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Maturation of pituitary-thyroid function in the anencephalic fetus
P Beck-Peccoz1, D Cortelazzi, L Persani
1Institute of Endocrine Sciences, Ospedale Maggiore IRCCS, University of Milan, Italy.
Acta Medica Austriaca
|January 1, 1992
Summary
The fetal hypothalamic-pituitary-thyroid axis matures independently of the hypothalamus. Fetal thyroid hormones and thyrotropin (TSH) show increased bioactivity and altered structure during development.
Area of Science:
- Endocrinology
- Developmental Biology
- Neuroendocrinology
Background:
- The maturation of the hypothalamic-pituitary-thyroid (HPT) axis is crucial for fetal development.
- Recent advancements in assay technology allow for detailed study of fetal HPT axis components.
Purpose of the Study:
- To investigate the maturation of the HPT axis in human fetuses (17-26 weeks gestation).
- To compare HPT axis development in normal and anencephalic fetuses.
- To analyze TSH bioactivity and carbohydrate structure during fetal development.
Main Methods:
- Cordocentesis for blood sampling.
- Ultrasensitive immunometric assays for TSH and its subunits.
- Direct assays for free thyroid hormones (FT4, FT3).
- TSH bioactivity measurement using cAMP accumulation in CHO cells.
- Lectin chromatography for TSH carbohydrate structure analysis.
Main Results:
- Circulating TSH and FT4 levels significantly increased from 17 to 26 weeks gestation in both normal and anencephalic fetuses.
- FT3 and alpha-subunit (alpha-SU) levels remained low and unchanged, with no difference between groups.
- Fetal TSH exhibited enhanced bioactivity and altered glycosylation compared to adult TSH.
Conclusions:
- The absence of the hypothalamus does not impede the maturation of pituitary-thyroid function.
- Mechanisms for secreting TSH with elevated bioactivity and altered glycosylation are independent of hypothalamic control.