Delayed cardioprotection is mediated via a non-peptide δ opioid agonist, SNC-121, independent of opioid receptor stimulation

Abstract.

Acute cardioprotection is mediated primarily through δ opioid receptor stimulation independent of μ or κ opioid receptor stimulation. Delayed cardioprotection is mediated by δ opioid receptor agonists but ambiguity remains about direct receptor involvement. Therefore, we investigated the potential of SNC-121, a non-peptide δ opioid agonist, to produce delayed cardioprotection and characterized the role of opioid receptors in this delayed response. All rats underwent 30 minutes of ischemia followed by 2 hours of reperfusion. SNC-121 induced a significant delayed cardioprotective effect. To determine the nature of this SNC-121-induced delayed cardioprotection, rats were treated with specific opioids receptor antagonists and underwent pertussis toxin (PT) treatment prior to opioid agonist stimulation. Control rats were injected with saline and allowed to recover for 24 hours. Pretreatment and early treatment with opioid receptor antagonists failed to inhibit the delayed protective effects of SNC-121, as did pretreatment with PT. Treatment with a free radical scavenger, 2-mercaptopropionyl glycine, at the time of opioid stimulation attenuated the delayed cardioprotective effects of SNC-121. These data suggest that delayed cardioprotection is stimulated via non-peptide δ opioid agonists by a mechanism unrelated to opioid receptor activation. The mechanism appears to be a non-opioid receptor mediated production of reactive oxygen species that triggers the signaling cascade leading to delayed cardioprotection.