Adsorption equilibria of thyroid hormones in the liver cell

The adsorptive distribution of L-thyroxine and L-triiodothyronine at 0.04--25nM concentrations was determined in suspensions of mitochondria in soluble cytoplasmic proteins from rat livers, at protein concentrations of 0.5--4.7 mg total protein/ml suspension. In the concentration ranges measured no saturation of both mitochondria and soluble proteins with thyroid hormones could be observed. The distribution of the hormones between the liquid phase of cytoplasmic proteins and the solid phase of the mitochondria depended mainly on the ratio of the amounts of proteins in both phases. Certain drugs such as chlorpromazine and phenobarbital in concentrations used therapeutically can interfere with the processes of adsorptive transport in vitro. Chlorpromazine, in the presence of desorptively functioning cytoplasmic proteins or serum proteins, promotes the adsorption of thyroxine and triiodothyronine onto the mitochondria. In contrast, phenobarbital weakens the binding of the hormones to the mitochondria. The processes of adsorptive binding of thyroid hormones to cell proteins in vitro are suggested as possible links in a transport chain between different compartments in vivo. The new model may also explain the effect of drugs on the distribution of thyroid hormones within the cell.