Opposite regulation of bilirubin and 4-nitrophenol UDP-glucuronosyltransferase mRNA levels by 3,3',5 triiodo-L-thyronine in rat liver.

The effects of 3,3',5 triiodo-L-thyronine (L-T3) on the constitutive levels of hepatic mRNA encoding two UDP-glucuronosyltransferase (UGT) isoforms implicated in the glucuronidation of planar phenolic substrates (UGT106) and bilirubin (UGT10) were investigated in rat liver. The amount of UGT mRNA was quantitated by reverse transcription and amplification methods (RT-PCR). Treatment with L-T3 significantly increased UGT106 and decreased UGT10 mRNA levels by 41% and 54%, respectively. The opposite situation was observed in thyroidectomised animals. A good relationship observed between UGT activity toward 4-nitrophenol and bilirubin and mRNA levels emphasizes the key role played by the thyroid hormone L-T3 on UGT expression.