Nucleotide metabolism: duration of adenosine action: 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.

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Biochemistry · Nucleotide metabolism: duration of adenosine action

Sample item

A rapid intravenous bolus of adenosine terminates supraventricular tachycardia, but its effect lasts only seconds. Which process mainly accounts for its extremely short half-life?

ASlow renal excretion of unchanged drugBHepatic glucuronidationCBinding to plasma proteins with release over minutesDUptake into red cells and endothelium with deamination to inosine

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

The answer and the reasoning

D. Uptake into red cells and endothelium with deamination to inosine

Adenosine is taken up rapidly by erythrocytes and vascular endothelium and is deaminated by adenosine deaminase to inosine, which is inactive at the receptor. The half-life is under ten seconds. Dipyridamole prolongs its effect by blocking uptake, and theophylline antagonises it at receptors.

Option by option

A. Slow renal excretion of unchanged drug
Renal excretion of unchanged drug is not a significant route and is far too slow.
B. Hepatic glucuronidation
Glucuronidation is a slow hepatic process and is not how adenosine is cleared.
C. Binding to plasma proteins with release over minutes
Binding to plasma proteins would prolong rather than shorten its action.
D. Uptake into red cells and endothelium with deamination to inosine (correct)
Correct. Cellular uptake and deamination to inosine clear adenosine within seconds.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Uptake into red cells and endothelium with deamination to inosine. Adenosine is taken up rapidly by erythrocytes and vascular endothelium and is deaminated by adenosine deaminase to inosine, which is inactive at the receptor.

Why is "Slow renal excretion of unchanged drug" not the answer?

Renal excretion of unchanged drug is not a significant route and is far too slow.

Why is "Hepatic glucuronidation" not the answer?

Glucuronidation is a slow hepatic process and is not how adenosine is cleared.

Why is "Binding to plasma proteins with release over minutes" not the answer?

Binding to plasma proteins would prolong rather than shorten its action.

What concept does this question test?

It tests Nucleotide metabolism: duration of adenosine action in Biochemistry. The half-life is under ten seconds. Dipyridamole prolongs its effect by blocking uptake, and theophylline antagonises it at receptors.

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 Nucleotide metabolism: duration of adenosine action?

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.