Chekoff, a young intern working in the lab of Jan Wolff at the NIH in the mid 60
ID: 3518390 • Letter: C
Question
Chekoff, a young intern working in the lab of Jan Wolff at the NIH in the mid 60's, found that high circulating levels of iodine have a paradoxical effect on thyroid function: it blocks thyroid hormone synthesis and release (this is now called the Chekoff-Wolff effect). This is important clinically because many antiseptics are iodine-based (e.g., betadine). It is still not uncommon that post-surgical treatment includes frequent and liberal application of these antiseptics for extended duration (this is especially problematic in infants).
What measurements would you make to determine that such a patient has reduced thyroid hormone levels in serum?
What measurements would you make to determine that the problem is with the thyroid gland? (explain your reasoning)
Describe what happens to thyroid hormones once they leave the thyroid gland, including how they act on target cells.
Explanation / Answer
What measurements would you make to determine that such a patient has reduced thyroid hormone levels in serum?
Answer: Free T3(Tri-iodo thyronine), Free T4(Thyroxine)
What measurements would you make to determine that the problem is with the thyroid gland? (explain your reasoning)
Answer: TSH (Thyroid Stimulating Hormone)
If TSH is reduced, the cause is either in pituitary or hypothalamus.
If TSH is normal or increased, the cause is in thyroid.
Describe what happens to thyroid hormones once they leave the thyroid gland, including how they act on target cells.
Answer: Thyroid hormones enter cells and T3 binds to Thyroid Receptor in the nuclei. T4 can also bind, but not as avidly. In most of its actions, T3 acts more rapidly and is three to five times more potent than T4. T3 is less tightly bound to plasma proteins than is T4, but binds more avidly to thyroid hormone receptors.
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