Changes in Myocardial Ultrastructure in Non-infarct Zone of Rats with Myocardial Infarction

Objective To study the changes in myocardial ultrastructure in non-infarct zone at different times after myocardial infarction (MI) in rats. Methods A total of 150 female Wistar rats were randomly divided into sham operation group and MI group. The rat model of MI was established by ligating the left anterior descending coronary artery. The rats were killed after 24 hours,1 week,2 weeks,and 4 weeks of the operation,respectively. The apoptosis of cardiac myocytes was detected by TUNEL method. The myocaridal ultrastructure was observed under transmission electron microscope. The expressions of collagen type Ⅰ and Ⅲ mRNA were determined by reverse transcription polymerase chain reaction. Results The infarction size was from 24% to 33%. No apoptosis of cardiac myocytes were found in the rats of sham operation group. In MI group,after 1 to 4 weeks of the operation,the yellow-brown color apoptotic nuclei were observed,the apoptotic index increased gradually,and the level of collagen type Ⅲ mRNA significantly increased (P 0.05 or P 0.01); after 2 to 4 weeks of the operation,the interstitial fibroblasts,collagen fibers,and the level of collagen type Ⅰ mRNA significantly increased (P 0.05 or P 0.01).Conclusion The apoptosis of cardiac myocytes occurs 2 weeks after MI in rats. Interstitial fibrosis and deposition of interstitial collagen might be one of the mechanisms leading to the apoptosis of cardiac myocytes in the non-infarct zone.