Maternal-Fetal Endocrine Interrelations: Effects of Synthetic Thyrotrophin Releasing Hormone (TRH) on the Fetal Pituitary-Thyroid System of the Rat

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Abstract
The capacity of the fetal pituitary-thyroid system to respond to synthetic TRH (pyroGlu-His-ProNH2) was tested by administration of the hypothalamic hormone on the last day of gestation to intact and hypophysectomized pregnant rats whose thyroids were labeled with 131I 24 h previously. Significant decrease in the ratios of thyroid-blood radioactivity occurred in newborn of TRH-treated mothers. Consistent reduction (30–70 %) in thyroidal 131I uptake and increase in blood radioactivity (12–60%) were observed. Bioassays (stasis tadpole) revealed significant elevation in plasma TSH levels and reduced hormone content of the pituitary in pups of mothers receiving TRH. In utero injections of the hypothalamic hormone into fetuses produced a similar pattern of TSH change within 15 min. Sufficient TSH release occurred to induce histologic activation in the thyroids of spontaneously delivered offspring. The effect of TRH on TSH release by the fetal hypophysis appeared to be specific. No indication of any substantial influence on maternal and fetal pituitary-adrenal system was observed.

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