Delta opioid receptors and low temperature myocardial protection

Background. Cardiac surgery continues to be limited by an inability to achi eve complete myocardial protection. This may result from the use of hypothe rmic cardioplegia. Interestingly, the subcellular changes of animal hiberna tion parallel the altered biology of induced hypothermic myocardial ischemi a, but are well tolerated by hibernated mammalian myocardium. Evidence indi cates this protection is mediated by activation of the delta opioid recepto r, which elicits profound metabolic effects at the whole animal, organ, and cell level. In this study, we sought to determine if pentazocine, with ago nist activity at the delta opioid receptor, could improve myocardial recove ry following global ischemia over a wide range of temperatures. Methods. Isolated rabbit hearts received either standard cardioplegia or we re pretreated with racemic, d or 1 isomer pentazocine. Hearts were then sub jected to 2 hours at 34 degrees C, or 3.5 hours at 20 degrees C, or 4 hours at 10 degrees C of cardioplegic ischemia and reperfused. Functional recove ry was compared to controls. Results. Isovolumic developed pressure, coronary flow oxygen consumption, a nd ultrastructural preservation were enhanced with pentazocine delta opioid mediated protection, which appears to be additive to standard cardioplegia , even at low temperatures. Conclusions. Teleologically, delta opioid protection parallels animal hiber nation, which occurs from 34 degrees down to 0 degrees C. The use of delta opioid receptor agonists may have important clinical implications for cardi ac surgery and deserves further study. (C) 1999 by The Society of Thoracic Surgeons.