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 mall. 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.