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(Stroke. 2004;35:970.)
© 2004 American Heart Association, Inc.

Original Contributions

Cerebral Ischemia Enhances Vascular Angiotensin AT₁ Receptor–Mediated Contraction in Rats

From the Division of Experimental Vascular Research, Department of Internal Medicine, Lund University, Lund, Sweden.

Correspondence to Emelie Stenman, Division of Experimental Vascular Research, Lund University, BMC A13, Sölvegatan 17, 221 84 Lund, Sweden. E-mail Emelie.Stenman{at}med.lu.se

Background and Purpose— The aim of the study was to examine how focal cerebral ischemia affects the expression and function of vascular angiotensin II receptors.

Materials and Methods— We used an intraluminal filament occlusion technique to occlude the right middle cerebral artery (MCA) of the rat. Myographs were used for functional studies of the MCA and real-time polymerase chain reaction, for determination of relative mRNA levels.

Results— The contractile responses to angiotensin II were stronger in the right occluded MCA compared with the left MCA and the MCA from sham-operated rats 48 hours after MCA occlusion (P<0.05). The angiotensin II type 1 (AT₁) receptor antagonists candesartan and losartan abolished the enhanced responses to angiotensin II (P<0.05), whereas the AT₂ receptor antagonist PD123319 had no effect. The amount of AT₁ receptor mRNA was lower in the occluded MCAs compared with nonoccluded MCAs 48 hours after occlusion (P<0.05), whereas the mRNA levels of angiotensin converting enzyme (ACE) were higher in the occluded arteries. The mRNA levels of the AT₂ receptor and nuclear factor-B were unchanged.

Conclusions— Focal cerebral ischemia in the rat upregulated the contractile responses to angiotensin II in the ipsilateral MCA, and this contraction was mediated by AT₁ receptors. Real-time polymerase chain reaction revealed decreased AT₁ receptor mRNA levels in the occluded MCA, whereas the amount of ACE mRNA was increased, suggesting locally enhanced angiotensin II production. These results support a role for AT₁ receptors in cerebral ischemia, and we think that AT₁ receptors might be a future therapeutic target in ischemic stroke.

Key Words: angiotensins • receptors, angiotensin • angiotensin converting enzyme inhibitors • cerebral ischemia

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