24-hour pretreatment with delta opioid enhances survival from hemorrhagic shock

Activation of peripheral delta opioid receptors increases cardiac tolerance to arrhythmogenic effect of ischemia/reperfusion

OBJECTIVES

The objective of this study was to investigate the role of peripheral μ, δ1, δ2, and nociceptin opioid receptors agonists in the regulation of cardiac tolerance to the arrhythmogenic effect of ischemia/reperfusion in rats.

METHODS

Anesthetized open-chest male Wistar rats were subjected to either 45 minutes of left coronary artery occlusion (phase 1a 10 minutes and phase 2b 35 minutes) and 2 hours of reperfusion in Experiment 1 or 10 minutes of ischemia and 10 minutes of reperfusion in Experiment 2. In Experiment 1, saline or vehicle controls and the mu-specific opioids dermorphin-H (Derm-H) and ([d-Ala2, N-Me-Phe4, Gly-ol5] enkephalin (DAMAGO); the delta-1-specific opioid d-Pen2,5enkephalin (DPDPE); nociceptin; and the delta-2-specific opioids deltorphin-II (Delt-II), Delt-Dvariant (Delt-Dvar), and deltorphin-E (Delt-E) were infused 15 minutes prior to ischemia. In Experiment 2, DPDPE, Delt-D, Delt-Dvar, and Delt-E were infused at 15 minutes prior to ischemia. The universal opioid receptor antagonist naltrexone, the peripherally acting antagonist naloxone methiodide, the selective δ1 antagonist 7-benzylidene naltrexone maleate, and the specific δ2 antagonist naltriben mesylate were infused 25 minutes prior to ischemia.

RESULTS

In Experiment 1, pretreatment with the μ opioids Derm-H and DAMGO, DPDPE, and nociceptin at all doses tested did not reduce the incidence of ischemia-induced arrhythmias compared to controls during 45 minutes of ischemia. The δ2 opioids Delt-II (0.12 mg/kg), Delt-Dvar (0.3 mg/kg), and Delt-E (0.18 mg/kg) all demonstrated significant antiarrhythmic effects at the 150 nmol/kg dose compared to saline or vehicle controls. Nine of 19 animals treated with Delt-II were tolerant without ventricular arrhythmias to the arrhythmogenic effect of ischemia during the first 10 minutes of ischemia (phase 1a) and 11 of 19 were without ventricular arrhythmias during the following 35 minutes of ischemia (phase 1b). Delt-II also decreased the incidence of premature ventricular contractions and ventricular tachycardia by almost half during phase 1a. Delt-II did not affect the incidence of ventricular fibrillation (VF). Pretreatment with Delt-Dvar and Delt-E completely blocked the incidence of VF in phase 1b. Delt-E also decreased premature ventricular contractions by 50%, and the incidence of ventricular tachycardia decreased over twofold in phase 1b of ischemia. There was no enhanced tolerance by any of the delta-2 opioids to the arrhythmogenic effect of reperfusion after long-term ischemia. In Experiment 2, after 10 minutes of ischemia and 10 minutes of reperfusion, Delt-II (0.12 mg/kg) reduced the incidence of premature ventricular contractions and ventricular tachycardia compared to controls, and completely blocked the incidence of VF following 10 minutes of reperfusion. Delt-Dvar and Delt-E were without effect, as was DPDPE following 10 minutes of reperfusion. The antiarrhythmic effect of Delt-II during 10 minutes of ischemia and 10 minutes of reperfusion was completely blocked by the peripherally acting opioid receptor inhibitor naloxone methiodide and the selective delta-2 opioid receptor inhibitor naltriben mesylate, but not by the selective delta-1 inhibitor 7-benzylidene naltrexone maleate. The antagonists alone had no effect on arrhythmogenesis.

CONCLUSIONS

Peripheral delta-2 opioid receptor activation by Delt-II, Delt-Dvar, and Delt-E enhanced cardiac tolerance to the arrhythmogenic effects of ischemia.

Opioid δ(1) and δ(2) receptor agonist attenuate myocardial injury via mPTP in rats with acute hemorrhagic shock

BACKGROUND

Studies have documented the beneficial roles of δ opioid receptor (OR) agonist for hemorrhagic shock. However, the myocardial protection roles and the mechanisms of hemodynamic stability during resuscitation of δ-OR agonist have not been explored. This study was designed to investigate myocardial protective effects and the mechanisms of high selective δ(1) and δ(2)-OR agonists during resuscitation of acute hemorrhagic shock.

MATERIALS AND METHODS

Forty-eight adult male SD rats were adopted 60-min hemorrhagic shock through removing 30% (5 mL) of the total blood volume, and followed by 2-h resuscitation with shed blood and L-lactated Ringer's solution. At the end of shock and prior to resuscitation, NS, δ(1)-OR agonist TAN-67 (10 mg/kg) and antagonist BNTX (3 mg/kg), and BNTX+TAN-67, DMSO, δ(2)-OR agonist Deltorphin II (1 mg/kg) and antagonist NTB (2 mg/kg), and NTB+Deltorphin II in 0.5 mL were administrated. Left ventricular function parameters were measured during the whole experimental period. Myocardial mitochondria were isolated to determine opening of mitochondrial permeability transition pore (mPTP). Morphologic changes in myocardium and mitochondria were observed by electron microscope.

RESULTS

The hemodynamic indexes in group TAN-67 and group Deltorphin II were higher than control group at each time point during resuscitation, respectively (P<0.05). TAN-67 and Deltorphin II decrease but their antagonists BNTX and NTB increase the opening of mPTP (P<0.05). Myocardial and mitochondrial damage were attenuated in group TAN-67 and group Deltorphin II.

CONCLUSIONS

δ(1)-OR agonist TAN-67 and δ(2)-OR agonist Deltorphin II protect the heart by targeting the mPTP in rats with acute hemorrhagic shock.

Mimetics of hormetic agents: stress-resistance triggers

Mimetics of hormetic agents offer a novel approach to adjust dose to minimize the risk of toxic response, and maximize the benefit of induction of at least partial physiological conditioning. Nature selected and preserved those organisms and triggers that promote tolerance to stress. The induced tolerance can serve to resist that challenge and can repair previous age, disease, and trauma damage as well to provide a more youthful response to other stresses. The associated physiological conditioning may include youthful restoration of DNA repair, resistance to oxidizing pollutants, protein structure and function repair, improved immunity, tissue remodeling, adjustments in central and peripheral nervous systems, and altered metabolism. By elucidating common pathways activated by hormetic agent's mimetics, new strategies for intervention in aging, disease, and trauma emerge. Intervention potential in cancer, diabetes, age-related diseases, infectious diseases, cardiovascular diseases, and Alzheimer's disease are possible. Some hormetic mimetics exist in pathways in primitive organisms and are active or latent in humans. Peptides, oligonucleotides, and hormones are among the mimetics that activate latent resistance to radiation, physical endurance, strength, and immunity to physiological condition tolerance to stress. Co-activators may be required for expression of the desired physiological conditioning health and rejuvenation benefits.

Ionic storm in hypoxic/ischemic stress: can opioid receptors subside it?

Neurons in the mammalian central nervous system are extremely vulnerable to oxygen deprivation and blood supply insufficiency. Indeed, hypoxic/ischemic stress triggers multiple pathophysiological changes in the brain, forming the basis of hypoxic/ischemic encephalopathy. One of the initial and crucial events induced by hypoxia/ischemia is the disruption of ionic homeostasis characterized by enhanced K(+) efflux and Na(+)-, Ca(2+)- and Cl(-)-influx, which causes neuronal injury or even death. Recent data from our laboratory and those of others have shown that activation of opioid receptors, particularly delta-opioid receptors (DOR), is neuroprotective against hypoxic/ischemic insult. This protective mechanism may be one of the key factors that determine neuronal survival under hypoxic/ischemic condition. An important aspect of the DOR-mediated neuroprotection is its action against hypoxic/ischemic disruption of ionic homeostasis. Specially, DOR signal inhibits Na(+) influx through the membrane and reduces the increase in intracellular Ca(2+), thus decreasing the excessive leakage of intracellular K(+). Such protection is dependent on a PKC-dependent and PKA-independent signaling pathway. Furthermore, our novel exploration shows that DOR attenuates hypoxic/ischemic disruption of ionic homeostasis through the inhibitory regulation of Na(+) channels. In this review, we will first update current information regarding the process and features of hypoxic/ischemic disruption of ionic homeostasis and then discuss the opioid-mediated regulation of ionic homeostasis, especially in hypoxic/ischemic condition, and the underlying mechanisms.

Delta 2-specific opioid receptor agonist and hibernating woodchuck plasma fraction provide ischemic neuroprotection

OBJECTIVES

The authors present evidence that the delta opioid receptor agonist Deltorphin-D(variant) (Delt-D(var)) and hibernating woodchuck plasma (HWP), but not summer-active woodchuck plasma (SAWP), can provide significant neuroprotection from focal ischemia in mice by a mechanism that relies in part on reducing nitric oxide (NO) release in ischemic tissue.

METHODS

Cerebral ischemia was produced in wild-type and NO synthase-deficient (NOS(-/-)) mice by transient, 1-hour middle cerebral artery occlusion (MCAO). Behavioral deficits were determined at 22 hours and infarct volume was assessed at 24 hours after MCAO. Mice were treated with saline or Delt-D(var) at 2.0 and 4.0 mg/kg, or 200 microL of HWP or SAWP. NOS(-/-) mice were treated with either saline or Delt-D(var) at 4.0 mg/kg. NO release was determined using an N9 microglial cell line pretreated with delta- or mu-specific opioids and HWP or SAWP prior to activation with lipopolysaccharide and interferon-gamma. Nitrate in the medium was measured as an indicator of NO production.

RESULTS

Infusion of Delt-D(var) or HWP (but not SAWP) decreased infarct volume and improved behavioral deficits following 1 hour of MCAO and 24 hours of reperfusion. In NOS(-/-) mice, endothelial NOS(+/+) is required to provide Delt-D(var)-induced neuroprotection. Delt-D(var) and HWP dose-dependently decreased NO release in cell culture, while SAWP and other delta- and mu-specific opioids did not.

CONCLUSIONS

Delt-D(var) and HWP, but not SAWP, are effective neuroprotectant agents in a mouse model of transient MCAO. In cell culture, the mechanism of this ischemic neuroprotection may rely in part on their ability to block NO release.