fore they were transplanted back into a recipient rabbit. While attached to the preservation apparatus, samples of the media output of the heart were taken every 2 hours and were assayed for their content. If the compound in the media showed up in large amounts in the assay, it could be concluded that the compound was not metabolized by the heart. If little or none of the compound placed in the media appeared in the assay, it could be concluded that compound was used up by the heart metabolism.The hearts that were given pyruvate in their media completely consumed the available substrate and were able to function at a nearly normal capacity once they were transplanted. Correspondingly, hearts that were preserved in a media that lacked pyruvate had a significantly lower rate of contractile function once they were transplanted. The superior preservation of the hearts with pyruvate most likely resulted from the hearts use of pyruvate through the citric acid cycle for the production of energy through direct ATP synthesis (from the reaction of succinyl-CoA to succinate via the enzyme succinyl CoA synthetase) as well as through the production of NADH + H+ for use in the electron transport chain to produce energy. After providing a preservation media that contained pyruvate, a better recovery of the heart tissue occurred. Most of the pyruvate consumed during preservation was probably oxidized by the myocardium in the citric acid cycle. Only a small amount of excess lactate was detected by the assays of the preservation media discharged by the heart. The lactate represented only 15% of the pyruvate consumed. If the major metabolic route taken by pyruvate during preservation had been to form lactate dehydrogenase for regeneration of NAD+ for continued anaerobic glycolysis, rather than by the aerobic citric acid cycle (pyruvate oxidation), then a higher ratio of excess lactate produced to pyruvate consumed would have been observed.Hearts given a g...
