Alpha2-adrenoceptors and endothelium-derived relaxing factor

Paul M. Vanhoutte, Virginia M Miller

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Abstract

The endothelium can release potent vasodilator substances, in particular prostacyclin and endothelium-derived relaxing factor. The triggers for the release of endothelium-derived relaxing factor include increases in levels of shear stress, neuro-transmitters, autacoids, platelet products, and hormones. The endothelium-dependent response to catecholamines involves stimulation of alpha2-adrenoceptors on the endothelial cells. Indeed, in a number of blood vessels, selective alpha2-adrenergic agonists cause endothelium-dependent relaxations. These are seen most typically in blood vessels with long-term exposure to high flows and high partial pressures of oxygen. In addition to the release of endothelium-derived relaxing factor, alpha2-adrenergic agonists can stimulate postjunctional (postsynaptic) alpha2-adrenoceptors on vascular smooth muscles. These receptors, which are more abundant in hypertensive blood vessels, activate the contractile process. However, the alpha2-adrenergic vasoconstrictors act as partial agonists (with a limited receptor reserve) and hence their vasoconstrictor response is very sensitive to functional antagonists such as endothelium-derived relaxing factor. Thus, the presence of endothelial cells can blunt the vasoconstrictor response to these substances not only because of an augmented release of endothelium-derived relaxing factor but also because the vasoconstriction that they induce is particularly susceptible to the inhibitory effect of the factor.

Original languageEnglish (US)
JournalThe American journal of medicine
Volume87
Issue number3 SUPPL. 3
DOIs
StatePublished - Sep 18 1989

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ASJC Scopus subject areas

  • Nursing(all)

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