How thyroid medicine affects hormone signals
Interrelationships in the regulation of TSH and prolactin secretion in man: effects of L-dopa, TRH and thyroid hormone in various combinations.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When people take thyroid hormone pills, their body stops responding as strongly to a signal (TRH) that normally tells the thyroid to make more hormone, but it still responds normally to signals that make prolactin.
Surprising Findings
TSH response to TRH was blunted during thyroid hormone replacement, but prolactin response remained unchanged.
It's counterintuitive that two hormones released by the same pituitary cell respond so differently to the same stimulus—suggesting highly specific, independent regulation.
Practical Takeaways
If you're on thyroid hormone replacement, don't assume your TSH level reflects your body's full hormonal activity—prolactin responses may still be normal.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When people take thyroid hormone pills, their body stops responding as strongly to a signal (TRH) that normally tells the thyroid to make more hormone, but it still responds normally to signals that make prolactin.
Surprising Findings
TSH response to TRH was blunted during thyroid hormone replacement, but prolactin response remained unchanged.
It's counterintuitive that two hormones released by the same pituitary cell respond so differently to the same stimulus—suggesting highly specific, independent regulation.
Practical Takeaways
If you're on thyroid hormone replacement, don't assume your TSH level reflects your body's full hormonal activity—prolactin responses may still be normal.
Publication
Journal
The Journal of clinical endocrinology and metabolism
Year
1974
Authors
S. Refetoff, V. Fang, B. Rapoport, H. Friesen
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Claims (3)
When thyroid hormone levels in the blood are high, the pituitary gland reduces production of thyroid-stimulating hormone. When thyroid-stimulating hormone levels are low, the thyroid gland produces thyroid hormones without normal regulatory control.
In people with normal thyroid function, taking L-dopa does not result in a detectable change in thyroid-stimulating hormone levels because any changes are too small to be measured by standard tests.
In people taking thyroid hormone medication who have normal thyroid function, the pituitary gland releases less TSH in response to TRH, but releases the same amount of prolactin as before, indicating that the two hormones are regulated differently during hormone replacement.