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Isoproterenol-induced myocardial ischemic injury in the rabbit: functional and ultrastructural alterations
Abstract:
The functional and ultrastructural changes observed during myocardial ischemic injury (MII) in the rabbit are described. MII was induced by repeated subcutaneous injections of increasing doses of isoproterenol (ISO; 0.5 mg/kg on day 1, to 15.5 mg/kg on day 15). Measurement of cardiovascular changes revealed a significant decrease in the mean arterial pressure and an increase in heart rate of the ISO-treated animals. ISO treatment also initiated a variety of atrial and ventricular arrhythmias, including ventricular fibrillation, as well as significant ST segment elevations and the appearance of Q waves. Electron-microscopic analysis of hearts from ISO-treated animals showed accumulation of lipid and depletion of glycogen. The myofibrils had poorly defined Z bands and appeared as a homogeneous mass. The most marked effects of ISO treatment were on the mitochondria, which appeared swollen and fragmented. The mitochondrial cristae were also disrupted and fragmented. A few amorphous electron-dense bodies were observed in and around the mitochondria. The changes observed in this study are qualitatively similar to those observed in the rabbit following coronary artery ligation.
Insights
This study details how isoproterenol (ISO) causes myocardial ischemic injury in rabbits, leading to heart dysfunction and cellular damage. The observed changes mimic those from coronary artery ligation, offering insights into heart attack mechanisms.
Area of Science:
- Cardiovascular Science
- Cell Biology
- Toxicology
Background:
- Myocardial ischemic injury (MII) is a critical condition affecting heart function.
- Understanding MII's cellular mechanisms is vital for developing effective treatments.
- Rabbit models are frequently used to study cardiac pathophysiology.
Purpose of the Study:
- To characterize the functional and ultrastructural changes in rabbit hearts induced by isoproterenol (ISO).
- To compare ISO-induced MII with changes seen in coronary artery ligation models.
- To elucidate the cellular and subcellular alterations associated with ISO-induced cardiac damage.
Main Methods:
- Myocardial ischemic injury (MII) was induced in rabbits via repeated subcutaneous injections of increasing doses of isoproterenol (ISO).
- Cardiovascular parameters including mean arterial pressure, heart rate, and electrocardiogram (ECG) were monitored.
- Cardiac tissue was analyzed using electron microscopy to assess ultrastructural changes.
Main Results:
- ISO treatment led to decreased mean arterial pressure, increased heart rate, and induced arrhythmias (including ventricular fibrillation), ST segment elevations, and Q waves.
- Electron microscopy revealed lipid accumulation, glycogen depletion, myofibril disorganization, and significant mitochondrial damage (swelling, fragmentation, disrupted cristae).
- The observed ultrastructural changes were comparable to those seen in rabbits following coronary artery ligation.
Conclusions:
- Isoproterenol administration effectively induces myocardial ischemic injury in rabbits, mirroring key functional and ultrastructural aspects of MII.
- Mitochondrial damage is a prominent feature of ISO-induced cardiac injury.
- This model provides a valuable tool for studying the pathophysiology of myocardial ischemia and potential therapeutic interventions.