L-Arginine supplementation does not impact cerebrovascular function in young adults Christopher J. Marley1, Aled Davies1, Danielle Hodson1,2, Julien V. Brugniaux1,3, Luke Liddle1,4 and Damian M. Bailey1  1Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, UK 2Department of Biomolecular and Sport Sciences, Coventry University, UK 3School of Science and Health, Western Sydney University, Australia 4School of Science and Sport, West Scotland University, UK Background Aims & Hypothesis L-Arginine (LA) is an amino acid, which when combined with oxygen, catalyses nitric oxide (NO), a potent vasodilator that is important for vascular regulation1. Both long2 and short-term3 supplementation of LA has been linked to improvements in vascular function in the systemic circulation, raising interest in its potential therapeutic use. However, less is known about its influence on the cerebral circulation. To determine the effect short-term LA supplementation has on cerebrovascular function. Short-term LA supplementation will result in improved cerebrovascular function. METHODS Participants 8 apparently healthy young male adults (age = 21 + 1 years). Experimental Procedures NO was assessed on the morning of each visit using ozone-based chemiluminescence (through the breath; Sievers NOA 280i, GE Analytical Instruments, UK). Study Design The study was a single-blinded, randomised, placebo-controlled study. Two visits were required, which were separated by a 7-day “washout” period. Middle cerebral artery velocity (MCAv) & mean arterial pressure (MAP) were assessed continuously using transcranial Doppler ultrasound (PMD 100, Spencer Technologies, USA) and photoplethysmography (Portapress, TPD Biomedical, Netherlands), respectively. Cerebrovascular resistance (CVR) & conductance (CVC) were calculated as MAP/MCAv & MCAv/MAP, respectively, following 5 minutes of seated rest. Supplementation Each visit to the laboratory was preceded by a 3-day oral supplementation of either: x7 500mg LA capsules (per day) x7 flour capsules OR The reactivity of the cerebral vessels in response to an increase (CVRCO2HYPER) and decrease (CVRCO2HYPO) in CO2 was calculated as the percentage change in MCAv from baseline per mmHg change in partial pressure of CO2 determined by capnography (ML 206, ADInstruments, UK), following 3 minutes of breathing 5% CO2 and 3 minutes controlled hyperventilation, respectively. Statistical Analysis Following confirmation of distribution of normality (Shapiro-W-Wilk Tests), data were analysed using paired samples t-tests. Significance was set 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 no confer any changes in cerebrovascular function (Table 1). Table 1. Cerebrovascular function Placebo  L-Arginine P Values MCAv (cm.s-1)  62 + 3 59 + 8 0.17 MAP (mmHg)  89 + 7 86 + 9 0.34 CVR (mmHg/cm.s-1)  1.45 + 0.22 1.47 + 0.20 0.71 CVC (cm.s-1/mmHg)  0.70 + 0.10 0.69 + 0.10 0.70 CVRCO2HYPER (%.mmHg-1)  3.37 + 1.23 3.34 + 0.83 0.95 CVRCO2HYPO (%.mmHg-1)  2.38 + 0.32 2.62 + 0.86 0.40 CVRCO2RANGE (%.mmHg-1)  5.75 + 1.43 5.96 + 1.48 0.42 Figure 1. Changes in exhaled NO Values are mean + SD. CVRCO2RANGE = CVRCO2HYPER + CVRCO2HYPO. Values are mean + SD; † P < 0.05 vs. Placebo. Conclusions Contrary to our hypothesis, short-term oral supplementation of LA does not impact cerebrovascular function in healthy young adults. ACKNOWLEDGEMENTS The present research was supported by the JPR Williams Trust, in co-ordination with the University of South Wales. CJM is supported by a travel grant from the Physiological Society. REFERENCES 1Moncada and Higgs (1993) NEJM, 329, 2002-2012; 2Lerman et al. (1998) Circulation, 97, 2123-2128; 3Nagaya et al. (2001) Am J Respir Crit Care Med, 163, 887-891.