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Changes in serum thyrotropin (TSH) in man during halofenate administration
The Journal of Clinical Endocrinology and Metabolism
|October 1, 1976
Summary
Halofenate increases thyroid hormone fractions, lowering TSH in hypothyroid patients. This suggests the pituitary-thyroid feedback responds to changes in free thyroid hormone fractions, not just absolute levels.
Area of Science:
- Endocrinology
- Pharmacology
Background:
- Thyroid hormone regulation involves complex feedback mechanisms.
- Thyroxine-binding globulin (TBG) influences thyroid hormone availability.
- Hypothyroidism often results from inadequate thyroxine (T4) replacement therapy.
Purpose of the Study:
- To investigate the effect of halofenate on thyroid hormone levels and TSH in hypothyroid patients.
- To explore the relationship between free thyroid hormone fractions and TSH response.
- To challenge the "free hormone hypothesis" in the context of TSH regulation.
Main Methods:
- Administration of halofenate to 8 hypothyroid subjects for 14 days.
- Measurement of serum dialyzable fraction T4 (DFT4) and T3 (DFT3).
- Monitoring of serum TSH, absolute free T4 (AFT4), and absolute free T3 (AFT3) concentrations.
Main Results:
- Halofenate significantly increased DFT4 and DFT3 in 7 out of 8 subjects.
- Serum TSH concentrations decreased significantly in parallel with increased DFT4 and DFT3.
- TSH changes correlated more strongly with DFT4/DFT3 than with AFT4/AFT3.
Conclusions:
- The pituitary-thyroid feedback appears sensitive to changes in the free fractions of circulating thyroid hormones (DFT4, DFT3).
- This response can occur independently of detectable changes in absolute free hormone concentrations (AFT4, AFT3).
- Halofenate's effect on TSH regulation may differ from predictions based solely on the free hormone hypothesis.