Division of Cardiovascular Medicine

Experimental Models

• Conscious rabbit model.  We have developed a unique conscious rabbit model of myocardial ischemia and reperfusion that enables us to study ischemic preconditioning both against myocardial stunning and myocardial infarction.  Rabbits are instrumented under sterile conditions and studied ten days later.  We can produce repeated coronary occlusions and reperfusions in the conscious state.  We can measure systolic wall thickening to assess regional myocardial function, and we can also measure myocardial infarct size.  In addition, we can measure regional myocardial blood flow with radioactive microspheres.  This is a very dependable, economic, and reproducible model that is now being used for most of our studies on ischemic preconditioning.

• Isolated cardiomyocytes.  Although the conscious rabbit offers the advantage of being a highly physiological preparation, and therefore providing data that are relevant to the clinical setting, some manipulations are simply not possible in the whole animal.  For this reason, we have developed an isolated cardiomyocyte model of ischemic preconditioning.  Adult rabbit cardiomyocytes are isolated and cultured for a few days.  They are preconditioned by subjecting them to simulated ischemia and then, 24 hours later, subjected to a more severe insult of simulated ischemia.  Using this model, we can overexpress selected genes, inhibit selected genes, and perform a number of other manipulations that will be important to decipher the mechanism of preconditioning.

• Mouse model of infarction.  With the advent of transgenic and knock-out mice, it is possible to conclusively interrogate the role of a specific gene in a physiological or pathophysiological process.  Accordingly, we have developed a new mouse model of myocardial infarction using microscopic surgery.  We have demonstrated for the first time that we can induce both the early and the late phase of ischemic preconditioning in the mouse.  We have developed a physiological-relevant mouse model of infarction, in which fundamental physiological variables (body temperature, arterial blood gases, arterial blood pressure, etc.) are carefully controlled and kept within normal physiological limits.  Utilizing this mouse model, we have demonstrated that targeted disruption of the NO synthase gene (NOS knock-out mice) results in loss of late preconditioning, providing conclusive genetic molecular evidence that the late phase of ischemic preconditioning is mediated by NOS.  We are now studying the role of other genes by producing ischemic preconditioning in transgenic and knock-out mice in which these genes are either overexpressed or selectively deleted, respectively.  This mouse model offers enormous potential to interrogate the role of individual genes in myocardial ischemia/reperfusion injury.  Since there is no other species in which both gene targeting and gene expression can be produced, the use of this model will be fundamental for many years to come.