Coronary arteriolar vasoconstriction in myocardial ischaemia: coronary vasodilator reserve during ischaemia

Area of Science:

• Cardiovascular Physiology
• Myocardial Perfusion Dynamics

Background:

• Coronary artery stenosis can lead to myocardial ischemia, particularly during increased demand like exercise.
• The role of residual vasomotor tone in limiting blood flow to ischemic myocardium is not fully understood.

Purpose of the Study:

• To investigate if vasomotor tone in coronary resistance vessels limits blood flow to ischemic myocardium during exercise in a canine model.
• To determine the adrenergic mechanisms involved in this potential limitation of coronary blood flow.

Main Methods:

• A chronic coronary stenosis was created in dogs using a hydraulic occluder.
• Myocardial blood flow was measured during treadmill exercise (6.5 km/h, 6% grade).
• The effects of alpha-1 (prazosin) and alpha-2 (idazoxan) adrenergic antagonists on myocardial blood flow were assessed.

Main Results:

• Exercise induced myocardial hypoperfusion in the region supplied by the stenotic artery, most severe in the subendocardium.
• Intracoronary prazosin significantly increased myocardial blood flow by 50% without altering perfusion pressure.
• Idazoxan showed a non-significant trend towards increasing blood flow.

Conclusions:

• Residual vasomotor tone, mediated partly by alpha-1 adrenergic receptors, limits blood flow to ischemic myocardium perfused by a stenotic coronary artery during exercise.
• Targeting alpha-1 adrenergic mechanisms may improve blood flow to ischemic heart regions.