Exogenous activation of delta- and kappa-opioid receptors affords cardioprotection in isolated murine heart

Controversy exists regarding the relative roles of delta- and kappa-opioid receptor activation as a potential cardioprotective mechanism. Furthermore, the function of opioid receptor activation in cardioprotection has not been examined in the murine heart. To this end, we employed various concentrations of selective delta- and kappa-opioid receptor agonists in an isolated murine heart model undergoing 20 min global ischemia followed by 45 min reperfusion. Left-ventricular developed pressure (LVDP) returned to 50.7+/-2.1% of baseline values in untreated hearts. Infusion of the non-selective opioid agonist, morphine (10 muM), lead to a marked improvement in post-ischemic contractile recovery where LVDP returned to 65.5+/-2.4% of baseline function. The delta-opioid selective agonist BW373U86 hydrochloride elicited maximal protection at a concentration of 1 muM which afforded 63.9+/-3.4% recovery of LVDP. This effect was blocked by the delta-opioid selective antagonist, BNTX. Furthermore, administration of the kappa-opioid selective agonist U50,488 (1 muM) produced a marked improvement in contractile recovery leading to a 72.5+/-5.3% recovery of LVDP. This degree of protection was also abolished by the kappa-opioid receptor antagonist, nor-BNI. No differences were noted in LDH efux from post-ischemic hearts. These data suggest that exogenous activation of delta- and kappa-opioid receptors afford protection against myocardial stunning in the isolated murine heart, an effect attenuated by selective receptor antagonists.