Aminophylline and interstitial adenosine during sustained exercise hyperemia

Area of Science:

• Exercise Physiology
• Skeletal Muscle Metabolism
• Cardiovascular Regulation

Background:

• Adenosine is a key mediator in regulating blood flow to skeletal muscles.
• Its role in exercise-induced vasodilation, particularly in high oxidative muscles, remains under investigation.

Purpose of the Study:

• To test if increased interstitial fluid (ISF) adenosine concentration drives vasodilation in canine skeletal muscle during sustained exercise.
• To evaluate the effect of adenosine receptor antagonism on exercise hyperemia.

Main Methods:

• Canine calf muscles underwent electrical stimulation (3 Hz) before and after aminophylline infusion.
• Adenosine receptor antagonist aminophylline was administered to block adenosine's effects.
• A mathematical model was used to assess ISF adenosine concentration versus venous plasma concentration.

Main Results:

• Aminophylline significantly blocked adenosine's vasodilatory effects but did not alter resting or exercise blood flow or O2 consumption.
• Adenosine release increased during exercise, but venous plasma adenosine concentration remained unchanged.
• The study determined that venous plasma adenosine concentration is a reliable index of ISF adenosine.

Conclusions:

• Aminophylline does not affect sustained exercise hyperemia because ISF adenosine concentration does not rise under these conditions.
• Adenosine does not contribute to vasodilation during 3-Hz sustained skeletal muscle exercise in canines.