Time-dependent changes of the susceptibility of cardiac contractile function to hypoxia-reoxygenation after myocardial infarction in rats.

In this study we analyzed the susceptibility of contractile function of the myocardium to hypoxia-reoxygenation after infarction. For this purpose, the contractility of isolated papillary muscles from rats was studied at high oxygen tension (pO2 80 kPa) and during hypoxia (pO2 3 kPa) with subsequent reoxygenation at variable intervals between 15 h and 9 weeks after permanent ligation of the left coronary artery. Hypoxic exposure reduced the contractile performance of the preparations to a similar extent in both groups. Notably, the contractility and, in particular, the relaxation rates recovered more completely from hypoxia in the hypertrophied myocardium of rats with coronary artery ligation than in sham-operated (SO) animals. The recovery of contractile function was improved maximally between 6 and 9 weeks after myocardial infarction (MI). The lower sensitivity of the (post)ischemic myocardium to hypoxia-reoxygenation correlated with enhanced left ventricular glutathione peroxidase (GSH-Px) activity (15 h to 9 weeks post-MI) and 2-3-fold increased expression levels (15 h to 6 weeks post-MI) of the 72 kDa heat shock protein (HSP72) in the papillary muscles. These findings suggest that the greater antioxidant potential and, possibly, stimulation of HSPs contribute to the sustained tolerance of the myocardium to hypoxia-reoxygenation injury after infarction.