Systolic and Diastolic Properties and Myocardial Blood Flow in the Heterotopically Transplanted Rat Heart during Acute Cardiac Rejection

. The aim of the study was to characterize the course of systolic and diastolic function, myocardial blood flow, and histologic changes during acute rejection in a model of heterotopic transplantation in rats. For this purpose isogenic Lewis-to-Lewis and allogenic DA (Dark Agouti)-to-Lewis rat cardiac transplants were studied 1 hour and 1, 3, and 5 days, respectively, after heterotopic intraabdominal transplantation. Myocardial tissue blood flow (MBF) was assessed by the hydrogen-clearance method. An implanted balloon was used to measure pressure–volume relations in the transplanted heart. Myocardial water content was determined at the end of the experiments, and histologic examinations were performed. The MBF recovered during the first day postoperatively in both groups and decreased again in the allogenic group after 3 and 5 days ( p < 0.05); it remained stable in the isogenic group. Myocardial relaxation was already prolonged in the allogenic group after 3 days and deteriorated further. Left ventricular end-diastolic pressure progressively increased in the allogenic group, whereas it remained unchanged in the isogenic group up to 5 days. After recovery from ischemia, the left ventricular peak systolic pressure was stable in the isogenic group for the entire further observation period, but it significantly decreased in the allogenic group after 5 days ( p < 0.05). Myocardial water content showed a significant increase in the allogenic group compared to that in the isogenic group after 5 days. In the allogenic group histologic examination confirmed mild to moderate rejection after 3 days and severe acute rejection after 5 days. Thus, after recovery from ischemia, mild to moderate cardiac rejection was associated with reduced MBF and impaired relaxation. In a typical sequence, generation of edema and impaired diastolic compliance were terminally followed by systolic dysfunction during severe rejection.