Nitroglycerin causes vasodilatation within ischaemic myocardium.

Area of Science:

• Cardiovascular Physiology
• Myocardial Ischaemia Research
• Pharmacology of Vasodilators

Background:

• Vasodilators like nitroglycerin are known to improve collateral blood flow to ischaemic myocardium.
• A potential mechanism involves the dilation of collateral vessels, but direct evidence for vasodilation within the ischaemic area itself was lacking.

Purpose of the Study:

• To investigate whether the dilation of coronary arteries within the acutely ischaemic myocardium contributes to the increase in collateral blood flow.
• To differentiate the effects of nitroglycerin from other vasodilators like adenosine in this context.

Main Methods:

• The study utilized a canine model with ligation of the left anterior descending coronary artery (LAD) to induce ischaemia.
• Peripheral LAD pressure (PLAD) and myocardial blood flow were measured using radioactive microspheres.
• Ischaemic bed vascular resistance was calculated, and the effects of nitroglycerin and adenosine infusions were assessed.

Main Results:

• Nitroglycerin infusion decreased ischaemic bed vascular resistance by 10-16% regardless of administration route (LAD, circumflex artery, or right atrium).
• In contrast, adenosine infusion into the LAD did not significantly alter ischaemic bed resistance.
• These findings indicate a specific vasodilatory effect of nitroglycerin within the ischaemic myocardial region.

Conclusions:

• Nitroglycerin increases collateral blood flow to ischaemic myocardium partly by dilating large coronary arteries within the ischaemic area.
• This direct vasodilatory action within the ischaemic zone is a significant contributor to its therapeutic effect.
• Adenosine does not appear to share this specific mechanism for increasing collateral flow in acute ischaemia.