Vasopressors & Inotropes Practice Test

What is the mechanism of action of T3 in the heart regarding adrenergic signaling and cAMP?

Independent of adrenergic receptors and cAMP Relies on adrenergic receptors and cAMP Requires calcium channel activation Inhibits Na-K ATPase

Correct Answer:

Independent of adrenergic receptors and cAMP

Explanation:

Thyroid hormone T3 boosts heart performance by increasing the heart’s responsiveness to catecholamines through the adrenergic signaling and cAMP pathway. It does this mainly by upregulating beta-1 adrenergic receptors and components of the cAMP-PKA cascade inside cardiac cells. When catecholamines bind these receptors, Gs activates adenylate cyclase, raising cAMP, which then activates PKA. PKA phosphorylates targets that enhance calcium handling (like L-type calcium channels and phospholamban/SERCA), leading to stronger contractions and faster heart rate. Because these effects depend on receptor signaling and the cAMP pathway, they are not independent of adrenergic receptors and cAMP.

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