Global ischemia impairs ATP-sensitive K+ channel function in cerebral arterioles in piglets

Background and Purpose Indirect evidence from studies in which calcitonin gene-related peptide was used indicates that anoxic stress suppresses functioning of cerebral vascular ATP-sensitive K+ channels. The purpose of this study was to directly examine effects of total global ischemia on cerebral arteriolar dilator responses to activators of ATP-sensitive K+ channels. Methods We measured pial arteriolar diameters in anesthetized piglets using a closed cranial window and intravital microscopy. Baseline diameters were approximately 100 mu m. Arteriolar responses to aprikalim (10(-8) and 10(-6) mol/L), a pharmacological activator of ATP-sensitive Kt channels, and iloprost (0.1 and 1 mu g/mL), a physiological activator of these channels, were determined before and 1, 2, and 4 hours after a 10-minute period of total global ischemia. Ischemia was caused by increasing intracranial pressure. Results Before ischemia, aprikalim dilated cerebral arterioles by 7+/-2% at 10(-8) mol/L and by 25+/-4% at 10(-6) mol/L (n=5). At 1 hour after ischemia, aprikalim did not cause significant dilation at either dose (3+/-2% at 10(-8) mol/L and 7+/-4% at 10(-6) mol/L; P<.05 compared with corresponding preischemic response). Arteriolar dilation returned toward normal values at 2 and 4 hours. Similar results were found with iloprost. Furthermore, prior treatment with indomethacin (5 mg/kg) preserved normal arteriolar dilation to aprikalim and iloprost after ischemia. In contrast, arteriolar dilator responses to prostaglandin E(2) were intact after ischemia. Conclusions Ischemia transiently eliminates cerebral arteriolar dilation to activation of ATP-sensitive K+ channels; arteriolar responses are suppressed at 1 hour and return toward normal over 2 to 4 hours. In addition, reduced responsiveness can be prevented by prior treatment with indomethacin.