Sustained exercise hyperemia during prolonged adenosine infusion in humans

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Pharmacology

Background:

• The role of Adenosine (ADO) in exercise hyperemia is debated.
• It is unclear if ADO can sustain vasodilation during prolonged exercise.

Purpose of the Study:

• To investigate if high-dose intra-arterial Adenosine (ADO) infusion causes sustained vasodilation in the human forearm over 3 hours.
• To determine if exercise hyperemia responses are maintained during ADO infusion.
• To test parallel hypotheses for nitric oxide (NO) using sodium nitroprusside (SNP).

Main Methods:

• Seventeen healthy young participants received intra-arterial infusions of ADO (n=9) or SNP (n=8).
• Participants performed rhythmic handgrip exercise bouts during saline and drug infusions.
• Forearm vascular conductance (FVC) was measured during rest and exercise over 3 hours.

Main Results:

• Both ADO and SNP significantly increased FVC.
• FVC did not wane over 3 hours of continuous ADO or SNP infusion.
• Exercise superimposed on ADO or SNP infusion consistently evoked additional vasodilation.

Conclusions:

• Exogenous Adenosine (ADO) and nitric oxide (NO) do not diminish endothelial or vascular smooth muscle responsiveness in humans.
• Superimposed exercise induces significant hyperemia even when exogenous vasodilators are present.