Propanol inhibits peripheral deidinasse
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propanol inhibition peripheral deiodinase thyroid hormone conversion
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propylthiouracil PTU deiodinase type 1 T4 to T3 conversion inhibition
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Your statement is correct in principle, but the drug names need clarification:
Propranolol and Peripheral Deiodinase Inhibition
You are likely referring to two drugs that are commonly grouped together in this context:
- Propylthiouracil (PTU) — a thionamide antithyroid drug
- Propranolol — a non-selective beta-blocker
Both inhibit peripheral T₄ → T₃ conversion by inhibiting Type I deiodinase (located primarily in the thyroid, liver, and kidneys).
Deiodinase Types (Harrison's, p. 10681)
| Type | Location | Function |
|---|---|---|
| Type I | Thyroid, liver, kidneys | Converts T₄ → T₃ (low affinity for T₄) |
| Type II | Pituitary, brain, brown fat, thyroid | Converts T₄ → T₃ locally (high affinity); induced in hypothyroidism |
| Type III | Placenta | Inactivates T₄ and T₃; major source of reverse T₃ (rT₃) |
Drugs That Impair Peripheral T₄ → T₃ Conversion
According to Harrison's, the following impair T₄ → T₃ conversion via deiodinase inhibition:
- Propylthiouracil (PTU) — most potent inhibitor; blocks Type I deiodinase
- Propranolol — inhibits peripheral conversion (Type I deiodinase)
- Amiodarone — structurally similar to thyroid hormone; inhibits both Type I and II
- Glucocorticoids — inhibit conversion peripherally
- Fasting, systemic illness, acute trauma, oral contrast agents — non-pharmacological causes
Clinical Relevance
This property makes PTU and propranolol preferred in the acute management of thyroid storm, where rapid reduction of active T₃ levels is critical. Unlike methimazole (which only blocks synthesis), PTU also blocks peripheral conversion — propranolol contributes the same peripheral effect while also controlling adrenergic symptoms.
Harrison's Principles of Internal Medicine, 21st Edition, p. 10681
Propanol inhibits peripheral deidinasse
Your statement is correct in principle, but the terminology needs clarification — the drug is propranolol (a beta-blocker), not "propanol" (which is simply an alcohol).
Similarly, the enzyme is deiodinase, not "deidinasse."
Key Point
Propranolol inhibits peripheral Type I deiodinase, thereby reducing the conversion of T₄ → T₃ in peripheral tissues (liver, kidneys).
This is the same mechanism shared by:
| Drug | Inhibits Synthesis? | Inhibits Peripheral T₄→T₃ Conversion? |
|---|---|---|
| Propylthiouracil (PTU) | Yes | Yes (most potent) |
| Propranolol | No | Yes |
| Amiodarone | No | Yes (Type I & II) |
| Glucocorticoids | No | Yes |
| Methimazole | Yes | No |
Clinical Use
Because propranolol blocks peripheral T₄ → T₃ conversion and controls sympathetic symptoms (tachycardia, tremor, anxiety), it is a cornerstone of thyroid storm management alongside PTU.
Source: Harrison's Principles of Internal Medicine, 21st Edition, p. 10681
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