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Carr JMJR, Hoiland RL, Fernandes IA, Schrage WG, Ainslie PN. Recent insights into mechanisms of hypoxia-induced vasodilatation in the human brain. J Physiol 2023. [PMID: 37655827 DOI: 10.1113/jp284608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Accepted: 08/07/2023] [Indexed: 09/02/2023] Open
Abstract
The cerebral vasculature manages oxygen delivery by adjusting arterial blood in-flow in the face of reductions in oxygen availability. Hypoxic cerebral vasodilatation, and the associated hypoxic cerebral blood flow reactivity, involve many vascular, erythrocytic and cerebral tissue mechanisms that mediate elevations in cerebral blood flow via micro- and macrovascular dilatation. This contemporary review focuses on in vivo human work - with reference to seminal preclinical work where necessary - on hypoxic cerebrovascular reactivity, particularly where recent advancements have been made. We provide updates with the following information: in humans, hypoxic cerebral vasodilatation is partially mediated via a - likely non-obligatory - combination of: (1) nitric oxide synthases, (2) deoxygenation-coupled S-nitrosothiols, (3) potassium channel-related vascular smooth muscle hyperpolarization, and (4) prostaglandin mechanisms with some contribution from an interrelationship with reactive oxygen species. And finally, we discuss the fact that, due to the engagement of deoxyhaemoglobin-related mechanisms, reductions in O2 content via haemoglobin per se seem to account for ∼50% of that seen with hypoxic cerebral vasodilatation during hypoxaemia. We further highlight the issue that methodological impediments challenge the complete elucidation of hypoxic cerebral reactivity mechanisms in vivo in healthy humans. Future research is needed to confirm recent advancements and to reconcile human and animal findings. Further investigations are also required to extend these findings to address questions of sex-, heredity-, age-, and disease-related differences. The final step is to then ultimately translate understanding of these mechanisms into actionable, targetable pathways for the prevention and treatment of cerebral vascular dysfunction and cerebral hypoxic brain injury.
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Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for Researching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
| | - Igor A Fernandes
- Department of Health and Kinesiology, Purdue University, Indiana, USA
| | - William G Schrage
- Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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2
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Hoiland RL, MacLeod DB, Stacey BS, Caldwell HG, Howe CA, Nowak-Flück D, Carr JMJR, Tymko MM, Coombs GB, Patrician A, Tremblay JC, Van Mierlo M, Gasho C, Stembridge M, Sekhon MS, Bailey DM, Ainslie PN. Hemoglobin and cerebral hypoxic vasodilation in humans: Evidence for nitric oxide-dependent and S-nitrosothiol mediated signal transduction. J Cereb Blood Flow Metab 2023; 43:1519-1531. [PMID: 37042194 PMCID: PMC10414015 DOI: 10.1177/0271678x231169579] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2022] [Revised: 01/20/2023] [Accepted: 03/10/2023] [Indexed: 04/13/2023]
Abstract
Cerebral hypoxic vasodilation is poorly understood in humans, which undermines the development of therapeutics to optimize cerebral oxygen delivery. Across four investigations (total n = 195) we investigated the role of nitric oxide (NO) and hemoglobin-based S-nitrosothiol (RSNO) and nitrite (NO 2 - ) signaling in the regulation of cerebral hypoxic vasodilation. We conducted hemodilution (n = 10) and NO synthase inhibition experiments (n = 11) as well as hemoglobin oxygen desaturation protocols, wherein we measured cerebral blood flow (CBF), intra-arterial blood pressure, and in subsets of participants trans-cerebral release/uptake of RSNO and NO 2 - . Higher CBF during hypoxia was associated with greater trans-cerebral RSNO release but not NO 2 - , while NO synthase inhibition reduced cerebral hypoxic vasodilation. Hemodilution increased the magnitude of cerebral hypoxic vasodilation following acute hemodilution, while in 134 participants tested under normal conditions, hypoxic cerebral vasodilation was inversely correlated to arterial hemoglobin concentration. These studies were replicated in a sample of polycythemic high-altitude native Andeans suffering from excessive erythrocytosis (n = 40), where cerebral hypoxic vasodilation was inversely correlated to hemoglobin concentration, and improved with hemodilution (n = 6). Collectively, our data indicate that cerebral hypoxic vasodilation is partially NO-dependent, associated with trans-cerebral RSNO release, and place hemoglobin-based NO signaling as a central mechanism of cerebral hypoxic vasodilation in humans.
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Affiliation(s)
- Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
- International Collaboration on Repair Discoveries, Vancouver, BC, Canada
| | - David B MacLeod
- Human Pharmacology & Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Hannah G Caldwell
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Connor A Howe
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Daniela Nowak-Flück
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Jay MJR Carr
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Michael M Tymko
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Geoff B Coombs
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Alexander Patrician
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Michelle Van Mierlo
- Department of Biomechanical Engineering, University of Twente, Enschede, The Netherlands
| | - Chris Gasho
- Department of Medicine, Division of Pulmonary and Critical Care, Loma Linda University School of Medicine, Loma Linda, CA, USA
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Mypinder S Sekhon
- International Collaboration on Repair Discoveries, Vancouver, BC, Canada
- Djavad Mowafaghian Centre for Brain Health, Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
- Division of Critical Care Medicine, Department of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, BC, Canada
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3
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Zheng Z, Li Z, Lv J. Loss of Kir6.1 facilitates peri-infarct depolarizations in focal cerebral ischemia. Neurol Res 2022; 44:797-806. [PMID: 35271426 DOI: 10.1080/01616412.2022.2051132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
OBJECTIVE Peri-infarct depolarizations (PIDs) are spontaneous waves that propagate slowly across the penumbra region following stroke, contributing to secondary infarct growth and negatively affecting stroke outcomes. KATP channels are generally spread in the brain. Under conditions of ischemia and/or hypoxia, KATP channels play a cytoprotective role in neurons. However, it is still unknown whether KATP channels are involved in the initiation and propagation of PIDs. METHODS The Kir6.1 knockout (Kir6.1-/-) mice, Kir6.2 knockout (Kir6.2-/-) mice, and wild-type C57Bl6 mice (n = 8) were used. The middle cerebral artery occlusion (MCAO) stroke model was made and PIDs were detected by an optical intrinsic signal (OIS) imaging system. RESULTS Much more PIDs appeared in Kir6.1-/-mice than that in Kir6.2-/- and WT mice in both the first hour and 4 hours following MCAO (3.9 ± 0.7 vs. 1.5 ± 0.3, p < 0,05; 3.9 ± 0.7 vs. 1.9 ± 0.3, p < 0.05; 20.0 ± 2.5 vs. 10.4 ± 2.4, p < 0.05; 20.0 ± 2.5 vs. 11.3 ± 1.4, p < 0.05). Furthermore, the first PID occurred much earlier in Kir6.1-/- mice than that in Kir6.2-/- mice and WT mice (21.3 ± 2.1 min vs. 34.1 ± 4.8 min, p < 0.05; 21.3 ± 2.1 min vs. 38.8 ± 3.4 min, p < 0.01). No significant differences in other characteristics of PIDs including originating sites, duration time, propagation patterns, and velocity were detected. Additionally, the migration of originating sites was observed. CONCLUSION This study shows that loss of Kir6.1, not Kir6.2 facilitates the induction of PIDs in focal cerebral ischemia, indicating that Kir6.1-forming channels in the brain may provide protection against PIDs.
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Affiliation(s)
- Zelong Zheng
- The Department of Neurosurgery, Guangzhou First People's Hospital, School of Medicine, South China University of Technology, Guangzhou, Guangdong, China
| | - Zhenyu Li
- The Department of Neurosurgery, Guangzhou First People's Hospital, School of Medicine, South China University of Technology, Guangzhou, Guangdong, China
| | - Jianping Lv
- The Department of Neurosurgery, Guangzhou First People's Hospital, School of Medicine, South China University of Technology, Guangzhou, Guangdong, China
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Carter KJ, Ward AT, Kellawan JM, Eldridge MW, Al-Subu A, Walker BJ, Lee JW, Wieben O, Schrage WG. Nitric oxide synthase inhibition in healthy adults reduces regional and total cerebral macrovascular blood flow and microvascular perfusion. J Physiol 2021; 599:4973-4989. [PMID: 34587648 PMCID: PMC9009720 DOI: 10.1113/jp281975] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 09/28/2021] [Indexed: 11/08/2022] Open
Abstract
The importance of nitric oxide (NO) in regulating cerebral blood flow (CBF) remains unresolved, due in part to methodological approaches, which lack a comprehensive assessment of both global and regional effects. Importantly, NO synthase (NOS) expression and activity appear greater in some anterior brain regions, suggesting region-specific NOS influence on CBF. We hypothesized that NO contributes to basal CBF in healthy adults, in a regionally distinct pattern that predominates in the anterior circulation. Fourteen healthy adults (7 females; 24 ± 5 years) underwent two magnetic resonance imaging (MRI) study visits with saline (placebo) or the NOS inhibitor, L-NMMA, administered in a randomized, single-blind approach. 4D flow MRI quantified total and regional macrovascular CBF, whereas arterial spin labelling (ASL) MRI quantified total and regional microvascular perfusion. L-NMMA (or volume-matched saline) was infused intravenously for 5 min prior to imaging. L-NMMA reduced CBF (L-NMMA: 722 ± 100 vs. placebo: 771 ± 121 ml/min, P = 0.01) with similar relative reductions (5-7%) in anterior and posterior cerebral circulations, due in part to the reduced cross-sectional area of 9 of 11 large cerebral arteries. Global microvascular perfusion (ASL) was reduced by L-NMMA (L-NMMA: 42 ± 7 vs. placebo: 47 ± 8 ml/100g/min, P = 0.02), with 7-11% reductions in both hemispheres of the frontal, parietal and temporal lobes, and in the left occipital lobe. We conclude that NO contributes to macrovascular and microvascular regulation including larger artery resting diameter. Contrary to our hypothesis, the influence of NO on cerebral perfusion appears regionally uniform in healthy young adults. KEY POINTS: Cerebral blood flow (CBF) is vital for brain health, but the signals that are key to regulating CBF remain unclear. Nitric oxide (NO) is produced in the brain, but its importance in regulating CBF remains controversial since prior studies have not studied all regions of the brain simultaneously. Using modern MRI approaches, a drug that inhibits the enzymes that make NO (L-NMMA) reduced CBF by up to 11% in different brain regions. NO helps maintain proper CBF in healthy adults. These data will help us understand whether the reductions in CBF that occur during ageing or cardiovascular disease are related to shifts in NO signalling.
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Affiliation(s)
- Katrina J Carter
- Department of Kinesiology, University of Wisconsin, Madison, WI, USA
| | - Aaron T Ward
- Department of Kinesiology, University of Wisconsin, Madison, WI, USA
| | - J Mikhail Kellawan
- Department of Health and Exercise Science, University of Oklahoma, Norman, OK, USA
| | | | - Awni Al-Subu
- Department of Pediatrics, University of Wisconsin, Madison, WI, USA
| | - Benjamin J Walker
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA
| | - Jeffrey W Lee
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA
| | - Oliver Wieben
- Department of Medical Physics, University of Wisconsin, Madison, WI, USA
- Department of Radiology, University of Wisconsin, Madison, WI, USA
| | - William G Schrage
- Department of Kinesiology, University of Wisconsin, Madison, WI, USA
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Claassen JAHR, Thijssen DHJ, Panerai RB, Faraci FM. Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation. Physiol Rev 2021; 101:1487-1559. [PMID: 33769101 PMCID: PMC8576366 DOI: 10.1152/physrev.00022.2020] [Citation(s) in RCA: 272] [Impact Index Per Article: 90.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.
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Affiliation(s)
- Jurgen A H R Claassen
- Department of Geriatrics, Radboud University Medical Center, Donders Institute for Brain, Cognition, and Behaviour, Nijmegen, The Netherlands
| | - Dick H J Thijssen
- Department of Physiology, Radboud Institute for Health Sciences, Nijmegen, The Netherlands
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Ronney B Panerai
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- >National Institute for Health Research Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
| | - Frank M Faraci
- Departments of Internal Medicine, Neuroscience, and Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, Iowa
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Dugan AJ, Nelson PT, Katsumata Y, Shade LMP, Boehme KL, Teylan MA, Cykowski MD, Mukherjee S, Kauwe JSK, Hohman TJ, Schneider JA, Fardo DW. Analysis of genes (TMEM106B, GRN, ABCC9, KCNMB2, and APOE) implicated in risk for LATE-NC and hippocampal sclerosis provides pathogenetic insights: a retrospective genetic association study. Acta Neuropathol Commun 2021; 9:152. [PMID: 34526147 PMCID: PMC8442328 DOI: 10.1186/s40478-021-01250-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 08/25/2021] [Indexed: 12/13/2022] Open
Abstract
Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is the most prevalent subtype of TDP-43 proteinopathy, affecting up to 1/3rd of aged persons. LATE-NC often co-occurs with hippocampal sclerosis (HS) pathology. It is currently unknown why some individuals with LATE-NC develop HS while others do not, but genetics may play a role. Previous studies found associations between LATE-NC phenotypes and specific genes: TMEM106B, GRN, ABCC9, KCNMB2, and APOE. Data from research participants with genomic and autopsy measures from the National Alzheimer’s Coordinating Center (NACC; n = 631 subjects included) and the Religious Orders Study and Memory and the Rush Aging Project (ROSMAP; n = 780 included) were analyzed in the current study. Our goals were to reevaluate disease-associated genetic variants using newly collected data and to query whether the specific genotype/phenotype associations could provide new insights into disease-driving pathways. Research subjects included in prior LATE/HS genome-wide association studies (GWAS) were excluded. Single nucleotide variants (SNVs) within 10 kb of TMEM106B, GRN, ABCC9, KCNMB2, and APOE were tested for association with HS and LATE-NC, and separately for Alzheimer’s pathologies, i.e. amyloid plaques and neurofibrillary tangles. Significantly associated SNVs were identified. When results were meta-analyzed, TMEM106B, GRN, and APOE had significant gene-based associations with both LATE and HS, whereas ABCC9 had significant associations with HS only. In a sensitivity analysis limited to LATE-NC + cases, ABCC9 variants were again associated with HS. By contrast, the associations of TMEM106B, GRN, and APOE with HS were attenuated when adjusting for TDP-43 proteinopathy, indicating that these genes may be associated primarily with TDP-43 proteinopathy. None of these genes except APOE appeared to be associated with Alzheimer’s-type pathology. In summary, using data not included in prior studies of LATE or HS genomics, we replicated several previously reported gene-based associations and found novel evidence that specific risk alleles can differentially affect LATE-NC and HS.
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Fernandes IA, Mattos JD, Campos MO, Rocha MP, Mansur DE, Rocha HM, Garcia VP, Alvares T, Secher NH, Nóbrega ACL. Reactive oxygen species play a modulatory role in the hyperventilatory response to poikilocapnic hyperoxia in humans. J Physiol 2021; 599:3993-4007. [PMID: 34245024 DOI: 10.1113/jp281635] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 07/08/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The proposed mechanism for the increased ventilation in response to hyperoxia includes a reduced brain CO2 -[H+ ] washout-induced central chemoreceptor stimulation that results from a decrease in cerebral perfusion and the weakening of the CO2 affinity for haemoglobin. Nonetheless, hyperoxia also results in excessive brain reactive oxygen species (ROS) formation/accumulation, which hypothetically increases central respiratory drive and causes hyperventilation. We then quantified ventilation, cerebral perfusion/metabolism, arterial/internal jugular vein blood gases and oxidant/antioxidant biomarkers in response to hyperoxia during intravenous infusion of saline or ascorbic acid to determine whether excessive ROS production/accumulation contributes to the hyperoxia-induced hyperventilation in humans. Ascorbic acid infusion augmented the antioxidant defence levels, blunted ROS production/accumulation and minimized both the reduction in cerebral perfusion and the increase in ventilation observed during saline infusion. Hyperoxic hyperventilation seems to be mediated by central chemoreceptor stimulation provoked by the interaction between an excessive ROS production/accumulation and reduced brain CO2 -[H+ ] washout. ABSTRACT The hypothetical mechanism for the increase in ventilation ( V ̇ E ) in response to hyperoxia (HX) includes central chemoreceptor stimulation via reduced CO2 -[H+ ] washout. Nonetheless, hyperoxia disturbs redox homeostasis and raises the hypothesis that excessive brain reactive oxygen species (ROS) production/accumulation may increase the sensitivity to CO2 or even solely activate the central chemoreceptors, resulting in hyperventilation. To determine the mechanism behind the HX-evoked increase in V ̇ E , 10 healthy men (24 ± 4 years) underwent 10 min trials of HX under saline and ascorbic acid infusion. V ̇ E , arterial and right internal right jugular vein (ijv) partial pressure for oxygen (PO2 ) and CO2 (PCO2 ), pH, oxidant (8-isoprostane) and antioxidant (ascorbic acid) markers, as well as cerebral blood flow (CBF) (Duplex ultrasonography), were quantified at each hyperoxic trial. HX evoked an increase in arterial partial pressure for oxygen, followed by a hyperventilatory response, a reduction in CBF, an increase in arterial 8-isoprostane, and unchanged PijvCO2 and ijv pH. Intravenous ascorbic acid infusion augmented the arterial antioxidant marker, blunted the increase in arterial 8-isoprostane and attenuated both the reduction in CBF and the HX-induced hyperventilation. Although ascorbic acid infusion resulted in a slight increase in PijvCO2 and a substantial decrease in ijv pH, when compared with the saline bout, HX evoked a similar reduction and a paired increase in the trans-cerebral exchanges for PCO2 and pH, respectively. These findings indicate that the poikilocapnic hyperoxic hyperventilation is likely mediated via the interaction of the acidic brain interstitial fluid and an increase in central chemoreceptor sensitivity to CO2 , which, in turn, seems to be evoked by the excessive ROS production/accumulation.
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Affiliation(s)
- Igor A Fernandes
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | - João D Mattos
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | - Monique O Campos
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | - Marcos P Rocha
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | - Daniel E Mansur
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | - Helena M Rocha
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | - Vinicius P Garcia
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
| | | | - Niels H Secher
- Department of Anaesthesia, Rigshospitalet, Institute for Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Antonio C L Nóbrega
- Laboratory of Exercise Sciences, Fluminense Federal University, Niterói, Brazil
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Colburn TD, Weber RE, Schulze KM, Sue Hageman K, Horn AG, Behnke BJ, Poole DC, Musch TI. Sexual dimorphism in vascular ATP-sensitive K + channel function supporting interstitial PO2 via convective and/or diffusive O 2 transport. J Physiol 2021; 599:3279-3293. [PMID: 34101850 PMCID: PMC8451062 DOI: 10.1113/jp281120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Accepted: 04/14/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Inhibition of pancreatic ATP-sensitive K+ (KATP ) channels is the intended effect of oral sulphonylureas to increase insulin release in diabetes. However, pertinent to off-target effects of sulphonylurea medication, sex differences in cardiac KATP channel function exist, whereas potential sex differences in vascular KATP channel function remain unknown. In the present study, we assessed vascular KATP channel function (topical glibenclamide superfused onto fast-twitch oxidative skeletal muscle) supporting blood flow and interstitial O2 delivery-utilization matching ( P O 2 is) during twitch contractions in male, female during pro-oestrus and ovariectomized female (F+OVX) rats. Glibenclamide decreased blood flow (convective O2 transport) and interstitial P O 2 in male and female, but not F+OVX, rats. Compared to males, females also demonstrated impaired diffusive O2 transport and a faster fall in interstitial P O 2 . Our demonstration, in rats, that sex differences in vascular KATP channel function exist support the tentative hypothesis that oral sulphonylureas may exacerbate exercise intolerance and morbidity, especially in premenopausal females. ABSTRACT Vascular ATP-sensitive K+ (KATP ) channels support skeletal muscle blood flow ( Q ̇ m ), interstitial O2 delivery ( Q ̇ O 2 )-utilization ( V ̇ O 2 ) matching (i.e. interstitial-myocyte O2 flux driving pressure; P O 2 is) and exercise tolerance. Potential sex differences in skeletal muscle vascular KATP channel function remain largely unexplored. We hypothesized that local skeletal muscle KATP channel inhibition via glibenclamide superfusion (5 mg kg-1 GLI; sulphonylurea diabetes medication) in anaesthetized female Sprague-Dawley rats, compared to males, would demonstrate greater reductions in contracting (1 Hz, 7 V, 180 s) fast-twitch oxidative mixed gastrocnemius (97% type IIA+IID/X+IIB) Q ̇ m (15 μm microspheres) and P O 2 is (phosphorescence quenching), resulting from more compromised convective ( Q ̇ O 2 ) and diffusive ( D O 2 ) O2 conductances. Furthermore, these GLI-induced reductions in ovary-intact females measured during pro-oestrus would be diminished following ovariectomy (F+OVX). GLI similarly impaired mixed gastrocnemius V ̇ O 2 in both males (↓28%) and females (↓33%, both P < 0.032) via reduced Q ̇ m (male: ↓31%, female: ↓35%, both P < 0.020), Q ̇ O 2 (male: 5.6 ± 0.5 vs. 4.0 ± 0.5, female: 6.4 ± 1.1 vs. 4.2 ± 0.6 mL O2 min-1 100 g tissue-1 , P < 0.022) and the resulting P O 2 is, with females also demonstrating a reduced D O 2 (0.40 ± 0.07 vs. 0.30 ± 0.04 mL O2 min-1 100 g tissue-1 , P < 0.042) and a greater GLI-induced speeding of P O 2 is fall (mean response time: Sex × Drug interaction, P = 0.026). Conversely, GLI did not impair the mixed gastrocnemius of F+OVX rats. Therefore, in patients taking sulphonylureas, these results support the potential for impaired vascular KATP channel function to compromise muscle Q ̇ m and therefore exercise tolerance. Such an effect, if present, would likely contribute to adverse cardiovascular events in premenopausal females more than males.
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Affiliation(s)
- Trenton D. Colburn
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Ramona E. Weber
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Kiana M. Schulze
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - K. Sue Hageman
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Andrew G. Horn
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Brad J. Behnke
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - David C. Poole
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, 66506, USA
| | - Timothy I. Musch
- Department of Kinesiology, Physiology, Kansas State University, Manhattan, KS, 66506, USA
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, 66506, USA
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9
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Hirai DM, Tabuchi A, Craig JC, Colburn TD, Musch TI, Poole DC. Regulation of capillary hemodynamics by K ATP channels in resting skeletal muscle. Physiol Rep 2021; 9:e14803. [PMID: 33932103 PMCID: PMC8087980 DOI: 10.14814/phy2.14803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 02/22/2021] [Indexed: 12/25/2022] Open
Abstract
ATP-sensitive K+ channels (KATP ) have been implicated in the regulation of resting vascular smooth muscle membrane potential and tone. However, whether KATP channels modulate skeletal muscle microvascular hemodynamics at the capillary level (the primary site for blood-myocyte O2 exchange) remains unknown. We tested the hypothesis that KATP channel inhibition would reduce the proportion of capillaries supporting continuous red blood cell (RBC) flow and impair RBC hemodynamics and distribution in perfused capillaries within resting skeletal muscle. RBC flux (fRBC ), velocity (VRBC ), and capillary tube hematocrit (Hctcap ) were assessed via intravital microscopy of the rat spinotrapezius muscle (n = 6) under control (CON) and glibenclamide (GLI; KATP channel antagonist; 10 µM) superfusion conditions. There were no differences in mean arterial pressure (CON:120 ± 5, GLI:124 ± 5 mmHg; p > 0.05) or heart rate (CON:322 ± 32, GLI:337 ± 33 beats/min; p > 0.05) between conditions. The %RBC-flowing capillaries were not altered between conditions (CON:87 ± 2, GLI:85 ± 1%; p > 0.05). In RBC-perfused capillaries, GLI reduced fRBC (CON:20.1 ± 1.8, GLI:14.6 ± 1.3 cells/s; p < 0.05) and VRBC (CON:240 ± 17, GLI:182 ± 17 µm/s; p < 0.05) but not Hctcap (CON:0.26 ± 0.01, GLI:0.26 ± 0.01; p > 0.05). The absence of GLI effects on the %RBC-flowing capillaries and Hctcap indicates preserved muscle O2 diffusing capacity (DO2 m). In contrast, GLI lowered both fRBC and VRBC thus impairing perfusive microvascular O2 transport (Q̇m) and lengthening RBC capillary transit times, respectively. Given the interdependence between diffusive and perfusive O2 conductances (i.e., %O2 extraction∝DO2 m/Q̇m), such GLI alterations are expected to elevate muscle %O2 extraction to sustain a given metabolic rate. These results support that KATP channels regulate capillary hemodynamics and, therefore, microvascular gas exchange in resting skeletal muscle.
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Affiliation(s)
- Daniel M. Hirai
- Department of Health and KinesiologyPurdue UniversityWest LafayetteIndianaUSA,Department of KinesiologyKansas State UniversityManhattanKansasUSA
| | - Ayaka Tabuchi
- Department of KinesiologyKansas State UniversityManhattanKansasUSA,Department of Engineering ScienceUniversity of Electro‐CommunicationsTokyoJapan
| | - Jesse C. Craig
- Department of KinesiologyKansas State UniversityManhattanKansasUSA,Department of Internal MedicineUniversity of UtahSalt Lake CityUtahUSA,Geriatric ResearchEducation and Clinical CenterVeterans Affairs Medical CenterSalt Lake CityUtahUSA
| | | | - Timothy I. Musch
- Department of KinesiologyKansas State UniversityManhattanKansasUSA,Department of Anatomy and PhysiologyKansas State UniversityManhattanKansasUSA
| | - David C. Poole
- Department of KinesiologyKansas State UniversityManhattanKansasUSA,Department of Anatomy and PhysiologyKansas State UniversityManhattanKansasUSA
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10
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Turner REF, Gatterer H, Falla M, Lawley JS. High-altitude cerebral edema: its own entity or end-stage acute mountain sickness? J Appl Physiol (1985) 2021; 131:313-325. [PMID: 33856254 DOI: 10.1152/japplphysiol.00861.2019] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
High-altitude cerebral edema (HACE) and acute mountain sickness (AMS) are neuropathologies associated with rapid exposure to hypoxia. However, speculation remains regarding the exact etiology of both HACE and AMS and whether they share a common mechanistic pathology. This review outlines the basic principles of HACE development, highlighting how edema could develop from 1) a progression from cytotoxic swelling to ionic edema or 2) permeation of the blood brain barrier (BBB) with or without ionic edema. Thereafter, discussion turns to the available neuroimaging literature in the context of cytotoxic, ionic, or vasogenic edema in both HACE and AMS. Although HACE is clearly caused by an increase in brain water of ionic and/or vasogenic origin, there is very little evidence that this type of edema is present when AMS develops. However, cerebral vasodilation, increased intracranial blood volume, and concomitant intracranial fluid shifts from the extracellular to the intracellular space, as interpreted from changes in diffusion indices within white matter, are observed consistently in persons acutely exposed to hypoxia and with AMS. Therefore, herein we explore the idea that intracellular swelling occurs alongside AMS, and is a critical precursor to extracellular ionic edema formation. We propose that this process produces a subtle modulation of the BBB, which either together with or independent of vasogenic edema provides a transvascular segue from the end-stage of AMS to HACE. Ultimately, this review seeks to shed light on the possible processes underlying HACE pathophysiology, and thus highlights potential avenues for future prevention and treatment.
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Affiliation(s)
- Rachel E F Turner
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Hannes Gatterer
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Marika Falla
- Center for Mind/Brain Sciences and Centre for Neurocognitive Rehabilitation, University of Trento, Rovereto, Italy
| | - Justin S Lawley
- Division of Performance Physiology & Prevention, Department of Sport Science, University of Innsbruck, Innsbruck, Austria
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11
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AlSalahi SE, Junejo RT, Bradley C, Balanos GM, Siebenmann C, Fisher JP. The middle cerebral artery blood velocity response to acute normobaric hypoxia occurs independently of changes in ventilation in humans. Exp Physiol 2021; 106:861-867. [PMID: 33527604 DOI: 10.1113/ep089127] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 01/28/2021] [Indexed: 12/22/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does the ventilatory response to moderate acute hypoxia increase cerebral perfusion independently of changes in arterial oxygen tension in humans? What is the main finding and its importance? The ventilatory response does not increase middle cerebral artery mean blood velocity during moderate isocapnic acute hypoxia beyond that elicited by reduced oxygen saturation. ABSTRACT Hypoxia induces ventilatory, cardiovascular and cerebrovascular adjustments to defend against reductions in systemic oxygen delivery. We aimed to determine whether the ventilatory response to moderate acute hypoxia increases cerebral perfusion independently of changes in arterial oxygenation. Eleven young healthy individuals were exposed to four 15 min experimental conditions: (1) normoxia (partial pressure of end-tidal oxygen, P ET O 2 = 100 mmHg), (2) hypoxia ( P ET O 2 = 50 mmHg), (3) normoxia with breathing volitionally matched to levels observed during hypoxia (hyperpnoea; P ET O 2 = 100 mmHg) and (4) hypoxia ( P ET O 2 = 50 mmHg) with respiratory frequency and tidal volume volitionally matched to levels observed during normoxia (i.e., restricted breathing (RB)). Isocapnia was maintained in all conditions. Middle cerebral artery mean blood velocity (MCA Vmean ), assessed by transcranial Doppler ultrasound, was increased during hypoxia (58 ± 12 cm/s, P = 0.04) and hypoxia + RB (61 ± 14 cm/s, P < 0.001) compared to normoxia (55 ± 11 cm/s), while it was unchanged during hyperpnoea (52 ± 13 cm/s, P = 0.08). MCA Vmean was not different between hypoxia and hypoxia + RB (P > 0.05). These findings suggest that the hypoxic ventilatory response does not increase cerebral perfusion, indexed using MCA Vmean , during moderate isocapnic acute hypoxia beyond that elicited by reduced oxygen saturation.
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Affiliation(s)
- Sultan E AlSalahi
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Rehan T Junejo
- Department of Life Sciences, Manchester Metropolitan University, Manchester, UK
| | - Chris Bradley
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - George M Balanos
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | | | - James P Fisher
- Department of Physiology, Faculty of Medical & Health Sciences, University of Auckland, Auckland, New Zealand
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12
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Smith KJ, Neill M, Hoiland RL. Scratching the surface of hypoxic cerebral vascular control: a potentially polarizing view of mechanistic research in humans. J Physiol 2020; 598:3313-3315. [DOI: 10.1113/jp280244] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Kurt J. Smith
- Integrative Physiology Laboratory Department of Kinesiology and Nutrition University of Illinois Chicago Chicgao IL USA
- School of Kinesiology Lakehead University Thunder Bay ON P7B 5E1 Canada
| | - Matthew Neill
- Integrative Physiology Laboratory Department of Kinesiology and Nutrition University of Illinois Chicago Chicgao IL USA
| | - Ryan L. Hoiland
- Centre for Heart, Lung, and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC V1V 1V7 Canada
- Department of Anesthesiology, Pharmacology, and Therapeutics Vancouver General Hospital 899 West 12th Avenue Vancouver BC V5Z 1M9 Canada
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