Abstract
The blood-flow regulation by coronary resistance microvessels is performed by integrating various vascular-relaxing factors, among which nitric oxide (NO) and EDHF are key factors. Hierarchically, NO mainly controls small arteries (>100 μm), while EDHF functions predominantly in arterioles (<100 μm). Recently, we demonstrated that an oxygen radical H2O2 operates as a EDHF in the autoregulation of coronary circulation, although the natures of EDHFs may differ among species.As for the sensing mechanicsof flow, i.e., a key issue of controlling blood flow, the bush-like structure of glycocalyx on endothelial surface with an each distance of 20 nm amplifies a small shearing force acting on the cell, providing sufficient leverage to deform the underlining cortical cytoskeleton. In fact, NO production inboth in vivo arteries and cultured aortic endothelial cells by an application of shear stress became negligibly small following degradation of glycocalyx layer by hyaluronidase or heparinase. A distinguishing characteristics ofintramyocardial coronary arteriolar flow is forward and backward movement of blood (oscillating flow) due to cardiac contraction/relaxation. However, oscillatory flow causes O2− production of intramyocardial coronary arterioles which quenches NO, suppressing vasodilation. Thus, integrating effects of reactive oxygen species are very important to understand physiology and pathophysiology of coronary microcirculation. [Jpn J Physiol 54 Suppl:S43 (2004)]
