Background and Purpose--Disturbances in cerebral arteriolar function, in addition to large vessel vasospasm, may be responsible for ischemia after subarachnoid hemorrhage. The purpose of this study was to test the hypothesis that subarachnoid hemorrhage alters cerebral microvascular reactivity.

Methods--An endovascular filament model was used to induce subarachnoid hemorrhage in halothane-anesthetized male Sprague-Dawley rats. We evaluated pial arteriolar responses to sciatic nerve stimulation, topically applied vasoactive agents (adenosine or sodium nitroprusside), and CO₂ inhalation in rats subjected to subarachnoid hemorrhage at 1 to 5 days after insult.

Results--In sham-operated rats, sciatic nerve stimulation evoked a 23.5±1.8% increase in arteriolar diameter, which was significantly attenuated to 13.7±0.9%, 12.8±2.5%, and 18.8±2.9% at 24, 48, and 72 hours after subarachnoid hemorrhage, respectively (P<0.05; n7). At 96 and 120 hours after subarachnoid hemorrhage, sciatic nerve stimulation-induced dilation recovered to sham levels. Somatosensory-evoked potentials were unaltered by subarachnoid hemorrhage. Pial vasodilatation to adenosine (10 µmol/L) and sodium nitroprusside (1 µmol/L) were significantly impaired, by 47% and 41%, respectively, at 48 hours after subarachnoid hemorrhage (P<0.05; n=7). In contrast, CO₂ reactivity was unaffected by subarachnoid hemorrhage.

Conclusions--Pial arteriolar responses to cortical activation may be decreased in the initial 2 to 3 days after experimental subarachnoid hemorrhage.