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Multiphasic thyrotropin responses to thyroid hormone administration in man
C A Spencer1, J S LoPresti, J T Nicoloff
1Department of Medicine, University of Southern California, School of Medicine, Los Angeles 90033.
The Journal of Clinical Endocrinology and Metabolism
|March 1, 1995
Summary
Thyroid hormone (T3, T4) suppression of thyroid-stimulating hormone (TSH) occurs in three distinct phases, independent of thyroid status. This biphasic process, involving inhibition of TSH release and synthesis, has implications for thyroid disease treatment.
Area of Science:
- Endocrinology
- Thyroid Physiology
- Hormone Action
Background:
- Thyroid-stimulating hormone (TSH) regulates thyroid hormone production.
- Understanding TSH suppression dynamics is crucial for managing thyroid disorders and hormone therapy.
Purpose of the Study:
- To investigate the temporal patterns and magnitude of serum TSH suppression following thyroid hormone administration.
- To characterize the phases of TSH suppression and their independence from thyroid status.
Main Methods:
- Utilized third and fourth generation TSH assays with high sensitivity.
- Administered single or multiple doses of thyroid hormone analogs (T3, T4, triiodothyroacetic acid) intravenously.
- Analyzed serum TSH levels over time in euthyroid and hypothyroid subjects.
Main Results:
- Identified three distinct phases of TSH suppression: rapid (1-20h), slower (10-20h to 6-8 weeks), and a chronic low level phase.
- TSH suppression patterns were similar in euthyroid and hypothyroid individuals, independent of basal T3 levels.
- Phase 1 suppression varied with administration time, while Phase 2 remained consistent.
Conclusions:
- Thyroid hormone suppression of TSH is a complex, reproducible, biphasic process.
- Phase 1 likely involves inhibition of TSH release, Phase 2 inhibition of synthesis/storage.
- Findings are relevant to thyroid hormone-suppressive therapy for benign and neoplastic thyroid diseases.
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