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Departments of Medical Physiology and Veterinary Biomedical Sciences, University of Missouri, Columbia, Missouri 65211
Flow-induced dilation is thought to contribute to dilation of skeletal muscle arteries and arterioles during exercise hyperemia. We sought to determine whether rat soleus feed arteries (SFA) exhibit flow-induced dilation and to evaluate the potential contribution of flow-induced dilation of SFA to exercise hyperemia. Rat SFA were isolated and cannulated to allow pressure and intraluminal flow to be independently controlled. Intraluminal pressure was maintained at 90 cmH2O throughout the experiment. All SFA (n = 13) developed spontaneous tone and dilated in response to flow. Flow of 10 and 14 µl/min produced a 34 ± 14 and 56 ± 17 µm increase above basal diameter (135 ± 12 µm), respectively. Flows >14 µl/min produced little further dilation. Maximum flow-induced dilation was 86 ± 3% of passive diameter determined in calcium-free physiological saline solution. Calculated shear stress was maintained at 4-6 dyn/cm2 at flows of 10-20 µl/min but increased at greater flows because SFA did not dilate further. To determine whether dilation in response to flows in this range may contribute to exercise hyperemia, we estimated in vivo SFA blood flows from previously published soleus blood flow data. Anesthetized rats are estimated to have flows of 10 µl/min per SFA, and conscious rats are estimated to have flows of 95 (nonexercising), 153 (walking), and 225 (running) µl/min per SFA. Corresponding shear stresses were estimated to be 26 (anesthetized), 47 (conscious, nonexercising), 75 (walking), and 111 (running) dyn/cm2. Because estimated in vivo values for both flow and wall shear stress are far greater than the flow and/or shear stresses at which maximal flow-induced dilation occurs in vitro, we conclude that flow-induced dilation contributes little to dilation of SFA during locomotory exercise.
shear stress; blood flow
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