L-Arginine supplementation does not impact cerebrovascular function in young adults

Christopher Marley, Aled Davies, Danielle Hodson, Julien Brugniaux, Luke Liddle, Damian Bailey

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Abstract

Background: L-Arginine (LA) is an amino acid, which when combined with oxygen, catalyses nitric oxide (NO), a potent vasodilator that is important for vascular regulation (1). Due to the anti-athrogenic properties of NO (2), there has been increasing interest in the potential therapeutic use of LA to treat vascular disease. Both long (3) and short-term (4) supplementation have been linked to improvements in vascular function in the systemic circulation. However, less is known about its influence on the cerebral vasculature.
Methods: Eight healthy males (age: 21 ± 1 years; body mass index: 24.3 ± 3.4 kg.m2) participated in this single-blinded randomised placebo-controlled trial. Middle cerebral artery velocity (MCAv; transcranial Doppler ultrasound), mean arterial pressure (MAP; photoplethsmography) and end-tidal carbon dioxide (CO2; capnography) were continuously recorded throughout each testing session, which was preceded by either a 3-day oral supplementation of LA (x7 500mg capsules per day) or placebo powder (flour). Cerebrovascular resistance (CVR) and cerebrovascular conductance (CVC) were calculated as MAP/MCAv and MCAv/MAP respectively, following 5 minutes seated rest. Cerebrovascular reactivity to CO2 was assessed in response to 3 minutes of breathing 5% CO2 (balanced air; CVRCO2HYPER) and following 3 minutes of controlled hyperventilation (15 breaths per minute; CVRCO2HYPO). Cerebrovascular range was calculated as CVRCO2HYPER + CVRCO2HYPO. A 7-day "washout" period was followed between trials. Exhaled nitric oxide (ozone-based chemiluminescence) was measured on the morning of each visit. Following confirmation of distribution of normality (Shapiro-W-Wilk Tests), data were analysed using paired samples t-tests. Significance was established at P < 0.05 and data are expressed as mean ± SD.

Results: Supplementation with LA elevated exhaled NO (Figure 1; P < 0.05). However, this did not confer any changes in cerebrovascular function (Table 1).
Conclusion: These findings indicate that short-term oral supplementation of LA does not impact cerebrovascular function in healthy young adults. Whether LA supplementation influences cerebrovascular function in clinically relevant populations remains to be fully elucidated.
Original languageEnglish
Title of host publicationProceedings of The Physiological Society
PublisherThe Physiological Society
Volume37
Publication statusPublished - 1 Jul 2016
EventJoint Meeting of the American Physiological Society and The Physiological Society - Convention Centre, Dublin, Ireland
Duration: 29 Jul 201631 Jul 2016

Conference

ConferenceJoint Meeting of the American Physiological Society and The Physiological Society
Abbreviated titlePhysiology 2016
Country/TerritoryIreland
CityDublin
Period29/07/1631/07/16

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