Regional time-dependent changes in vasopressin V2 receptor expression in the rat kidney during water restriction.

Elevations of arginine vasopressin (AVP) binding to renal vasopressin V2 receptors (V2R) enhance water and urea reabsorption in the collecting duct epithelium. This study was designed to quantify the levels of V2R mRNA and protein within the distinct regions of the Sprague-Dawley rat kidney (i.e., the cortex and outer and inner medulla) during 24 and 48 h of water restriction. A competitive reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to quantify changes in the V2R mRNA, in which a deletion mutant RNA transcript was used to control for the efficiency of RT-PCR. Western blot analysis was utilized for the quantification of the V2R protein. The results showed that the steady-state levels of the V2R mRNA decreased in a time-dependent manner in the cortex and outer and inner medulla throughout 48 h of water restriction. Western blot analysis revealed that the V2R protein in the renal cortex decreased after the initial 24 h of water restriction and remained decreased at 48 h. In contrast, outer medullary V2R protein decreased significantly only after 48 h of water restriction, whereas no significant change in the inner medullary V2R protein was observed throughout the 48 h of water restriction. These results suggest that water restriction leads to a regional time-dependent downregulation of the V2R mRNA and protein within the rat kidney. The stability of the plasma membrane V2R protein within the inner medulla may allow for the optimization of urine concentration and minimize water loss during periods of water restriction.