Summary
Acute myocardial infarction was produced in rats by ligation of the left coronary
artery. Different phases of healing, up to 6 weeks, were studied in order to compare
its normal histology with the appearance and localization of fibrinolytic activity.
The fibrinolytic activity was studied by the histochemical method using plasminogen
rich fibrin substrate for demonstration of plasminogen activator, and a plasminogen
free fibrin substrate (heat treated) for protease estimation. In all the specimens
studied only plasminogen activator was detected.
The usual morphological features were essentially the same as those described by previous
authors. The fibrinolytic activity in the normal ventricular wall was sparsely distributed
and was localized to the small blood vessels. In the early infarct fibrinolytic activity
had disappeared, but it reappeared in the thrombosed small blood vessels as organization
and recanalization took place. It was present in increased amounts in the newly formed
blood vessels growing into the infarcted area and persisted in these vessels after
healing was complete though slowly decreasing in frequency of distribution and in
concentration. The results show that healing of myocardial infarcts follows the pattern
of a normal tissue repair process, and they substantiate the role of the fibrinolytic
system in wound healing.
