GluN2A-selective positive allosteric modulator-nalmefene-flumazenil reverses ketamine-fentanyl-dexmedetomidine-induced anesthesia and analgesia in rats.

Anesthetics are used to produce hypnosis and analgesic effects during surgery, but anesthesia for a long time after the operation is not conducive to the recovery of animals or patients. Therefore, finding appropriate treatments to counter the effects of anesthetics could enhance postoperative recovery. In the current study, we discovered the novel role of a GluN2A-selective positive allosteric modulator (PAM) in ketamine-induced anesthesia and investigated the effects of the PAM combined with nalmefene and flumazenil (PNF) in reversing the actions of an anesthetic combination (ketamine-fentanyl-dexmedetomidine, KFD). PAM treatment dose-dependently decreased the duration of the ketamine-induced loss of righting reflex (LORR). Compared with those in the KFD group, the duration of LORR and the analgesic effect of the KFD + PNF group were obviously decreased. Meanwhile, successive administration of PNF and KFD had no adverse effects on the cardiovascular and respiratory systems. Both the KFD group and the KFD + PNF group showed no changes in hepatic and renal function or cognitive function in rats. Moreover, the recovery of motor coordination of the KFD + PNF group was faster than that of the KFD group. In summary, our results suggest the potential application of the PNF combination as an antagonistic treatment strategy for anesthesia.

Evaluation of atipamezole as a treatment for dexmedetomidine-induced cardiovascular depression in anesthetized cats.

OBJECTIVE: To evaluate the cardiovascular effects of atipamezole administered at half the volume or the same volume as dexmedetomidine to isoflurane-anesthetized cats. ANIMALS: 6 adult (1 to 2 years old) domestic shorthair cats (body weight, 3 to 6 kg). PROCEDURES: Each cat was anesthetized with isoflurane and rocuronium 3 times; there was a 1-week washout period between successive anesthetic procedures. For each anesthetic procedure, dexmedetomidine (5 µg/kg) was administered IV. Five minutes after dexmedetomidine was administered, atipamezole (25 or 50 µg/kg) or saline (0.9% NaCl) solution was administered IM. Pulse rate, mean arterial blood pressure (MAP), cardiac output (CO), and systemic vascular resistance (SVR) were measured during anesthesia before dexmedetomidine administration (baseline), after dexmedetomidine administration, and 15, 30, 60, and 120 minutes after administration of atipamezole or saline solution. Pulse rate and MAP were also recorded when MAP was at its lowest value. Hemodynamic variables were compared among treatments at baseline, after dexmedetomidine administration, and after administration of atipamezole or saline solution. Effects of treatment and time on all variables were assessed with mixed-effects models. RESULTS: Both doses of atipamezole resulted in a significantly lower MAP than did saline solution. Pulse rate, CO, and SVR were not significantly different among treatments after atipamezole or saline solution were administered. CONCLUSIONS AND CLINICAL RELEVANCE: Atipamezole administered IM at half the volume or the same volume as dexmedetomidine was ineffective at increasing pulse rate or CO in anesthetized cats that received dexmedetomidine. However, atipamezole caused short-lasting but severe arterial hypotension.

The effect of aquapuncture at Pericardium 6 (PC-6) on dexmedetomidine-induced nausea and vomiting in cats.

OBJECTIVE: To determine the effect of aquapuncture at acupuncture point Pericardium 6 (PC-6) on the incidence of dexmedetomidine-induced vomiting and nausea in cats. STUDY DESIGN: Randomized, prospective, crossover study. ANIMALS: A group of 22 cats, 14 females and eight males, aged 1-12 years and weighing 3.8-5.9 kg. METHODS: Each cat was administered treatments in random order at ≥1 week intervals. For treatment (DEX-A), cats were administered PC-6 stimulation by aquapuncture (0.25 mL/250 µg vitamin B12 injection subcutaneously at PC-6). After 30 minutes, dexmedetomidine (10 µg kg-1) was administered intramuscularly (IM). For control treatment (DEX), cats were administered only dexmedetomidine (10 µg kg-1) IM. Incidence of vomiting, number of vomiting episodes and time to first vomiting were recorded by an observer unaware of treatment allocation. At 30 minutes after dexmedetomidine administration, atipamezole (0.1 mg kg-1) was injected IM. Behavior was video recorded and later scored by two observers for clinical signs of nausea. A regression model (analysis of covariance) was used to detect the influence of aquapuncture on vomiting and nausea. Significance was set at p < 0.05. RESULTS: Of 21 cats, 18 (85%) and 16 cats (76%) vomited in DEX-A and DEX, respectively. There was no significant difference in the incidence of vomiting (p = 0.55), number of vomiting episodes (p = 0.55), mean time to vomit (p = 0.88) or nausea score (p = 0.51) between DEX-A and DEX. CONCLUSIONS AND CLINICAL RELEVANCE: PC-6 aquapuncture did not reduce the incidence of dexmedetomidine-induced vomiting or severity of nausea in cats.

Cardiovascular effects of dexmedetomidine, with or without MK-467, following intravenous administration in cats.

OBJECTIVE: To characterize the cardiovascular effects of dexmedetomidine, with or without MK-467, following intravenous (IV) administration in cats. STUDY DESIGN: Prospective Latin square experimental study. ANIMALS: Six healthy adult purpose-bred cats. METHODS: Cats were anesthetized with desflurane in oxygen for instrumentation with a carotid artery catheter and a thermodilution catheter in the pulmonary artery. One hour after discontinuation of desflurane, cats were administered dexmedetomidine (25 µg kg-1), MK-467 (600 µg kg-1), or dexmedetomidine (25 µg kg-1) and MK-467 (600 µg kg-1). All treatments were administered IV as a bolus. Cardiovascular variables were measured prior to drug administration and for 8 hours thereafter. Only data from the dexmedetomidine and dexmedetomidine-MK-467 treatments were analyzed. RESULTS: Dexmedetomidine produced significant decreases in heart rate, cardiac index and right ventricular stroke work index, and significant increases in arterial blood pressure, central venous pressure, pulmonary artery pressure and systemic vascular resistance index. Dexmedetomidine combined with MK-467 resulted in significant but transient decrease in blood pressure and right ventricular stroke work index. CONCLUSION AND CLINICAL RELEVANCE: Following IV co-administration, MK-467 effectively attenuated dexmedetomidine-induced cardiovascular effects in cats. The drug combination resulted in transient reduction in arterial blood pressure, without causing hypotension.

Dexmedetomidine increases tau phosphorylation under normothermic conditions in vivo and in vitro.

There is developing interest in the potential association between anesthesia and the onset and progression of Alzheimer's disease. Several anesthetics have, thus, been demonstrated to induce tau hyperphosphorylation, an effect mostly mediated by anesthesia-induced hypothermia. Here, we tested the hypothesis that acute normothermic administration of dexmedetomidine (Dex), an intravenous sedative used in intensive care units, would result in tau hyperphosphorylation in vivo and in vitro. When administered to nontransgenic mice, Dex-induced tau hyperphosphorylation persisting up to 6 hours in the hippocampus for the AT8 epitope. Pretreatment with atipamezole, a highly specific α2-adrenergic receptor antagonist, blocked Dex-induced tau hyperphosphorylation. Furthermore, Dex dose-dependently increased tau phosphorylation at AT8 in SH-SY5Y cells, impaired mice spatial memory in the Barnes maze and promoted tau hyperphosphorylation and aggregation in transgenic hTau mice. These findings suggest that Dex: (1) increases tau phosphorylation, in vivo and in vitro, in the absence of anesthetic-induced hypothermia and through α2-adrenergic receptor activation, (2) promotes tau aggregation in a mouse model of tauopathy, and (3) impacts spatial reference memory.

A preliminary trial of the sedation induced by intranasal administration of midazolam alone or in combination with dexmedetomidine and reversal by atipamezole for a short-term immobilization in pigeons.

OBJECTIVE: To assess the sedative and immobilization effect of intranasal administration (INS) of midazolam (MID) without or with INS dexmedetomidine (DXM), and some physiological changes induced by the drugs. The ability of INS atipamezole to reverse the DXM component was also assessed. STUDY DESIGN: Prospective 'blinded' experimental study. ANIMALS: In total, 15 pigeons. METHODS: Pigeons were sedated by INS MID alone at a dose of 5 mg kg(-1) (group MID, n = 6) or in combination with INS DXM at a dose 80 µg kg(-1) (group MID-DXM, n = 6). Measurements were made of heart rate (HR), respiratory rate (fR ) and cloacal temperature (CT). The degree of sedation was assessed at 15 minutes prior to, immediately after, and at intervals until 100 minutes after drug administrations. Following MID-DXM, INS atipamezole (250 µg kg(-1) ) was administered and the same indices measured 5 and 10 minutes later. RESULTS: MID had no effect on HR and fR , and although CT decreased, it remained within physiological range. MID-DXM caused significant falls in HR, fR and CT that persisted until the end of sedation. Atipamezole antagonized sedation and cardiorespiratory side effects of MID-DXM within 10 minutes of application. In addition, for MID compared to MID-DXM, the lowest sedation scores [10 (7-14) and 10.5 (5-14) versus 2 (1-4) and 2 (1-5)] were achieved in the 10th and 20th minute versus the 20th and 30th minute of the sedation, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: MID alone, given INS had minimal side effects on vital functions but caused inadequate immobilization of pigeons for restraint in dorsal recumbency. MID-DXM caused an effective degree of immobilization from 20 to 30 minutes after administration, at which time birds tolerated postural changes without resistance. Atipamezole antagonized both side effects and sedation, but complete recovery had not occurred within 10 minutes after its application.

An investigation about the inhibition of acute ischemia/reperfusion damage by dexmedetomidine in rat ovarian tissue.

Reperfusion has always been "the emergency intervention" to ischemic tissue. For a given period of time, tissue injury due to ischemia and reperfusion is more serious than injury due to ischemia only. Groups were as: Group 1: 25 µg/kg dexmedetomidine + ischemia/reperfusion group. Group 2: 10 mg/kg yohimbine +25 µg/kg dexmedetomidine + ischemia/reperfusion group. Group 3: Ischemia/reperfusion (control) group. Group 4: Healthy rats. Rat ovaries were exposed to a 3-hour ischemia and then reperfusion ensured for 2 hours. After ischemia/reperfusion, total glutathione, malondialdehyde, 8-hydroxyguanine levels and histopathological investigation were studied. The highest total glutathione and the lowest malondialdehyde and DNA damage levels were determined in dexmedetomidine group when compared to control group. The difference between yohimbine + dexmedetomidine and the control group was insignificant. Dexmedetomidine protects the ovarian tissue of the rat from I/R injury. It is hypothesized that this protective effect of dexmedetomidine is mediated by the α-2 adrenergic receptors. Dexmedetomidine could be useful for attenuation of tissue damage after I/R and prevention of I/R-related complications.

Dexmedetomidine attenuates remote lung injury induced by renal ischemia-reperfusion in mice.

BACKGROUND: Renal ischemia-reperfusion (I/R) may cause acute lung injury (ALI). The mortality of combined acute kidney injury and ALI is extremely high. Dexmedetomidine, an α(2) adrenergic agonist, exerts potent anti-inflammatory and organoprotective effects in addition to its sedative and analgesic properties. We sought to elucidate whether dexmedetomidine can attenuate lung injury following renal I/R in a murine model of renal I/R. METHODS: Adult C57BL/6J male mice were randomized to five groups: sham-operated control (Sham); renal I/R (I/R); intraperitoneal injection of dexmedetomidine 25 µg/kg before ischemia (pre-dex) and after perfusion (post-dex); combination of α(2) adrenergic antagonist atipamezole 250 µg/kg prior to dexmedetomidine pre-treatment (atip-dex). Kidney I/R was induced by bilateral renal pedicle clamping for 45 min and followed by 6 h reperfusion. The pulmonary tissues were harvested for histopathological evaluation, wet/dry ratio measurement, biochemical analysis of myeloperoxidase (MPO), Polymerase chain reaction (PCR) determination of Inter-cellular adhesion molecule (ICAM-1) and Tumor necrosis factor - alpha (TNF-α) mRNA. RESULTS: Renal IR induced significant pulmonary injuries, increased wet/dry ratio together with the enhanced of MPO activities and increased ICAM-1 and TNF-α mRNA level. Both pre- and post-treatment with dexmedetomidine markedly reduced lung edema and inflammatory response and lowered MPO activity and ICAM-1 and TNF-α mRNA expression. The protective effects of dexmedetomidine in the lung were partially reversed by atipamezole, but there were no effect on ICAM-1 and TNF-α mRNA expression level. CONCLUSIONS: Dexmedetomidine is capable of attenuating remote lung injury induced by renal IR via both α(2) adrenoceptors dependent and independent mechanisms.

Effects of nitric oxide synthase inhibition on dexmedetomidine-induced vasoconstriction in healthy human volunteers.

BACKGROUND: This study aimed to assess the contribution of endothelial nitric oxide synthesis to the net responses of human peripheral blood vessels in vivo to the selective alpha(2)-adrenoceptor agonist dexmedetomidine. METHODS: Two groups of healthy young men were studied. In the first experiment, after brachial plexus block, the responses of digital arteries to systemically administered dexmedetomidine (target plasma concentration 1.2 ng ml(-1)) were studied using a photoplethysmograph (n=10) during i.a. infusions of saline and the nitric oxide synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA) (8 micromol min(-1)). In a separate experiment, after pre-treatment with acetylsalicylic acid, responses to increasing doses of dexmedetomidine (0.01-164 ng min(-1)) in the presence and absence of L-NMMA were compared in dorsal hand veins (DHV) (n=10) using linear variable differential transformers. RESULTS: L-NMMA significantly augmented dexmedetomidine-induced vasoconstriction of digital arteries as assessed by an increase in light transmission through a finger and by a decrease in finger temperature. The mean (95% confidence interval) extent of the additional effect of L-NMMA over the constrictor effect of dexmedetomidine alone was 19% (14-24) (P<0.0001). In DHV, L-NMMA had variable effects on the dexmedetomidine-constriction dose-response curve. In three subjects, the curve was shifted significantly to the left (with a >10-fold difference in ED(50)), but ED(50) was only marginally affected by L-NMMA in the other subjects (difference in ED(50)

Dexmedetomidine enhances the local anesthetic action of lidocaine via an alpha-2A adrenoceptor.

BACKGROUND: Clonidine, an alpha-2 adrenoceptor agonist, is a common adjunct in both central and peripheral blocks. Dexmedetomidine, a more selective alpha-2 adrenoceptor agonist, is also known to enhance central neural blockades. Its peripheral effect, however, has not been fully elucidated. Thus, we evaluated the effect of dexmedetomidine and other alpha-2 adrenoceptor agonists on the local anesthetic action of lidocaine at the periphery and explored the mechanism involved. METHODS: alpha-2 Adrenoceptor agonists, including dexmedetomidine, clonidine, and oxymetazoline, combined with lidocaine were intracutaneously injected into the back of male guinea pigs. The test of six pinpricks was applied every 5 min until 60 min after the injection. The number of times which the prick failed to elicit a response during the 60-min period was added and the sum served as an anesthetic score indicating the degree of local anesthesia. Differences from the control value within the group were analyzed using an analysis of variance followed by a post hoc Dunnett's test. Furthermore, we evaluated the antagonism of the effect of dexmedetomidine by yohimbine, an alpha-2A, 2B, and 2C adrenoceptor antagonist, or prazosin, an alpha-1, alpha-2B, and 2C adrenoceptor antagonist, analyzed using a two-way analysis of variance. RESULTS: All alpha-2 adrenoceptor agonists enhanced the degree of local anesthesia of lidocaine in a dose-dependent manner. Furthermore, yohimbine inhibited the effect of dexmedetomidine, whereas prazosin did not. CONCLUSION: We demonstrated that alpha-2 adrenoceptor agonists enhanced the local anesthetic action of lidocaine, and suggest that dexmedetomidine acts via alpha-2A adrenoceptors.

Signalling pathways for transactivation by dexmedetomidine of epidermal growth factor receptors in astrocytes and its paracrine effect on neurons.

BACKGROUND AND PURPOSE: Stimulation of astrocytes by the alpha(2)-adrenoceptor agonist dexmedetomidine, a neuroprotective drug, transactivates epidermal growth factor (EGF) receptors. The present study investigates signal pathways leading to release of an EGF receptor ligand and those activated during EGF receptor stimulation, and the response of neurons to dexmedetomidine and to astrocyte-conditioned medium. EXPERIMENTAL APPROACH: Phosphorylation of ERK(1/2) was determined by western blotting and immunocytochemistry, and phosphorylation of EGF receptors by immunoprecipitation and western blotting. mRNA expression of fos family was measured by RT-PCR. KEY RESULTS: Pertussis toxin (0.2 microg ml(-1)) an inhibitor of betagamma subunit dissociation from Galpha(i) protein, and GF 109203X (500 nM), a protein kinase C inhibitor, abolished ERK(1/2) phosphorylation. PP1 (10 microM), inhibiting Src kinase and GM 6001 (10 microM), an inhibitor of Zn-dependent metalloproteinase, abolished ERK(1/2) phosphorylation by dexmedetomidine (50 nM), but not that by EGF (10 ng ml(-1)), showing Src kinase and metalloproteinase activation during the first stage only; AG 1478 (1 microM), an inhibitor of the EGF receptor tyrosine kinase, abolished ERK(1/2) phosphorylation. Dexmedetomidine-induced EGF receptor phosphorylation was prevented by AG 1478, GM 6001, PP1 and GF 109203X and its induction of cfos and fosB by AG 1478 and by U0126 (10 microM), an inhibitor of ERK phosphorylation, indicating downstream effects of ERK(1/2) phosphorylation. EGF and conditioned medium from dexmedetomidine-treated astrocytes, but not dexmedetomidine itself, induced ERK phosphorylation in primary cultures of cerebellar neurons. CONCLUSIONS AND IMPLICATIONS: Dexmedetomidine-induced transactivation pathways were delineated. Its paracrine effect on neurons may account for its neuroprotective effects.

Pharmacological characterization and CNS effects of a novel highly selective alpha2C-adrenoceptor antagonist JP-1302.

BACKGROUND AND PURPOSE: Pharmacological validation of novel functions for the alpha2A-, alpha2B-, and alpha2C-adrenoceptor (AR) subtypes has been hampered by the limited specificity and subtype-selectivity of available ligands. The current study describes a novel highly selective alpha2C-adrenoceptor antagonist, JP-1302 (acridin-9-yl-[4-(4-methylpiperazin-1-yl)-phenyl]amine). EXPERIMENTAL APPROACH: Standard in vitro binding and antagonism assays were employed to demonstrate the alpha2C-AR specificity of JP-1302. In addition, JP-1302 was tested in the forced swimming test (FST) and the prepulse-inhibition of startle reflex (PPI) model because mice with genetically altered alpha2C-adrenoceptors have previously been shown to exhibit different reactivity in these tests when compared to wild-type controls. KEY RESULTS: JP-1302 displayed antagonism potencies (KB values) of 1,500, 2,200 and 16 nM at the human alpha2A-, alpha2B-, and alpha2C-adrenoceptor subtypes, respectively. JP-1302 produced antidepressant and antipsychotic-like effects, i.e. it effectively reduced immobility in the FST and reversed the phencyclidine-induced PPI deficit. Unlike the alpha2-subtype non-selective antagonist atipamezole, JP-1302 was not able to antagonize alpha2-agonist-induced sedation (measured as inhibition of spontaneous locomotor activity), hypothermia, alpha2-agonist-induced mydriasis or inhibition of vas deferens contractions, effects that have been generally attributed to the alpha2A-adrenoceptor subtype. In contrast to JP-1302, atipamezole did not antagonize the PCP-induced prepulse-inhibition deficit. CONCLUSIONS AND IMPLICATIONS: The results provide further support for the hypothesis that specific antagonism of the alpha2C-adrenoceptor may have therapeutic potential as a novel mechanism for the treatment of neuropsychiatric disorders.

Sedative, analgesic, and cardiovascular effects of levomedetomidine alone and in combination with dexmedetomidine in dogs.

OBJECTIVE: To determine whether a high dose of levomedetomidine had any pharmacologic activity or would antagonize the sedative and analgesic effects of dexmedetomidine in dogs. ANIMALS: 6 healthy Beagles. PROCEDURE: Each dog received the following treatments on separate days: a low dose of levomedetomidine (10 microg/kg), IV, as a bolus, followed by continuous infusion at a dose of 25 microg/kg/h; a high dose of levomedetomidine (80 microg/kg), IV, as a bolus, followed by continuous infusion at a dose of 200 microg/kg/h; and a dose of isotonic saline (0.9% NaCl) solution, IV, as a bolus, followed by continuous infusion (control). For all 3 treatments, the infusion was continued for 120 minutes. After 60 minutes, a single dose of dexmedetomidine (10 microg/kg) was administered IV. Sedation and analgesia were scored subjectively, and heart rate, blood pressure, respiratory rate, arterial blood gas partial pressures, and rectal temperatures were monitored. RESULTS: Administration of levomedetomidine did not cause any behavioral changes. However, administration of the higher dose of levomedetomidine enhanced the bradycardia and reduced the sedative and analgesic effects associated with administration of dexmedetomidine. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that administration of dexmedetomidine alone may have some cardiovascular benefits over administration of medetomidine, which contains both dexmedetomidine and levomedetomidine. Further studies are needed to confirm the clinical importance of the effects of levomedetomidine in dogs.

Effect of dexmedetomidine on the release of [3H]-noradrenaline from rat kidney cortex slices: characterization of alpha2-adrenoceptor.

The presynaptic modulation of [3H]-noradrenaline (NA) release from rat kidney cortex slices, a method used for the first time, was investigated. Rat kidney cortex slices were loaded with [3H]-NA and the release of radioactivity at rest and in response to field stimulation was determined. The alpha(2)-adrenoceptor agonist, dexmedetomidine inhibited the stimulation-evoked release of NA from kidney slices in a concentration-dependent manner, whereas alpha(2)-adrenoceptor antagonist CH-38083 (7,8-methyenedioxy-14-alpha-hydroxyalloberbane HCl), an alpha(2)-adrenoceptor antagonists, enhanced it. When dexmedetomidine and BRL-44408, a selective alpha(2A) antagonist, were added together, the effect of dexmedetomidine was significantly antagonized. In contrast, ARC-239 (2-(2,4-(o-piperazine-1-yl)-ethyl-4,4-dimethyl-1,3-(2H, 4H)disoguinolinedione chloride), a selective alpha(2B)-antagonist, had no effect on the release and failed to prevent the effect of dexmedetomidine. Prazosin, an alpha(1)- and alpha(2B/C)-adrenoceptor antagonist enhanced the release evoked by field stimulation. It is therefore suggested that there is a negative feedback modulation of NA release at the sympathetic innervation of kidney cortex, and dexmedetomidine, a clinically used anesthetic adjunct inhibits the release via activation of alpha(2C)-adrenoceptors.