Endocrine System MCAT Practice Question
A research team investigating thyroid regulation administers propranolol to a hyperthyroid patient. Within hours, the patient reports significant symptomatic improvement in tremor and palpitations, though serum T3 and T4 levels remain elevated. Which of the following best explains this clinical observation?
Answer choices
- APropranolol directly inhibits thyroid peroxidase, reducing thyroid hormone synthesis
- BPropranolol blocks beta-adrenergic receptors, reducing peripheral manifestations of excess thyroid hormone without affecting hormone levelsCorrect answer
- CPropranolol increases hepatic metabolism of thyroid hormones, lowering bioavailable T3 and T4
- DPropranolol stimulates TSH secretion, suppressing thyroid hormone production through negative feedback
- EPropranolol inhibits peripheral conversion of T4 to the more active T3 form
- FPropranolol inhibits the nuclear thyroid hormone receptors, preventing cellular effects of excess thyroid hormone despite elevated serum levels
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