Exam 2 - Alpha/Beta Antagonists

Question 1

Describe and compare the effects of an α blocker on the blood pressure and heart rate.

Answer 1

α blockers cause vasodilation by blocking α1 receptors on vascular smooth muscle, leading to a decrease in blood pressure. Reflexively, this can cause a compensatory increase in heart rate (reflex tachycardia) due to baroreceptor activation​

Question 2

List the alpha and beta blockers described in class, and their clinical uses.

Answer 2

α blockers: Prazosin: Used for hypertension and benign prostatic hyperplasia (BPH).
Phentolamine: Used for pheochromocytoma and to reverse vasoconstriction.

β blockers: Propranolol (non-selective): Used for hypertension, arrhythmias, and angina.
Metoprolol (β1 selective): Used for heart failure, hypertension, and arrhythmias

Question 3

Differentiate the effects of a blocker in the presence or absence of an agonist.

Answer 3

In the PRESENCE of an agonist (like epinephrine), α blockers prevent vasoconstriction, reducing blood pressure.

In the ABSENCE of an agonist, α blockers primarily cause baseline vasodilation, but their effect on BP is less pronounced since no vasoconstrictive stimuli are present​

Question 4

Explain the following sentence: Phentolamine converts a pressor (epinephrine) into a depressor.

Answer 4

Phentolamine blocks α receptors, preventing the vasoconstrictive effects of epinephrine (a pressor). With α receptors blocked, epinephrine’s β2-mediated vasodilation dominates, causing a drop in blood pressure (depressor effect)​

Question 4

Define the difference between selective and non-selective beta-blockers.

Answer 4

Selective: Target only β1 receptors (e.g., metoprolol), affecting primarily the heart (lowering heart rate and contractility).

Non-selective: Block both β1 and β2 receptors (e.g., propranolol), affecting the heart as well as the lungs and vascular smooth muscle (potential for bronchoconstriction)​

Question 5

Describe the clinical indications and toxicities of typical α and β blockers

Answer 5

α Blockers:
Indications: Hypertension, BPH.
Toxicities: Orthostatic hypotension, reflex tachycardia.

β Blockers:
Indications: Hypertension, arrhythmias, heart failure, angina.
Toxicities: Bradycardia, bronchoconstriction (non-selective), fatigue​