Endothelium: from whence to whither.

Today's perspective of the endothelial cell recognizes its real significance, heretofore neglected, and anticipates important future contributions to improved medical management. Like trustworthy posted guards of the vascular frontier, endothelial cells oversee and regulate not only fluid and solute traffic (between lumen and tissue) but also contribute valuable protective forces to act at each of its boundaries. Uniquely different from its guardian colleague, the nonnucleated platelet lacks ability to regenerate blocked metabolic functions (for example, thromboxane production), whereas the nucleated endothelial cell is metabolically complete and therefore able to regenerate blocked metabolic functions (for example, PGI2 production). The endothelial cell commands and modulates the circulation, regulating the contractility of its underlying smooth musculature and the rheologic properties of its overlying circulating fluid. Many overlooked contributions of the endothelial cells, from its luminal, abluminal, and abutting surfaces, modulate important, even critical, physiologic functions. Only very recently have management techniques begun to exploit these endothelial functions; but developing new techniques promise exciting therapeutic possibilities soon. As we look to that future, we must apply our knowledge to coronary artery disease, congestive heart failure, cerebrovascular disease, thromboembolism, diabetic degenerative disease, hemolytic uremic syndrome, shock lung, vasospastic disorders, and a great variety of other today's inadequately managed disorders of man and animals.