John Wiley & Sons, Ltd.

Sex‐specific changes in thyroid gland function and circulating thyroid hormones in nestling American kestrels (Falco sparverius) following embryonic exposure to PBDEs by maternal transfer

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High concentrations of polybrominated diphenyl ethers (PBDEs) accumulate in predatory birds. Several PBDE congeners are considered thyroid disruptors however avian studies are limited. Here, we examined circulating thyroid hormones, thyroid gland function of nestling American kestrels (Falco sparverius) at 17‐20 d of age, following embryonic exposure by maternal transfer only to environmentally relevant levels of PBDEs (DE‐71 technical mixture). Nestlings were exposed to in ovo sum (Σ) PBDE concentrations of 11,301 ± 95 ng/g ww (high exposure), 289 ± 33 ng/g ww (low exposure), or 3.0 ± 0.5 ng/g ww (controls; background exposure). Statistical comparisons are made to controls of respective sexes and account for the relatedness of siblings within broods. Circulating concentrations of plasma total thyroxine (TT4) and triiodothyronine (TT3) in female nestlings were significantly influenced overall by the exposure to DE‐71. Following the intra‐muscular administration of thyroid stimulating hormone (TSH), the temporal response of the thyroid gland in producing and/or releasing TT4 was also significantly affected by the females' exposure to DE‐71. The altered availability of T4 for conversion to T3 outside of the gland, and/or changes in thyroid‐related enzymatic activity, may explain the lower TT3 concentrations (baseline, overall) and moderately altered temporal TT3 patterns (p = 0.06) of the treatment females. Controlling for the significant effect on TT3 levels of the delayed hatching of treatment females, baseline TT3 levels were significantly and positively correlated with body mass (10, 15, 20 d), with PBDE‐exposed females generally being smaller and having lower TT3 concentrations. Given that exposure concentrations were environmentally relevant, similar thyroidal changes and associated thyroid‐mediated processes relating to growth, may also occur in wild female nestlings. This article is protected by copyright. All rights reserved

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