What is the primary action of phosphodiesterase inhibitors in the heart and vasculature?

What is the primary action of phosphodiesterase inhibitors in the heart and vasculature?

• A. Decrease cAMP and cGMP
• B. Inhibit calcium entry
• C. Increase cAMP and cGMP
• D. Block adrenergic receptors

Answer: (C)

Phosphodiesterase inhibitors work by preventing the breakdown of cyclic nucleotides, so they raise levels of cAMP and/or cGMP. In the heart, higher cAMP activates protein kinase A, boosting calcium cycling and contractility (positive inotropy) and also aiding relaxation through effects on calcium handling. In the vasculature, increased cAMP and cGMP promote smooth muscle relaxation, leading to vasodilation. That combination—raising cyclic nucleotide levels to enhance heart performance and dilate vessels—is why increasing cAMP and cGMP is the correct primary action. They do not directly decrease cyclic nucleotides, block calcium entry, or block adrenergic receptors.

Phosphodiesterase inhibitors work by preventing the breakdown of cyclic nucleotides, so they raise levels of cAMP and/or cGMP. In the heart, higher cAMP activates protein kinase A, boosting calcium cycling and contractility (positive inotropy) and also aiding relaxation through effects on calcium handling. In the vasculature, increased cAMP and cGMP promote smooth muscle relaxation, leading to vasodilation. That combination—raising cyclic nucleotide levels to enhance heart performance and dilate vessels—is why increasing cAMP and cGMP is the correct primary action. They do not directly decrease cyclic nucleotides, block calcium entry, or block adrenergic receptors.