Delta opioid receptors and low temperature myocardial protection

Background. Cardiac surgery continues to be limited by an inability to achieve complete myocardial protection. This may result from the use of hypothermic cardioplegia. Interestingly, the subcellular changes of animal hibernation parallel the altered biology of induced hypothermic myocardial ischemia, but are well tolerated by hibernated mammalian myocardium. Evidence indicates this protection is mediated by activation of the delta opioid receptor, which elicits profound metabolic effects at the whole animal, organ, and cell level. In this study, we sought to determine if pentazocine, with agonist activity at the delta opioid receptor, could improve myocardial recovery following global ischemia over a wide range of temperatures. Methods. Isolated rabbit hearts received either standard cardioplegia or were pretreated with racemic, d or l isomer pentazocine. Hearts were then subjected to 2 hours at 34°C, or 3.5 hours at 20°C, or 4 hours at 10°C of cardioplegic ischemia and reperfused. Functional recovery was compared to controls. Results. Isovolumic developed pressure, coronary flow, oxygen consumption, and 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 hibernation, which occurs from 34° down to 0°C. The use of delta opioid receptor agonists may have important clinical implications for cardiac surgery and deserves further study.