A 60-year-old man takes a non-selective beta-blocker for hypertension. During insulin-induced hypoglycemia, which sympathetic adrenergic symptom will be MOST effectively suppressed by his medication?
- A Sweating
- B Tachycardia ✓
- C Tremor
- D Hunger
Correct answer: B. Tachycardia
Explanation
During hypoglycemia, sympathetic activation produces tachycardia (β1), tremor (β2 on skeletal muscle), sweating (cholinergic sympathetic), hunger (central), and palpitations. Non-selective beta-blockers suppress the beta-1-mediated tachycardia and the beta-2-mediated tremor and glycogenolysis. However, sweating is mediated by cholinergic sympathetic fibres (muscarinic M3 receptors on sweat glands) and is not blocked by beta-blockers — it may actually be enhanced. Sweating thus becomes the most reliable warning symptom in patients on beta-blockers.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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