REPERFUSION DECREASES MYOGENIC REACTIVITY AND ALTERS MIDDLE CEREBRAL-ARTERY FUNCTION AFTER FOCAL CEREBRAL-ISCHEMIA IN RATS

Background and Purpose After focal cerebral ischemia, the function of cerebral arteries is critical to maintain cerebrovascular resistance a nd minimize damage to ischemic brain regions during reperfusion. In th is study we examined the contractile function of isolated and pressuri zed middle cerebral arteries (MCAs) after 2 hours of occlusion with ei ther 1 to 2 minutes or 24 hours of reperfusion using the intraluminal suture model of transient focal ischemia in rats. Methods MCAs were di ssected after 2 hours of occlusion with either 1 to 2 minutes (OCC, n= 8) or 24 hours (RPF, n=5) of reperfusion and compared with those of co ntrols that did not have surgery (n=5). Isolated MCAs were mounted on two glass cannulas in an arteriograph chamber that allowed control ove r transmural pressure (TMP) and measurement of lumen diameter. Respons es to changes in TMP (including myogenic reactivity, basal tone, and p assive distensibility) and sensitivity to serotonin and acetylcholine were compared. Results Increasing TMP from 25 to 75 mm Hg caused vasoc onstriction and development of tone that was similar in control and OC C arteries: percent tone was 33+/-5% versus 25+/-7% (P>.05). In contra st, tone was severely diminished in RPF MCAs after 24 hours of reperfu sion: percent tone=8+/-4% (P<.01). Sensitivity to serotonin was reduce d in OCC arteries, increasing the EC(50) value from 0.04+/-0.1 to 0.11 +/-0.02 mu mol/L (P<.05); after 24 hours of reperfusion, sensitivity o f RPF MCAs was similar to control. Vasodilation to 10.0 mu mol/L acety lcholine was significantly impaired only in RPF arteries: percent incr eased lumen diameter was 19+/-3% (control) and 13+/-4% (OCC, P>.05) ve rsus 9+/-2% (RPF, P<.01). Passively, OCC MCAs were more distensible, w hich was reversed after 24 hours of reperfusion; RPF vessels had diste nsibility similar to that of control arteries but thicker arterial wal ls. Conclusions Abnormal structure and function of MCAs occur after 2 hours of ischemia, with diminished myogenic reactivity and tone associ ated with longer reperfusion.