Establishment of a rat model of myocardial infarction with a high survival rate: A suitable model for evaluation of efficacy of stem cell therapy

Abstract

The most common rat model of myocardial infarction (MI) is by ligation of left anterior descending (LAD) coronary artery but it is associated with high mortality and large variations in the infarct size. We evolved certain innovations/modifications in the existing technique including immobilization of the heart without exteriorization, identification of the LAD by pressing it proximal to the site of ligation by an ear-bud, and subsequently its ligation 8 mm from its origin, no touch technique of the lungs during surgery, removal of air from the chest cavity prior to its closure using an in-house tubing, and deflation of the lungs before extubation. We induced MI in 24 Sprague- Dawley (SD) rats using these modifications and carried out post-MI evaluation of hemodynamic parameters, serum cardiac enzymes and histological studies upto 90 days using 13 sham operated and 3 healthy SD rats as controls. Three of the 24 rats (13%) died <24 hours of MI, but thereafter no mortality was observed till the follow-up period of 90 days. The infarct size was consistent in all the rats (21±4% of left ventricular area). This model with low early and no long-term mortality may be suitable for studying efficacy of stem cell therapy in MI, where a follow-up of at least 13 weeks is required to assess myocardial regeneration.

Keywords: High Survival Rate; Innovations in LAD Ligation; Myocardial Infarction; Rat Model; Stem Cell Therapy.

Figure 1

Serum levels of Creatinine Kinase-MB (CK-MB) in healthy rats, sham operated rats and MI induced rats at different time points of follow-up. Values are mean ± SD of 3 rats *p<0.05, **p< 0.01, ***p< 0.001 (MI induced or sham operated rats vs. healthy rats).

Figure 2

Serum levels of Lactate Dehydrogenase (LDH) in healthy rats, sham operated rats and MI induced rats at different time points of follow-up. Values are mean ± SD of 3 rats *p<0.05, **p< 0.01, ***p< 0.001 (MI induced or sham operated rats vs. healthy rats).

Figure 3

Representative heart sections stained with H&E (X400) of (A) healthy rats showing centrally located nuclei in intact myocytes and (B) of MI induced rats showing the following sequential histopathological changes after MI.: (B.i) nucleomegaly and (B.ii) loss of cross striations in myocytes at 3-6 hours; (B.iii) loss of cardiomyocyte boundary after 24 hours; (B.iv) infarct zone after 24 hours; (B.v) wavy fibers and (B.vi) neutrophilic infiltration at 3 days; (B.vii) degeneration of myocytes and cellular swelling and (B.viii) early granulation tissue with formation of fibroblasts, fibrocytes and capillaries at 1 week; (B.ix) granulation tissue with early scar formation at 2 weeks; (B.x) granulation tissue with dense scar formation at 3 weeks.

Figure 4

Triphenyl Tetrazolium Chloride stained cross-section of the heart of (A) Healthy rat showing uniform staining pattern (B) MI induced rat, with the arrow showing a pale, TTC negative area of infarct.