Interactions of hormones with the vascular endothelium. Effects on the control of vascular tone

Due to their anatomical location vascular endothelial cells are an obvious target for hormones which are transported by the bloodstream. Studies on cultured endothelial cells, isolated vessels and the intact organism revealed the existence of multiple interactions between endothelial cells and circulating hormones. Not only are endothelial cells involved in the clearance of some specific circulating hormones, but they also form a tight barrier for other hormones thus preventing or attenuating their direct effects on vascular smooth muscle. Endothelial cells are also involved in the production of circulating angiotensin II by the angiotensin converting enzyme. Probably the most significant effect of hormones in vascular control is the ability of many of them to modulate the release of vasoactive autacoids such as nitric oxide, prostaglandins and endothelin-1. Aside from acute stimulating effects on autacoid production, some hormones, particularly steroids, exert chronic effects on vasoactive-factor gene expression. Apparently, in the control of vascular tone, interactions between circulating hormones and the endothelium play a major role. However, the functional significance of these interactions, especially in pathophysiologic conditions remains to be determined.