Triiodothyronine-receptor complex in rat brain: effects of thyroidectomy, fasting, food restriction, and diabetes.
In vitro saturation analysis combined with quantification of T3, by an isotopic equilibrium technique or RIA, were used to examine the effects of thyroidectomy, fasting, diabetes, and food restriction on T3 concentration and specific binding in cerebral cortex and cerebellum. Fasting and food restriction did not affect the T3 binding parameters in the brain areas studied. Both thyroidectomy and diabetes were accompanied by a reduction in T3 content in nuclei from both cerebral cortex and cerebellum, but a decrease in T3 binding sites was only observed in both brain areas of diabetic animals. No significant differences in the binding affinity values among the experimental groups were seen. The diabetes-induced decrease in T3 content and receptor number were completely reversed by insulin treatment. Studies with fractionated nuclei from cerebral cortex and cerebellum showed that diabetes resulted in a reduction in T3 content and the number of receptors in glial nuclei from both brain areas. Although T3 content was also decreased in neuronal nuclei, the receptor concentration in these nuclear preparations did not change in concentration or affinity under the same conditions. These observations indicate that glial cells, not only have T3-binding characteristics similar to those of neuronal cells, but the T3 receptor number is decreased in the diabetes state.