Effects of oxygen consumption by arteriolar walls on oxygen transport to tissue under physiological condition

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To examine the formation of pO_2 gradients in arterioles, the oxygen consumption rates of arteriolar walls were determined under physiological conditions. A phosphorescence quenching technique was used to quantify the intra- and perivascular pO_2 values in rat cremaster arterioles. Using the measured pO_2 values, and a theoretical model, the O_2 consumption rates of the arteriolar walls were then estimated. We found that the O_2 consumption rate of functional arterioles was 100 times greater than that seen in in vitro experiments, and the O_2 consumption rate of the arteriolar walls in resting skeletal muscle was significantly higher than that during vasodilation. Furthermore, the O_2 consumption rate was the highest in the 1A arterioles, which are located upstream where the blood pressure is highest. These findings suggest that the high O_2 consumption rates of arteriolar walls depend on the workload of the smooth muscle, rather than the endothelium. These results confirm the strong involvement of O_2 consumption by the arteriolar wall itself in the formation of pO_2 gradients in arterioles. Furthermore, an important physiological function of arterioles was demonstrated: large amounts of O_2 are consumed by the vessel walls in resting skeletal muscle arterioles, enabling the arterioles to restrict blood perfusion into skeletal muscle. Consequently, an adequate blood supply to the other organs is ensured, even with a limited systemic blood flow. During exercise, on the other hand the arteriolar O_2 consumption decreases as a result of the relaxation of the vascular smooth muscle, thereby efficiently supplying O_2 to the skeletal muscle.