Endocrine effects of the plasticizer bisphenol A on thyroid and reproductive system during larval development of the South African clawed frog (Xenopus laevis)

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This study investigates the effects of the plasticizer bisphenol A (BPA) on the thyroid and reproductive systems during the larval development of Xenopus laevis using semistatic and flow-through exposure systems. BPA did not affect metamorphosis, with parameters such as completion time, developmental stage, body length, hind limb length, and TSHß-mRNA expression remaining unchanged after long-term exposure. However, body weight and length increased significantly at 10-8 M BPA in the flow-through system. Moderate anti-thyroidal effects were noted on TH-dependent gene expression after short-term exposure, with BPA inhibiting T3-induced mRNA expression for TRß and BTEB at various time points. The sex ratio in metamorphosed froglets was unaffected by BPA. Histological analysis revealed oogonia and lacunae in testes at the lowest BPA concentration of 10-9 M, indicating feminization. E2 and the highest BPA concentration of 10-6 M inhibited ARO-mRNA expression in the brain, while BPA uniquely inhibited FSHß-mRNA expression. LHß-mRNA levels remained unchanged across treatments. BPA significantly altered hepatic gene expression of VTG and IGF-1 in metamorphosed froglets, with 10-6 M BPA dramatically increasing VTG-mRNA in both sexes, while lower concentrations showed levels similar to controls. IGF-1-mRNA increased in males but not females, raising concerns about the low-dose effects on liver and gonads at environmentally relevant conc