Effect of glibenclamide on thyroid hormone metabolism in rats.

This study was undertaken to elucidate the effect of glibenclamide, one of sulfonylurea drugs, on thyroid hormone metabolism in vivo and on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat liver and kidney. Glibenclamide (0.2 mg/kg body weight) was intraperitoneally administered to normal and streptozotocin-induced (50 mg/kg) diabetic rats for 14 days. The liver and kidney of normal rats were perfused for 30 minutes with a synthetic medium containing 20 micrograms/dl T4 and glibenclamide (200 or 400 ng/ml), and production of T3 in the tissues was measured by radioimmunoassay. Serum T4 and T3 levels in control and streptozotocin-induced diabetic rats were not changed by daily intraperitoneal glibenclamide administration. The production of T3 (111 +/- 40 and 95 +/- 16 ng/g/30 min, mean +/- SD) and the conversion rate of T4 to T3 (11.1 +/- 2.9 and 10.2 +/- 2.3%) in the liver perfused with glibenclamide (200 and 400 ng/ml) were not significantly different from those in controls (109 +/- 41 ng/g/30 min and 12.8 +/- 5.4%). And those (120 +/- 33 and 99 +/- 19 ng/g/30 min, and 3.5 +/- 0.6 and 2.5 +/- 0.4%) in the kidney perfused with glibenclamide (200 and 400 ng/ml) were similar to those in controls (98 +/- 33 ng/g/30 min and 3.0 +/- 1.5%).