Cholinergic vasodilator mechanism in human fingers

Area of Science:

• Physiology
• Pharmacology
• Cardiovascular Research

Background:

• Understanding the regulation of fingertip blood flow is crucial for various physiological and pathological conditions.
• Cholinergic mechanisms are known to influence vascular tone, but their specific role in fingertip capillary blood flow requires further elucidation.

Purpose of the Study:

• To investigate the effect of a muscarinic cholinergic agonist and antagonist on finger blood flow (FBF) and specifically capillary blood flow (FCF).
• To determine if a cholinergic vasodilator mechanism exists in the fingertip.

Main Methods:

• Ten healthy subjects underwent measurements of total FBF using venous occlusion and air plethysmography.
• Capillary blood flow (FCF) was assessed by the washout rate of a radioisotope injected into the fingertip.
• Methacholine (cholinergic agonist) was infused intra-arterially, followed by administration of atropine (cholinergic antagonist) in some subjects.

Main Results:

• Methacholine infusion did not significantly alter total FBF or vascular resistance.
• However, methacholine significantly decreased the half-time of radioisotope disappearance, indicating a marked increase in FCF (P < 0.01).
• Atropine alone had no effect but blocked the methacholine-induced increase in FCF and prevented local autonomic responses like redness and sweating.

Conclusions:

• This study demonstrates a specific muscarinic cholinergic vasodilator pathway in the fingertip.
• This pathway selectively enhances capillary blood flow, independent of major changes in total FBF or vascular resistance.
• These findings highlight a unique microcirculatory regulation mechanism in the fingertip mediated by cholinergic neurotransmission.