Long-term protection of ischaemic myocardium by nitroglycerin ointment

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.

Relationship between sarcolemmal damage and appearance of amorphous matrix densities in mitochondria following occlusion of coronary artery in rats

The relationship between the progression of sarcolemmal damage and the appearance of amorphous matrix densities (AMDs) within myocardial mitochondria in the early phase of ischemia was studied in coronary-ligated rats by means of electron microscopy. The animals were divided into six groups according to the duration of ischemia (from 10 to 120 min). The severity of sarcolemmal damage was graded into four classes according to the ultrastructural ischemic changes, as follows: grade 0, normal cells; grade 1, slight ischemic changes in cellular organelles but intact sarcolemma; grade 2, formation of subsarcolemmal blebs, but overall sarcolemmal integrity; and grade 3, sarcolemmal disruption. In the experiment, grade 1 cells decreased and those of grade 3 increased with a longer period of ischemia. The appearance of grade 3 cells was distinct at 30 min of ischemia. This cellular damage proceeded from the subendocardial layer to the subepicardial layer indicating the "wavefront phenomenon." The number of AMDs within the mitochondria increased as the sarcolemmal damage became more severe. It was noteworthy that AMDs could be found in cells with an intact sarcolemma after subjection to 10 min of ischemia. Myoglobin staining of the myocardium obtained after 10 min of ischemia followed by 6 hr of reperfusion revealed no loss of myoglobin, indicating no irreversible cell damage. This finding suggests that the formation of AMDs may occur prior to the disruption of the sarcolemma or irreversible cell damage.

Early loss of myocardial myoglobin detected immunohistochemically following occlusion of the coronary artery in rats

The time course of the loss of myoglobin from the rat ventricular myocardium in the early phase of ischemia was studied with the use of an immunohistochemical technique and an image analyzer. The loss of myoglobin, as an index of myocardial injury, was evident in the left ventricular subendocardium as early as 0.5 hr after occlusion of the left main coronary artery. A clear-cut demarcation of the myoglobin-depleted area helped quantification of the injured areas with an image analyzer. The area with depleted myoglobin became transmural and reached maximum after 2 and 3 hr of occlusion, respectively. Electron microscopic observation of the myoglobin-depleted region revealed amorphous dense bodies in the mitochondria, indicating irreversible damage to the myocardial cells. On the other hand, no irreversible changes could be detected with hematoxylin-eosin stain until 6 hr after the start of the ischemia, and the distinction between the reversible and irreversible areas was unclear. We suggest that depletion of myoglobin from the myocardium serves as a marker for irreversible ischemic injury. Quantitative assessment of the injured areas by immunohistochemical staining for myoglobin together with an image analyzer could be of great value for the evaluation of early ischemic myocardial damage.