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 T4 to T3 and rT3 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 T4 (30 micrograms/kg s.c. daily) treatment were perfused for 30 min with a synthetic medium containing T4 (6 micrograms/dl), and production of T3 and rT3 in the tissues was measured by radioimmunoassay. The production of T3 (111 +/- 38 ng/g/30 min, mean +/- SD) and conversion rate of T4 to T3 (19.7 +/- 5.8%) in the liver of diabetic rats without T4 treatment and those (124 +/- 41 ng/g/30 min and 21.6 +/- 4.9%) in the liver of diabetic rats with T4 treatment were significantly lower than those of controls (196 +/- 48 ng/g/30 min and 30.6 +/- 5.2%), respectively. The production of rT3 and conversion rate of T4 to rT3 in the liver of diabetic rats with or without T4 treatment were similar to those of controls. The production of T3 and rT3, and conversion rate of T4 to T3 and T4 to rT3, in the kidney of diabetic rats with or without T4 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 T4 to T3 conversion that occurs in diabetic rats.