Microvascular and tissue oxygen gradients in the rat mesentery

Abstract

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 .