Differences in Pial Arteriolar Responses To Hypoxia and Hypercapnia After Global Cerebral Ischemia in Piglets 23

Vascular ATP-sensitive K⁺ channels (K_ATP) are sensitive to ischemic stress. Pial arteriolar dilation to arterial hypoxia is mediated partially by activation of K_ATP. We determined whether ischemia/reperfusion alters cerebral arteriolar dilation to hypoxic hypoxia. In anesthetized piglets, pial arteriolar diameters were measured using a cranial window and intravital microscopy. Global cerebral ischemia was caused by increasing intracranial pressure. We examined arteriolar responses to arterial hypoxia (8.5 and 7.5% O₂), hypercapnia (5 and 10% CO₂), and topical adenosine (10^-5 and 10^-4 mol/L) before and 1 - 4 hr after 10 min of ischemia. Before ischemia, arterioles dilated by 19±3% to moderate and 29±4% to severe hypoxia (n=7, p<0.05), by 18±2% to 5% and by 28±3% to 10% CO₂ (n=6; p<0.05), by 13±2% to 10^-5 and by 20±1% to 10^-4 mol/L adenosine(n=9; p<0.05). After ischemia arteriolar responses to hypoxia and adenosine were unchanged. Ischemia impaired arteriolar dilation to hypercapnia(1±1% and 2±1% at 1 hr and 10±1% and 14±2% at 2 hr to 5% and to 10% CO₂, respectively). We conclude that pial arteriolar dilation is selectively inhibited following ischemia and despite impairment in K_ATP function hypoxia dilates arterioles.