Ovine thyroid stimulating hormone (TSH) heterologously stimulates production of thyroid hormones from Chinese soft-shell turtle (Pelodiscus sinensis) and bullfrog (Rana catesbeiana and Rana rugulosa) thyroids in vitro

Thyroid hormones are important for regulating a variety of developmental processes in vertebrates, including growth, differentiation, metamorphosis, and oxidative metabolism. In particular, this study focused on the in vitro production of thyroxine (T4) and triiodothyronine (T3) from thyroids in American bullfrogs (Rana catesbeiana), Chinese bullfrogs (Rana rugulosa Wiegmann), and Chinese soft-shell turtles (Pelodiscus sinensis) treated with ovine thyroid stimulating hormone (TSH) at different culture intervals (2, 4, 8, and 12 h) and dosages (1, 10, 50 or 100 ng). The levels of T4 and T3 in the tested animals were elevated upon stimulation in a time- and dose-dependent manner, indicating de novo synthesis of T4 and T3. Significantly higher hormone levels were observed in the Chinese bullfrog compared to the other two species, for both the time–course and dose–response experiments. Although the bullfrog secreted significantly higher levels of T4 and T3, a higher T4-conversion capacity was found in the Chinese soft-shell turtle. The highest ratios of T3 to T4 were observed in the American bullfrog and Chinese soft-shell turtle for the time–course and dose–response experiments, respectively. These findings suggest that the Chinese soft-shell turtle and bullfrog thyroids can accept ovine TSH for T4- and T3-formation in a time- and dose-dependent manner, supporting the hypothesis that the binding interactions between TSHs and thyroidal receptors are conserved in vertebrates.