Thyrotropin-Stimulated DNA Synthesis and Thyroglobulin Expression in Normal and Hyperthyroid Feline Thyrocytes in Monolayer Culture

Feline hyperthyroidism is a common, spontaneous disease in older cats that is similar clinically and histopathologically to human toxic multinodular goiter (TNG). In this study, the functional response of feline normal thyroid (NT) and hyperthyroid (HT) cells grown in monolayer culture to thyrotropin (TSH) was determined. Basal levels of DNA synthesis were similar in NT and HT cells. TSH stimulated concentrationdependent DNA synthesis in NT and HT cells, with maximal stimulation seen at 1 and 10 mU/mL TSH in NT and HT cells, respectively. HT cells had higher basal levels of thyroglobulin (Tg) expression. TSH stimulated Tg expression in NT and HT cells in a concentration-dependent fashion, with maximal activity at 0.5 and 5 mU/mL TSH, respectively. These results demonstrate that NT and HT cells in monolayer culture exhibit growth and functional responses to TSH. HT cells have higher basal Tg expression than NT cells and require higher TSH concentrations to stimulate DNA synthesis and Tg expression, two measures of thyroid cell activation. These data support the idea that feline hyperthyroidism is caused by cell abnormalities, resulting in dysregulated growth and hormone synthesis, and emphasize its importance as an animal model for TNG.