Abstract
Fourteen isolated ejecting hearts were perfused with a suspension of red cells in Tyrode solution. In five hearts comparison was made between glucose alone as substrate and glucose plus free fatty acid (palmitate). In five hearts the effect of additional lactate was studied. In the remaining hearts no substrate changes were made (controls). There were only transient changes in cardiac output of the hearts (at fixed mean aortic pressure) when the perfusion media were switched from one to another. There were no consistent steady-state changes in myocardial oxygen consumption, mean external power, efficiency, cardiac output or coronary blood flow associated with any of the changes in substrate consumption. Thus we were unable to confirm an increase in oxygen consumption and decrease in efficiency associated with either free fatty acid or lactate as substrates. Isolated rat trabeculae were deprived of exogenous substrate; their mechanical performance remained constant for approximately 10 min. Subsequent deterioration was restored by any of the three exogenous substrates. We conclude that there is no oxygen wasting effect of these substrates as has previously been postulated, nor any deleterious effect of changing exogenous or endogenous carbohydrate or lipid substrate.