Anoxidative work and metabolism of isolated perfused rat hearts as influenced by artificially increased heart rate.

Under anoxidative conditions the capacity of mechanical activity and the metabolism of isolated rat hearts were studied at various pacemaker-induced heart rates. Isovolumic work decreased to about one third of its initial rate within a 5 min period of anoxidative perfusion and remained almost constant during a further 10 min observation time. Increased heart rate (100, 175, and 250 b.p.m.) was associated with an increase in left ventricular diastolic pressure and with decreases in systolic pressure and maximal dp/dt. Lactate production, tissue creatine phosphate and inorganic phosphate had no consistent relationship to heart rate, whereas tissue ATP decreased with increasing heart rate. It is concluded that the rate of anoxidative isovolumic work cannot be increased by raising the heart rate since anoxidative carbohydrate breakdown cannot be more activated than at the lowest heart rate studied and cannot be more activated than at the lowest heart rate studied and cannot exceed a rate of 30 mumol hexose/min-g dry weight in the perfused heart.