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

为了研究pO_2梯度在小动脉内的形成，测定了生理条件下小动脉壁的耗氧量。采用磷光猝灭技术定量测定大鼠小动脉血管内和血管周围的pO_2值。利用测量的pO_2值和理论模型，估计了小动脉壁的O_2消耗率。我们发现功能小动脉的O_2消耗率是体外实验的100倍，静止骨骼肌小动脉壁的O_2消耗率明显高于血管舒张时的O_2消耗率。此外，位于血压最高的上游1A小动脉的O_2消耗率最高。这些结果表明，小动脉壁的高氧消耗率取决于平滑肌的负荷，而不是内皮。这些结果证实了小动脉壁自身消耗O_2对小动脉pO_2梯度形成的强烈参与。此外，小动脉还具有重要的生理功能：在静息状态下，骨骼肌小动脉的血管壁消耗大量的氧气，使小动脉能够限制血液向骨骼肌的灌注。因此，即使全身血流量有限，也能保证其他器官有充足的血液供应。另一方面，在运动过程中，由于血管平滑肌的松弛，小动脉O_2消耗减少，从而有效地向骨骼肌供应O_2。

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.