Autonomic Nervous System Pharmacology Flashcards

A patient with pheochromocytoma requires surgical removal. Which alpha-blocker is used preoperatively to prevent hypertensive crisis?

Answer: Phenoxybenzamine

Phenoxybenzamine is a non-selective, irreversible alpha-blocker used preoperatively in pheochromocytoma to prevent catecholamine-induced hypertensive crises.

Which muscarinic receptor subtype is primarily responsible for the decrease in heart rate caused by vagal stimulation?

Answer: M2

M2 receptors in the sinoatrial node mediate the negative chronotropic effect of acetylcholine released by vagal stimulation.

Bethanechol is used to treat postoperative urinary retention. What is its mechanism of action?

Answer: Directly stimulates muscarinic receptors

Bethanechol is a direct-acting muscarinic agonist that stimulates bladder detrusor contraction without significant nicotinic activity.

A patient takes a non-selective beta-blocker and later uses an epinephrine auto-injector. Which cardiovascular effect is most likely?

Answer: Severe hypertension with bradycardia

With beta-blockade, epinephrine's alpha-1 vasopressor effect is unopposed, causing severe hypertension; the reflex bradycardia is enhanced by beta-blockade.

Which drug causes mydriasis and cycloplegia by blocking muscarinic receptors in the eye?

Answer: Atropine

Atropine blocks M3 receptors on the iris sphincter and ciliary muscle, causing pupil dilation (mydriasis) and loss of accommodation (cycloplegia).

Guanethidine lowers blood pressure by which mechanism?

Answer: Depleting norepinephrine from sympathetic nerve terminals

Guanethidine is taken up into adrenergic neurons and depletes norepinephrine stores, preventing sympathetic vasoconstriction.

Which beta-2 agonist is used as a tocolytic to suppress premature uterine contractions?

Answer: Ritodrine

Ritodrine is a selective beta-2 agonist that relaxes uterine smooth muscle and is used as a tocolytic agent.