[Protective role of pericardial tissue on injured myocardium in rats].

OBJECTIVE:To define the protective role of pericardial tissue and identify the subcellular population with potential contribution to cardiac protection after injury in a rat model. METHODS:Myocardial infarction (MI) was created by the ligation of left anterior descending artery (LAD) in rats while the pericardial sac was either completely removed (-PC, n = 10) or surgically closed after ligation (+PC, n = 8). The follow-up functional and structure benefits were analyzed by echocardiography and 2,3,5- triphenyl-2H-tetrazolium, chloride(TTC) and bromodeoxyuridine (BrdU) staining. The contributions of cardiac stem cells (sca-1, c-kit and KDR) were evaluated by immunohistochemistry. RESULTS:The integrity of pericardial sac showed significant benefits of cardiac contractile function (ejection fraction and short axis fractional shortening) in comparison to the controls (52 ± 12 vs 37 ± 12 and 36 ± 14 vs 25 ± 13, both P < 0.05). The observed functional amelioration after MI was obvious based on structural repair examined by TTC staining and BrdU incorporation, showing significantly more de novo cardiomyocytes in +PC rats. Interestingly, we have immunohistologically identified a sub-population of KDR+(flk-1+) cells in pericardial tissue which clone genetically distributed and mildly expressed cardiac specific proteins (cTnT). It suggested that the KDR+ cells might act as cardiac progenitors and therefore play an important role in cardiac repair. Meanwhile, rare SCA-1 and c-kit positive cells were detected in pericardial tissue. CONCLUSION:The intact pericardial tissue exerts protective effects after MI. It may be related with a specific cell population of KDR+ cells from pericardial tissue.