Hexamethonium is administered intravenously to a supine volunteer. Which set of cardiovascular changes is expected?

• A Tachycardia and hypertension due to unopposed sympathetic activity
• B No change, because hexamethonium acts only at the neuromuscular junction
• C Bradycardia and hypotension due to blockade of both divisions at the ganglia ✓
• D Bradycardia alone, because parasympathetic tone dominates at rest

Explanation

Hexamethonium blocks neuronal nicotinic receptors at all autonomic ganglia, interrupting both sympathetic and parasympathetic transmission. In a supine subject, loss of sympathetic vasomotor tone causes hypotension, and loss of the dominant resting vagal tone removes its braking effect, yet the net observed response includes impaired reflexes and reduced pressure support. It does not act at the somatic neuromuscular junction, where the nicotinic receptor subtype differs.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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