Dynamic Progression of Contractile and Endothelial Dysfunction and Infarct Extension in the Late Phase of Reperfusion Zhi-Qing Zhao, M.D., Ph.D.,* ,1 Masanori Nakamura, M.D., Ph.D.,* Ning-Ping Wang, M.D.,* Daniel A. Velez, M.D.,* Karlene O. Hewan-Lowe, M.D.,† Robert A. Guyton, M.D.,* and Jakob Vinten-Johansen, Ph.D.* *Department of Cardiothoracic Surgery and †Department of Pathology, Emory University School of Medicine, Atlanta, Georgia 30365-2225 Submitted for publication May 11, 2000 Published online November 1, 2000 Background. Myocardial injury during early reper- fusion (R) has been well documented. However, the extent and time course of myocardial injury during late R are still unclear. The purpose of this study was to determine the extent of regional contractile and endothelial dysfunction and myocardial blood flow (MBF) defect as well as extension of infarction in as- sociation with neutrophil (PMN) actions during R. Materials and methods. A total of 29 dogs underwent a protocol of 1 h LAD ischemia followed by 6, 24, 48, and 72 h of R, respectively. Regional contractile function (sonomicrometry), MBF (colored microspheres), infarct size (triphenyltetrazolium chloride staining), and PMN localization (immunohistochemistry) were determined. Results. Percentage segmental shortening at 6, 24, 48, and 72 h of R was significantly blunted (1.8  1.2,*  0.37  0.6,* 0.04  0.2,* and 5.9  1.2* vs baseline 17.7  0.8). MBF (ml/min/g) was attenuated at 24 (0.27  0.03*), 48 (0.46  0.07*), and 72 h of R (0.48  0.06*) vs 6 h of R (0.65  0.06). Infarct size increased from 6 (27  2%) to 24 h of R (41  2%*) with no further increase at 48 and 72 h of R, consistent with a peak of creatine kinase activity. PMN adherence (mm 2 endothelium) to left anterior descending coronary artery (LAD) seg- ments was increased after 6 h of R (63  3*) vs non- ischemic left circumflex coronary artery (LCX) seg- ments (42  2) with a peak at 48 h of R (111  5*). Endothelium-dependent vascular relaxation in the LAD was also blunted at 6, 24, and 48 h of R. Immuno- staining revealed CD18-positive PMNs were mainly accumulated in intravascular space during 6 h of R with an increase in migration of PMNs seen at 24 h of R, consistent with a peak of myeloperoxidase release. Myeloperoxidase activity in a given area at risk sam- ple was significantly correlated with infarct extension during the first 24 h of R. Conclusions. These results provide pathologic evi- dence for myocardial injury during the extended R and a basis for exploration of interventions designed to limit myocardial injury after ischemia. (*P < 0.05 vs Baseline, 6 h of R and LCX segments.) © 2000 Academic Press Key Words: contractile function; infarct size; myocar- dial blood flow; neutrophil; reperfusion; endothelium. INTRODUCTION The benefits of early restoration of blood flow to ischemic myocardium with thrombolytic therapy, per- cutaneous transluminal coronary angioplasty, or coro- nary artery bypass graft surgery have been well docu- mented. A great deal of evidence, however, indicates that reperfusion (R) has additional deleterious effects on the ischemic myocardium through eliciting an in- flammatory reaction [1–5]. Cell– cell interactions be- tween activated neutrophils (PMNs), vascular endo- thelial cells and myocytes have been suggested to play a major role in the induction of myocardial injury [6 –9]. Accordingly, a number of experiments aimed at diminishing myocyte cell death with scavengers of ox- ygen free radicals [10], inhibiting the interaction be- tween PMN and vascular endothelium by using mono- clonal antibodies directed against adhesion molecules [3, 11, 12], and depleting PMNs from the circulation [13, 14] at R have shown an attenuation in postisch- emic myocardial injury. However, most of these inter- 1 To whom correspondence should be addressed at The Depart- ment of Cardiothoracic Surgery, The Carlyle Fraser Heart Center/ Crawford Long Hospital, Emory University School of Medicine, 550 Peachtree St. N.E., Atlanta, GA 30365-2225. Fax: (404) 686-4888. E-mail: zzhao@emory.edu. Journal of Surgical Research 94, 133–144 (2000) doi:10.1006/jsre.2000.6029, available online at http://www.idealibrary.com on 133 0022-4804/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.