Which of the Following is Most Apt to Cause a (+)Inotropic

Question

Which of the following is most apt to cause a (+)inotropic effect?
A) Activation of the alpha1-adrenergic receptors by ACh
B) Activation of the muscarinic receptors by NE
C) Blockade of alpha1-adrenergic receptors
D) Use of a beta1-adrenergic agonist

Accepted Answer

Use of a beta1-adrenergic agonist is most likely to cause a (+) inotropic effect as beta1 receptors are located on the myocardium and their activation increases intracellular cyclic AMP, leading to increased contractility. Activation of alpha1-adrenergic receptors (option A) also results in a (+) inotropic effect, but it is unlikely to be caused by ACh as activation of muscarinic receptors (option B) by ACh results in the opposite effect. Blockade of alpha1-adrenergic receptors (option C) would result in a (-) inotropic effect.