Amrinone functions as a phosphodiesterase III inhibitor, resulting in increased intracellular cAMP and what combined effect?

Amrinone functions as a phosphodiesterase III inhibitor, resulting in increased intracellular cAMP and what combined effect?

• A. Positive inotropy and vasodilation
• B. Negative inotropy and vasoconstriction
• C. Decreased heart rate with vasoconstriction
• D. No effect on contractility

Answer: (A)

Amrinone inhibits phosphodiesterase III, which raises intracellular cAMP in both heart muscle and vascular smooth muscle. In cardiac myocytes, more cAMP activates PKA, increasing calcium availability and enhancing contractility (positive inotropy). In vascular smooth muscle, the same cAMP/PKA signaling reduces calcium sensitivity and promotes relaxation, leading to vasodilation. The net effect is improved cardiac output with decreased afterload. So combining positive inotropy with vasodilation best fits the described action.

Amrinone inhibits phosphodiesterase III, which raises intracellular cAMP in both heart muscle and vascular smooth muscle. In cardiac myocytes, more cAMP activates PKA, increasing calcium availability and enhancing contractility (positive inotropy). In vascular smooth muscle, the same cAMP/PKA signaling reduces calcium sensitivity and promotes relaxation, leading to vasodilation. The net effect is improved cardiac output with decreased afterload. So combining positive inotropy with vasodilation best fits the described action.