Age-dependent changes in the tolerance of the rabbit heart to ischemia

Many studies in several species have demonstrated an enhanced ischemic tolerance in the immature myocardium when compared with the adult. Little is known about the rate at which these changes occur. We have compared the extent of post-ischemic recovery using isolated working hearts from rabbits of various ages (7-90 days). Hearts (n = 8/group) from rabbits of 7, 14, 21, 28, 31, 40 and 60-90 days of age were perfused aerobically (37 degrees C) for 20 min and control indices of cardiac function were recorded. The hearts were then arrested (2 min infusion) with the St. Thomas' Hospital cardioplegic solution and subjected to global ischemia for 45 min (37 degrees C). The hearts were then reperfused for 15 min in the Langendorff mode and 20 min in the working mode. Leakage of creatine kinase (CK) during Langendorff reperfusion and the recovery of cardiac function during working perfusion were measured. Pre-ischemic cardiac output (CO) was 58.6 +/- 2.6, 80.1 +/- 2.9, 117.5 +/- 4.5, 131.9 +/- 3.2, 134.1 +/- 2.1, 152.0 +/- 1.6 and 165.8 +/- 4.6 ml/min in the 7, 14, 21, 28, 31, 40 and 60-90 day-old groups, respectively. Following ischemia, CO recovered to 82.9 +/- 3.6, 79.2 +/- 3.1, 77.9 +/- 3.4, 72.3 +/- 2.7, 55.3 +/- 2.1, 35.7 +/- 2.9 and 33.1 +/- 6.9%, respectively. CK leakage correlated poorly with recovery and was 31.5 +/- 4.7, 32.0 +/- 8.5, 33.6 +/- 7.9, 35.8 +/- 7.0, 37.3 +/- 4.4, 38.7 +/- 4.8 and 30.4 +/- 5.9 IU/15 min per gram dry weight, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)