[Effect of thyroid hormones on the beta-adrenergic receptor internalization in isolated rat hepatocytes]

The effect of the thyroid hormone(T4) on the internalization of beta-adrenergic receptors in isolated hepatocytes was examined. Uptake of [3H]-dihydroalprenolol(DHA) by the cells, which were prepared from untreated-rats, was increased by the time-dependent manner in vitro. The amount of incorporated-[3H]-DHA was decreased by further incubation in the presence of 10(-5) M of d, 1-isoproterenol. However, about 30% of incorporated-[3H]-DHA remained in the cells by this treatment. The amount of this [3H]-DHA remaining in the cells was lowered by pretreatment of the cells with methylamine, monodansylcadaverine, d, 1-isoproterenol or d, 1-propranolol. Then the amount of this [3H]-DHA was recognized as an internalized-receptor-hormone(or -DHA) complex. The total uptake(internalized- + membrane bound-) of [3H]-DHA by the cells was not significantly different between the thyroidectomized (TX + Saline) and T4-treated-thyroidectomized(TX + T4) rats. However, the rate of disappearance of incorporated-[3H]-DHA was greater in the TX + T4 animals compared to that in the TX + Saline animals. In the cells obtained from the TX + T4 animals, internalized-[3H]-DHA was significantly higher than that of the TX + Saline animals. The number of membrane associated beta adrenergic receptors was significantly lower in the TX + T4 group. These results suggest that the thyroid hormone induces an acceleration of internalization of beta adrenergic receptors in hepatocytes.