Effect of thyroid hormone‐disrupting chemicals on swim bladder inflation and thyroid hormone‐related gene expression in Japanese medaka and zebrafish

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Abstract
We compared the influence of thyroid hormone‐disrupting chemicals (heptafluorobutanoic acid, PFBA and tris[1,3‐dichloro‐2‐propyl] phosphate, TDCPP) and thyroid hormone (3,3′,5‐triiodo‐L‐thyronine, T3) on swim bladder inflation and thyroid hormone‐related gene expression in Japanese medaka and zebrafish. The swim bladder of most larvae had inflated at 4 h post hatching (hph) in Japanese medaka and at 48 hph in zebrafish in controls. In both fish species, the swim bladder inflation was inhibited in larvae exposed to PFBA (lowest observed effect concentration [LOEC] in medaka: 40 mg/L; in zebrafish: 80 mg/L), TDCPP (LOEC in medaka: 1 mg/L; in zebrafish: 0.5 mg/L), and T3 (no inhibition in Japanese medaka; LOEC in zebrafish: 7.5 μg/L). We also examined the influence of PFBA, TDCPP, and T3 on the expression of thyroid stimulating hormone subunit beta (tshβ) or thyroid hormone receptor alpha (trα) and beta (trβ). No changes were observed in the expression of genes after PFBA and TDCPP exposure; however, T3 exposure upregulated trα and trβ expression in both fish species. When the results were compared between Japanese medaka and zebrafish, swim bladder inflation in both species was found to be inhibited by exposure to thyroid hormone‐disrupting chemicals. Our results show that inhibition of the swim bladder inflation at 4 hph in Japanese medaka and 48 hph in zebrafish is a potential indicator of thyroid hormone‐disturbing activity of chemicals.

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