Endothelial cell dysfunction and abnormal tissue perfusion.

OBJECTIVE: To determine the precise role of the myoendothelial regulatory unit in improved tissue perfusion and metabolic regulation. DATA SOURCES AND STUDY SELECTION: A review of the published literature (MEDLINE and other original articles and reviews) on endothelial cells, vascular reactivity, and tissue perfusion. DATA EXTRACTION AND SYNTHESIS: According to the concept of intrinsic metabolic regulation, vasodilation in tissues with relatively high metabolic rates competes with sympathetic vasoconstrictor tone, thereby adjusting the balance between local tissue oxygen supply and demand. Although the nature of the oxygen-sensitive structures acting at the local tissue level is not completely understood, endothelial cells in direct contact with blood have a number of properties that confer the potential to act as effective oxygen sensors. The endothelium and smooth muscle of arteries and arterioles seem to be coupled both structurally and functionally. Sensing involves local depolarization and hyperpolarization of the capillary endothelial cell, and communication is achieved by an electronic spread via endothelium-smooth muscle cell-to-cell gap junctions. Therefore, during hypoxic challenge, the ability of a tissue to extract oxygen-and to minimize shunting through areas with a high rate of perfusion relative to their oxygen uptake-may be considered an integrative test of endothelium function and microcirculatory coordination.
CONCLUSION: Endothelial cells seem to play a central role in coordinating the microcirculatory system and promoting tissue perfusion and oxygen supply. In a pathologic situation such as sepsis, abnormal interendothelial cell coupling and an abnormal arteriolar conducted response may account for impaired tissue perfusion and abnormal oxygen extraction.