Microcirculatory control of tissue oxygenation

Microvascular vasomotor tone plays an essential role in the defense of tissue oxygenation when O-2 supply is reduced. Endothelial derived vasodilators nitric oxide (NO) and prostacyclin (PGI(2)), and ATP-sensitive K+ (K-ATP) channel-mediated hyperpolarization are involved in this defense. Microvascular network deendothelialization is associated with severe limitation in O-2 extraction ability. Double block of NO and PGI(2) causes a significant decrease in critical O-2 extraction ratio, although block of NO does not appear to be preponderant in doing so. K-ATP channel-mediated hyperpolarization and associated-vasodilation during hypoxia seem essential to adjust O-2 transport to meet O-2 demand. indeed, hyperpolarization may be conducted bidirectionally along arterioles for several millimiters. This system displays functional characteristics that are appropriate for controlling the distribution and magnitude of blood flow and red blood cells content into the microvascular network.