Insulin Action and Endothelial Function

The endothelium is a diaphanous cellular monolayer lining the lumen of the vasculature throughout the body and weighs approximately 1.8 kg in a 70 kg man. In addition to its well-recognized passive barrier and transport functions, the endothelium actively participates in processes related to local vascular and tissue health. These include active control of vascular tone (1,2), regulation of blood fluidity (3), and modulation of monocyte adhesion (4,5), inflammation (6,7), and lipid peroxidation (8, 9, 10), to name but a few processes. More recently, the endothelium has been recognized as an endocrine organ, Indeed, the endothelium produces a variety of hormones acting in a paracrine fashion to regulate vascular tone as well as growth and remodeling of the vascular wall (11, 12, 13, 14). The endothelium also possesses receptors for humoral ligands. These receptors, whose predominant role was initially thought to be transendothelial transfer of hormones, are now known to directly activate signaling cascades and physiological responses.