Question

Mechanism of action of theophylline in bronchial asthma includes all of the following except:

• A. Phosphodiesterase inhibition
• B. Adenosine receptor antagonism
• C. Increased histone deacetylation
• D. Beta-2 receptor stimulation

Hint:

Three are real xanthine actions; one belongs to direct beta-2 agonists.

Answer 1

The Correct Option is D

Step 1: List the established mechanisms of theophylline, a methylxanthine. It inhibits phosphodiesterase, raising intracellular cyclic AMP and producing bronchodilation. It antagonizes adenosine (A1 and A2) receptors, blocking adenosine-induced bronchoconstriction. At low doses it activates histone deacetylase, which increases histone deacetylation and reduces transcription of inflammatory genes, giving an anti-inflammatory and corticosteroid-enhancing effect.
Step 2: Examine the option that does not fit. Theophylline does not act by stimulating beta-2 adrenergic receptors. Beta-2 stimulation is the mechanism of beta-2 agonists like salbutamol, which act on the receptor directly. Theophylline works downstream and through adenosine and PDE pathways, not by binding beta-2 receptors.
Step 3: Confirm the other three are correct mechanisms, so they cannot be the exception. Phosphodiesterase inhibition, adenosine receptor antagonism, and increased histone deacetylation are all genuine theophylline actions.
Step 4: Because the question asks for the exception, the action that is not part of theophylline's mechanism is beta-2 receptor stimulation (option D).