Angina: Why does nitroglycerine help?

Exogenous nitroglycerine is imitating the native mechanism, in which endothelial cells produce nitric oxide, which is a natural agonist that produces vasodilation. This system is very important in physiological regulation, so we can give a drug that will enhance this relaxing mechanism. You can build a tolerance for nitroglycerine so that it no longer works so well. Nitric oxide works its way through the endothelial cells of the vessel and gets to the smooth muscle. In the smooth muscle you have activation of guanylate cyclase, which produces cGMP out of GTP, the cGMP goes to interfere with protein kinase phosphorylation mechanisms that are required for contraction—thus you get relaxation.

If you have a coronary arteriosclerotic plaque, this will not be dilated because its already stiffened. So this is NOT the way that nitroglycerine works. Instead, nitroglycerine goes through the entire body and vasodilates a lot of arteries and veins to keep the blood out of circulation so that both the pre-load (venous return) and the after-load (arterial pressure) are decreased. So what you do is decrease the work of the heart. (When this happens there is a reflex increase in heart rate.)

Summary:

Medication Used to Treat Angina: Nitrates

Mechanism: arterial and venous dilation

Heart rate: reflex tachycardia can occur due to arterial dilation

Blood Pressure: reduced

Side Effects: headaches, tachycardia, tolerance

Category: Pharmacology Notes