Reactive hyperemia in arterioles and capillaries of frog skeletal muscle following microocclusion.

We studied the localization of blood flow control in skeletal muscle by shortterm microocclusions (30-60 seconds) of capillaries and arterioles of the pectoralis muscle in anesthetized frogs (Rana pipiens). The muscle was surgically exposed to permit transillumination and measurement of red cell velocity in the microvessels, but innervation and blood supply were kept intact. About one-third of the arterioles showed postocclusion hyperemia. In some muscles every arteriole showed hyperemia following occlusion, but in others none responded, presumably because of preparatory trauma. The average duration of hyperemia after a 1-minute occlusion was 74 ± 45 (sx>) seconds. We also compared the effectiveness of arteriolar and capillary occlusions in producing reactive hyperemia in capillaries. Peak capillary blood flow after occlusion of the supply arteriole was 233% above control, and flow debt repayment was 278%. After occlusion of several capillaries, peak capillary blood flow was 67% above control, and flow debt repayment was 74%. In an individual capillary, peak blood flow after occlusion of that capillary was 15% above control, and flow debt repayment was 13%. In a majority of instances there was no discernible reactive hyperemia with single capillary occlusion. The results do not support the concept that flow in individual capillaries is regulated in accordance with each capillary's metabolic environment. Rather, flow in a capillary appears to depend on the metabolic environment of the arteriole supplying that capillary.