Muscle metaboreflex activation during dynamic exercise vasoconstricts ischemic active skeletal muscle

Area of Science:

• Exercise Physiology
• Autonomic Nervous System Regulation
• Skeletal Muscle Physiology

Background:

• Metabolite accumulation in active skeletal muscle stimulates chemosensitive afferents, initiating the muscle metaboreflex.
• Muscle metaboreflex activation (MMA) is known to cause vasoconstriction in non-exercising vascular beds.
• The effect of MMA on the vascular resistance of the ischemic muscle itself remains unclear.

Purpose of the Study:

• To investigate whether muscle metaboreflex activation causes vasoconstriction in the ischemic skeletal muscle.
• To determine the adrenergic mechanisms underlying potential vasoconstriction in the active muscle during MMA.
• To assess the impact of MMA-induced vasoconstriction on blood flow regulation in exercising skeletal muscle.

Main Methods:

• Chronic instrumentation in canines to measure hindlimb blood flow (HLBF) and femoral arterial pressure during mild dynamic exercise.
• Graded reductions in HLBF to elicit and activate the muscle metaboreflex.
• Pharmacological blockade of adrenergic receptors using prazosin (α1-blocker), propranolol (β-blocker), and combined blockade.
• Calculation of hindlimb vascular resistance (femoral arterial pressure/HLBF).

Main Results:

• Initially, reduced HLBF during exercise led to vasodilation.
• Once the muscle metaboreflex was activated, hindlimb resistance significantly increased.
• This increase in hindlimb resistance was abolished by α1-adrenergic blockade and exacerbated by β-adrenergic blockade.
• The vasoconstriction was attributed to sympathetically mediated α-adrenergic mechanisms.

Conclusions:

• Muscle metaboreflex activation during submaximal dynamic exercise induces sympathetically mediated α-adrenergic vasoconstriction in the ischemic skeletal muscle.
• This vasoconstrictive response in the active muscle limits the potential benefits of the muscle metaboreflex in improving blood flow.
• Understanding this mechanism is crucial for comprehending exercise hyperemia and autonomic control during physical activity.