title: Effect of thyrotropin on conversion of T4 to T3 in perfused rat liver.
abstract: The present study was undertaken to elucidate the direct effect of thyrotropin (TSH) on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat liver. The liver was perfused without recirculation with a synthetic medium containing 10 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 examined. T4 uptake in the perfused liver was not changed by the addition of TSH. The release of T3 (10.3 +/- 1.4 ng/g/30min, mean +/- SD), tissue T3 production (99.5 +/- 21.4 ng/g/30min), net T3 production (102.6 +/- 20.2 ng/g/30min), and the conversion rate of T4 to T3 (14.8 +/- 3.5%) in the liver perfused with 250 microU/ml TSH were significantly higher than those in controls (8.1 +/- 1.2 ng/g/30min, 69.0 +/- 6.8 ng/g/30min, 69.9 +/- 6.1 ng/g/30min, and 10.0 +/- 0.8%), respectively. These results suggest that TSH may directly enhance hepatic conversion of T4 to T3 in rats in vitro.
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000502:physiology; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D013972:Thyrotropin / Q000494:pharmacology*; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D000242:Cyclic AMP; D013974:Thyroxine