Effect of TSH on conversion of T4 to T3 in perfused rat kidney.

This study was undertaken to elucidate the effect of thyrotropin (TSH) on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat kidney. The kidney was perfused with a synthetic medium containing 20 micrograms/dL T4 and the effect of constant infusion of bovine TSH (125 or 250 microU/mL) on the conversion of T4 to T3 was investigated. T4 uptake in the perfused kidney was not changed by the addition of TSH. However, the release of T3 (89 +/- 11 ng/g/30 min, mean +/- SD), tissue T3 (190 +/- 23 ng/g/30 min), net T3 production (227 +/- 37 ng/g/30 min), and the conversion rate of T4 to T3 (9.5 +/- 1.6%) in the kidney perfused with 250 microU/mL TSH were significantly (P less than 0.005) greater than those in controls (63 +/- 9, 143 +/- 15, 152 +/- 36 ng/g/30 min, and 6.3 +/- 1.9%), respectively. Degradation rate of T3 in perfused rat kidney was not changed by the addition of 250 microU/mL TSH. These results suggest that TSH may directly affect renal iodothyronine-monodeiodinating activity in rats in vitro.