alpha-adrenergic vasoconstriction in active skeletal muscles during dynamic exercise.

Area of Science:

• Exercise Physiology
• Cardiovascular Regulation
• Adrenergic Signaling

Background:

• Sympathetic vasoconstriction in active muscles during dynamic exercise is a known phenomenon.
• Previous studies demonstrated this effect using alpha(1)-adrenergic antagonists.

Purpose of the Study:

• To investigate the roles of both alpha(1)- and alpha(2)-adrenergic receptors in mediating vasoconstriction within active skeletal muscles during exercise.
• To determine if these receptor-mediated effects persist across varying exercise intensities.

Main Methods:

• Six dogs were instrumented with flow probes on iliac arteries and catheters in the femoral artery.
• Dogs underwent treadmill exercise at three intensities (mild, moderate, heavy).
• Selective alpha(1)- (prazosin) and alpha(2)-adrenergic antagonists (rauwolscine) were infused intra-arterially during exercise.

Main Results:

• Prazosin and rauwolscine infusions significantly increased iliac conductance and blood flow at all exercise intensities.
• The magnitude of vasoconstriction, measured by increased conductance, decreased as exercise intensity increased.
• Systemic blood pressure and contralateral iliac blood flow remained unaffected by antagonist infusions.

Conclusions:

• Both alpha(1)- and alpha(2)-adrenergic receptors contribute to sympathetic vasoconstriction in exercising skeletal muscles.
• This receptor-mediated vasoconstriction is present even at high exercise intensities.
• The degree of vasoconstriction mediated by these receptors diminishes with increasing exercise intensity.