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

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.

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.

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.

The intact pericardial tissue exerts protective effects after MI. It may be related with a specific cell population of KDR+ cells from pericardial tissue.