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Excess iodide and thyroid function in the developing chick embryo
N Daugeras-Bernard1, B A Demeneix, F Lachiver
1Laboratoire de Physiologie Générale et Comparée, Muséum National d'Histoire Naturelle, Unité d'Endocrinologie Comparée associée au CNRS, Paris, France.
General and Comparative Endocrinology
|January 1, 1993
Summary
Excess iodide in egg yolks increases embryonic plasma iodine and thyroid iodine early in development. Later, thyroid hormone levels remain stable despite goiter formation in chick embryos.
Area of Science:
- Embryology
- Endocrinology
- Developmental Biology
Background:
- Thyroid hormone is crucial for embryonic development.
- Iodide is an essential component of thyroid hormones.
- Understanding iodide transfer and thyroid regulation in ovo is important.
Purpose of the Study:
- To investigate the impact of excess iodide on chick embryo development.
- To quantify iodide transfer to the embryo and its effect on thyroid function.
- To examine thyroid hormone regulation during critical developmental stages.
Main Methods:
- In ovo injection of excess iodide (0.5 or 1 mg) into egg yolks on day 2 of incubation.
- Measurement of embryonic plasma and allantoic fluid iodine levels from day 8 to 18.
- Analysis of embryonic thyroid iodine content, weight, and iodo-amino acid distribution.
- Assessment of thyroid hormone levels in circulating plasma.
Main Results:
- Embryonic plasma and allantoic fluid iodine levels increased significantly and dose-dependently.
- Early in development (up to day 10), thyroid iodine content correlated with plasma iodine.
- After day 10, thyroid iodine increase slowed despite continued high plasma iodine, with similar thyroid iodine concentrations but doubled thyroid weight.
- Iodide excess did not impair iodine organification or alter iodo-amino acid profiles.
- Circulating thyroid hormone levels remained unchanged in treated embryos despite goiter formation.
Conclusions:
- Excess iodide is efficiently transferred to the chick embryo, increasing plasma and thyroid iodine levels early in development.
- The developing hypothalamo-adenohypophyseal-thyroid axis modulates iodide uptake and processing, preventing excessive thyroid hormone accumulation.
- Embryonic thyroids can accommodate increased iodide levels without compromising hormone synthesis or release, indicating robust regulatory mechanisms.