| Abstract: | The in vitro handling of thyroid hormones was studied in isolated rat hepatocytes by measuring 1) the cellular uptake of T4, 2) the conversion of T4 to T3 and 3) the degradation of T4 and T3. The in vitro conversion of T4 to T3 increased significantly by adding ethanol 2% or carbamazepine (CBZ) 400 microM in ethanol 2% to the incubation medium. As there was no difference between ethanol and CBZ/ethanol on the T3 formation, this effect was probably caused by ethanol. The T3 formation was unaffected by phenytoin (PHT) in conc. up to 400 microM, while propylthiouracil (PTU) 100 and 400 microM inhibited the conversion completely. The T4 to T3 conversion in hepatocytes from rats pretreated with CBZ or PHT for 2 weeks was not significantly different from untreated controls. The cellular uptake of T4 was reduced by about 30% in the presence of PHT and unaltered by CBZ and ethanol. The degradation of T4 and T3 was not influenced by the in vitro addition of CBZ or PHT, nor was the degradation of T4 and T3 significantly different from untreated controls in hepatocyte suspensions from CBZ or PHT pretreated rats. Our findings suggest that the handling of thyroid hormones in isolated rat hepatocytes is not influenced by the in vitro or in vivo exposure to CBZ or PHT. |
