Is adenosine a modulator of peripheral vasoconstrictor responses?

Area of Science:

• Physiology
• Pharmacology
• Cardiovascular Regulation

Background:

• Local vasoconstrictor reflexes, including the vascular myogenic response (VMR) and veno-arterial reflex (VAR), are vital for maintaining blood flow and pressure during orthostatic stress.
• The precise molecular mechanisms underlying these reflexes remain largely unknown.
• Adenosine was hypothesized to play a role in activating these local circulatory reflexes.

Purpose of the Study:

• To investigate the involvement of adenosine in the activation of local vasoconstrictor reflexes, specifically the VMR and VAR.
• To determine if blocking adenosine influences the physiological responses of these reflexes.

Main Methods:

• Ten healthy males underwent forearm blood flow measurements using veno-occlusive plethysmography.
• VAR was induced by local venous congestion, and VMR by limb dependency.
• Measurements were repeated after local infusion of saline (control) or aminophylline (adenosine blocker) via Bier block.

Main Results:

• Aminophylline significantly increased baseline forearm blood flow by 34% compared to saline.
• The VAR response, a decrease in forearm blood flow of 49%, was significantly attenuated by aminophylline (35% decrease), while saline had no effect.
• Neither saline nor aminophylline affected the VMR.

Conclusions:

• The veno-arterial reflex (VAR) appears to be at least partially modulated by adenosine.
• Adenosine blockade with aminophylline significantly alters the VAR response, suggesting a role for adenosine in this reflex.
• Further pharmacological and physiological research is warranted to fully elucidate the role of adenosine in this sensory reflex.