The beneficial effects of thyroxine on nephrotoxic acute renal failure in the rat.

We were able to confirm previous studies demonstrating that administration of thyroxine is capable of ameliorating the severity of acute nephrotoxic renal failure in the rat. Nephrotoxic acute renal failure was induced by the subcutaneous injection of potassium dichromate (6.25 mg/kg) into Sprague-Dawley rats. Twenty-four hours after this injection, rats received an intraperitoneal injection of either thyroxine (80 micrograms/kg body wt) or normal saline. Forty-eight hours after the potassium dichromate injection, renal clearance studies were performed. Inulin clearance was significantly higher in the thyroxine-treated than in the saline-treated acute renal failure rats: 1.12 +/- 0.13 (SEM) mL/g versus 0.75 +/- 0.07 mL/min/g kidney wt (P = 0.025). Thyroxine treatment also effected an increase of p-aminohippuric acid extraction from 0.23 +/- 0.03 to 0.33 +/- 0.02 (P = 0.011) and a decrease in the fractional excretion of sodium from 0.38 +/- 0.21 to 0.11 +/- 0.03% (P = 0.037 by Mann-Whitney U test). In order to investigate one potential mechanism of the beneficial effect of thyroxine we studied renal tubular regeneration in this model of acute renal failure. Renal cortical uptake of labeled thymidine into DNA was significantly increased 48 h after the injection of potassium dichromate, and thyroxine administration further enhanced this repair process: 53.9 +/- 3.6 versus 81.4 +/- 5.3 dpm/200 pg of DNA (P = 0.0033).