INCREASED EXPRESSION OF VASCULAR ANGIOTENSIN-II TYPE 1A RECEPTOR GENE IN GLUCOCORTICOID-INDUCED HYPERTENSION

Objectives: We recently demonstrated that glucocorticoid increases the number of angiotensin II type 1 (AT(1)) receptors and their gene expression in cultured vascular smooth muscle cells. To clarify whether this mechanism participates in glucocorticoid-induced hypertension, we investigated the effect of dexamethasone on the modulation of vascular AT(1) receptor messenger RNA (mRNA) expression in rats. Methods: The effects were studied of administering dexamethasone orally to rats at a dose of 0.1 mg/day on the modulation of the expression of vascular AT(1) receptor mRNA and the blood pressure. The effects of enalapril maleate, an angiotensin converting enzyme inhibitor, were also evaluated. Results: The dexamethasone-treated rats showed a rise in systolic blood pressure beginning on day 3. On day 5 the blood pressure rose significantly. Before dexamethasone administration the vascular AT(1) receptor mRNA was difficult to detect by Northern blot analysis. However, the level of vascular AT(1A) receptor mRNA began to increase on day 2, when the blood pressure was not yet elevated, and increased further on day 5. The concurrent administration of dexamethasone and enalapril maleate attenuated the elevation of blood pressure. However, as in the dexamethasone-treated rats, the level of AT(1A) receptor mRNA began to increase on day 2 and increased further on day 5. In rats treated with enalapril maleate alone, the AT(1) receptor mRNA was difficult to detect during the experiment. Conclusion: Glucocorticoid increased the amount of vascular AT(1) receptor mRNA and contributed to the elevation of blood pressure.