Age-Related Changes in Response of Brain Stem Vessels to Opening of ATP-Sensitive Potassium Channels

Abstract

Background and Purpose This study was designed to determine regional differences and age-related changes in the contribution of ATP-sensitive potassium (K ATP ) channels to vasodilator responses in the brain stem circulation in vivo. Methods Changes in diameter of the basilar artery (baseline diameter, 270±5 μm [mean±SEM]), its large branch (112±5 μm), and its small branch (49±2 μm) in response to K ATP channel openers levcromakalim and Y-26763 were measured through a cranial window in anesthetized adult (4 to 6 months) and aged (24 to 26 months) Sprague-Dawley rats. Results Topical application of levcromakalim and Y-26763 produced concentration-dependent vasodilation that was similar among the three vessel groups in adult rats. In aged rats, dilator 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 this 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 channel openers in the brain stem circulation in vivo. In aged rats, although K ATP channels are also functional in the brain stem circulation, dilator response of the microvessels but not of the large arteries to direct activation of K ATP channels is impaired.