[Histochemical and histoenzymatic study of experimental myocardial infarction in the rat by temporary and permanent ligation of the left coronary artery (author's transl)]

A simple, automatic method for morphometric analysis of the left ventricle in rats with myocardial infarction

Induction of acute myocardial infarction in the rat is an established model for studying effects of therapeutic interventions. Images of sections of the rat left ventricle, stained with nitroblue tetrazolium, were digitized and several parameters estimated by dedicated software on an image analyzer (IBAS 2.0). The method was tested on 7 rats with 48-hr-old myocardial infarction and 4 sham-operated controls. Infarct size can be evaluated by two largely used methods, based on area or on angular extension of the lesion. Results of the two methods are linearly correlated, but area calculations give values half of those obtained from angular extension. Five minutes were needed for a complete evaluation of a section of the left ventricle. Estimates of the parameters showed a relatively low between- and within-operator variability and a good correlation with a classic, but time-consuming, planimetric method. The method simultaneously measures infarct size and left ventricular geometry in the rat. The advantages over previous nonautomatic methods are simplicity, good reproducibility, and speed of execution, which make it particularly useful in the evaluation of drug effects.

A model of acute regional myocardial ischemia and reperfusion in the rat

Studies were conducted in 76 rats to describe and validate a new closed-chest in vivo model for acute ischemia and reperfusion of the left coronary artery. Radiolabeled microsphere distribution in six rat hearts confirmed a significant reduction in arteriolar flow at the center of the ischemic zone (93% reduction of total myocardial counts compared to nonischemic region, P less than 0.01) after 7 min of occlusion. Arteriolar flow returned to control values upon reperfusion. While hemodynamic parameters in 10 rats during 7 min of occlusion and 7 min of reperfusion were monitored, end diastolic pressures increased significantly (P less than 0.01) during occlusion. Finally, the utility of this rat model was demonstrated in a study of contrast enhanced magnetic resonance imaging (N = 4). Normal myocardium could not be differentiated from acutely ischemic myocardium on noncontrast-enhanced MR images. After 5 min of myocardial ischemia and following contrast administration (albumin-Gd-DTPA), the ischemic zone appeared less enhanced than normal myocardium. Upon release of the occluder the left ventricular free wall once again yielded a homogeneous signal similar to that of the normal myocardium.

Reversibility of muscular ischemia: a histochemical quantification by the nitroblue tetrazolium (NBT) test

The degree of muscular ischemia and its reversibility can be quantified in the early stages. This histochemical enzymatic study utilized Nitroblue tetrazolium (NBT) which when reduced by tissue dehydrogenase produces a blue pigment: "formazan." Seventy Wistar rats were subjected to transient hindlimb ischemia by means of a tourniquet for 3, 6, 9, 12, 15 and 18 hours, followed by reperfusion. Microsurgical muscle biopsies were obtained in each rat at 1 and 12 hours, and 3, 7, 14 days after reperfusion. Time increased in muscle staining demonstrated a succino-dehydrogenase deficit confirmed by clinical and histopathological follow-up. NBT staining time was 2 minutes (+/- 8 sec.) in the control group, between 2 and 6 minutes in the reversible ischemia group (rats with 3 and 6 hours of tourniquet), and more than 9 minutes (+/- 14 sec.) in the irreversible ischemia group (animals with more than 9 hours of tourniquet). In vascular surgery and in limb reimplantation this protocol is a practical method of evaluating cytoplasmic enzymatic activity and the status of myofibrillar oxidation in the early phases of ischemic injury, before histologic changes are clearly delineated.

Experimental right-ventricular infarction in rats by abdominodiaphragmal access to the heart. A new technique in the study of infarcted myocardium

An abdominodiaphragmal way of producing right-ventricular myocardial infarction is introduced, allowing of ligation of the right-coronary artery and vein without further manipulation of the heart. Of the rats operated upon, 22% died perioperatively. Of the surviving part, 89% had myocardial infarction macroscopically. This method was used to study enzyme decreases in infarcted myocardium. Our biochemical results correlate very well with histological and histobiochemical findings reported by other investigators. Therefore, we conclude that right-coronary artery ligation in rats by transabdominal, transdiaphragmal access to the heart can be a useful way to study biochemical aspects of infarcted myocardium.

Histoenzymological study of myocardial ATPase activity in experimental infarction in the rat

Histoenzymological techniques were used to examine ATPase activity in rat heart muscle fibres after experimental infarction. 25 hours after coronary ligation, ATPase activity in all ventricular section fibres was high, homogeneous at pH 9.4, sections. 48 hours after ligation, necrotic ventricular fibres appeared, leaving only a thin layer of fibres which had apparently preserved their myofibrillar ATPase. These results indicate that, unlike mitochondrial enzyme activity, myofibrillar ATPase activity is relatively resistant to ischaemia.

Experimental myocardial infarction in the rat as a quantitative model for the study of anti-ischemic interventions

The identification of metabolic and drug interventions able to reduce myocardial injury after coronary artery occlusion requires experimental models. The rat model of ischemic injury is technically simple, unexpensive, informative and accessible to quantitative studies. In this present study, 41 rats underwent temporary myocardial ischemia of variable duration using left coronary artery ligation. They were sacrificed at 48 hours, and the heart was immediately frozen in liquid nitrogen. Serial 8 micrometer sections of known intervals were tested for succinodehydrogenase (NBT stain). Gross sectional areas measured planimetrically were utilized to calculate total myocardial volume (Vmyocardium) and infarcted myocardial volume (Vinfarct) with the aid of a programmable calculator. The data showed a linear regression for Vinfarct/Vmyocardium according to the time of ischemia (p 0,001). We suggest to test the efficiency of metabolic and drug interventions on the regression curve of the necrotic tissue using a multiple linear analysis. Since ischemic changes evolve more rapidly in this model, the intervention under study should be set up at the time of coronary artery occlusion.

The influence of long-term application of isoproterenol on the results of temporary ischemia of the rat heart muscle

The results presented demonstrate that long-term application of small doses of isoproterenol produces an adaptive reaction in the heart muscle with increase of its tolerance of oxygen deficiency induced by temporary ischemia. After adapting animals in the described manner muscle necrosis appears delayed and to a smaller extent. Our results also emphasize the view that the definitive myocardial damage is determined by the secondary disturbances of microcirculation. Furthermore, our findings support the idea of a pharmacologically induced adaptation of the heart muscle resulting in an increased tolerance of ischemic injury.

Emergency myocardial revascularization

From 1969 to 1975, 175 patients with acute coronary insufficiency underwent emergency saphenous vein aorto-coronary bypass grafting (SVBG). The patients were divided into two groups: group I, unstable angina (165 patients) and group II, acute evolving myocardial infarction (ten patients). In group I, the hospital mortality was 8-4%, the incidence of post-operative myocardial infarction was 10-3%. Long-term follow-up was obtained for an average of 25 months, functional improvement was definite in the majority of the patients and actuarial survival curves show 87% patients alive at the end of 48 months. In group II, the hospital mortality was 30%; seven of ten patients had good results.

Microcirculatory changes following early reperfusion in experimental myocardial infarction

69 rats underwent temporary or permanent ligation of the left coronary artery and were studied by the injection of colloidal carbon following fixation-perfusion. 10 rats were using the same protocol and served as controls. Localized myocardial ischemia was accompanied by microvascular changes which produced capillary obstruction when blood flow was reestablished. This phenomenon of "no-reflow" was characterized by the presence of large non perfused areas seen after brief periods of ischemia (15 min). These areas were increased when the period of ischemia was lengthened. After 30 to 60 min of interruption of blood flow the non perfused area extended over the major portion of the ischemic area. During reperfusion the "no-reflow" phenomenon displayed during the first hour showing a transitory improvement in capillary perfusion which was soon followed by a progressive reexpansion of the non injected zones. After 24 hours of reperfusion, the latter zones were identical in their extent to those cases showing tissue necrosis following permanent ischemia. This "no-reflow" phenomenon appears to play a role in the evolution of the reperfused ischemic area by excluding certain areas from the benefits of reperfusion. The most probable factors involved in this process are: increased blood viscosity, endothelial changes peri-capillary edema and the contractile state of the myocardium. The incidence of these microvascular changes, using various methods of myocardial preservation during open heart surgery operations, as well as the present attempts directed towards metabolic therapy of myocardial anoxia, are under investigation.