Vasopressin-dependent upregulation of aquaporin-2 gene expression in glucocorticoid-deficient rats

We determined alterations in renal aquaporin-2 (AQP2) gene expression in association with impaired water excretion in glucocorticoid-deficient rats. After adrenalectomy, Sprague-Dawley rats were administered aldosterone alone by osmotic pumps (glucocorticoid-deficient rats). As a control, both aldosterone and dexamethasone were administered. These animals were subjected to the studies on days 7-14. The expressions of AQP2 mRNA and protein in kidney of the glucocorticoid-deficient rats were increased by 1.6- and 1.4-fold compared with the control rats, respectively. An acute oral water load test verified the marked impairment in water excretion in the glucocorticoid-deficient rats. One hour after the water load, the expressions of AQP2 mRNA and protein were significantly reduced in the control rats, but they remained unchanged in the glucocorticoid- deficient rats. However, there was no alteration in [H-3] arginine vasopressin (AVP) receptor binding and AVP V-2 receptor mRNA expression in the glucocorticoid- deficient rats. A V-2-receptor antagonist abolished the increased expressions of AQP2 mRNA and protein in the glucocorticoid- deficient rats. These results indicate that augmented expression of AQP2 participates in impaired water excretion, dependent on AVP, in glucocorticoid deficiency.