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Aims: Dexmedetomidine, which has been increasingly used as an anesthetic adjuvant, is more lipophilic and more active than another α2-adrenergic agonist clonidine and enantiomeric levomedetomidine. Lipophilicity and stereostructure affect the clinical effects of α2-adrenergic agonists. We aimed to compare the membrane interactivity of dexmedetomidine with clonidine and levomedetomidine from a point of view different from the mode of action on α2-adrenergicreceptors.Methodology:Unilamellar vesicles were prepared with phospholipids and cholesterol to mimic the lipid compositions of peripheral nerve cell, central nerve cell and cardiomyocyte membranes, and lipid rafts. They were subjected to the reactions with dexmedetomidine, clonidine and levomedetomidine at 10-200 μM, followed by measuring fluorescence polarization to determine the membrane interactivity to change membrane fluidity and specify the membrane regionfor the stereostructure-specific interaction.Original ResearchArticle Results:Dexmedetomidine and clonidine acted on lipid bilayers to increase the membrane fluidity with potencies varying by a compositional difference of membrane lipids. Dexmedetomidine showed greater interactivity with neuro-mimetic and cardiomyocyte-mimetic membranes than clonidine, being consistent with their comparative lipophilicity and activity. The effects of α2-adrenergic agonists on lipid raft model membranes were much weaker than those on other membranes, indicating that lipid rafts are not mechanistically relevant to them. Higher interactive dexmedetomidine was discriminated from lower interactive levomedetomidine in the presence of chiral cholesterol in membranes. An interactivity difference between two enantiomers was largest in the superficial region of lipid bilayers and the rank order of their membrane-interacting potency was reversed by replacing cholesterol with epicholesterol, suggesting that cholesterol’s 3β-hydroxyl groups positioned close to the membrane surface are responsible for the enantioselective interaction.Conclusion:Dexmedetomidine structure-specifically interacts with biomimetic membranes depending on their lipid compositions more potently than clonidine and levomedetomidine. Such membrane interactivity associated with higher lipophilicity and stereostructure characterizes dexmedetomidine in addition to higher affinity for α2-adrenergic receptors
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Aims: Dexmedetomidine, anα2adrenergicagonist, provides neuroprotection in various cerebral ischemia models and against anesthesia-related neurotoxicity. Dexmedetomidine also improves paraplegia induced by intrathecal morphine after short-term spinal ischemia. In this preliminary study, we investigated whether dexmedetomidine provides spinal protection against transient spinal ischemia in rats. Methodology: Adult male Sprague-Dawley rats were randomly divided into the following 3 groups: 1) intravenous infusion of 0.9% NaCl at a rate of 0.5 mL/h (control), 2) dexmedetomidine 1 μg/kg/h, and 3) intravenous infusion of 0.9% NaCl without spinal ischemia (sham). The rats received saline solution or dexmedetomidine 30 min before spinal cord ischemia and for 24 h. Spinal cord ischemia was induced by intra-aortic balloon occlusion combined with proximal arterial hypotension for 10 min. Ischemic injury was assessed by the neurological deficit score and by the number of viable motor nerve cells in the anterior spinal cord at 24 h of reperfusion. Results: The neurological deficit score was significantly lower in the dexmedetomidine group compared to the control group (p< 0.05). The number of viable motor nerve cells in the dexmedetomidine group was significantly greater than was that in the control group (p< 0.05), but was lower than was that in the sham group.Conclusion: Our findings suggest that continuous administration of dexmedetomidine ameliorates short-term neurological and histological outcomes induced by transient spinal cord ischemia and reperfusion in rats; thus, dexmedetomidine appears to protect the spinal as well as the brain.
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Objective To observe the effects of selective α2-adrenergic receptor agonist alpha-Methylnore-pinephrine(α-MNE) as a vasopressin agent on hemodynamics, troponin T(cTnT) and myocardium in the rabbit cardiopulmonary resuscitation. Method Eighteen health rabbits, weighing 2.5 - 3.5 kg, both male and female,were provided by Lanzhou institute of veterinary medicine. After setting up rabbit model of cardiopulmonary resuscitation, 18 rabbits were randomly divided into three groups. The rabbits in group A as a operation-control group were processed with anesthesia, endotracheal intubation, and surgery without ventricular fibrillation induced. The rabbits in group B as a epinephrine group were administered with 30 ug/kg epinephrineduring CPR. The rabbits in group C as a MNE group were administered with 100 ug/kg α-MNE during CPR. The left ventrictdar end-diastolic pressure(LVEDP), left ventricular pressure rise and fall rate(± dp/dt) and serum concentrations of BNP were measured. Statistic package of SPSS 10.0 was used for the data analysis and significant differences between means were evaluated by ANOVA analysis. Results Compared with group A, LVEDP of other two groups gradually increased respectively(P < 0. 01), and peak ± dp/dt decreased in other two groups(P<0.01). Increase in LVEDP in group C was less than that in group B(P<0.05), whereas peak ± dp/dt in group C were higher than that in group B(P<0.05), at the same stage. Compared with group A, the cTnT of the remaining two groups increased(P<0.01, respectively),and reached peak at 30 minutes. In group C, the elevation of cTnT was less than that in group B(P<0.05) during the same period. In group B and C, myocardial injury was seen under a light microscope, but the injury in group C was lighter than that in group B. Conclusion The methylnorepinephrine can lessen the myocardial dysfunction after CPR.
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BACKGROUND:Recent studies have shown that α2-adrenergic agonists can reduce postresuscitation myocardial injury. This study was undertaken to observe changes of hemodynamics, myocardial injury markers cTnT and cardiac morphology by establishing a cardiopulmonary resuscitation model with rabbits, and to detect whether α-methyl norepinephrine (α-MNE) can reduce the myocardial injury after CPR and improve cardiac function. METHODS:Eighteen health rabbits, weighing 2.5-3.5 kg, both male and female, were provided by the Lanzhou Institute of Veterinary Medicine. After setting up a rabbit model of cardiopulmonary resuscitation, 18 rabbits were randomly divided into three groups. The rabbits in group A as an operation-control group were subjected to anesthesia, endotracheal intubation, and surgery without induction of ventricular fibrillation. The rabbits in group B as an epinephrine group were administered with 30 g/kg epinephrineduring CPR. The rabbits in group C as a MNE group were administered with 100 g/kg a-MNE during CPR. The left ventricular end-diastolic pressure (LVEDP), left ventricular pressure rise and fall rate (±dp/dt) and serum concentrations of BNP were measured. Statistical package of SPSS 10.0 was used for data analysis and significant differences between means were evaluated by ANOVA. RESULTS:Compared to group A, the LVEDP of other two groups increased respectively (P<0.01 all), and peak±dp/dt decreased in the other two groups (P<0.01). The increase of LVEDP was lower in group C than in group B (P<0.05), whereas peak±dp/dt was higher in group C than in group B (P<0.05) at the same stage. Compared to group A, the cTnT of the remaining two groups increased, respectively (P<0.01), and peaked at 30 minutes. cTnT was less elevated in group C than in group B (P<0.05) during the same period. In groups B and C, myocardial injury was seen under a light microscope, but the injury in group C was lighter than that in group B. CONCLUSION:Methylnorepinephrine can lessen myocardial dysfunction after CPR.