Angiotensin II Upregulates the Expression of Vasopressin V2 mRNA in the Inner Medullary Collecting Duct of the Rat

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Title: Angiotensin II Upregulates the Expression of Vasopressin V2 mRNA in the Inner Medullary Collecting Duct of the Rat
Authors: Wong, Ph.D., Norman L. M.; Tsui, Joseph K. C.
Publisher: Metabolism
Date Published: March 01, 2003
Reference Number: 626
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Previous in vivo studies in cardiomyopathic hamsters suggested that the expression of vasopressin (AVP) V2 mRNA is up-regulated by angiotensin II. The present study was performed to determine whether angiotensin II plays a role in regulating the expression of AVP V2 mRNA and aquaporin-2 (AQP2) mRNA in the inner medullary collecting duct (IMCD) of the male Wistar rat. The expression of AVP V2 mRNA and AQP2 mRNA in the IMCD was measured by competitive reverse-transcriptase polymerase chain reaction (RT-PCR). Six groups of experiments were performed. In the first group, we incubated IMCD with 3 different doses of angiotensin II (10(-11), 10(-9) and 10(-7) mol/L). Angiotensin II caused a significant increase in the AVP V2 mRNA in a dose-dependent manner but its effect on AQP2 mRNA was modest. This effect of angiotensin II was inhibited by angiotensin II receptor antagonist, [Sar1,Ile8]-angiotensin II. To examine the role of PKA in mediating an increase in AVP V2 mRNA expression, we incubated IMCD with 10(-7) and 10(-11) M of angiotensin II in the presence of a specific protein kinase A (PKA) inhibitor, Rp diasteroisomer of adenosine 3'-5'-cylic monophosphothionate (Rp-cAMPS). The angiotensin II-induced upregulation of V2 mRNA was abolished. In the fourth group, we examined the effect of protein kinase C (PKC) inhibition on V2 mRNA expression. The upregulation of V2 mRNA induced by angiotensin II was greatly exaggerated when IMCD was incubated with angiotensin II and RO-31-8220 (PKC inhibitor). In the fifth and sixth groups of studies, we determined the direct effect of PKA and PKC on regulating the expression of V2 mRNA and AQP2 mRNA in the IMCD, respectively. Dibutryl cAMP stimulated an upregulation in the expression of V2 mRNA and AQP2 mRNA, whereas phorbol esters suppressed the expression of V2 mRNA. These results suggested that PKA stimulates and PKC suppresses the expression of V2 mRNA in the IMCD of the kidney. Copyright 2003, Elsevier Science (USA). All rights reserved.

This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)

Angiotensin II is a member of the family of vasopressor hormones. These hormones stimulate the contraction of the muscular tissue of capillaries and arteries. Wong and Tsui sought to determine if angiotensin II plays a role in upping the number of vasopressin 2 receptor (V2R) mRNA and aquaporin 2 (AQP2) mRNA in the inner medullary collecting ducts (IMCD) of rats.

To do this, they removed kidneys from rats and created laboratory cell cultures with them. In these they placed varying amounts of angiotensin II for varying amounts of time. The researchers found that modest amounts of angiotensin II incubated with the IMCD cells for 17 hours induced a significant increase in V2R mRNA and a more modest increase in AQP2 mRNA.

When the researchers placed in the cell cultures both angiotensin II and an agent that inhibits angiotensin II, there were much smaller increases in the V2R mRNA and no effect on the AQP2 mRNA. This indicates that it was angiotensin II that caused the increase. To see if protein kinase A (PKA) helped angiotensin II increase V2R mRNA, Wong and Tsui placed a PKA inhibitor in the cell cultures and, upon examination, they found no gain in V2R mRNA. To determine if protein kinase C (PKC) had an effect on the number of V2R mRNA angiotensin II was able to produce, the researchers placed a PKC inhibitor in the cultures. They found that this enabled angiotensin II to greatly increase the number of V2R mRNA.

The researchers then tested the direct effect of PKA and PKC on regulating the expression of V2R mRNA and AQP2 mRNA. Their results suggest that PKA stimulates and PKC suppresses V2R mRNA and AQP2 mRNA in rat kidney IMCD.