Cyclic nucleotides: sildenafil: practice question

A Biochemistry 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.

Try it

Biochemistry · Cyclic nucleotides: sildenafil

Sample item

A man with erectile dysfunction takes sildenafil. Which nucleotide-related mechanism produces smooth muscle relaxation?

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

The answer and the reasoning

D. Inhibition of phosphodiesterase 5, which prevents breakdown of cGMP generated after nitric oxide activates guanylyl cyclase

Nitric oxide from nerve terminals and endothelium activates soluble guanylyl cyclase to produce cGMP, which relaxes vascular smooth muscle in the corpus cavernosum. PDE5 hydrolyses cGMP; sildenafil inhibits it and so prolongs the effect. Concurrent nitrates are contraindicated because of profound hypotension, and PDE6 cross-inhibition can give visual disturbance.

Option by option

  • A. Inhibition of guanylyl cyclase, which lowers cGMP

    Inhibiting guanylyl cyclase would reduce cGMP and cause vasoconstriction.

  • B. Release of calcium from the sarcoplasmic reticulum through IP3

    IP3-mediated calcium release produces contraction rather than relaxation.

  • C. Activation of adenylyl cyclase, which raises cAMP

    Raising cAMP is the effect of agents like beta-agonists and forskolin, not sildenafil.

  • D. Inhibition of phosphodiesterase 5, which prevents breakdown of cGMP generated after nitric oxide activates guanylyl cyclase (correct)

    Preventing cGMP degradation amplifies the nitric oxide signal and sustains relaxation.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Inhibition of phosphodiesterase 5, which prevents breakdown of cGMP generated after nitric oxide activates guanylyl cyclase. Nitric oxide from nerve terminals and endothelium activates soluble guanylyl cyclase to produce cGMP, which relaxes vascular smooth muscle in the corpus cavernosum.

Why is "Inhibition of guanylyl cyclase, which lowers cGMP" not the answer?

Inhibiting guanylyl cyclase would reduce cGMP and cause vasoconstriction.

Why is "Release of calcium from the sarcoplasmic reticulum through IP3" not the answer?

IP3-mediated calcium release produces contraction rather than relaxation.

Why is "Activation of adenylyl cyclase, which raises cAMP" not the answer?

Raising cAMP is the effect of agents like beta-agonists and forskolin, not sildenafil.

What concept does this question test?

It tests Cyclic nucleotides: sildenafil in Biochemistry. PDE5 hydrolyses cGMP; sildenafil inhibits it and so prolongs the effect. Concurrent nitrates are contraindicated because of profound hypotension, and PDE6 cross-inhibition can give visual disturbance.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Cyclic nucleotides: sildenafil?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.