Neuroprotective Effects and Suppression of Ischemia-induced Glutamate Elevation by β1-Adrenoreceptor Antagonists Administered Before Transient Focal Ischemia in Rats

Background: beta-adrenoreceptor antagonists provide neuroprotective effects after focal cerebral ischemia in experimental settings. This study was conducted to compare the neuroprotective effects of low-dose and high-dose of selective beta(1)-adrenoreceptor antagonists in rats after focal cerebral ischemia. We also investigated whether glutamate and norepinephrine contribute to neuroprotection of the beta-adrenoreceptor antagonists. Methods: Sprague-Dawley rats were subjected to 120 minutes middle cerebral artery occlusion. The rats received intravenous infusion of saline 0.5 mL/h, esmolol 200, esmolol 2000, landiolol 50, or landiolol 500 mu g/kg/min. Infusion of all the drugs were started 30 minutes before ischemia and continued for 24 hours. Neurological deficit scores were evaluated at 1, 4, and 7 days, whereas the brains were removed and stained at 7 days after ischemia. In the esmolol 200, and landiolol 50 mu g/kg/min groups of additional rats, glutamate and norepinephrine concentrations in the striatum were measured separately by microdialysis during ischemia (glutamate, 120 min; norepinephrine, 110 min) and reperfusion (40 min). Results: Neurological deficit scores were smaller in rats treated with esmolol or landiolol than in saline-treated rats at 1, 4, and 7 days. The cortical and striatal infarct volumes were smaller in rats receiving beta-adrenoreceptor antagonists than in the saline-treated rats. There were no significant differences in neurological score or infarct volume between the groups receiving the different doses of beta(1)-adrenoreceptor antagonists. The area under the curve of glutamate in the esmolol-treated or landiolol-treated rats was significantly smaller than that in the saline-treated rats, whereas no significant differences were noted in the norepinephrine concentration among the groups. Conclusions: This study indicates that the improvement in neurological and histologic outcomes by selective beta(1)-adrenoreceptor antagonists after transient focal cerebral ischemia is partly attributed to attenuation of glutamate release.