Utilization of glycolytic energy for external heart work

An isolated guinea pig heart preparation capable of stroke work was perfused with Krebs solution containing glucose and oxygen. The aortic pressure and the left ventricular output were kept constant. Addition of cyanide to the perfusion medium (1, 2 or 3 × 10 −4 mol/l) effected a small decrease of the heart rate and of dp dt , whereas the left ventricular end-diastolic pressure increased. The tissue content of the energy-rich phosphates was lowered. Though the stroke work was kept constant, the oxygen uptake was reduced, and a lactate production appeared. These changes took place within a few minutes. During the following observation time lasting 15 min, there was a steady state. The lactate production was correlated with the decrease of the oxygen uptake. It is concluded that the energy source required for steady-state performance of stroke work can shift at least partly from oxidative to anaerobic metabolism. Obviously, energy liberated from carbohydrate breakdown to lactate can be converted to stroke work under steady-state conditions. Under the influence of 3 × 10 −4 mol/l of cyanide, 12% of the total energy requirement were covered by glycolytic energy.