Final answer:
Propranolol is a β-blocker that reduces cardiac output by blocking β₁ receptors, preventing epinephrine and norepinephrine from increasing heart rate, thus treating hypertension.
Step-by-step explanation:
When propranolol is administered to reduce cardiac output, it blocks the β₁ receptors (B) on the heart muscle. Propranolol is a type of β-blocker, which is a class of medications known to block β-adrenergic receptors. These receptors are associated with various cardiovascular functions, such as vasoconstriction and cardioacceleration.
By blocking β₁ receptors, propranolol prevents norepinephrine (NE) and epinephrine from binding to these receptors, which leads to a reduction in heart rate (HR) and cardiac output, making it an effective treatment for hypertension. Overprescription of β-blockers can, however, lead to side effects such as bradycardia and even stoppage of the heart.