A patient in cardiogenic shock with low cardiac output despite dobutamine is given an agent that increases contractility without acting on beta receptors. Which mechanism does this agent share with the vasodilating bronchodilator theophylline?

• A Stimulation of adenylate cyclase through Gs coupling
• B Inhibition of cyclic AMP degradation by phosphodiesterase inhibition ✓
• C Inhibition of the sodium potassium ATPase pump
• D Opening of ATP dependent potassium channels

Explanation

Milrinone is a selective phosphodiesterase 3 inhibitor that prevents breakdown of cAMP in cardiac myocytes, raising intracellular calcium and improving contractility while also relaxing vascular smooth muscle, so it is called an inodilator. The same enzyme family is inhibited by theophylline in airway smooth muscle. Dobutamine acts upstream through beta 1 receptor stimulation of adenylate cyclase, and digoxin inhibits Na K ATPase, so both mechanisms differ from milrinone's site of action.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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