Cyclooxygenase blockade limits blood flow to collateral-dependent myocardium during exercise

Area of Science:

• Cardiovascular Physiology
• Pharmacology
• Myocardial Ischemia Research

Background:

• Cyclooxygenase (COX) blockade is known to induce coronary collateral vasoconstriction in animal models.
• Understanding the impact of COX blockade on collateral-dependent myocardium during physiological stress like exercise is crucial.

Purpose of the Study:

• To investigate whether cyclooxygenase blockade limits blood flow to collateral-dependent heart muscle during exercise.
• To assess the effects of indomethacin on coronary collateral function and myocardial perfusion.

Main Methods:

• Conducted studies in 8 adult mongrel dogs with induced collateral-dependent myocardium.
• Measured myocardial blood flow using radioactive microspheres at rest and during treadmill exercise.
• Administered indomethacin (5 mg/kg i.v.) to assess its effects on coronary hemodynamics and flow.

Main Results:

• Indomethacin significantly increased the aortic-to-distal coronary pressure gradient and transcollateral resistance during exercise.
• A 27% decrease in subendocardial flow within the collateral-dependent zone was observed post-indomethacin.
• No significant changes in normal zone blood flow or subepicardial collateral zone flow occurred.

Conclusions:

• Cyclooxygenase blockade causes coronary collateral vasoconstriction in intact, awake animals.
• This vasoconstriction can impair blood flow to the myocardium dependent on collateral circulation, particularly during exercise.
• Findings suggest potential risks of COX inhibitors in patients with compromised coronary circulation.