Use of an Isolated Heart Model to Test the Utilization of Substrates for Inclusion in Cardioplegic Solutions

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Abstract
Previous studies from our laboratory utilized an isolated isovolumic Langendorff heart preparation to study myocardial metabolism and preservation of left ventricular function following global ischemia and reperfusion. The present study employed a similar preparation to assess the utilization of various glycolytic substrates by monitoring the level of left ventricular developed pressure. Twenty-one rabbit hearts were perfused with an oxygenated but substrate-free Krebs-Ringer-bicarbonate solution in order to deplete the hearts of endogeneous substrate stores. Following a brief period of anoxic, substrate-free perfusion, hearts were perfused with one of seven test substrates under anaerobic, then aerobic conditions. Under anaerobic conditions only perfusion of glucose resulted in a measurable increase in ventricular function which was still less than 20% of control. Under aerobic conditions, provision of glucose, pyruvate, or the combination of alpha-glycerol phosphate and pyruvate resulted in significant increases in contractile function which were 40-70% of control. These results obtained in normal hearts will provide a base line for future studies of the metabolism of postischemic hearts which may have altered cell membrane permeability and/or enzymatic activity.