AGE-RELATED-CHANGES IN RESPONSE OF BRAIN-STEM VESSELS TO OPENING OF ATP-SENSITIVE POTASSIUM CHANNELS

Background and Purpose This study was designed to determine regional d ifferences and age-related changes in the contribution of ATP-sensitiv e potassium (K-ATP) channels to vasodilator responses in the brain ste m circulation in vivo. Methods Changes in diameter of the basilar arte ry (baseline diameter, 270+/-5 mu m [mean+/-(-SEM]), its large branch (112+/-5 mu m), and its small branch (49+/-2 mu m) in response to K-AT P channel openers levcromakalim and Y-26763 were measured through a cr anial window in anesthetized adult (4 to 6 months) and aged (24 to 26 months) Sprague-Dawley rats. Results Topical application of levcromaka lim and Y-26763 produced concentration-dependent vasodilation that was similar among the three vessel groups in adult rats. In aged rats, di lator responses of the branches, but not of the basilar artery, to the K-ATP channel openers were smaller than those in adult rats (P<.05). Glibenclamide, a selective K-ATP channel blocker, almost abolished thi s vasodilation in both groups of rats. Vasodilator responses to sodium nitroprusside were preserved in aged rats. Conclusions In adult rats, there is no regional heterogeneity in vasodilator response to K-ATP c hannel openers in the brain stem circulation in vivo. In aged rats, al though K-ATP channels are also functional in the brain stem circulatio n, dilator response of the microvessels but not of the large arteries to direct activation of K-ATP channels is impaired.