Tri-iodothyronine-induced increase in rat liver nuclear thyroid-hormone receptors associated with increased mitochondrial alpha-glycerophosphate dehydrogenase activity.
The effect of tri-iodothyronine injection on the nuclear tri-iodothyronine receptor (putative thyroid-hormone receptor) was examined in rat liver. Nuclear receptors were extracted from isolated nuclei with 0.4 M-KCl, and their association constants (Ka) and maximal binding capacities (Cmax.) were determined by Scatchard analyses with and without correction for the endogenous hormone. The amount of endogenous tri-iodothyronine bound to non-histone protein was estimated on the basis of the specific radio-activity of [125I]tri-iodothyronine injected 2 h before the rats were killed. It was demonstrated that Cmax. of the nuclear receptors was 2.5-fold higher in severely hyperthyroid than in hypothyroid rats. However, irrespective of the thyroid status, the Ka of the receptors remained unchanged when corrected for endogenous tri-iodothyronine bound to non-histone protein. The validity of the correction was supported by experiments in vitro in which nuclear receptors were preincubated with unlabelled tri-iodothyronine. The increase in Cmax. of nuclear receptors was directly related to mitochondrial alpha-glycerophosphate dehydrogenase activity. These results suggest a hormonal modulation of the nuclear receptors which is associated with hormonal action.
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000201:enzymology; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D013268:Stimulation, Chemical; D014284:Triiodothyronine / Q000378:metabolism / Q000494:pharmacology*
D002868:Chromosomal Proteins, Non-Histone; D011956:Receptors, Cell Surface; D014284:Triiodothyronine; D005993:Glycerolphosphate Dehydrogenase