title: Nitric oxide mediates hypoxia-induced cerebral vasodilation in humans.
abstract: Nitric oxide (NO) plays a pivotal role in the regulation of peripheral vascular tone. Its role in the regulation of cerebral vascular tone in humans remains to be elucidated. This study investigates the role of NO in hypoxia-induced cerebral vasodilatation in young healthy volunteers. The effect of the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) on the cerebral blood flow (CBF) was assessed during normoxia and during hypoxia (peripheral O(2) saturation 97 and 80%, respectively). Subjects were positioned in a magnetic resonance scanner, breathing normal air (normoxia) or a N(2)-O(2) mixture (hypoxia). The CBF was measured before and after administration of L-NMMA (3 mg/kg) by use of phase-contrast magnetic resonance imaging techniques. Administration of L-NMMA during normoxia did not affect CBF. Hypoxia increased CBF from 1,049 +/- 113 to 1,209 +/- 143 ml/min (P < 0.05). After L-NMMA administration, the augmented CBF returned to baseline (1,050 +/- 161 ml/min; P < 0.05). Similarly, cerebral vascular resistance declined during hypoxia and returned to baseline after administration of L-NMMA (P < 0.05 for both). Use of phase-contrast magnetic resonance imaging shows that hypoxia-induced cerebral vasodilatation in humans is mediated by NO.
authors.affiliation: Department of General Internal Medicine, Section of Gerontology and Geriatrics, Leiden University Medical Center, 2300 RC Leiden, The Netherlands.
authors.forename: Annette H M
authors.initials: AH
authors.lastname: Van Mil
authors.forename: Aart
authors.initials: A
authors.lastname: Spilt
authors.forename: Mark A
authors.initials: MA
authors.lastname: Van Buchem
authors.forename: Edward L E M
authors.initials: EL
authors.lastname: Bollen
authors.forename: Luc
authors.initials: L
authors.lastname: Teppema
authors.forename: Rudi G J
authors.initials: RG
authors.lastname: Westendorp
authors.forename: Gerard J
authors.initials: GJ
authors.lastname: Blauw
mesh_terms: D000328:Adult; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D012016:Reference Values; D014655:Vascular Resistance / Q000187:drug effects; D014664:Vasodilation / Q000502:physiology*; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D009569:Nitric Oxide