Autoradiographic demonstration of thyroid hormone binding to intact liver cells in vivo.

Adult rats were injected intravenously with [125I]-3,5,3'-triiodothyronine (T3) of [125I]-thyroxine (T4). Others were similarly treated, except for the addition of a 500-fold excess of the appropriate unlabeled hormone. Light microscopic autoradiography of semi-thin sections of liver from these animals demonstrated high affinity, low capacity binding of T3 and, to a much lesser extent, T4 to the nuclei of the liver cells. Labeling over the cytoplasmic portion of the cells was greater than that over the nucleus with either hormone, but was not decreased significantly with the addition of unlabelled hormone, suggesting the absence of specific binding sites in this location.