Work Performance of the Isolated Perfused Beating Heart in the Hereditary Myocardiopathy of the Syrian Hamster

The work performance of the isolated beating heart of control Syrian hamsters and hamsters suffering from an inbred myocardiopathy was studied in a system using a myographic differential force transducer. A stretch force of either 3.75 or 8.75 g was applied to the hearts. Myocardial metabolism of pyruvate-3- 14 C and palmitate-1- 14 C was studied with and without a stretch force. A definite reduction in work performance of the myopathic heart could be demonstrated. Peak height of contraction, tension-time index, tension time per minute and heart rate were significantly lower. The progressive myocardial fiber lengthening, caused by the stretch force, was less in the myopathic hearts. No difference was observed between the uptake and oxidation of pyruvate-3- 14 C and palmitate-1- 14 C by control and myopathic hearts. The presence of a stretch force affected metabolism of both hearts in a similar manner. Two mechanisms for explaining the reduction in work performance by the myopathic heart were observed, namely, a reduction in heart rate and a relative inability of the myopathic muscle fibers to lengthen. The depressed mechanical performance could not be related directly with altered substrate metabolism or with reduction in total muscle mass.