naltrindole and Hypoxia

Intermittent, normobaric hypoxia confers robust cardioprotection against ischemia-induced myocardial infarction and lethal ventricular arrhythmias. δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) have been implicated in cardioprotective phenomena, but their roles in intermittent hypoxia are unknown. This study examined the contributions of DOR and ROS in mediating intermittent hypoxia-induced cardioprotection. Mongrel dogs completed a 20 day program consisting of 5-8 daily, 5-10 min cycles of moderate, normobaric hypoxia (FIO2 0.095-0.10), with intervening 4 min room air exposures. Subsets of dogs received the DOR antagonist naltrindole (200 μg/kg, sc) or antioxidant N-acetylcysteine (250 mg/kg, po) before each hypoxia session. Twenty-four hours after the last session, the left anterior descending coronary artery was occluded for 60 min and then reperfused for 5 h. Arrhythmias detected by electrocardiography were scored according to the Lambeth II conventions. Left ventricles were sectioned and stained with 2,3,5-triphenyl-tetrazolium-chloride, and infarct sizes were expressed as percentages of the area at risk (IS/AAR). Intermittent hypoxia sharply decreased IS/AAR from 41 ± 5 % (n = 12) to 1.8 ± 0.9 % (n = 9; P < 0.001) and arrhythmia score from 4.1 ± 0.3 to 0.7 ± 0.2 (P < 0.001) vs. non-hypoxic controls. Naltrindole (n = 6) abrogated the cardioprotection with IS/AAR 35 ± 5 % and arrhythmia score 3.7 ± 0.7 (P < 0.001 vs. untreated intermittent hypoxia). N-acetylcysteine (n = 6) interfered to a similar degree, with IS/AAR 42 ± 3 % and arrhythmia score 4.7 ± 0.3 (P < 0.001 vs. untreated intermittent hypoxia). Without the intervening reoxygenations, hypoxia (n = 4) was not cardioprotective (IS/AAR 50 ± 8 %; arrhythmia score 4.5 ± 0.5; P < 0.001 vs. intermittent hypoxia). Thus DOR, ROS and cyclic reoxygenation were obligatory participants in the gradually evolving cardioprotection produced by intermittent hypoxia.

Topics: Acetylcysteine; Animals; Arrhythmias, Cardiac; Dogs; Female; Hematocrit; Hypoxia; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardium; Naltrexone; Reactive Oxygen Species; Receptors, Opioid, delta

Intermittent hypoxia training (IHT) produces robust myocardial protection against ischemia-reperfusion induced infarction and arrhythmias. Blockade of this cardioprotection by antagonism of either β1-adrenergic or δ-opioid receptors (δ-OR) suggests autonomic and/or opioidergic adaptations.. To test the hypothesis that IHT shifts cardiac autonomic balance toward greater cholinergic and opioidergic influence.. Mongrel dogs completed 20d IHT, non-hypoxic sham training, or IHT with the δ-OR antagonist naltrindole (200μg/kgsc). The vagolytic effect of the δ-OR agonist met-enkephalin-arg-phe delivered by sinoatrial microdialysis was evaluated following IHT. Sinoatrial, atrial and left ventricular biopsies were analyzed for changes in δ-OR, the neurotrophic monosialoganglioside, GM-1, and cholinergic and adrenergic markers.. IHT enhanced vagal bradycardia vs. sham dogs (P<0.05), and blunted the δ2-OR mediated vagolytic effect of met-enkephalin-arg-phe. The GM-1 labeled fibers overlapped strongly with cholinergic markers, and IHT increased the intensity of both signals (P<0.05). IHT increased low and high intensity vesicular acetylcholine transporter labeling of sinoatrial nodal fibers (P<0.05) suggesting an increase in parasympathetic arborization. IHT reduced select δ-OR labeled fibers in both the atria and sinoatrial node (P<0.05) consistent with moderation of the vagolytic δ2-OR signaling described above. Furthermore, blockade of δ-OR signaling with naltrindole during IHT increased the protein content of δ-OR (atria and ventricle) and vesicular acetylcholine transporter (atria) vs. sham and untreated IHT groups. IHT also reduced the sympathetic marker, tyrosine hydroxylase in ventricle (P<0.05).. IHT shifts cardiac autonomic balance in favor of parasympathetic control via adaptations in opioidergic, ganglioside, and adrenergic systems.

Topics: Animals; Dogs; Enkephalin, Methionine; Heart Atria; Hypoxia; Microdialysis; Naltrexone; Narcotic Antagonists; Neuronal Plasticity; Norepinephrine; Receptors, Opioid, delta; Sinoatrial Node; Vagus Nerve

Delta-opioid receptor (DOR) is an oxygen-sensitive protein whose function in the rat retina is unknown. We examined whether DOR is involved in hypoxic preconditioning (HPC)-mediated retinoprotection following intraocular pressure (IOP) elevation. Rats were exposed to intermittent hypoxia (10% oxygen) to induce HPC. Unilateral retinal ischemia/reperfusion injury was induced by elevating IOP to 100 mmHg for 1 h. HPC attenuated the loss of neuronal marker expression and increased pro-apoptotic caspase 3 activity in the IOP retina. Excess superoxide production and 8-iso-prostaglandin F2alpha accumulation caused by enhanced oxidant protein expression and reduced antioxidant enzyme level after IOP elevation were largely abrogated by HPC. HPC markedly increased the expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and DOR, but intravitreal administration of HIF-1alpha-specific small interfering RNA abrogated the up-regulation of DOR. This suggested that DOR functions downstream of HIF-1alpha. However, the endogenous content of leucine enkephalin in retinas was not affected by HPC or IOP. Treatment of retinas with the DOR antagonist naltrindole attenuated the HPC-induced protection and activation of extracellular signal-regulated kinase. These results suggest a novel mechanism of HPC-mediated retinoprotection whereby HIF-1alpha induces the expression of DOR, and DOR-mediated activation of extracellular signal-regulated kinase triggers cellular events that correct the redox imbalance in the post-ischemic retina.

Topics: Animals; Antioxidants; Blotting, Western; Dinoprost; Enkephalin, Leucine; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Immunohistochemistry; Intraocular Pressure; Ischemic Preconditioning; Lipid Peroxidation; Male; Naltrexone; Narcotic Antagonists; Oxidative Stress; Rats; Rats, Wistar; Receptors, Opioid, delta; Retina; Retinal Vessels; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering; Signal Transduction; Spectrometry, Fluorescence; Superoxides

Hypoxia preconditioning (HPC), rapid or delayed, has been reported to induce neuroprotection against subsequent severe stress. Because delta-opioid receptor (DOR) plays an important role in delayed HPC-induced neuroprotection against severe hypoxic injury, we asked whether DOR is also involved in the rapid HPC-induced neuroprotection.. Cultured rat cortical neurons at culture days 8 to 9 were exposed to a short-term hypoxia (1% O2 for 30 minutes) to induce HPC followed by 30-minute normoxia before exposing to glutamate toxicity (100 micromol/L; 4 hours). Neuronal viability was assessed by lactate dehydrogenase leakage and morphological assessment. Protein and mRNA levels of DOR were detected by receptor binding and RT-PCR, respectively. Naltrindole was used to block DOR. Developmental changes in NMDA receptor expression was measured by Western blots.. HPC significantly reduced the glutamate-induced neuronal injury. Receptor binding showed that HPC increased DADLE (a DOR ligand) binding density in the cultured cortical neurons by >90% over control level (P<0.05), although RT-PCR did not detect any appreciable change in DOR mRNA. DOR inhibition with naltrindole had no effect on neuronal injury and completely abolished the HPC-induced neuroprotection. In contrast to HPC-induced increase in DADLE binding density, prolonged hypoxia caused severe neuronal injury with a significant decrease in DADLE binding density and DOR mRNA level.. DOR is involved in neuroprotection induced by rapid HPC in cortical neurons.

Topics: Animals; Cells, Cultured; Cellular Senescence; Cerebral Cortex; Enkephalin, Leucine-2-Alanine; Glutamic Acid; Hypoxia; Ischemic Preconditioning; L-Lactate Dehydrogenase; N-Methylaspartate; Naltrexone; Narcotic Antagonists; Neurons; Rats; Receptors, Opioid, delta; RNA, Messenger; Time Factors; Up-Regulation

Topics: Adaptation, Physiological; Animals; Arrhythmias, Cardiac; Enkephalin, Leucine; Epinephrine; Heart; Hypoxia; Immobilization; Male; Naltrexone; Narcotic Antagonists; Plant Extracts; Rats; Rats, Wistar

Although the interactions between the mu- and the delta-opiate receptor subtypes are well documented with regard to supraspinal analgesia, less is known about the mutual interactions on respiratory depression. To clarify the functional interactions between both opiate receptor subtypes with regard to antinociception and respiratory depression, male Wistar rats were intravenously injected with 2.5 microg/kg of the mu-opiate agonist sufentanil and subsequently intravenously challenged with the delta antagonist naltrindole (NTI) or naltrindole 5'-isothiocyanate (5'-NTII), a delta-2 antagonist. Antinociception was measured by means of the tail-flick latency, and respiratory depression was evaluated by means of analysis of PaCO2, PaO2, and oxygen saturation. To quantify the antagonistic properties of NTI and 5'-NTII, mean areas under the curve were calculated for groups treated with sufentanil, control vehicle, and sufentanil plus a dose of the antagonists. NTI, but not 5'-NTII, antagonized the sufentanil-induced antinociception at 10 mg/kg NTI. Below this dose the effects were inconsistent. The sufentanil-induced hypercapnia and hypoxia were diminished with 10 mg/kg NTI or 5'-NTII. These data indicate that NTI antagonizes the sufentanil-induced antinociception and respiratory depression in rats. A dissociation between the antinociception and respiratory depression following intravenous sufentanil could be obtained with 10 mg/kg 5'-NTII pointing to different regulatory effects of opiate delta receptor subtypes on mu-opiate agonist-induced behavioral effects.

Topics: Analgesics, Opioid; Animals; Depression, Chemical; Hydrogen-Ion Concentration; Hypercapnia; Hypoxia; Isothiocyanates; Male; Naltrexone; Narcotic Antagonists; Pain Measurement; Rats; Rats, Wistar; Reaction Time; Receptors, Opioid, mu; Respiration; Sufentanil

Previously an acute adaptation to hypoxia was induced by intermittent, severe hypoxia and this conditioned increase in survival time during subsequent hypoxia was blocked by naloxone. The current study further defined the opioid nature and the receptor type(s) involved in hypoxic adaptation by the use of (+)-naloxone (inactive isomer) and selective opioid antagonists. (+)-Naloxone failed to change significantly the survival times of hypoxic or sham conditioned mice during subsequent hypoxia. The selective opioid antagonists, 7-benzylidenenaltrexone, naltrindole, beta-funaltrexamine and norbinaltorphimine were administered subcutaneously before hypoxic or sham conditioning. The delta-1 and delta-2 selective antagonists, 7-benzylidenenaltrexone and naltrindole respectively, blocked the hypoxic conditioning-induced increase in survival time. The lowest effective 7-benzylidenenaltrexone dose was 3000-fold lower than the lowest effective naltrindole dose indicating that the acute adaptation to hypoxia was predominantly sensitive to delta-1 blockade. Neither the mu antagonist, beta-funaltrexamine, nor the kappa antagonist, norbinaltorphimine, significantly changed survival time in sham or hypoxic conditioned mice. These results support a delta-1 receptor mediated mechanism of acute adaptation to hypoxia.

Topics: Adaptation, Physiological; Animals; Benzylidene Compounds; Hypoxia; Male; Mice; Naltrexone; Narcotic Antagonists; Receptors, Opioid, delta