Theophylline produces bronchodilation in asthma partly by prolonging the intracellular action of beta-2 adrenergic stimulation in airway smooth muscle. The molecular basis of this interaction is inhibition of:

• A Adenylate cyclase
• B Phosphodiesterase, slowing cAMP degradation ✓
• C Protein kinase A
• D Gs alpha GTPase activity

Explanation

Methylxanthines such as theophylline and caffeine are competitive inhibitors of cyclic nucleotide phosphodiesterases, the enzymes that hydrolyze cAMP to 5'-AMP. By blocking cAMP breakdown, they amplify and prolong PKA-mediated bronchial smooth muscle relaxation achieved by beta-2 agonists. Adenylate cyclase and PKA are unaffected, so options A and C are wrong, and methylxanthines do not touch the intrinsic GTPase of Gs alpha, which is how option D would work if true.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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