MICROVASCULAR AND TISSUE OXYGEN GRADIENTS IN THE RAT MESENTERY

One of the most important functions of the blood circulation is O-2 de livery to the tissue. This process occurs primarily in microvessels th at also regulate blood flow and are the site of many metabolic process es that require O-2. We measured the intraluminal and perivascular pO( 2) in rat mesenteric arterioles in vivo by using noninvasive phosphore scence quenching microscopy. From these measurements, we calculated th e rate at which O-2 diffuses out of microvessels from the blood. The r ate of O-2 efflux and the O-2 gradients found in the immediate vicinit y of arterioles indicate the presence of a large O-2 sink at the inter face between blood and tissue, a region that includes smooth muscle an d endothelium. Mass balance analyses show that the loss of O-2 from th e arterioles in this vascular bed primarily is caused by O-2 consumpti on in the microvascular mall. The high metabolic rate of the vessel wa ll relative to parenchymal tissue in the rat mesentery suggests that i n addition to serving as a conduit for the delivery of O-2 the microva sculature has other functions that require a significant amount of O-2 .