Thyroid hormone action. Demonstration of similar receptors in isolated nuclei of rat liver and cultured GH1 cells.

High-affinity, limited-capacity nuclear binding activities, putative receptors for triiodothyronine, were detected after incubation of hormone with intact rat pituitary GH1 cells in culture, isolated GH1 cell nuclei, or rat liver nuclei. The total number of triiodothyronine binding sites per nucleus was similar in each case (approximately 8,000). The estimated equilibrium dissociation constants were virtually identical in isolated GH1 cell nuclei and rat liver nuclei, and both values were similar to that determined in intact GH2 cells. These results suggest that mechanisms of thyroid hormone action defined in cell culture could apply to thyroid hormone regulatory effects in vivo.