Endothelium-Dependent Responses in Hypertension.

The endothelium controls the tone of the underlying vascular smooth muscle by releasing relaxing factors. These include prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). In certain types of hypertension, endothelium-dependent relaxations are curtailed, because of a reduced production and/or action of endothelium-derived NO and EDHF. In the spontaneously hypertensive rat, endothelium-dependent relaxations are reduced, because of the endothelium-dependent production of vasoconstrictor prostanoids (endoperoxides and, in some cases, thromboxane A2). These prostanoids may be produced in the vascular smooth muscle cells rather than in the endothelium. The endothelial dysfunction observed in hypertensive blood vessels is likely to be a consequence rather than a cause of the disease process.