The mechanism of
cardiac rupture after MI (
myocardial infarction) is not fully understood.
Rupture has not been reported in most laboratory species, including the rat, but does occur in mice. We have reported previously that beta2-TG mice (transgenic mice with cardiac-restricted overexpression of beta2-
adrenergic receptors) had a lower incidence of
rupture compared with NTG (non-transgenic) littermates. We hypothesized that the difference in the incidence of
rupture between rodents and specific mouse strains is due to the difference in
collagen content following MI. In the present study, we compared the difference in matrix remodelling post-MI between beta2-TG and NTG mice and between mice and rats. MI was induced by
ligation of the left main coronary artery. Following MI, tensile strength, insoluble and soluble
collagen content and
gelatinase expression were determined in the infarcted and non-infarcted myocardium. Better preserved tensile strength measured as TTR [tension-to-
rupture; 88+/-14 and 58+/-3% of the respective
sham group values for beta2-TG compared with NTG mice (P<0.05); 108+/-7 and 32+/-4% of the respective
sham group values for rats compared with 129sv mice (P<0.01)] and less severe acute
infarct expansion after MI were found in rats compared with mice or in beta2-TG compared with NTG mice. These differences were associated with a higher content of pre-existing fibril
collagen in the normal myocardium of beta2-TG compared with NTG mice (1.6-fold) or rats compared with 129sv mice (2-fold) and an accelerated fibrotic healing in the infarcted myocardium. Additionally, a less pronounced increase in MMP-9 (matrix metalloproteinase-9) activity was observed in the infarcted myocardium of rats compared with 129sv mice. We conclude that a higher
collagen level is associated with facilitated fibrotic healing of an
infarct and preserves the tensile strength of infarcted myocardium, thereby preventing
cardiac rupture and acute ventricular remodelling.