Abstract
Abstract The aim of our study was to investigate if the thyroid axis of newborn calves is affected by prenatal application of propylthyouracil (PTU). The study included 20 late pregnant Holstein cows. One group (n=10) was treated with PTU (4 mg/kg of BW daily) from day 20 before expected calving until the day of calving. The other group (n=10) was non-treated. Placental samples of dams were obtained for measuring mRNA expression of iodothyronine deiodinases type I (D1), type II (D2) and type III (D3). After parturition calves were separated from the dams and included in the study. Blood samples were taken daily from each calf starting on the day of birth until day 7 of age. Blood T3, T4 and TSH concentrations were measured. PCR analysis of the placental tissue revealed an abundance of all three types of placental deiodinases in non-treated cows, and a significant elevation of mRNA levels for all three types of deiodinases after PTU treatment. Calves that originated from dams treated with PTU had significantly lower T3 and T4 and significantly higher TSH concentrations compared to non-treated calves during the first 2 days of life. Starting from day 4 until day 6 of life the opposite effect was observed meaning that calves prenatally exposed to PTU had significantly higher T3 and T4 and slightly lower TSH. Our study, for the first time, provides information related to iodothyronine deiodinases mRNA expression in bovine placenta, and confirm that PTU treatment of pregnant dams provokes depression of thyroid function in newborns during the first days of life.
Highlights
Thyroid hormones (THs), that include thyroxine (T4) and triiodothyronine (T3), are crucial regulators of growth and development of fetal and neonatal calves [1]
MRNA level of D3, which is an enzyme involved in the inactivation of thyroid hormones, was significantly elevated in placental samples of dams treated with PTU (Figure 3, **p
PTU treatment during late pregnancy had a significant impact on the thyroid axis in newborn calves
Summary
Thyroid hormones (THs), that include thyroxine (T4) and triiodothyronine (T3), are crucial regulators of growth and development of fetal and neonatal calves [1]. Their secretion is under regulation of the hypothalamic-pituitary-thyroid axis that is active during both prenatal and postnatal life [2]. Davicco and coworkers (1982) [12] showed that THs secretion stimulated by TSH results in significantly higher plasma THs concentrations in 21 days old than in 3 hours old calves, indicating on lower receptor abundance for TSH during the early postnatal period. Authors concluded that fetal thyroid axis is essential in providing sufficient amounts of THs for early postnatal development [12]. It is well known that the degree of maturation of the thyroid axis at birth is essential for an adequate response of the newborn to environmental conditions immediately after birth [1,13]
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