Cerebral Ischemia Enhances Vascular Angiotensin AT 1 Receptor–Mediated Contraction in Rats

Abstract

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 (AT 1 ) receptor antagonists candesartan and losartan abolished the enhanced responses to angiotensin II ( P <0.05), whereas the AT 2 receptor antagonist PD123319 had no effect. The amount of AT 1 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 AT 2 receptor and nuclear factor-κB 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 AT 1 receptors. Real-time polymerase chain reaction revealed decreased AT 1 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 AT 1 receptors in cerebral ischemia, and we think that AT 1 receptors might be a future therapeutic target in ischemic stroke.