Cardiovascular system: paradoxical coronary constriction with acetylcholine: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Cardiovascular system: paradoxical coronary constriction with acetylcholine

Sample item

During coronary angiography, intracoronary acetylcholine dilates the arteries of a young control but constricts the arteries of a patient with advanced atherosclerosis. Why?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Damaged endothelium cannot release nitric oxide, so direct muscarinic constriction of smooth muscle appears

Acetylcholine normally acts on endothelial muscarinic receptors to release nitric oxide, which dilates the vessel. When the endothelium is dysfunctional, no nitric oxide is made and the direct constrictor action on smooth muscle is unmasked. This is the basis of the test for endothelial dysfunction.

Option by option

  • A. Atherosclerotic smooth muscle lacks muscarinic receptors

    The smooth muscle does carry muscarinic receptors, which is why constriction occurs.

  • B. Plaque releases large amounts of nitric oxide that exhaust the receptors

    Plaque does not release enough nitric oxide to cause paradoxical constriction.

  • C. Acetylcholine acts only on the endothelium in diseased arteries

    Acetylcholine acts on the endothelium in healthy vessels; diseased endothelium fails to respond.

  • D. Damaged endothelium cannot release nitric oxide, so direct muscarinic constriction of smooth muscle appears (correct)

    Correct. Loss of endothelial NO release unmasks the direct smooth muscle effect.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Damaged endothelium cannot release nitric oxide, so direct muscarinic constriction of smooth muscle appears. Acetylcholine normally acts on endothelial muscarinic receptors to release nitric oxide, which dilates the vessel.

Why is "Atherosclerotic smooth muscle lacks muscarinic receptors" not the answer?

The smooth muscle does carry muscarinic receptors, which is why constriction occurs.

Why is "Plaque releases large amounts of nitric oxide that exhaust the recept…" not the answer?

Plaque does not release enough nitric oxide to cause paradoxical constriction.

Why is "Acetylcholine acts only on the endothelium in diseased arteries" not the answer?

Acetylcholine acts on the endothelium in healthy vessels; diseased endothelium fails to respond.

What concept does this question test?

It tests Cardiovascular system: paradoxical coronary constriction with acetylcholine in Physiology. When the endothelium is dysfunctional, no nitric oxide is made and the direct constrictor action on smooth muscle is unmasked. This is the basis of the test for endothelial dysfunction.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Cardiovascular system: paradoxical coronary constriction with acetylcholine?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.