KATP channels modulate cerebral blood flow and oxygen delivery during isocapnic hypoxia in humans.

ATP-sensitive K+ (KATP ) channels mediate hypoxia-induced cerebral vasodilatation and hyperperfusion in animals. We tested whether KATP channels blockade affects the increase in cerebral blood flow (CBF) and the maintenance of oxygen delivery (CDO2 ) during hypoxia in humans. Nine healthy men were exposed to 5-min trials of normoxia and isocapnic hypoxia (IHX, 10% O2 ) before (BGB) and 3 h after glibenclamide ingestion (AGB). Mean arterial pressure (MAP), arterial saturation ( S a O 2 ), partial pressure of oxygen ( P a O 2 ) and carbon dioxide ( P aC O 2 ), internal carotid artery blood flow (ICABF), vertebral artery blood flow (VABF), total (t)CBF (Doppler ultrasound) and CDO2 were quantified during the trials. IHX provoked similar reductions in S a O 2 and P a O 2 , while MAP was not affected by oxygen desaturation or KATP blockade. A smaller increase in ICABF (ΔBGB: 36 ± 23 vs. ΔAGB 11 ± 18%, p = 0.019) but not in VABF (∆BGB 26 ± 21 vs. ∆AGB 27 ± 27%, p = 0.893) was observed during the hypoxic trial under KATP channels blockade. Thus, IHX-induced increases in tCBF (∆BGB 32 ± 19 vs. ∆AGB 14 ± 13%, p = 0.012) and CDO2 relative changes (∆BGB 7 ± 13 vs. ∆AGB -6 ± 14%, p = 0.048) were attenuated during the AGB hypoxic trial. In a separate protocol, 6 healthy men (5 from protocol 1) underwent a 5-min exposure to normoxia and IHX before and 3 h after placebo (5 mg of cornstarch) ingestion. IHX reduced S a O 2 and P a O 2 , but placebo did not affect the ICABF, VABF, tCBF, or CDO2 responses. Therefore, in humans, KATP channels activation modulates vascular tone in the anterior rather than the posterior circulation of the brain, contributing to tCBF and CDO2 responses to hypoxia.