Factors of Importance for the Degree of Ischemic Injury in the Isolated Rat Heart*

Isolated working rat hearts were made ischemic by introducing a one-way aortic ball valve. After the ischemic period the hearts were perfused in a retrograde non-working way for 30 min. Flow rates, glycogen, ATP, and creatine-phosphate went down during the time of ischemia, whereas tissue lactate accumulated. For shorter periods of ischemia these values were normalized but after 30 min of ischemia the hearts seemed to be irreversibly damaged. There was a leakage of GOT, GPT, LDH, and CPK from all hearts when ischemic from 5 to 30 min. Different factors that might be of importance for the degree of ischemic injury were tested. The injury tended to be more severe at higher heart rates. Addition of adrenaline 10(-6)M resulted in excessive myocardial damage. A variation of pH from 7.1 to 7.7 did not alter the effects of the ischemic injury. One group of rats were injected with adrenaline for 8 weeks to simulate chronic stress. When hearts from these rats were made ischemic they were more prone to fail compared to controls. The failing hearts, on the other hand, had a lower leakage of enzymes, possibly due to a less severe myocardial damage. A high mechanical performance and a normal noradrenaline content of the hearts are key factors for the development of myocardial infarction, as indicated by this study.