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Thyroid hormone replacement restores circulating enkephalin concentrations in hypophysectomized fetal sheep
G Simonetta1, I R Young, I C McMillen
1Department of Physiology, Monash University, Clayton, Victoria, Australia.
Journal of Neurochemistry
|October 1, 1994
Summary
Fetal hypophysectomy (HX) in sheep reduces free methionine-enkephalin (free Met-Enk) levels. Thyroxine (T4) replacement partially restores these levels, indicating the fetal pituitary-thyroid axis regulates free Met-Enk.
Area of Science:
- Endocrinology
- Neuroscience
- Reproductive Biology
Background:
- The fetal pituitary gland plays a crucial role in development.
- Thyroid hormones influence fetal growth and metabolism.
- Methionine-enkephalin is an endogenous opioid peptide with various physiological roles.
Purpose of the Study:
- To investigate the impact of fetal hypophysectomy (HX) and thyroxine (T4) replacement on fetal plasma concentrations of free methionine-enkephalin (free Met-Enk), noradrenaline, and adrenaline.
- To elucidate the role of the fetal pituitary-thyroid axis in regulating these neurochemicals.
Main Methods:
- Fetal hypophysectomy (HX) was performed in late gestation sheep fetuses.
- Thyroxine (T4) or saline was administered to HX fetuses.
- Plasma concentrations of free Met-Enk, noradrenaline, and adrenaline were measured.
Main Results:
- Plasma adrenaline was lower in HX fetuses (with or without T4) compared to intact controls.
- Plasma free Met-Enk concentrations were significantly reduced in HX fetuses.
- T4 replacement partially restored free Met-Enk levels in HX fetuses.
- Intact fetuses and HX fetuses with T4 replacement showed higher free Met-Enk than HX fetuses with saline.
Conclusions:
- Fetal pituitary removal significantly decreases circulating free Met-Enk.
- The reduction in free Met-Enk following HX is largely due to functional athyroidism (thyroid deficiency).
- The fetal pituitary-thyroid axis is critical for maintaining normal free Met-Enk concentrations in late gestation.