivity of blood elements such as platelets and neutrophils by the release of mediators, in particular nitric oxide, prostacyclin and endothelin-1. The first two of these are potent vasodilators which also inhibit platelet and neutrophil aggregation and adhesion, while endothelin-1 is the most potent mammalian vasoconstrictor peptite yet found. There are also interactions between these mediators. For instance, endothelin-1 acts on specific receptors on the endothelium to increase the release of nitric oxide and prostacyclin, while nitric oxide depresses the production and/or release of endothelin-1 from endothelial cells. Endothelin-1 and prostacyclin do not appear to be involved in the basal regulation of blood pressure whereas nitric oxide does for inhibition of its production in normotensive animals produces a marked elevation in blood pressure. Conversely, numerous vascular disease states have been associated with elevations in the production and/or release of endothelin-1 and it has been implicated in the deleterious changes associated with ischaemia/reperfusion injury, subarachnoid haemorrhage and hypertension. Endothelin-1 has also been proposed to be pro-atherogenic, as have reductions in the production of the vasodilator mediators nitric oxide and prostacyclin.