Cardiac function and glycogen content after twenty-four-hour preservation with various metabolic substrates

Previous work has suggested that recovery of cardiac function after long preservation periods is improved if a suitable exogenous substrate is provided. However, interpretation of existing data on the benefit of added substrate is complicated by differing preservation media and protocols studied, as well as differing models used to evaluate postpreservation recovery. These experiments were designed to evaluate glucose, pyruvate, aspartate, and glutamate as exogenous substrates for prolonged perfusion preservation of hearts with a rat heart model preserved with crystalloid medium and with function quantified in an isolated working heart preparation.

Cardiac function (n = 5/group) and tissue glycogen content (n = 5/group) were measured in fresh control rat hearts and four groups of hearts preserved for 24 hours in an extracellular-type cardioplegic medium containing 11 mmol/L glucose and either 20 mmol/L sodium aspartate, 20 mmol/L sodium glutamate, 20 mmol/L sodium pyruvate, or no other substrate. Postpreservation cardiac function was measured in an isolated working rat heart preparation for a 4-hour reperfusion period. Exogenous substrate consumption during preservation and tissue glycogen content at the end of preservation were measured with spectrophotometric assays.

All hearts in the aspartate- and glutamate-preserved groups functioned for the full 4-hour period with stroke work that was 50% to 60% of control. Hearts preserved with only glucose substrate had inconsistent recovery: two of five hearts in that group did not recover, whereas three recovered similar to the aspartate and glutamate groups. None of the pyruvate-preserved hearts recovered contractile function. There was no association between postpreservation tissue glycogen content and extent of cardiac function recovery.

Aspartate or glutamate plus glucose was the best substrate mixture among those tested for long-term perfusion preservation of hearts. These amino acids offer advantages over pyruvate because they produced better recovery of the hearts and because they are chemically more stable than pyruvate. Aspartate or glutamate plus glucose also produced better postpreservation function compared with glucose alone.