Previous studies showed that aquaporin 2 (AQP2) is elevated in the kidney of the heart failure rat suggesting that an increased amount of AQP2 contributes to water retention in heart failure. We performed the present study to determine whether angiotensin II play a role in causing an increase in the expression of arginine vasopressin (AVP) V2 and AQP2 mRNA in the kidney of the cardiomyopathic hamster. The expression of AVP V2 and AQP2 mRNA in the inner medullary collecting duct (IMCD) was measured by competitive reverse transcriptase-polymerase chain reaction (RT-PCR) before and after treatment with an angiotensin-converting enzyme inhibitor, enalapril. Our results showed that the expression of AVP V2 (0.53 +/- 0.05 v 1.03 +/- 0.15 amol/microg of total RNA, P <.01) and AQP2 mRNA (0.027 +/- 0.002 v 0.036 +/- 0.002 amol/microg of total RNA, P <.05) in the IMCD of the cardiomyopathic hamster is upregulated. Treating the cardiomyopathic hamster with enalapril for 7 days negated the changes. In situ hybridization experiments confirmed the intensity of the signals for both AVP V2 and AQP2 mRNA was more intense in the IMCD of the cardiomyopathic hamster. Enalapril treatment reduced the signal intensity to a level comparable to the normal hamster. These results suggested that the increases in the expression of AVP V2 and AQP2 mRNA are mediated by angiotensin II.
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