Posterior pituitary drugs: desmopressin: practice question

A Pharmacology 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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Pharmacology · Posterior pituitary drugs: desmopressin

Sample item

After a head injury a man passes 6 litres of dilute urine per day, with urine osmolality 120 mOsm/kg that rises to 600 mOsm/kg after desmopressin. By what mechanism does desmopressin act?

AStimulation of ADH release from the posterior pituitaryBInhibition of the sodium-chloride cotransporter in the distal tubuleCV1a receptor stimulation in vascular smooth muscleDV2 receptor stimulation in the collecting duct, increasing aquaporin-2 insertion

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

The answer and the reasoning

D. V2 receptor stimulation in the collecting duct, increasing aquaporin-2 insertion

The picture is central diabetes insipidus, where the kidney responds to exogenous ADH. Desmopressin is a V2-selective analogue that raises cAMP in collecting duct cells and drives insertion of aquaporin-2 water channels, concentrating urine. Water intoxication and hyponatraemia are the key adverse effects.

Option by option

A. Stimulation of ADH release from the posterior pituitary
Desmopressin replaces ADH and does not trigger pituitary release.
B. Inhibition of the sodium-chloride cotransporter in the distal tubule
Inhibition of the Na-Cl cotransporter is the thiazide mechanism, used in nephrogenic diabetes insipidus.
C. V1a receptor stimulation in vascular smooth muscle
V1a stimulation causes vasoconstriction and is minimal with desmopressin.
D. V2 receptor stimulation in the collecting duct, increasing aquaporin-2 insertion (correct)
Correct. V2 activation inserts aquaporin-2 and enhances water reabsorption.

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.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, V2 receptor stimulation in the collecting duct, increasing aquaporin-2 insertion. The picture is central diabetes insipidus, where the kidney responds to exogenous ADH.

Why is "Stimulation of ADH release from the posterior pituitary" not the answer?

Desmopressin replaces ADH and does not trigger pituitary release.

Why is "Inhibition of the sodium-chloride cotransporter in the distal tubule" not the answer?

Inhibition of the Na-Cl cotransporter is the thiazide mechanism, used in nephrogenic diabetes insipidus.

Why is "V1a receptor stimulation in vascular smooth muscle" not the answer?

V1a stimulation causes vasoconstriction and is minimal with desmopressin.

What concept does this question test?

It tests Posterior pituitary drugs: desmopressin in Pharmacology. Desmopressin is a V2-selective analogue that raises cAMP in collecting duct cells and drives insertion of aquaporin-2 water channels, concentrating urine. Water intoxication and hyponatraemia are the key adverse effects.

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 Posterior pituitary drugs: desmopressin?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology 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.