Effect of Diabetes on Triiodothyronine and Reverse Triiodothyronine Production in the Perfused Rat Liver and Kidney

This study was undertaken to elucidate the effect of diabetes on the conversion of T 4 to T 3 and rT 3 in the isolated, perfused rat liver and kidney. The livers and kidneys from streptozocin (STZ)-induced (50 mg/kg i.p. 2 wk before killing) diabetic rats with or without T 4 (30 μg/kg s.c. daily) treatment were perfused for 30 min with a synthetic medium containing T 4 (6 μg/dl), and production of T 3 and rT 3 in the tissues was measured by radioimmunoassay. The production of T 3 (111 ± 38 ng/g/30 min, mean ± SD) and conversion rate of T 4 to T 3 (19.7 ± 5.8%) in the liver of diabetic rats without T 4 treatment and those (124 ± 41 ng/g/30 min and 21.6 ± 4.9%) in the liver of diabetic rats with T 4 treatment were significantly lower than those of controls (196 ± 48 ng/g/30 min and 30.6 ± 5.2%), respectively. The production of rT 3 and conversion rate of T 4 to rT 3 in the liver of diabetic rats with or without T 4 treatment were similar to those of controls. The production of T 3 and rT 3 , and conversion rate of T 4 to T 3 and T 4 to rT 3 , in the kidney of diabetic rats with or without T 4 treatment were not significantly different from those of controls. These results suggest that the liver is far more important than the kidney in the overall reduction in the T 4 to T 3 conversion that occurs in diabetic rats.