Capillary lengths and anastomoses in rat hindlimb muscles, studied by Aquablak perfusion during rest versus exercise.

This investigation shows that provided an adequate perfusion time of the capillary network is allowed following injection of Aquablak, the presence of arterioles and capillaries having zero or near-zero flow rates can be demonstrated in resting muscle. During hyperemia, "flow recruitment" occurs in these vessels, as indicated by their perfusion with Aquablak. Our observations of Aquablak perfusion in hyperemic muscles show that in medial gastrocnemius, gracilis, and soleus the mean arteriolar-to-venular distances, and also the mean capillary pathlengths, were not dramatically different. What was striking, however, was the fact that capillary pathlengths in soleus were divided into twice the number of segments found in gastrocnemius and gracilis. This suggests the possibility that in oxidative muscles the capillary network may exhibit a much higher degree of branching than in glycolytic muscles. This would increase the area for diffusional exchange between blood and tissue in oxidative compared to glycolytic muscle.