Microvascular and tissue oxygen gradients in the rat mesentery

One of the most important functions of the blood circulation is O(2) delivery to the tissue. This process occurs primarily in microvessels that also regulate blood flow and are the site of many metabolic processes that require O(2). We measured the intraluminal and perivascular pO(2) in rat mesenteric arterioles in vivo by using noninvasive phosphorescence quenching microscopy. From these measurements, we calculated the rate at which O(2) diffuses out of microvessels from the blood. The rate of O(2) efflux and the O(2) gradients found in the immediate vicinity of arterioles indicate the presence of a large O(2) sink at the interface between blood and tissue, a region that includes smooth muscle and endothelium. Mass balance analyses show that the loss of O(2) from the arterioles in this vascular bed primarily is caused by O(2) consumption in the microvascular wall. The high metabolic rate of the vessel wall relative to parenchymal tissue in the rat mesentery suggests that in addition to serving as a conduit for the delivery of O(2) the microvasculature has other functions that require a significant amount of O(2).