Published Online
on February 13, 2006

A more recent version of this article appeared on February 21, 2006

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Submitted on September 21, 2005
Revised on November 7, 2005
Accepted on December 15, 2005

Postconditioning Protects Against Endothelial Ischemia-Reperfusion Injury in the Human Forearm

Stavros P. Loukogeorgakis BSc, PhD^*, Anna T. Panagiotidou BSc, Derek M. Yellon PhD, DSc, FRCP, John E. Deanfield BA, BCh, MB, FRCP, and Raymond J. MacAllister MA, MD, FRCP

From the Vascular Physiology Unit (S.P.L., A.T.P., J.E.D.), Institute of Child Health; Hatter Cardiovascular Institute and Centre for Cardiology (D.M.Y.); and Centre for Clinical Pharmacology and Therapeutics (S.P.L., A.T.P., R.J.M.), University College London, London, United Kingdom.

^* To whom correspondence should be addressed. E-mail: s.loukogeorgakis{at}ich.ucl.ac.uk.

Background--Hypoxic cell death follows interruption of blood supply to tissues. Although successful restoration of blood flow is mandatory for salvage of ischemic tissues, reperfusion can paradoxically place tissues at risk of further injury. Brief periods of ischemia applied at the onset of reperfusion have been shown to reduce ischemia-reperfusion (IR) injury, a phenomenon called postconditioning. The aim of this study was to determine whether postconditioning protects against endothelial IR injury in humans, in vivo.

Methods and Results--Brachial artery endothelial function was assessed by vascular ultrasound to measure flow-mediated dilation (FMD) in response to forearm reactive hyperemia. FMD was measured before and after IR (20 minutes of arm ischemia followed by 20 minutes of reperfusion) in healthy volunteers. To test the protective effects of postconditioning, 3 cycles of reperfusion followed by ischemia (each lasting 10 or 30 seconds) were applied immediately after 20 minutes of arm ischemia. To determine whether postconditioning needs to be applied at the onset of reperfusion, a 1-minute period of arm reperfusion was allowed before the application of the 10-second postconditioning stimulus. IR caused endothelial dysfunction (FMD 9.1±1.2% pre-IR, 3.6±0.7% post-IR, P<0.001; n=11), which was prevented by postconditioning applied as 10-second cycles of reperfusion/ischemia (FMD 9.9±1.7% pre-IR, 8.3±1.4% post-IR, P=NS; n=11) and 30-second cycles of reperfusion/ischemia (FMD 10.8±1.7% pre-IR, 9.5±1.5% post-IR, P=NS; n=10) immediately at the onset of reperfusion. No protection was observed when the application of the 10-second postconditioning stimulus was delayed for 1 minute after the onset of reperfusion (FMD 9.8±1.2% pre-IR, 4.0±0.9% post-IR, P<0.001; n=8).

Conclusions--This study demonstrates for the first time that postconditioning can protect against endothelial IR injury in humans. Postconditioning might reduce tissue injury when applied at the onset of reperfusion by modifying the reperfusion phase of IR.

Key words: endothelium • ischemia • reperfusion • reperfusion injury • postconditioning

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