AUTHOR=Johansson Pär I. , Bergström Anita , Aachmann-Andersen Niels J. , Meyer Martin A. S. , Ostrowski Sisse R. , Nordsborg Nikolai B. , Olsen Niels V. 

TITLE=Effect of acute hypobaric hypoxia on the endothelial glycocalyx and digital reactive hyperemia in humans

JOURNAL=Frontiers in Physiology

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2014.00459

DOI=10.3389/fphys.2014.00459

ISSN=1664-042X

ABSTRACT=<p><bold>Introduction:</bold> Hypoxia is associated with increased capillary permeability. This study tested whether acute hypobaric hypoxia involves degradation of the endothelial glycocalyx.</p><p><bold>Methods:</bold> We exposed 12 subjects to acute hypobaric hypoxia (equivalent to 4500 m for 2–4 h) and measured venous blood concentrations of biomarkers reflecting endothelial and glycocalyx degradation (catecholamines, syndecan-1, soluble CD40 ligand, protein C, soluble thrombomodulin, tissue-type plasminogen activators, histone-complexed DNA fragments, and nitrite/nitrate). Endothelial function was assessed by the hyperemic response to brachial artery occlusion by peripheral arterial tonometry.</p><p><bold>Results:</bold> Compared with normoxic baseline levels, hypoxia increased concentrations of syndecan-1 from 22 (95% confidence interval: 17–27) to 25 (19–30) ng/ml (<italic>p</italic> &lt; 0.02) and protein C from 76 (70–83)% to 81 (74–88)% (<italic>p</italic> &lt; 0.02). Nitrite/nitrate decreased from 23 (18–27) μM at baseline to 19 (14–24) μM and 18 (14–21) μM in hypoxia and recovery, respectively (<italic>p</italic> &lt; 0.05). Other biomarkers remained unchanged. The post-occlusion/pre-occlusion ratio (reactive hyperemia index, RHI) decreased from 1.80 (1.52–2.07) in normoxia to 1.62 (1.28–1.96) after 2–4 h of hypobaric hypoxia and thereafter increased to 2.43 (1.99–2.86) during normoxic recovery (<italic>p</italic> &lt; 0.01).</p><p><bold>Conclusions:</bold> The increase in syndecan-1 and protein C suggests that acute hypobaric hypoxia produces a minor degree of glycocalyx degradation and overall cellular damage. After hypoxia RHI rebounded to higher than baseline levels suggesting improved endothelial functionality.</p>