Tissue-specific changes in insulin receptor mRNA concentrations in dexamethasone-treated and adrenalectomized rats

The relative concentrations of total insulin receptor (IR) mRNA were measured in the epididymal adipose tissue and liver of intact untreated rats, dexamethasone-treated rats, adrenalectomized rats and adrenalectomized rats treated with dexamethasone, using RNA blot assays and a specific IR cDNA probe. Northern blot assays revealed two IR mRNA species of approximately 9.5 and 7.5 kb, in both tissues. Dot-Blot assays followed by densitometry indicated that dexamethasone induced an approximately three-fold increase in IR mRNA in liver, but not in epididymal adipose tissue. By contrast, neither adrenalectomy alone nor the combination of adrenalectomy plus dexamethasone treatment altered the IR mRNA concentrations in liver nor in adipose tissue, which indicates that adrenalectomy was able to prevent the stimulation of IR gene expression caused by dexamethasone in rat liver. These results provide evidence for an "in vivo" tissue-specific regulation of IR gene expression, at the mRNA level, in rats under experimental conditions of an excess or insufficiency of glucocorticoids.