Serum thyroid hormone levels and thyroid hormone metabolism by 10% liver homogenate from adult lean and obese (ob/ob) mice

While there was no difference in serum T₃ values between ob/ob mice and their lean littermates (64.2±9 vs 53.3±7 ng/dl, n=9), ob/ob mice had significantly decreased levels of serum rT₃ (19.8±7 vs 28.8±9 ng/dl, n=9, p<0.05). There was no difference in the ability to 5'-monodeiodinate ¹²⁵I-T₄ to form ¹²⁵I-T₃ (2.33±0.6 vs 2.06±0.3% mean ± SD, n=9) nor was there any difference in excess iodide production (iodide minus T₃ generated) (6.2±1.7 vs 5.5±2.1 mean % ± SD), a useful indicator of the 5-monodeiodinase pathway of ¹²⁵I-T₄ degradation. Reverse T₃ was degraded equally as well by liver homogenates from ob/ob and lean mice.