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1Medizinische Klinik Innenstadt, Ludwig-Maximilians-Universität München, Germany.
Thyroidology
|December 1, 1990
Summary
Thyroid growth is regulated by local growth factors like IGF-I and EGF, not TSH. High iodine levels inhibit proliferation, suggesting organified iodine products play a role in thyroid regulation.
Area of Science:
- Endocrinology
- Cell Biology
- Thyroid Research
Background:
- Thyroid growth regulation is complex, involving various factors.
- Understanding paracrine communication between thyroid cells, endothelial cells, and fibroblasts is crucial.
Purpose of the Study:
- To investigate the direct effects of TSH, EGF, IGF-I, and iodine on porcine thyroid follicle growth.
- To examine the paracrine interactions between thyroid follicles and surrounding cells.
Main Methods:
- Utilized an ex vivo system of isolated porcine thyroid follicles.
- Assessed the dose-dependent effects of growth factors and iodine on cell proliferation.
- Investigated the role of iodide organification using PTU and MMI inhibitors.
Main Results:
- IGF-I and EGF dose-dependently stimulated thyroid cell proliferation.
- TSH did not affect thyroid cell growth when iodine levels were normal.
- High iodine concentrations inhibited EGF, IGF-I, and FCS-induced proliferation.
- Organified iodine products were responsible for the growth inhibitory effect of iodide.
- Thyroid follicles secreted a FGF-like substance affecting fibroblasts and endothelial cells.
- TSH stimulation decreased FGF secretion, while EGF enhanced it.
- Iodide pretreatment abolished the growth-promoting effect of conditioned medium.
Conclusions:
- Local growth factors (IGF-I, EGF) drive thyroid cell proliferation.
- TSH primarily stimulates specific thyroid cell function and hypertrophy.
- Organified iodine compounds act as growth inhibitors for thyroid cells.
- Thyroid follicles modulate the growth of associated endothelial cells and fibroblasts via secreted factors.