Dual α2-Adrenergic Agonist and α1-Adrenergic Antagonist Actions of Dexmedetomidine on Human Isolated Endothelium-Denuded Gastroepiploic Arteries

Effects of intravenous lidocaine, dexmedetomidine, and their combination on IL-1, IL-6 and TNF-α in patients undergoing laparoscopic hysterectomy: a prospective, randomized controlled trial

BACKGROUND

Surgical-related inflammatory responses have negative effects on postoperative recovery. Intravenous (IV) lidocaine and dexmedetomidine inhibits the inflammatory response. We investigated whether the co-administration of lidocaine and dexmedetomidine could further alleviate inflammatory responses compared with lidocaine or dexmedetomidine alone during laparoscopic hysterectomy.

METHODS

A total of 160 patients were randomly allocated into four groups following laparoscopic hysterectomy: the control group (group C) received normal saline, the lidocaine group (group L) received lidocaine (bolus infusion of 1.5 mg/kg over 10 min, 1.5 mg/kg/h continuous infusion), the dexmedetomidine group (group D) received dexmedetomidine (bolus infusion of 0.5 μg/kg over 10 min, 0.4 μg/kg/h continuous infusion), and the lidocaine plus dexmedetomidine group (group LD) received a combination of lidocaine (bolus infusion of 1.5 mg/kg over 10 min, 1.5 mg/kg/h continuous infusion) and dexmedetomidine (bolus infusion of 0.5 μg/kg over 10 min, 0.4 μg/kg/h continuous infusion). The levels of plasma interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) at different time points were the primary outcomes. Secondary outcomes included hemodynamic variables, postoperative visual analogue scale (VAS) scores, time to first flatus, and incidence of nausea and vomiting after surgery.

RESULTS

The levels of plasma IL-1, IL-6, and TNF-α were lower in groups D and LD than in group C and were lowest in group LD at the end of the procedure and 2 h after the operation (P < 0.05). The VAS scores were decreased in groups D and LD compared with group C (P < 0.05). The heart rate (HR) was decreased at the end of the procedure and 2 h after the operation in groups D and LD compared to groups C and L (P < 0.001). The mean blood pressure (MBP) was lower at 2 h after the operation in groups L, D, and LD than in group C (P < 0.001). There was a lower incidence of postoperative nausea and vomiting (PONV) in group LD than in group C (P < 0.05).

CONCLUSIONS

The combination of lidocaine and dexmedetomidine significantly alleviated the inflammatory responses, decreased postoperative pain, and led to fewer PONV in patients undergoing laparoscopic hysterectomy.

TRIAL REGISTRATION

ClinicalTrials.gov ( NCT03276533 ), registered on August 23, 2017.

Intravenous Dexmedetomidine Combined with Ultrasound-Guided Rectus Sheath Block for Open Gastrectomy: a Prospective Randomized Trial

PURPOSE

To compare the incidences of positive hemodynamic response (HR > 100 beats min^-1 or SBP > 160 mmHg) during abdominal exploration and moderate pain after surgery, when using dexmedetomidine infusion and rectus sheath block.

METHODS

One hundred patients undergoing open gastrectomy were randomized to receive rectus sheath block with ropivacaine (Group B, n = 25), initial loading dose of 0.6 μg kg^-1 dexmedetomidine, followed by a continuous infusion of 0.2 μg kg^-1 h^-1 throughout surgery (Group D, n = 25), both rectus sheath block and dexmedetomidine (Group BD, n = 25), or neither rectus sheath block nor dexmedetomidine (Group C, n = 25). General anesthesia techniques were standardized. HR, SBP, and positive hemodynamic response at peritoneum incision (T_PI), 5 min (T_AE-5), 10 min (T_AE-10), and 15 min (T_AE-15) after the start of abdominal exploration, and incidences of moderate postoperative pain were recorded.

RESULTS

Positive hemodynamic responses during abdominal exploration were more common in Groups B (82%) and C (74%) than in Groups D (14%) and BD (9%) (all P = 0.000). HR and SBP were lower in Groups D and BD, compared with those in Groups C and B (all P < 0.05). Compared with T_PI, HR and SBP increased significantly in Groups B and C during abdominal exploration (all P < 0.05)_, but not in Group BD (except HR at T_AE-15). The incidences of moderate pain in Groups B and BD were noticeably lower than in Groups C and D at 1 h, 2 h, and 6 h after surgery (all P < 0.0083).

CONCLUSION

Dexmedetomidine infusion combined with rectus sheath block provided more hemodynamic stability during abdominal exploration and better analgesia after surgery.

Effects of dexmedetomidine on porcine pulmonary artery vascular smooth muscle

Background

The α₂-receptor agonist dexmedetomidine (Dex) has been shown to produce sedative and analgesic effects not only with systemic administration but also when administered in the extradural space and around peripheral nerves. The effects and mechanism of action of Dex on pulmonary arteries, however, have not been determined. This study therefore aimed to investigate the effect of Dex on pulmonary arterial vascular smooth muscle by evaluating changes in isometric contraction tension. We then attempted to determine the effects of Dex on depolarization stimulation and receptor stimulation.

Methods

Endothelium-denuded porcine pulmonary arteries were sliced into 2- to 3-mm rings. We then exposed them to certain substances at various concentrations under different conditions of baseline stimulation (with KCl, adrenaline, caffeine, or histamine) and to α₂-receptor stimulants or antagonists, or α₁-receptor antagonists (imidazoline, yohimbine, rauwolscine, prazosin), and different conditions of Ca²⁺ depletion of the intracellular reservoir or extracellular stores. We measured the changes in isometric contraction tension with each addition or change in conditions.

Results

Dex enhanced the contraction induced by high-concentration KCl stimulation. Dex-induced enhancement of contraction induced by high-concentration KCl was completely suppressed by yohimbine and rauwolscine, which are α₂-receptor antagonists, but not by prazosin. Dex, imidazoline, yohimbine, and rauwolscine reduced the increases in contraction tension induced by the receptor stimulant adrenaline. Dex suppressed the adrenaline-induced increases in contraction tension after depletion of the Ca²⁺ reservoir. In the absence of extracellular Ca²⁺, Dex suppressed the adrenaline- and histamine-induced increases in contraction tension but did not affect caffeine-induced increases.

Conclusions

Dex-enhanced, high-concentration KCl-induced contraction was mediated by α₂-receptors. Adrenaline-induced contraction was suppressed by the α₂-receptor stimulant Dex and α₂-receptor antagonists yohimbine and rauwolscine, suggesting that the effect of Dex on adrenaline-induced contraction is attributable to its α₂-receptor-blocking action. Dex inhibited receptor-activated Ca²⁺ channels and phosphatidylinositol-1,4,5-triphosphate-induced Ca²⁺ release but not Ca²⁺-induced Ca²⁺ release.

L-arginine and Arginase Products Potentiate Dexmedetomidine-induced Contractions in the Rat Aorta

BACKGROUND

The α2-adrenergic sedative/anesthetic agent dexmedetomidine exerts biphasic effects on isolated arteries, causing endothelium-dependent relaxations at concentrations at or below 30 nM, followed by contractions at higher concentrations. L-arginine is a common substrate of endothelial nitric oxide synthase and arginases. This study was designed to investigate the role of L-arginine in modulating the overall vascular response to dexmedetomidine.

METHODS

Isometric tension was measured in isolated aortic rings of Sprague Dawley rats. Cumulative concentrations of dexmedetomidine (10 nM to 10 μM) were added to quiescent rings (with and without endothelium) after previous incubation with vehicle, N-nitro-L-arginine methyl ester hydrochloride (L-NAME; nitric oxide synthase inhibitor), prazosin (α1-adrenergic antagonist), rauwolscine (α2-adrenergic antagonist), L-arginine, (S)-(2-boronethyl)-L-cysteine hydrochloride (arginase inhibitor), N-hydroxy-L-arginine (arginase inhibitor), urea and/or ornithine. In some preparations, immunofluorescent staining, immunoblotting, or measurement of urea content were performed.

RESULTS

Dexmedetomidine did not contract control rings with endothelium but evoked concentration-dependent increases in tension in such rings treated with L-NAME (Emax 50 ± 4%) or after endothelium-removal (Emax 74 ± 5%; N = 7 to 12). Exogenous L-arginine augmented the dexmedetomidine-induced contractions in the presence of L-NAME (Emax 75 ± 3%). This potentiation was abolished by (S)-(2-boronethyl)-L-cysteine hydrochloride (Emax 16 ± 4%) and N-hydroxy-L-arginine (Emax 18 ± 4%). Either urea or ornithine, the downstream arginase products, had a similar potentiating effect as L-arginine. Immunoassay measurements demonstrated an upregulation of arginase I by L-arginine treatment in the presence of L-NAME (N = 4).

CONCLUSIONS

These results suggest that when vascular nitric oxide homeostasis is impaired, the potentiation of the vasoconstrictor effect of dexmedetomidine by L-arginine depends on arginase activity and the production of urea and ornithine.

Dexmedetomidine protects mice against myocardium ischaemic/reperfusion injury by activating an AMPK/PI3K/Akt/eNOS pathway

Acute myocardial ischaemia/reperfusion (MIR) injury leads to severe arrhythmias and has a high rate of lethality. In the present study, we aim to determine the effect of dexmedetomidine (Dex) on heart injury parameters following MIR surgery. We examined the effects of Dex on heart function parameters and infarct size following MIR surgery. Proinflammatory cytokines, oxidative products and anti-oxidative enzymes in the myocardium were measured to evaluate the anti-inflammatory and anti-oxidative effects of Dex. The role of the adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)/phosphatidylino-sitol 3-kinase (PI3k)/Akt/endothelial nitric oxide synthase (eNOS) pathway was investigated using their inhibitors. The alteration of haemodynamic parameters, histopathological results, and infarct size caused by MIR was attenuated by Dex. The interleukine-1 beta (IL-1β), IL-6, tumour necrosis factor-a (TNF-α) and myeloperoxidase (MPO) were all significantly decreased. Anti-oxidative enzymes superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) were restored by Dex. Oxidative products8-OHdG, MDA and protein carbonyl were all decreased by Dex (P<.05). Dex activated AMPK expression, eNOS and Akt phosphorylation. The influence of Dex on cardiac function was reversed by the inhibitors of the eNOS, AMPK and PI3K/Akt pathways. These results indicate that Dex protected the cardiac functional, histological changes, inflammation and oxidative stress induced by MIR. Our results present a novel signalling mechanism that Dex protects MIR injury by activating an AMPK/PI3K/Akt/eNOS pathway.

Injectable Anesthesia for Mice: Combined Effects of Dexmedetomidine, Tiletamine-Zolazepam, and Butorphanol

Anesthetic protocols for murine models are varied within the literature and medetomidine has been implicated in the development of urethral plugs in male mice. Our objective was to evaluate the combination of butorphanol, dexmedetomidine, and tiletamine-zolazepam. A secondary objective was to identify which class of agent was associated with urethral obstructions in male mice. BALB/c male (n = 13) and female (n = 23) mice were assigned to dexmedetomidine and tiletamine-zolazepam with or without butorphanol or to single agent dexmedetomidine or tiletamine-zolazepam. Anesthesia was achieved in 58% (14/24) of mice without butorphanol and in 100% (24/24) of mice with butorphanol. The combination of dexmedetomidine (0.2 mg/kg), tiletamine-zolazepam (40 mg/kg), and butorphanol (3 mg/kg) resulted in an induction and anesthetic duration of 12 and 143 minutes, respectively. Urethral obstructions occurred in 66% (25/38) of trials in male mice that received dexmedetomidine with a mortality rate of 38% (5/13). Tiletamine-zolazepam, when used alone, resulted in a 0% (0/21) incidence of urethral obstructions. Combination use of dexmedetomidine, tiletamine-zolazepam, and butorphanol results in a longer and more reliable duration of anesthesia than the use of dexmedetomidine and tiletamine-zolazepam alone. Dexmedetomidine is not recommended for use in nonterminal procedures in male mice due to the high incidence of urethral obstructions and resultant high mortality rate.

Dexmedetomidine-Induced Contraction Involves CPI-17 Phosphorylation in Isolated Rat Aortas

Dexmedetomidine, a highly selective α-2 adrenoceptor agonist, produces vasoconstriction, which leads to transiently increased blood pressure. The goal of this study was to investigate specific protein kinases and the associated cellular signal pathways responsible for the increased calcium sensitization induced by dexmedetomidine in isolated rat aortas, with a particular focus on phosphorylation-dependent inhibitory protein of myosin phosphatase (CPI-17). The effect of Y-27632 and chelerythrine on the dexmedetomidine-induced intracellular calcium concentration ([Ca²⁺]_i) and tension were assessed using fura-2-loaded aortic strips. The effects of rauwolscine, Y-27632, chelerythrine, and ML-7 hydrochloride on the dexmedetomidine-induced phosphorylation of CPI-17 or of the 20-kDa regulatory light chain of myosin (MLC₂₀) were investigated in rat aortic vascular smooth muscle cells. The effects of rauwolscine, Y-27632, and chelerythrine on the membrane translocation of Rho-kinase and protein kinase C (PKC) phosphorylation induced by dexmedetomidine were assessed. Y-27632 and chelerythrine each reduced the slopes of the [Ca²⁺]_i-tension curves of dexmedetomidine-induced contraction, and Y-27632 more strongly reduced these slopes than did chelerythrine. Rauwolscine, Y-27632, chelerythrine, and ML-7 hydrochloride attenuated the dexmedetomidine-induced phosphorylation of CPI-17 and MLC₂₀. Taken together, these results suggest that dexmedetomidine-induced contraction involves calcium sensitization, which appears to be mediated by CPI-17 phosphorylation via Rho-kinase or PKC.

Dexmedetomidine inhibits vasoconstriction via activation of endothelial nitric oxide synthase

Despite the complex vascular effects of dexmedetomidine (DEX), its actions on human pulmonary resistance arteries remain unknown. The present study tested the hypothesis that DEX inhibits vascular tension in human pulmonary arteries through the endothelial nitric oxide synthase (eNOS) mediated production of nitric oxide (NO). Pulmonary artery segments were obtained from 62 patients who underwent lung resection. The direct effects of DEX on human pulmonary artery tension and changes in vascular tension were determined by isometric force measurements recorded on a myograph. Arterial contractions caused by increasing concentrations of serotonin with DEX in the presence or absence of L-NAME (endothelial nitric oxide synthase inhibitor), yohimbine (α₂-adrenoceptor antagonist) and indomethacin (cyclooxygenase inhibitor) as antagonists were also measured. DEX had no effect on endothelium-intact pulmonary arteries, whereas at concentrations of 10^–8~10^–6 mol/L, it elicited contractions in endothelium-denuded pulmonary arteries. DEX (0.3, 1, or 3×10^–9 mmol/L) inhibited serotonin-induced contraction in arteries with intact endothelium in a dose-dependent manner. L-NAME and yohimbine abolished DEX-induced inhibition, whereas indomethacin had no effect. No inhibitory effect was observed in endothelium-denuded pulmonary arteries. DEX-induced inhibition of vasoconstriction in human pulmonary arteries is mediated by NO production induced by the activation of endothelial α₂-adrenoceptor and nitric oxide synthase.

Dexmedetomidine preconditioning ameliorates kidney ischemia-reperfusion injury

Kidney ischemia-reperfusion (I/R) injury is a common cause of acute kidney injury. We tested whether dexmedetomidine (Dex), an alpha2 adrenoceptor (α2-AR) agonist, protects against kidney I/R injury. Sprague-Dawley rats were divided into four groups: (1) Sham-operated group; (2) I/R group (40 min ischemia followed by 24 h reperfusion); (3) I/R group + Dex (1 μg/kg i.v. 60 min before the surgery), (4) I/R group + Dex (10 μg/kg). The effects of Dex postconditiong (Dex 1 or 10 μg/kg i.v. after reperfusion) as well as the effects of peripheral α2-AR agonism with fadolmidine were also examined. Hemodynamic effects were monitored, renal function measured, and acute tubular damage along with monocyte/macrophage infiltration scored. Kidney protein kinase B, toll like receptor 4, light chain 3B, p38 mitogen-activated protein kinase (p38 MAPK), sirtuin 1, adenosine monophosphate kinase (AMPK), and endothelial nitric oxide synthase (eNOS) expressions were measured, and kidney transciptome profiles analyzed. Dex preconditioning, but not postconditioning, attenuated I/R injury-induced renal dysfunction, acute tubular necrosis and inflammatory response. Neither pre- nor postconditioning with fadolmidine protected kidneys. Dex decreased blood pressure more than fadolmidine, ameliorated I/R-induced impairment of autophagy and increased renal p38 and eNOS expressions. Dex downregulated 245 and upregulated 61 genes representing 17 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, in particular, integrin pathway and CD44. Ingenuity analysis revealed inhibition of Rac and nuclear factor (erythroid-derived 2)-like 2 pathways, whereas aryl hydrocarbon receptor (AHR) pathway was activated. Dex preconditioning ameliorates kidney I/R injury and inflammatory response, at least in part, through p38-CD44-pathway and possibly also through ischemic preconditioning.

Absorption characteristics of epidural levobupivacaine with adrenaline and clonidine in children

AIM

To determine if the addition of adrenaline, clonidine, or their combination altered the pharmacokinetic profile of levobupivacaine administered via the caudal epidural route in children.

METHODS

Children aged <18 years old scheduled to undergo sub-umbilical surgery were administered caudal levobupivacaine plain 2.5 mg · ml(-1) or with adjuvants adrenaline 5 mcg · ml(-1) or clonidine 2 mcg · ml(-1) or their combination. Covariate analysis included weight and postnatal age (PNA). Time-concentration profile analysis was undertaken using nonlinear mixed effects models. A one-compartment linear disposition model with first-order input and first-order elimination was used to describe the data. The effect of either clonidine or adrenaline on absorption was investigated using a scaling parameter (Fabs(CLON), Fabs(ADR)) applied to the absorption half-life (Tabs).

RESULTS

There were 240 children (median weight 11.0, range 1.9-56.1 kg; median postnatal age 16.7, range 0.6-167.6 months). Absorption of levobupivacaine was faster when mixed with clonidine (Fabs(CLON) 0.60; 95%CI 0.44, 0.83) but slower when mixed with adrenaline (Fabs(ADR) 2.12; 95%CI 1.45, 3.08). The addition of adrenaline to levobupivacaine resulted in a bifid absorption pattern. While initial absorption was unchanged (Tabs 0.15 h 95%CI 0.12, 0.18 h), there was a late absorption peak characterized by a Tabs(LATE) 2.34 h (95%CI 1.44, 4.97 h). The additional use of clonidine with adrenaline had minimal effect on the bifid absorption profile observed with adrenaline alone. Neither clonidine nor adrenaline had any effect on clearance. The population parameter estimate for volume of distribution was 157 l 70 kg(-1). Clearance was 6.5 l · h(-1) 70 kg(-1) at 1-month PNA and increased with a maturation half-time of 1.6 months to reach 90% of the mature value (18.5 l · h(-1) 70 kg(-1)) by 5 months PNA.

CONCLUSIONS

The addition of adrenaline decreases the rate of levobupivacaine systemic absorption, reducing peak concentration by half. Levobupivacaine concentrations with adrenaline adjuvant were reduced compared to plain levobupivacaine for up to 3.5 hours. Clonidine as an adjuvant results in faster systemic absorption of levobupivacaine and similar concentration time profile to levobupivacaine alone. Adding adrenaline with clonidine does not alter the concentration profile observed with adrenaline alone.

Vasodilatory mechanisms of beta receptor blockade

Beta-blockers are widely prescribed for the treatment of a variety of cardiovascular pathologies. Compared to traditional beta-adrenergic antagonists, beta-blockers of the new generation exhibit ancillary properties such as vasodilation through different mechanisms. This translates into a more favorable hemodynamic profile. The relative affinities of beta-adrenoreceptor antagonists towards the three beta-adrenoreceptor isotypes matter for predicting their functional impact on vasomotor control. This review will focus on the mechanisms underlying beta-blocker-evoked vasorelaxation with a specific emphasis on agonist properties of beta(3)-adrenergic receptors.

Vascular reactivity in human arteries: from experimental study to clinical application

The principal function of VSM cells in mature animals is contraction. The endothelium is now recognized to elaborate various vasoactive factors and to play a critical part in regulation of vascular tone. Many circulating mediators and hormones have effects on vascular tone that are mediated via multiple receptors. Vasoactive agents also exert their effects on tissues by acting on one or more processes in the contraction–relaxation cycle in VSM. In humans,systemic, pulmonary, and various organ circulation(s) are maintained by an intricate and complex cardiovascular system. We expect future studies to clarify the sophisticated but complex mechanisms of VSM in humans.

Calcium sensitization involved in dexmedetomidine-induced contraction of isolated rat aorta

Dexmedetomidine, a full agonist of the α2B-adrenoceptor that is mainly involved in vascular smooth muscle contraction, is primarily used for analgesia and sedation in intensive care units. High-dose dexmedetomidine produces hypertension in children and adults. The goal of this in vitro study was to investigate the role of the calcium (Ca2+) sensitization mechanism involving Rho-kinase, protein kinase C (PKC), and phosphoinositide 3-kinase (PI3-K) in mediating contraction of isolated rat aortic smooth muscle in response to dexmedetomidine. The effect of dexmedetomidine on the intracellular Ca2+ level ([Ca2+]i) and tension was measured simultaneously. Dexmedetomidine concentration–response curves were generated in the presence or absence of the following antagonists: rauwolscine, Y 27632, LY 294002, GF 109203X, and verapamil. Dexmedetomidine-induced phosphorylation of PKC and membrane translocation of Rho-kinase were detected with Western blotting. Rauwolscine, Y 27632, GF 109203X, LY 294002, and verapamil attenuated dexmedetomidine-induced contraction. The slope of the [Ca2+]i–tension curve for dexmedetomidine was higher than that for KCl. Dexmedetomidine induced phosphorylation of PKC and membrane translocation of Rho-kinase. These results suggest that dexmedetomidine-induced contraction involves a Ca2+ sensitization mechanism mediated by Rho-kinase, PKC, and PI3-K that is secondary to α2-adrenoceptor stimulation in rat aortic smooth muscle.

Dexmedetomidine does not produce vasocontraction on human isolated gastroepiploic artery

Background

Recently, the addition of dexmedetomidine to sedation regimens after cardiac surgery had been reported and there is a possibility that dexmedetomidine can cause vasoconstriction. Vasopressin has been used as a prophylactic treatment for refractory vasodilatory shock during coronary artery bypass graft (CABG). Also, vasopressin may play an important role in initiating spasms at the graft artery. Here we evaluate the direct effect of dexmedetomidine on isolated human gastroepiploic arteries and the synergistic effect of dexmedetomidine and vasopressin.

Methods

Discarded gastroepiploic arteries from elective subtotal gastrectomy (n = 10) were used in this study. We measured the level of contraction in isolated human gastroepiploic arteries induced by increasing concentrations of dexmedetomidine (10^-10 to 10^-6 M) with or without vasopressin (10^-10, 10^-9 M). Arterial contractions caused by increasing concentrations of vasopressin (10^-10 to 10^-7.5 M) with or without dexmedetomidine (10^-9, 10^-7 M) were also measured in the tissue samples.

Results

Supraclinical concentrations of dexmedetomidine elicited contractions at concentrations of 10^-7 M and 10^-6 M (P < 0.05 versus resting tension). The same concentrations of dexmedetomidine (10^-7, 10^-6 M) significantly enhanced vasopressin-induced contractions (P < 0.05 versus vasopressin-induced contraction). Vasopressin produced concentration-dependent contractions and vasopressin (10^-10, 10^-9.5, 10^-9 M) also increased the intensity of dexmedetomidine (10^-7 M) induced contractions.

Conclusions

There was a synergistic effect between supraclinical doses of dexmedetomidine and vasopressin on the degree of contraction in isolated human gastroepiploic arteries. However, a sedative dose of dexmedetomidine (clinical dose: 0.2-0.7 µg/kg/hr, plasma concentration: 0.36-1.25 ng/ml) did not enhance vasopressin induced-contraction in isolated human gastroepiploic arteries.

Effects of a novel benzodiazepine derivative, JM-1232(-), on human gastroepiploic artery in vitro

OBJECTIVE

To investigate the effects of JM-1232(-) on norepinephrine (10(-6) mol/L)- and high K(+) (40 mmol/L)-induced contractions in isolated human gastroepiploic arteries (GEA), and to compare them with the effects of midazolam and propofol. In addition, to investigate whether the benzodiazepine-receptor antagonist, flumazenil, or μ-opioid-receptor antagonist, naloxone, influenced the vascular effects of JM-1232(-).

DESIGN

An in vitro experimental study.

SETTING

University laboratory.

PARTICIPANTS

GEA segments were used from 69 patients undergoing coronary artery bypass graft surgery.

MEASUREMENTS AND MAIN RESULTS

JM-1232(-) produced dose-dependent relaxation effects in the rings. Although these effects of JM-1232(-) were greater than those of midazolam and propofol at high concentrations (10(-5)-10(-4) mol/L), there were no significantly different relaxation effects at the clinical concentrations of 3 × 10(-6) mol/L JM-1232(-), 3 × 10(-6) mol/L midazolam, and 1 × 10(-5) mol/L propofol. In addition, all these effects were independent of the presence of a functional endothelium. Vasorelaxation induced by JM-1232(-) on norepinephrine-preconstricted GEA was inhibited by flumazenil, but not by naloxone.

CONCLUSIONS

These results indicate that JM-1232(-) dose-dependently relaxes smooth muscle in human GEA, this effect being independent of the endothelium. Within the ranges of plasma concentrations achieved in clinical practice, JM-1232(-) had similar vasorelaxation effects to midazolam and propofol. JM-1232(-)-induced vasorelaxation was inhibited by flumazenil, indicating that JM-1232(-)-induced vasorelaxation occurred via peripheral benzodiazepine receptor activation in the GEA.

Independent regulation of α1 and α2 adrenergic receptor-mediated vasoconstriction in vivo

BACKGROUND

Vascular α1 and α2 adrenergic receptors mediate vasoconstriction and are major determinants of peripheral vascular tone. There is a wide variability in vasoconstrictor sensitivity to α1 and α2 adrenergic receptor agonists among individuals. In previous studies, this variability was not explained by identified α1 and α2 adrenergic receptor genetic variants. Thus, we hypothesized that adrenergic vasoconstrictor sensitivity is determined by shared constrictor mechanisms downstream of the individual receptors and that α1 and α2 adrenergic receptor-mediated vasoconstrictor sensitivity would therefore be correlated.

METHODS

Dorsal hand vein responses to increasing doses of the α1 adrenergic receptor agonist phenylephrine (12-12 000 ng/min) and the α2 adrenergic receptor agonist dexmedetomidine (0.01-100 ng/min) were measured in healthy individuals using a linear variable differential transformer. From individual dose-response curves, we calculated the dose of phenylephrine and dexmedetomidine that produced 50% (ED50) of maximum venoconstriction (Emax) for each patient. We examined the correlation between phenylephrine and dexmedetomidine ED50 and Emax before and after adjustment for covariates (age, sex, ethnicity, BMI, blood pressure, heart rate, and baseline plasma norepinephrine concentrations).

RESULTS

In 62 patients (36 men, 34 African-American, 28 whites), the median ED50 for dexmedetomidine was 1.32 ng/min [interquartile range (IQR) 0.45-5.37 ng/min] and for phenylephrine 177.8 ng/min (IQR 40.7-436.5 ng/min). The Emax for phenylephrine was 90.8% (82.2-99.6%) and for dexmedetomidine 80.0% (64.7-95.2%). There was no correlation between individual sensitivities (ED50) to phenylephrine and dexmedetomidine, before and after adjustment for covariates (P > 0.30).

CONCLUSION

Both phenylephrine and dexmedetomidine produce strong venoconstriction in the dorsal hand vein; however, there is no significant correlation between vascular sensitivity to an α1 and α2 adrenergic receptor agonist. These findings suggest the independent regulation of vascular α1 and α2 adrenergic receptor-mediated responses.

Dexmedetomidine Produces Dual α2-Adrenergic Agonist and α1-Adrenergic Antagonist Actions on Human Isolated Internal Mammary Artery

OBJECTIVE

To investigate the direct effects of dexmedetomidine (DEX) on isolated human internal mammary artery (IMA).

DESIGN

In vitro experimental study.

SETTING

Cardiovascular Pharmacology Laboratory, Department of Pharmacology, Gulhane School of Medicine, Ankara, Turkey.

PARTICIPANTS

IMA segments were obtained from 18 patients undergoing coronary artery bypass surgery.

INTERVENTIONS

The response in IMA was recorded isometrically by a force displacement transducer in isolated organ baths. DEX-induced contractions were tested in the presence of the alpha2-adrenoceptor antagonist yohimbine (10(-7) mol/L) and the alpha1-adrenoceptor antagonist prazosin (10(-8) M). The effect of DEX (10(-7), 10(-6), and 10(-5) mol/L) on phenylephrine (10(-9)-3 x 10(-4) mol/L)-induced contactions was also tested.

MEASUREMENT AND MAIN RESULTS

DEX (10(-9) mol/L-3 x 10(-5) mol/L) caused contraction in IMA segments. The contraction at lower concentrations of DEX (10(-9) mol/L-3 x 10(-7) mol/L) was attenuated by yohimbine (10(-7) mol/L), whereas prazosin (10(-8) mol/L) attenuated the contractions at higher concentrations of DEX (10(-6) mol/L-3 x 10(-5) mol/L). Incubation of IMA segments with high concentrations of DEX (10(-6) mol/L and 10(-5) mol/L) caused an inhibition of phenylephrine (10(-9) mol/L-3 x 10(-4) mol/L)-induced contraction.

CONCLUSION

These data suggest that DEX causes contraction by activating alpha2-adrenoceptors at lower concentrations, but it may also activate alpha1-adrenoceptors at higher concentrations in IMA. The action of DEX on phenylephrine-induced contraction may be related to an alpha1-adrenoceptor antagonistic effect produced via partial alpha1-adrenoceptor agonistic action.

Opioid consumption in total intravenous anesthesia is reduced with dexmedetomidine: a comparative study with remifentanil in gynecologic videolaparoscopic surgery

STUDY OBJECTIVE

To evaluate the capacity of dexmedetomidine (DEX), an alpha(2) adrenergic agonist drug, as a substitute for remifentanil (REM), a potent opioid, in total intravenous anesthesia (TIVA), in patient undergoing gynecologic videolaparoscopy.

DESIGN

Randomized, single-blinded study.

SETTING

University-affiliated hospital.

PATIENTS

30 ASA physical status I and II women, patients (22-56 yrs), scheduled for gynecologic videolaparoscopy.

INTERVENTIONS

Patients were anesthetized with DEX or REM in continuous venous infusion, associated with propofol, in a target-controlled infusion.

MEASUREMENTS

Heart rate, mean blood pressure (MBP), systolic blood pressure (SBP), diastolic blood pressure (DBP), plasma glucose, and cortisol were determined before anesthetic induction, 5 minutes after tracheal intubations and 30 minutes after initial surgical incision. Extubation and orientation times, and postanesthesia care unit (PACU) discharge times were noted.

MAIN RESULTS

Blood cortisol levels were higher in the DEX group than in the REM group at 30minutes after surgical incision. Cortisol levels decreased as a function of time in the REM group, whereas intheDEX group they decreased in the second sample and returned to basal levels at 30 minutes. Hyperglycemia was higher in DEX than in REM during the second and third sample collection. However, glucose increased as a function of time in both groups. Analysis of MBP and DBP indicated adecrease in blood pressure at 5 minutes after tracheal intubations in both groups. At 30 minutes afterincision, MBP and DBP returned to basal levels in the DEX group, whereas the variables were significantly lower in the REM group. There were significant differences between groups for systolic blood pressure and heart rate at 5 and 30 minutes after incision with a greater decrease in REM. The extubation and orientation times were significantly increased in the DEX group, when compared with those of the REM group. There were no differences in postanesthesia care unit discharge times between groups.

CONCLUSIONS

Dexmedetomidine was a clinically effective drug as a REM substitute in TIVA, during minimally invasive video gynecologic surgical procedures; however, patients anesthetized with DEX showed a more prolonged recovery time for some parameters such as orientation and extubation times.

Differential pharmacologic sensitivities of phosphodiesterase-3 inhibitors among human isolated gastroepiploic, internal mammary, and radial arteries

Systematic investigations of the actions of phosphodiesterase (PDE)-3 inhibitors on different human vascular tissues have not been performed. We investigated the effects of specific PDE-3 inhibitors (olprinone, milrinone, and amrinone) on contracted human gastroepiploic arteries (n = 70), internal mammary arteries (n = 72), and radial arteries (n = 70) harvested from a total of 134 patients, all of whom were undergoing coronary artery bypass surgery. Each of these PDE-3 inhibitors dose-dependently diminished the contractile responses to 10(-6) mol/L norepinephrine and to either 10(-9) or 10(-8) mol/L of the thromboxane A2 analog U46619. In inducing vasorelaxations, these inhibitors were significantly more potent in norepinephrine-contracted rings than in those contracted with U46619. Further, at concentrations similar to the maximum therapeutic plasma concentrations (10(-7) mol/L olprinone; 10(-6) mol/L milrinone; 10(-5) mol/L amrinone) olprinone and milrinone were more potent at inducing relaxations than amrinone in gastroepiploic arteries and radial arteries, whereas in internal mammary arteries milrinone was more potent than the others. These results suggest different activities for the three PDE-3 inhibitors among human arteries located in different regions and may be informative about the effectiveness of these inhibitors in preventing spasms in the various arterial grafts used in revascularization.

IMPLICATIONS

Because three phosphodiesterase-3 inhibitors (milrinone, olprinone, and amrinone) differed in their vasodilator potencies (against the contractile response to either norepinephrine or a thromboxane A2 analog) among human arteries removed from different parts of the body, their vascular relaxation profiles should be considered before they are used clinically.

Selective alpha2-adrenergic properties of dexmedetomidine over clonidine in the human forearm

We tested the hypothesis that dexmedetomidine (Dex) has greater alpha(2)- vs. alpha(1) selectivity than clonidine and causes more alpha(2)-selective vasoconstriction in the human forearm. After local beta-adrenergic blockade with propranolol, forearm blood flow (plethysmography) responses to brachial artery administration of Dex, clonidine, and phenylephrine (alpha(1)-agonist) were determined in healthy young adults before and after alpha(2)-blockade with yohimbine (n = 10) or alpha(1)-blockade with prazosin (n = 9). Yohimbine had no effect on phenylephrine-mediated vasoconstriction but blunted Dex-mediated vasoconstriction (mean +/- SE: -41 +/- 5 vs. -11 +/- 2%; before vs. after yohimbine) more than clonidine-mediated vasoconstriction (-39 +/- 5 vs. -28 +/- 4%; before vs. after yohimbine) (P < 0.02). Prazosin blunted phenylephrine-mediated vasoconstriction (-39 +/- 4 vs. -8 +/- 2%; before vs. after prazosin) but had similar effects on both Dex- (-30 +/- 4 vs. -39 +/- 6%; before vs. after prazosin) and clonidine-mediated vasoconstriction (-29 +/- 3 vs. -41 +/- 7%; before vs. after prazosin) (P > 0.7). Both Dex and clonidine reduced deep forearm venous norepinephrine concentrations to a similar extent (-59 +/- 12 vs. -55 +/- 10 pg/ml; Dex vs. clonidine, P > 0.6); this effect was abolished by yohimbine and blunted by prazosin. These results suggest that Dex causes more alpha(2)-selective vasoconstriction in the forearm than clonidine. The similar vasoconstrictor responses to both drugs after prazosin might be explained by the presynaptic effects on norepinephrine release.