A patient having prinzmetal angina is started with ISMN. Patient got symptomatic relief from angina. What is the MOA?
**Core Concept**
The underlying principle being tested is the management of **Prinzmetal's angina**, also known as variant angina, which is caused by **coronary artery vasospasm**. The medication used, **ISMN (Isosorbide Mononitrate)**, is a type of **nitrate**.
**Why the Correct Answer is Right**
ISMN works by releasing **nitric oxide**, which then activates **guanylyl cyclase**, leading to an increase in **cGMP (cyclic guanosine monophosphate)**. This increase in cGMP causes **smooth muscle relaxation** in the coronary arteries, thereby relieving the vasospasm and improving blood flow to the heart muscle.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not related to the mechanism of ISMN.
**Option B:** Incorrect as it does not describe the action of ISMN in Prinzmetal's angina.
**Option C:** Incorrect because, although ISMN does reduce preload, its primary benefit in Prinzmetal's angina is related to its vasodilatory effects on coronary arteries.
**Option D:** Incorrect as it does not accurately describe the mechanism by which ISMN relieves angina symptoms.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that nitrates, like ISMN, are particularly effective in **Prinzmetal's angina** due to their ability to directly relax vascular smooth muscle, counteracting the coronary vasospasm characteristic of this condition.
**Correct Answer:** D. Isosorbide mononitrate causes smooth muscle relaxation by increasing the levels of cGMP.