Evaluation of thyroid gland activity by hormone assays and flow cytometry in rats

Spontaneous variations in the activity of thyroids and changes induced by methimazole, phenobarbital and 2,4--diaminoanisole sulfate were assessed in rats by repeated measurements of serum T3, T4 and TSH concentrations and cell cycle analysis in isolated nuclei of the thyroids. Methimazole caused a decrease in T3 and T4, and elevation in TSH, reduction of cells in G1 and increase in the percentage of cells in S and G2 phases. With phenobarbital T4 concentrations were decreased, but a mitogenic effect was only seen after 8 weeks. With 2,4-diaminoanisole sulfate the most prominent change observed was a decrease in T3 concentrations.