Flow-Induced Dilation of Skeletal Muscle Feed Arteries: Relevance to Exercise Hyperemia
Presentation Type
Poster
Keywords
Blood flow, exercise, flow-induced dilation, shear stress
Department
Sports Medicine
Major
Sports Medicine
Abstract
Flow-induced dilation is the dilatory response seen in arteries as a result of an increase in shear stress along the endothelium. It is often thought that flow-induced dilation contributes to arterial dilation during exercise as blood flow is increased to working muscle. Previous research compared in vivoshear stress values during rest and exercise to in vitro shear stress values and concluded that flow-induced dilation of rat soleus feed arteries (Jasperse & Laughlin) is unlikely to contribute to exercise hyperemia. However, the predominantly slow-twitch soleus is unique in that it contributes to postural maintenance and receives higher amounts of blood flow during stance compared to other hindlimb muscles. Therefore, the aim of the present study was to determine if feed arteries from the predominantly fast-twitch rat gastrocnemius muscle (GFA) demonstrated flow-induced dilation and to further assess the potential role of flow-induced dilation in GFA during exercise. GFA (n=12) from male Sprague-Dawley rats were isolated and cannulated on two glass micropipettes and intraluminal diameter was measured using videomicroscopy. Pressure was maintained at 90 cmH2O using two independent fluid reservoirs. Changing the height of the fluid reservoirs created a pressure gradient that induced flow through the arteries. Pressure gradients of 2, 4, 6, 8, 10, 15, 20, 30, and 40 cmH2O were used. GFA dilated to increasing flow and shear stress values ranged up to 8.0 ± 0.8 dyn/cm2. The in vitro shear stress response range was compared to calculated in vivo shear stress values from previously published studies. Estimated GFA blood flow values in standing rats are 431 µl/min, in walking rats 816 µl/min, and in running rats 1510 µl/min. Corresponding shear stress values were 95 dyn/cm2 (standing), 180 dyn/cm2 (walking), and 332 dyn/cm2 (running). These in vivo shear stress values far exceed the shear stress values to which GFA dilated in vitro. This comparison suggests that maximal flow-induced dilation occurs at shear stress values far below those present in GFA in non-exercising rats and that flow-induced dilation of GFA is an unlikely contributor to the increase in blow flow seen during exercise.
Faculty Mentor
Dr. Jeff Jasperse
Location
Waves Cafeteria
Start Date
1-4-2016 2:00 PM
End Date
1-4-2016 3:00 PM
Flow-Induced Dilation of Skeletal Muscle Feed Arteries: Relevance to Exercise Hyperemia
Waves Cafeteria
Flow-induced dilation is the dilatory response seen in arteries as a result of an increase in shear stress along the endothelium. It is often thought that flow-induced dilation contributes to arterial dilation during exercise as blood flow is increased to working muscle. Previous research compared in vivoshear stress values during rest and exercise to in vitro shear stress values and concluded that flow-induced dilation of rat soleus feed arteries (Jasperse & Laughlin) is unlikely to contribute to exercise hyperemia. However, the predominantly slow-twitch soleus is unique in that it contributes to postural maintenance and receives higher amounts of blood flow during stance compared to other hindlimb muscles. Therefore, the aim of the present study was to determine if feed arteries from the predominantly fast-twitch rat gastrocnemius muscle (GFA) demonstrated flow-induced dilation and to further assess the potential role of flow-induced dilation in GFA during exercise. GFA (n=12) from male Sprague-Dawley rats were isolated and cannulated on two glass micropipettes and intraluminal diameter was measured using videomicroscopy. Pressure was maintained at 90 cmH2O using two independent fluid reservoirs. Changing the height of the fluid reservoirs created a pressure gradient that induced flow through the arteries. Pressure gradients of 2, 4, 6, 8, 10, 15, 20, 30, and 40 cmH2O were used. GFA dilated to increasing flow and shear stress values ranged up to 8.0 ± 0.8 dyn/cm2. The in vitro shear stress response range was compared to calculated in vivo shear stress values from previously published studies. Estimated GFA blood flow values in standing rats are 431 µl/min, in walking rats 816 µl/min, and in running rats 1510 µl/min. Corresponding shear stress values were 95 dyn/cm2 (standing), 180 dyn/cm2 (walking), and 332 dyn/cm2 (running). These in vivo shear stress values far exceed the shear stress values to which GFA dilated in vitro. This comparison suggests that maximal flow-induced dilation occurs at shear stress values far below those present in GFA in non-exercising rats and that flow-induced dilation of GFA is an unlikely contributor to the increase in blow flow seen during exercise.