Question

What is the predominant adrenoceptor in heart muscle?

• A. \( \alpha_1 \)-adrenoreceptor
• B. \( \alpha_2 \)-adrenoreceptor
• C. \( \beta_1 \)-adrenoreceptor
• D. \( \beta_2 \)-adrenoreceptor

Answer 1

The Correct Option is C

Step 1: Understanding Adrenoceptor Distribution in the Heart - The heart muscle is primarily regulated by \( \beta_1 \)-adrenoceptors, which are responsible for increasing heart rate (chronotropy), contractility (inotropy), and conduction velocity (dromotropy). - These receptors mediate the sympathetic nervous system response to catecholamines (adrenaline and noradrenaline).


Step 2: Evaluating the Given Options - \( \alpha_1 \)-adrenoreceptors (Option A): Primarily involved in vasoconstriction but not dominant in the heart.
- \( \alpha_2 \)-adrenoreceptors (Option B): Mainly found in presynaptic nerve terminals, where they inhibit neurotransmitter release.
- \( \beta_1 \)-adrenoreceptors (Option C): The correct answer, as they are the predominant receptors in the myocardium.
- \( \beta_2 \)-adrenoreceptors (Option D): Present in vascular and bronchial smooth muscles, responsible for vasodilation and bronchodilation.


Step 3: Selecting the Correct Answer - Since \( \beta_1 \)-adrenoreceptors are the major subtype in cardiac muscle, the correct choice is (C) \( \beta_1 \)-adrenoreceptor.