Figure 1.

Design of animal experiments to study thyroid hormone treatment and withdrawal and corresponding thyroid function test measurements during the study. A, Schematic of animal experiments. Adult male mice (8–10 wk old) were treated with 20 μg liothyronine (L-T₃) per 100 g body weight for 1 day or 14 days followed by cessation of L-T₃ for 10 days. Mice were killed at each of the indicated time points. Arrowheads represent L-T₃ injections and arrows represent the time points of the animals were killed and tissue collection. B–D, Measurements of serum thyroid hormone and TSH levels during the study described above. Serum total T₃ (B), total T₄ (C), and TSH (D) concentrations were determined at indicated T₃-treatment periods after the first and the last L-T₃ injection. No treatment (blank); acute T₃ treatment (black); chronic T₃ treatment (hashed); early T₃ withdrawal (hashed); T₃ withdrawal (striped) are shown. Note that the same data points were used for the chronic T₃ treatment and early T₃ withdrawal groups (hashed). The limits of detection were 0.25 μg/dL for serum total T₄ and 10 mU/L for TSH. Data are presented as means ± SEM (n = 4–5/group). *, P < .05, **, P < .01, ***, P < .001, compared with nontreated mice (0 d) by one-way ANOVA.