HEAT ACCLIMATION IMPROVES CARDIAC MECHANICS AND METABOLIC PERFORMANCEDURING ISCHEMIA AND REPERFUSION

Cardiac mechanics and metabolic performance were studied in isolated p erfused hearts of heat-acclimated (AC) rats (at 34-degrees-C for 1 mo) and their age-matched controls (C). Diastolic and systolic pressures, coronary flow, and the appearance of ischemic contracture (IC) were m easured during progressive graded ischemia, total ischemia (TI), and r eperfusion. ATP, phosphocreatine, and intracellular pH were measured d uring TI and reperfusion with the use of P-31-nuclear magnetic resonan ce spectroscopy. Systolic pressure was greater in AC hearts than in C hearts (P < 0.0001). During 50% of perfusion pressure 15 and 46% of AC and C hearts, respectively, showed IC (P < 0.001). During 25% of perf usion pressure 85% of the hearts in both groups developed IC. The onse t of IC in AC hearts was delayed compared with in C hearts. On reperfu sion 93 and 66% of AC and C hearts, respectively, resumed contraction. Recovery of diastolic pressure was 78 and 36% for the AC and C hearts , respectively (P < 0.05). During TI ATP declined by 0.94 and 1.20 mum ol/min in AC and C hearts, respectively, resulting in 21 +/- 2.8% pres ervation of the ATP pool in AC hearts after 30 min of TI (P < 0.001). The AC group also showed a delayed decline in intracellular pH (P < 0. 001). The data suggest beneficial effects of heat acclimation on the h eart, which were exhibited by greater pressure generation and by the e mergence of protecting features during ischemia and reperfusion, possi bly via energy-sparing mechanisms.