Role of the Endothelium in the Flow Regulation of Vascular Tone

The strategic location of the endothelium between the flowing intraluminal blood and the vascular smooth muscle cells in the blood vessel wall implies that it should play a crucial role in the blood flow regulation of vascular tone. However, the nature of many of the cellular mechanisms involved in this inter-relationship remain speculative and controversial. The author's hypothesis is that flow can initiate two responses as the result of shear stress activation of a common sensor -the characteristic response is dilation but constriction occurs at lower and can also occur at higher tone levels. At lower levels of tone, flow-contraction and -dilation interact influencing wall tone towards a balance point. Current theories of flow sensing include deformation of viscoelastic molecules attached to the lumenal surface of the endothelium, deformation of the lumenal surface of endothelial cells and flow-dependent, endogenous agonist -lumenal endothelial surface receptor interaction. There are a number of ways in...