Selective modulation of different GABAA receptor isoforms by diazepam and etomidate in hippocampal neurons

Endothelium-dependent relaxation induced by etomidate in the aortas of insulin-resistant rats

INTRODUCTION

Few reports have mentioned the effect of etomidate on the aortas of insulin-resistant (IR) rats. In this study, we investigated the effect of etomidate on isolated IR aortas of rats, and explored its underlying mechanism.

MATERIAL AND METHODS

The IR rat model was established through feeding with a high-fructose diet. The systolic blood pressure (SBP) was measured by the tail-cuff method before grouping and at the end of the 8-week feeding; blood samples were also obtained for analysis. Thoracic aorta rings of IR rats were isolated and suspended in a tissue bath. The tensile force was recorded isometrically. The effect of etomidate on provoked contraction of the rings was assessed with or without a potassium channel blocker or NO synthase inhibitor.

RESULTS

Etomidate-induced relaxation in IR rings was greater than normal control (NC) rings (all p < 0.001 with etomidate log M of -4 to -6). NG-nitro-L-arginine methyl ester (L-NAME, an NO synthase inhibitors) inhibited etomidate-induced relaxation in NC rings, but had no effect on the IR rings (all p < 0.001 with etomidate log M of -4 to -6). Pre-incubation with glibenclamide (Gli, a potassium channel blocker) significantly inhibited etomidate-induced relaxation in NC and IR rings (all p < 0.001 with etomidate log M of -4 to -6), and had no inhibited effect on endothelial denuded aortic rings.

CONCLUSIONS

Insulin resistance increased etomidate-induced relaxation in rat aortas. Etomidate causes vasodilation in IR rat aortas via both endothelium-dependent and independent ways; impaired NO-mediated relaxation was disrupted and ATP-sensitive potassium (K_ATP) channel-mediated relaxation may be involved in the endothelium-dependent relaxation of etomidate in IR rats.

Sperm gamma-aminobutyric acid type A receptor delta subunit (GABRD) and its interaction with purinergic P2X2 receptors in progesterone-induced acrosome reaction and male fertility

The mechanism underlying the non-genomic action of progesterone in sperm functions and related Ca²⁺ mobilisation remains elusive. Herein we report the expression of gamma-aminobutyric acid type A receptor delta subunit (GABRD) in human and rodent sperm and its involvement in mediating the progesterone-induced acrosome reaction. GABRD was localised in the sperm head/neck region. A δ_(392-422)-specific inhibitory peptide against GABRD blocked the progesterone-induced acrosome reaction and the associated increase in intracellular Ca²⁺. Similarly, an inhibitory effect against both progesterone-induced Ca²⁺ influx and the acrosome reaction was observed with a P2X₂ receptor antagonist. The lack of synergism between the GABRD and P2X₂ inhibitors suggests that these two receptors are playing a role in the same pathway. Furthermore, a co-immunoprecipitation experiment demonstrated that GABRD could undergo protein-protein interactions with the Ca²⁺-conducting P2X₂ receptor. This interaction between the receptors could be reduced following progesterone (10μM) inducement. Significantly reduced GABRD expression was observed in spermatozoa from infertile patients with reduced acrosome reaction capacity, suggesting that normal expression of GABRD is critical for the sperm acrosome reaction and thus male fertility. The results of the present study indicate that GABRD represents a novel progesterone receptor or modulator in spermatozoa that is responsible for the progesterone-induced Ca²⁺ influx required for the acrosome reaction through its interaction with the P2X₂ receptor.

Etomidate uniquely modulates the desensitization of recombinant α1β3δ GABA(A) receptors

Central GABA(A) receptors mediate GABAergic phasic and tonic inhibition. While synaptic αβγ GABA(A) receptors primarily mediate phasic inhibition, extrasynaptic αβδ receptors play an important role in mediating tonic inhibition. Etomidate is a general anesthetic that produces its effects by enhancing GABA(A) receptor activity. We previously showed that etomidate modulates the gating of oocyte-expressed αβγ and αβδ receptors with similar overall allosteric impact, but different pharmacological patterns. In αβγ receptors, etomidate enhances apparent GABA sensitivity (reduces GABA EC50), modestly increases maximal GABA efficacy, and slows current deactivation without affecting desensitization (Zhong et al., 2008). In αβδ receptors characterized by low GABA efficacy, etomidate dramatically increases responses to both low and maximal GABA. The effects of etomidate on desensitization and deactivation of αβδ receptors are unknown. To investigate the kinetic effects of etomidate on α1β3δ receptors of defined subunit arrangement, we expressed concatenated trimer (β3-α1-δ) and dimer (β3-α1) GABA(A) receptor subunit assemblies in human embryonic kidney (HEK)293T cells and recorded whole-cell voltage-clamp currents during rapid external solution exchanges. As expected, etomidate substantially increased maximal GABA-induced currents and prolonged deactivation. Moreover, desensitization was significantly decreased by etomidate. During prolonged GABA applications, etomidate enhanced steady-state currents more than peak currents. Thus, etomidate enhances tonic GABAergic inhibition through extrasynaptic αβδ receptors by both augmenting gating and reducing desensitization.

Brain tissue distribution of spinosin in rats determined by a new high-performance liquid chromatography-electrospray ionization-mass/mass spectrometry method

Spinosin, a flavone-C-glycoside, is a bioactive ingredient isolated from a traditional Chinese herb Zizyphi Spinosi Semen. In this study, a new high-performance liquid chromatography-electrospray ionization-mass/mass spectrometry method was developed and validated to determine spinosin in brain tissues including olfactory region, hippocampus, corpus striatum, cerebrum (cerebral cortex) and cerebellum, after intravenous administration with the dose of 5 mg/kg. The tissue homogenate samples were pretreated and extracted with acetonitrile by a simple protein precipitation method. The separation was performed on a YMC ODS-AQ(TM) column (250 × 2.0 mm, 3.5 μm) with the mobile phase of acetonitrile-aqueous phase (0.1% formic acid) (25 : 75, v/v) at a flow rate of 0.3 mL/min. The retention times of spinosin and naringin (internal standard) were 3.3 and 5.1 min, respectively. Multiple reaction monitoring mode was used to monitor precursor/product ion transitions of m/z 607.2 → 427.0 for spinosin and m/z 579.2 → 271.0 for naringin. The proposed method was successfully applied to the preclinical brain tissue distribution of spinosin in rats. The results showed that there was a wide brain regional tissue distribution of spinosin. The concentrations of spinosin in corpus striatum and hippocampus were higher than that in other areas.

Clinical study of etomidate emulsion combined with remifentanil in general anesthesia

BACKGROUND

The aim of this study was to investigate and evaluate the safety, recovery time, and side effects of general anesthesia with different doses of etomidate emulsion combined with remifentanil.

METHODS

One hundred ten patients of American Society of Anesthesiologists class 1 or 2 who underwent gynecological general anesthesia with a 1-3-hour operation time were randomly divided into the following groups: etomidate emulsion group 1 ([E1] n = 30); etomidate emulsion group 2 ([E2] n = 30); etomidate emulsion group 3 ([E3] n = 20); and propofol group ([P group] n = 30). For induction of anesthesia, 0.3 mg/kg etomidate emulsion, and the continuous remifentanil infusion also to induce anesthesia (0.1~0.3 μg · kg(-1) · min(-1)), was applied in all cases. Afterwards, continuous infusion of etomidate emulsion and remifentanil, respectively (E1: 10 μg · kg(-1) · min(-1) and 0.1 μg · kg(-1) · min(-1); E2: 15 μg · kg(-1) · min(-1) and 0.2 μg · kg(-1) · min(-1); E3: 20 μg · kg(-1) · min(-1) and 0.2 μg · kg(-1) · min(-1)), and propofol (P group: 6~10 mg · kg(-1) · h(-1)) were administered. Changes in blood flow kinetics and adverse reactions were noted and compared between the four groups.

RESULTS

Both arterial blood pressure (BP) and heart rate (HR) decreased after induction of anesthesia (P < 0.05). Systolic (SBP) and diastolic (DBP) BP changed only slightly, and HRs were slightly infected in E1, E2, and E3. SBP, DBP, and HR during the operation all decreased significantly in P group (P < 0.05). Muscle tremor at the time of induction occurred in 13 cases (11.8%). Following etomidate emulsion anesthesia maintenance, postoperative agitation occurred in seven cases (8.75%), lethargy in 20 cases (25%), and vomiting in 19 cases (23.75%). No adverse reactions were found in P group.

CONCLUSION

Continuous infusion of etomidate emulsion at 10 μg · kg(-1) · minute(-1) combined with remifentanil during anesthesia has the advantages of hemodynamic stability, quick wake-up, and few adverse reactions. Increasing the dose of etomidate emulsion increases the incidence of adverse reactions.