A Close Look at the Endothelium: Its Role in the Regulation of Vasomotor Tone

ContextThe endothelium is known to have a major regulatory role in cardiovascular functions, including the control of vascular tone. Its disturbance leads to hypertension and atherosclerosis.ObjectiveTo present a concise narrative review of the main structural and functional features of the endothelium as they relate to the regulation of vascular smooth muscle contractility.Evidence acquisitionAn extensive search was performed in MedLine (1970 to March 2008) of research articles and reviews describing endothelial signaling mechanisms that are relevant to the regulation of vascular tone. Additional references were obtained from bibliographic reviews.Evidence synthesisThe mechanisms of several endothelium-generated messengers eliciting both relaxation (nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factors) and contraction (thromboxane A2, endothelin 1, reactive oxygen species, and angiotensin II) of the underlying vascular smooth muscle cells are well documented. These messengers also interact within the endothelial cells to regulate their function.ConclusionsThe normal endothelium plays a key role in the regulation of vascular tone and organ blood flow through a delicate interplay between vasodilator and vasoconstrictor signals. In normal circumstances, the former predominate, but that balance is reversed by several cardiovascular risk factors and established vascular pathologies.