The general anesthetic propofol enhances the function of gamma-aminobutyric acid-coupled chloride channel in the rat cerebral cortex

Dose-dependent changes in orientation amplitude maps in the cat visual cortex after propofol bolus injections

A general intravenous anesthetic propofol (2,6-diisopropylphenol) is widely used in clinical, veterinary practice and animal experiments. It activates gamma- aminobutyric acid (GABAa) receptors. Though the cerebral cortex is one of the major targets of propofol action, no study of dose dependency of propofol action on cat visual cortex was performed yet. Also, no such investigation was done until now using intrinsic signal optical imaging. Here, we report for the first time on the dependency of optical signal in the visual cortex (area 17/area 18) on the propofol dose. Optical imaging of intrinsic responses to visual stimuli was performed in cats before and after propofol bolus injections at different doses on the background of continuous propofol infusion. Orientation amplitude maps were recorded. We found that amplitude of optical signal significantly decreased after a bolus dose of propofol. The effect was dose- and time-dependent producing stronger suppression of optical signal under the highest bolus propofol doses and short time interval after injection. In each hemisphere, amplitude at cardinal and oblique orientations decreased almost equally. However, surprisingly, amplitude at cardinal orientations in the ipsilateral hemisphere was depressed stronger than in contralateral cortex at most time intervals. As the magnitude of optical signal represents the strength of orientation tuned component, these our data give new insights on the mechanisms of generation of orientation selectivity. Our results also provide new data toward understanding brain dynamics under anesthesia and suggest a recommendation for conducting intrinsic signal optical imaging experiments on cortical functioning under propofol anesthesia.

Effect of propofol on salivary secretion from the submandibular, sublingual, and labial glands during intravenous sedation

Background

Recent animal studies have suggested the role of GABA type A (GABA-_A) receptors in salivation, showing that GABA-_A receptor agonists inhibit salivary secretion. This study aimed to evaluate the effects of propofol (a GABA-_A agonist) on salivary secretions from the submandibular, sublingual, and labial glands during intravenous sedation in healthy volunteers.

Methods

Twenty healthy male volunteers participated in the study. They received a loading dose of propofol 6 mg/kg/h for 10 min, followed by 3 mg/kg/h for 15 min. Salivary flow rates in the submandibular, sublingual, and labial glands were measured before, during, and after propofol infusion, and amylase activity was measured in the saliva from the submandibular and sublingual glands.

Results

We found that the salivary flow rates in the submandibular, sublingual, and labial glands significantly decreased during intravenous sedation with propofol (P < 0.01). Similarly, amylase activity in the saliva from the submandibular and sublingual glands was significantly decreased (P < 0.01).

Conclusion

It can be concluded that intravenous sedation with propofol decreases salivary secretion in the submandibular, sublingual, and labial glands via the GABA-_A receptor. These results may be useful for dental treatment when desalivation is necessary.

Propofol reduces the amplitude of transcranial electrical motor-evoked potential without affecting spinal motor neurons: a prospective, single-arm, interventional study

PURPOSE

Propofol inhibits the amplitudes of transcranial electrical motor-evoked potentials (TCE-MEP) in a dose-dependent manner. However, the mechanisms of this effect remain unknown. Hence, we investigated the spinal mechanisms of the inhibitory effect of propofol on TCE-MEP amplitudes by evaluating evoked electromyograms (H-reflex and F-wave) under general anesthesia.

METHODS

We conducted a prospective, single-arm, interventional study including 15 patients scheduled for spine surgery under general anesthesia. Evoked electromyograms of the soleus muscle and TCE-MEPs were measured at three propofol concentrations using target-controlled infusion (TCI: 2.0, 3.0, and 4.0 µg/mL). The primary outcome measure was the left H-reflex amplitude during TCI of 4.0- compared to 2.0-µg/mL propofol administration.

RESULTS

The median [interquartile range] amplitudes of the left H-reflex were 4.71 [3.42-6.60] and 5.6 [4.17-7.46] in the 4.0- and 2.0-μg/mL TCI groups (p = 0.4, Friedman test), respectively. There were no significant differences in the amplitudes of the right H-reflex and the bilateral F-wave among these groups. However, the TCE-MEP amplitudes significantly decreased with increased propofol concentrations (p < 0.001, Friedman test).

CONCLUSION

Propofol did not affect the amplitudes of the H-reflex and the F-wave, whereas TCE-MEP amplitudes were reduced at higher propofol concentrations. These results suggested that propofol can suppress the TCE-MEP amplitude by inhibiting the supraspinal motor pathways more strongly than the excitability of the motor neurons in the spinal cord.

Actions of Propofol on Neurons in the Cerebral Cortex

Propofol is primarily a hypnotic, and is widely used for induction and maintenance of anesthesia, as well as for sedation in various medical procedures. The exact mechanisms of its action are not well understood, although its neural mechanisms have been explored in in vivo and in vitro experiments. Accumulating evidence indicates that one of the major targets of propofol is the cerebral cortex. The principal effect of propofol is considered to be the potentiation of GABA_A receptor-mediated inhibitory synaptic currents, but propofol has additional roles in modulating ion channels, including voltage-gated Na⁺ channels and several K⁺ channels. We focus on the pharmacological actions of propofol on cerebrocortical neurons, particularly at the cellular and synaptic levels.

Thalamocortical synchronization during induction and emergence from propofol-induced unconsciousness

General anesthesia (GA) is a reversible drug-induced state of altered arousal required for more than 60,000 surgical procedures each day in the United States alone. Sedation and unconsciousness under GA are associated with stereotyped electrophysiological oscillations that are thought to reflect profound disruptions of activity in neuronal circuits that mediate awareness and cognition. Computational models make specific predictions about the role of the cortex and thalamus in these oscillations. In this paper, we provide in vivo evidence in rats that alpha oscillations (10-15 Hz) induced by the commonly used anesthetic drug propofol are synchronized between the thalamus and the medial prefrontal cortex. We also show that at deep levels of unconsciousness where movement ceases, coherent thalamocortical delta oscillations (1-5 Hz) develop, distinct from concurrent slow oscillations (0.1-1 Hz). The structure of these oscillations in both cortex and thalamus closely parallel those observed in the human electroencephalogram during propofol-induced unconsciousness. During emergence from GA, this synchronized activity dissipates in a sequence different from that observed during loss of consciousness. A possible explanation is that recovery from anesthesia-induced unconsciousness follows a "boot-up" sequence actively driven by ascending arousal centers. The involvement of medial prefrontal cortex suggests that when these oscillations (alpha, delta, slow) are observed in humans, self-awareness and internal consciousness would be impaired if not abolished. These studies advance our understanding of anesthesia-induced unconsciousness and altered arousal and further establish principled neurophysiological markers of these states.

Effects of propofol on conditioned place preference in male rats: Involvement of nitrergic system

BACKGROUND

Drug-induced conditioned place preference (CPP) is linked to the addictive properties of the drug used. The number of studies that have investigated the effects of propofol on CPP is limited. Research findings suggest that nitric oxide (NO) might play an important role in substance use disorders.

OBJECTIVES

The present study sought to investigate the role of the nitrergic system on the rewarding effects of propofol by using the CPP protocol in rats.

METHODS

The experiment followed habituation, pre-conditioning, conditioning, and post conditioning sessions. Male Wistar albino rats weighing 240-290 g were divided into eight groups: control (saline), propofol (10, 20, and 40 mg/kg), the NO synthase (NOS) inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) alone (30 and 60 mg/kg), and in combination with propofol (30 and 60 mg/kg L-NAME plus 40 mg/kg propofol) (n = 8 for each group). The CPP effects of propofol, L-NAME, saline, and their combinations were evaluated. All the drug and saline administrations were performed by intraperitoneal (ip) injections.

RESULTS

Propofol (10-40 mg/kg) produced CPP that was statistically significant relative to saline. Propofol-induced CPP was significantly reversed by pretreatment with L-NAME. When administered alone, L-NAME did not produce CPP and also did not produce any significant change on locomotor activity of naïve rats.

CONCLUSION

Our results suggest that propofol produces CPP effects in rats and that NO-related mechanisms may be responsible for propofol-induced CPP. Thus, propofol might have the potential to be addictive, and this possibility should be considered during clinical applications of this drug.

Clinical concentrations of chemically diverse general anesthetics minimally affect lipid bilayer properties

General anesthetics have revolutionized medicine by facilitating invasive procedures, and have thus become essential drugs. However, detailed understanding of their molecular mechanisms remains elusive. A mechanism proposed over a century ago involving unspecified interactions with the lipid bilayer known as the unitary lipid-based hypothesis of anesthetic action, has been challenged by evidence for direct anesthetic interactions with a range of proteins, including transmembrane ion channels. Anesthetic concentrations in the membrane are high (10-100 mM), however, and there is no experimental evidence ruling out a role for the lipid bilayer in their ion channel effects. A recent hypothesis proposes that anesthetic-induced changes in ion channel function result from changes in bilayer lateral pressure that arise from partitioning of anesthetics into the bilayer. We examined the effects of a broad range of chemically diverse general anesthetics and related nonanesthetics on lipid bilayer properties using an established fluorescence assay that senses drug-induced changes in lipid bilayer properties. None of the compounds tested altered bilayer properties sufficiently to produce meaningful changes in ion channel function at clinically relevant concentrations. Even supra-anesthetic concentrations caused minimal bilayer effects, although much higher (toxic) concentrations of certain anesthetic agents did alter lipid bilayer properties. We conclude that general anesthetics have minimal effects on bilayer properties at clinically relevant concentrations, indicating that anesthetic effects on ion channel function are not bilayer-mediated but rather involve direct protein interactions.

Seizure prevention by the naturally occurring phenols, carvacrol and thymol in a partial seizure-psychomotor model

The natural compounds carvacrol and thymol completely prevented seizures in the 6 Hz, 32 mA partial seizure model. Carvacrol and thymol, both exhibited an ED₅₀ = 35.8 mg/kg, ip and yielded protective indices of 5.3 and 3.4, respectively. At 44 mA current intensity, carvacrol and thymol exhibited ED₅₀s of 88.82 mg/kg (PI = 2.15) and 73.0 mg/kg (PI = 1.65), respectively. Thymol, but not carvacrol showed partial inhibitory activity in the maximal electroshock (MES), sc Metrazol (scMET) and Corneal-kindled models. These results suggest that carvacrol and thymol are more efficacious anticonvulsants than suggested by their lower efficacies in the conventional MES and scMET tests.

Loss of Consciousness Is Associated with Stabilization of Cortical Activity

What aspects of neuronal activity distinguish the conscious from the unconscious brain? This has been a subject of intense interest and debate since the early days of neurophysiology. However, as any practicing anesthesiologist can attest, it is currently not possible to reliably distinguish a conscious state from an unconscious one on the basis of brain activity. Here we approach this problem from the perspective of dynamical systems theory. We argue that the brain, as a dynamical system, is self-regulated at the boundary between stable and unstable regimes, allowing it in particular to maintain high susceptibility to stimuli. To test this hypothesis, we performed stability analysis of high-density electrocorticography recordings covering an entire cerebral hemisphere in monkeys during reversible loss of consciousness. We show that, during loss of consciousness, the number of eigenmodes at the edge of instability decreases smoothly, independently of the type of anesthetic and specific features of brain activity. The eigenmodes drift back toward the unstable line during recovery of consciousness. Furthermore, we show that stability is an emergent phenomenon dependent on the correlations among activity in different cortical regions rather than signals taken in isolation. These findings support the conclusion that dynamics at the edge of instability are essential for maintaining consciousness and provide a novel and principled measure that distinguishes between the conscious and the unconscious brain.

SIGNIFICANCE STATEMENT

What distinguishes brain activity during consciousness from that observed during unconsciousness? Answering this question has proven difficult because neither consciousness nor lack thereof have universal signatures in terms of most specific features of brain activity. For instance, different anesthetics induce different patterns of brain activity. We demonstrate that loss of consciousness is universally and reliably associated with stabilization of cortical dynamics regardless of the specific activity characteristics. To give an analogy, our analysis suggests that loss of consciousness is akin to depressing the damper pedal on the piano, which makes the sounds dissipate quicker regardless of the specific melody being played. This approach may prove useful in detecting consciousness on the basis of brain activity under anesthesia and other settings.

Caffeine accelerates recovery from general anesthesia

General anesthetics inhibit neurotransmitter release from both neurons and secretory cells. If inhibition of neurotransmitter release is part of an anesthetic mechanism of action, then drugs that facilitate neurotransmitter release may aid in reversing general anesthesia. Drugs that elevate intracellular cAMP levels are known to facilitate neurotransmitter release. Three cAMP elevating drugs (forskolin, theophylline, and caffeine) were tested; all three drugs reversed the inhibition of neurotransmitter release produced by isoflurane in PC12 cells in vitro. The drugs were tested in isoflurane-anesthetized rats. Animals were injected with either saline or saline containing drug. All three drugs dramatically accelerated recovery from isoflurane anesthesia, but caffeine was most effective. None of the drugs, at the concentrations tested, had significant effects on breathing rates, O2 saturation, heart rate, or blood pressure in anesthetized animals. Caffeine alone was tested on propofol-anesthetized rats where it dramatically accelerated recovery from anesthesia. The ability of caffeine to accelerate recovery from anesthesia for different chemical classes of anesthetics, isoflurane and propofol, opens the possibility that it will do so for all commonly used general anesthetics, although additional studies will be required to determine whether this is in fact the case. Because anesthesia in rodents is thought to be similar to that in humans, these results suggest that caffeine might allow for rapid and uniform emergence from general anesthesia in human patients.

Reticular formation responses to magnetic brain stimulation of primary motor cortex

Transcranial magnetic stimulation (TMS) of cerebral cortex is a popular technique for the non-invasive investigation of motor function. TMS is often assumed to influence spinal circuits solely via the corticospinal tract. We were interested in possible trans-synaptic effects of cortical TMS on the ponto-medullary reticular formation in the brainstem, which is the source of the reticulospinal tract and could also generate spinal motor output. We recorded from 210 single units in the reticular formation of three anaesthetized macaque monkeys whilst TMS was performed over primary motor cortex. Short latency responses were observed consistent with activation of a cortico-reticular pathway. However, we also demonstrated surprisingly powerful responses at longer latency, which often appeared at lower threshold than the earlier effects. These late responses seemed to be generated partly as a consequence of the sound click made by coil discharge, and changed little with coil location. This novel finding has implications for the design of future studies using TMS, as well as suggesting a means of non-invasively probing an otherwise inaccessible important motor centre.

Pharmacological characterization of the Haemonchus contortus GABA-gated chloride channel, Hco-UNC-49: modulation by macrocyclic lactone anthelmintics and a receptor for piperazine

Invertebrate ligand-gated chloride channels are well recognized as important targets for several insecticides and anthelmintics. Hco-UNC-49 is a GABA-gated chloride channel from the parasitic nematode Haemonchus contortus and is an orthologue to the neuromuscular receptor (Cel-UNC-49) from the free-living nematode Caenorhabditis elegans. While the receptors from the two nematodes are similar in sequence, they exhibit different sensitivities to GABA which may reflect differences in in vivo function. The aim of the current study was to further characterize the pharmacology of the Hco-UNC-49 receptor by examining its sensitivity to various insecticides and anthelmintics using two-electrode voltage clamp. Specifically, the insecticides fipronil and picrotoxin appear to inhibit the channel in a similar manner. The IC(50) of picrotoxin on the homomeric channel was 3.65 ± 0.64 μM and for the heteromeric channel was 134.56 ± 44.12 μM. On the other hand, dieldrin, a well-known insect GABA receptor blocker, had little effect on the UNC-49 channel. The anthelmintics ivermectin and moxidectin both moderately potentiated the activation of Hco-UNC-49 by GABA, while piperazine was able to directly activate both the Hco-UNC-49 homomeric and heteromeric channels with EC(50) values of 6.23 ± 0.45 mM and 5.09 ± 0.32 mM, respectively. This piperazine current was reversibly blocked by picrotoxin which demonstrates that the anthelmintic specifically targets Hco-UNC-49. These results demonstrate that Hco-UNC-49 exhibits binding sites for several molecules including piperazine and macrocyclic lactone anthelmintics. In addition, this is the first report of the heterologous expression and subsequent characterization of a receptor for piperazine.

Propofol post-conditioning induced long-term neuroprotection and reduced internalization of AMPAR GluR2 subunit in a rat model of focal cerebral ischemia/reperfusion

We previously reported that propofol (20 mg/kg/h) post-conditioning provided acute (up to 24 h) neuroprotection in rats with transient middle cerebral artery occlusion. In this study, we extend these data by examining long-term protection and exploring underlying mechanisms involving AMPA receptor GluR2 subunit internalization. Rats were treated with propofol 20 mg/kg/h after 60 min of occlusion (beginning of reperfusion for 4 h). Propofol post-conditioning reduced infarct volume and improved spatial memory deficiencies (up to 28 days) induced by ischemia/reperfusion injury. Additionally, Propofol post-conditioning promoted neurogenesis in the dentate gyrus of hippocampus, as measured by bromodeoxyuridine and neuron-specific nuclear protein immunofluorescence-double staining at day 28 after reperfusion. Finally, propofol post-conditioning increased the surface expression of AMPA receptor GluR2 subunit, thus inhibited the internalization of this part until 28 days after stroke. In conclusion, our data suggest that propofol post-conditioning provides long-term protection against focal cerebral ischemia/reperfusion injury in rats. Furthermore, we found that the inhibition of AMPA receptor GluR2 subunit internalization may contributed to this long-term neuroprotection.

Alcohol withdrawal syndromes in the intensive care unit

This article reviews the pathophysiology, diagnosis, and treatment of alcohol withdrawal syndromes in the intensive care unit as well as the literature on the optimal pharmacologic strategies for treatment of alcohol withdrawal syndromes in the critically ill. Treatment of alcohol withdrawal in the intensive care unit mirrors that of the general acute care wards and detoxification centers. In addition to adequate supportive care, benzodiazepines administered in a symptom-triggered fashion, guided by the Clinical Institute Withdrawal Assessment of Alcohol scale, revised (CIWA-Ar), still seem to be the optimal strategy in the intensive care unit. In cases of benzodiazepine resistance, numerous options are available, including high individual doses of benzodiazepines, barbiturates, and propofol. Intensivists should be familiar with the diagnosis and treatment strategies for alcohol withdrawal syndromes in the intensive care unit.

PET and macro- and microautoradiographic studies combined with immunohistochemistry for monitoring rat intestinal ulceration and healing processes

18F-FDG PET is used mainly in clinical settings for imaging focal cancer sites, but the usefulness of the modality in imaging gastrointestinal ulcers has not been established. We investigated whether PET can be used for noninvasive monitoring of indomethacin-induced small-intestine ulceration.

METHODS

Intestinal ulcers were induced in rats by subcutaneous administration of indomethacin. An 18F-FDG PET scan was obtained at 1, 2, and 7 d after indomethacin administration. 18F-FDG uptake in the small intestine was quantified by gamma-counting, and macro- and microautoradiographic studies were performed to determine the site of 18F-FDG uptake in tissue and at the cellular level.

RESULTS

Ulcers observed in the intestine (mainly in the ileum) 1-4 d after indomethacin administration were most severe at 1 d after administration and were almost healed at day 7. The PET study showed increased 18F-FDG uptake in the intestine correlating to the severity of ulceration, returning to the basal level on day 7. Ex vivo imaging and gamma-counting showed that these regions of high uptake corresponded to regions of ulceration. A microautoradiographic study combined with immunohistochemistry revealed heavy accumulation of 18F-FDG in inflammatory cells containing peroxidase on day 1 and in cells forming granulation tissue (alpha-smooth muscle actin-positive myofibroblasts and ED2-positive macrophages) on days 2-4 in and around ulcers. Proliferating (Ki67-immunopositive) intestinal crypt cells were also densely labeled with 18F-FDG in intact intestinal tissue taken from the indomethacin-treated and the control animals.

CONCLUSION

Our experimental data suggest that 18F-FDG PET may be useful for evaluating the occurrence of small-intestine ulcers. Ulceration could be visualized early by the prominent uptake of 18F-FDG by inflammatory cells and by the formation of granulation tissue by cells in and around ulcers.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

[Propofol-induced myocardial depression: possible role of atrial muscarinic cholinergic receptors]

OBJECTIVE

To investigate the possible role of muscarinic cholinergic receptors (MCRs) in the depression of myocardial function induced by propofol, an intravenous anesthetic chemically unrelated to other drugs. Although adverse effects are rare, bradycardia has been reported and this can lead to cardiac arrest in some patients. The mechanism behind this effect is still unknown but a possible role for MCRs has been suggested.

MATERIAL AND METHODS

The interaction of propofol with human atrial MCRs was determined by means of inhibition tests using [3H] quinuclidinyl benzilate ([3H] QNB).

RESULTS

The displacement of [3H] QNB binding to human atrial MCRs by propofol was concentration dependent but the observed effect was not consistent with a model of simple competition between propofol and [3H] QNB.

CONCLUSION

Propofol appears to have the ability to modify the activity of human atrial MCRs and this effect may be related to its ability to induce bradycardia.

A strategy of escalating doses of benzodiazepines and phenobarbital administration reduces the need for mechanical ventilation in delirium tremens

OBJECTIVE

Patients with severe alcohol withdrawal and delirium tremens are frequently resistant to standard doses of benzodiazepines. Case reports suggest that these patients have a high incidence of requiring intensive care and many require mechanical ventilation. However, few data exist on treatment strategies and outcomes for these subjects in the medical intensive care unit (ICU). Our goal was a) to describe the outcomes of patients admitted to the medical ICU solely for treatment of severe alcohol withdrawal and b) to determine whether a strategy of escalating doses of benzodiazepines in combination with phenobarbital would improve outcomes.

DESIGN

Retrospective cohort study.

SETTING

Inner-city municipal hospital.

PATIENTS

Subjects admitted to the medical ICU solely for the treatment of severe alcohol withdrawal.

INTERVENTIONS

Institution of guidelines emphasizing escalating doses of diazepam in combination with phenobarbital.

MEASUREMENTS AND MAIN RESULTS

Preguideline (n = 54) all subjects were treated with intermittent boluses of diazepam with an average total and maximal individual dose of 248 mg and 32 mg, respectively; 17% were treated with phenobarbital. Forty-seven percent required intubation due to inability to achieve adequate sedation and need for constant infusion of sedative-hypnotics. Intubated subjects had longer length of stay (5.6 vs. 3.4 days; p = .09) and higher incidence of nosocomial pneumonia (42 vs. 21% p = .08). Postguideline (n = 41) there were increases in maximum individual dose of diazepam (32 vs. 86 mg; p = .001), total amount of diazepam (248 vs. 562 mg; p = .001), and phenobarbital use (17 vs. 58%; p = .01). This was associated with a reduction in the need for mechanical ventilation (47 vs. 22%; p = .008), with trends toward reductions in ICU length of stay and nosocomial pneumonia.

CONCLUSIONS

Patients admitted to a medical ICU solely for treatment of severe alcohol withdrawal have a high incidence of requiring mechanical ventilation. Guidelines emphasizing escalating bolus doses of diazepam, and barbiturates if necessary, significantly reduced the need for mechanical ventilation and showed trends toward reductions in ICU length of stay and nosocomial infections.

Development of propofol-loaded microemulsion systems for parenteral delivery

The aim of the present study was to develop the aqueous parenteral formulation containing propofol using o/w microemulsion systems. Propofol itself was chosen as the oil phase and its content was fixed to 1%, w/w. Pseudoternary phase diagrams were constructed to obtain the concentration range of surfactant and cosurfacatnt and the optimum ratio between them for microemulsion formation. Consequently, the suitability of the chosen microemulsion system as a parenteral formulation was evaluated from the stability and hemolysis tests on that. Among the surfactants and cosurfactants screened, the mixture of Solutol HS 15-ethyl alcohol (5/1) showed the largest o/w mocroemulsion region in the phase diagram. When 1% (w/w) of propofol was solubilized with 8% (w/w) of Solutol HS 15-ethyl alcohol (5/1), the average droplet size (150 nm) and the content of propofol in the systems were not significantly changed at 40 degrees C for 8 weeks. The hemolysis test showed that this formulation was nontoxic to red blood cells. In conclusion, propofol was successfully solubilized with the o/w microemulsion systems.

Ethyl 2-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-4-imidazolecarboxylate is a novel positive modulator of GABAA receptors

Ethyl 2-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-4-imidazolecarboxylate (TG41) enhanced the binding both of gamma-aminobutyric acid (GABA) and of flunitrazepam to rat cerebral cortical membranes. Electrophysiological recordings from Xenopus oocytes expressing various recombinant GABA(A) receptor subtypes revealed that TG41 enhanced the function of all receptor subunit combinations tested. The potency of TG41 at receptors containing alpha1, beta2, and gamma2L subunits was greater than that of alphaxalone, etomidate, propofol, or pentobarbital. The potency of TG41 was also greater at receptors containing alpha1 or alpha2 subunits than at those containing alpha4 and it was markedly higher at receptors containing beta2 or beta3 subunits than at those containing beta1. This drug induced a reversible loss of the righting reflex in Xenopus tadpoles and it elicited hypnosis (5 mg/kg) after intravenous administration in rats. These results indicate that the pharmacological profile of TG41 is similar to that of general anesthetics which potentiate the activity of GABA(A) receptors containing the beta2 or beta3 subunit.

Intravenous self-administration of abused solvents and anesthetics in mice

Volatile organic solvents, fuels and anesthetics are subject to abuse. The aim of the present study was to evaluate i.v. self-administration of several of these chemicals in drug- and experiment-naive mice using a commercially available vehicle, intralipid. Two strains of mice (DBA/2 and Swiss) were allowed to self-administer toluene (0.0017-0.17 micromol/infusion), 1,1,1-trichloroethane (0.006-0.19 micromol/infusion), ethanol (0.32-1.6 micromol/infusion), cyclohexane (0.0017-0.052 micromol/infusion), propofol (0.01-0.53 micromol/infusion) and flurothyl (0.00042-0.072 micromol/infusion) or their vehicles during 30-min tests. During the test, each nose-poke of the master mouse resulted in a 1.88-microl i.v. infusion to the master mouse and a yoked control mouse. When the delivery line was loaded with a reinforcing drug solution, the number of nose-pokes of the master mice significantly exceeded that for yoked control mice. In the present experiments, significant differences in rates of nose-poking were observed between mice receiving response-contingent and response-noncontingent deliveries of ethanol and toluene in both strains of mice and of 1,1,1-trichloroethane in Swiss mice. These data suggest that the reinforcing effects of abused inhalants can be studied using i.v. self-administration procedures.

Assessment of microPET performance in analyzing the rat brain under different types of anesthesia: comparison between quantitative data obtained with microPET and ex vivo autoradiography

MicroPET (positron emission tomography) has been implemented for use in experiments with small animals. However, the quantification and optimal conditions for scanning are not established yet. The aim of this study was to compare the results obtained by microPET with those by ex vivo autoradiography of rat brain slices, based on the 2-[18F]fluoro-2-deoxy-D-glucose (FDG) method, and to establish the optimal conditions for scanning. As an example, we examined glucose metabolism in the rat brain under 6 types of anesthesia and in the conscious state. The scanning conditions for the rat brain were (1) use of a 4-mm-thick leaden jacket, (2) an energy window of 350-650 keV, and (3) a coincidence time window of 6 ns. Under these conditions, the quantitative ROI data from microPET showed a good correlation with the corresponding ROI data from FDG autoradiography in the animal study (r2=0.81). With our protocol, when anesthesia was started 40 min after the FDG injection, the glucose metabolism was almost the same as that in the conscious rat brain.

Novel alpha-amino-acid phenolic ester derivatives with intravenous anaesthetic activity

A novel series of alpha-amino-acid phenolic ester derivatives containing sulphide, sulphoxide, sulphone, ester and amide side chains were prepared and shown to display potent intravenous anaesthetic activity.

The difference between sleep and anaesthesia is in the intracellular signal: propofol and GABA use different subtypes of the GABA(A) receptor beta subunit and vary in their interaction with actin

BACKGROUND

Propofol is known to interact with the gamma-aminobutyric acidA (GABA(A)) receptor, however, activating the receptor alone is not sufficient for producing anaesthesia.

METHODS

To compare propofol and GABA, their interaction with the GABAA receptor beta subunit and actin were studied in three cellular fractions of cultured rat neurons using Western blot technique.

RESULTS

Propofol tyrosine phosphorylated the GABA(A) receptor beta2 (MW 54 and 56 kDa) and beta3 (MW 57 kDa) subtypes. The increase was shown in both the cytoskeleton (beta2(54) and beta2(56) subtypes) and the cell membrane (beta2(54) and beta3 subtypes). Concurrently the 56 kDa beta2 subtype was reduced in the cytosol. Propofol, but not GABA, also tyrosine phosphorylated actin in the cell membrane and cytoskeletal fraction. Without extracellular calcium available, the amount of actin decreased in the cytoskeleton, but tyrosine phosphorylation was unchanged. GABA caused increased tyrosine phosphorylation of beta2(56) and beta3 subtypes in the membrane and both beta2 subtypes in the cytoskeleton but no cytosolic tyrosine phosphorylation.

CONCLUSION

The difference between propofol and GABA at the GABA(A) receptor was shown to take place in the membrane, where the beta2(54) was increased by propofol and instead the beta2(56) subtype was increased by GABA. Only propofol also tyrosine phosphorylated actin in the cell membrane and cytoskeletal fraction. This interaction between the GABAA receptor and actin might explain the difference between anaesthesia and physiological neuronal inhibition.

4D-QSAR analysis of a set of propofol analogues: mapping binding sites for an anesthetic phenol on the GABA(A) receptor

A training set of 27 propofol (2,6-diisopropylphenol) analogues was used to construct four-dimensional (4D) quantitative structure-activity relationship (QSAR) models for three screens of biological activity: loss of righting reflex (LORR) in tadpoles, enhancement of agonist activity at the gamma-aminobutyric acid type A (GABA(A)) receptor, and direct (agonist-independent) activation of the receptor. The three resulting 4D-QSAR models are almost identical in form, and all suggest three key ligand-receptor interaction sites. The formation of an intermolecular hydrogen bond involving the proton of the ligand -OH group is the most important binding interaction. A hydrophobic pocket binding interaction involving the six-substituent is the second most significant binding site, and a similar hydrophobic pocket binding interaction near the two-substituent is the third postulated binding site from the 4D-QSAR models. A test set of eight compounds was used to evaluate the tadpole LORR 4D-QSAR model. Those compounds highly congeneric to the training set compounds were accurately predicted. However, compounds exploring substituent sites and/or electronic structures different from the training set were less well-predicted. Overall, the results show a striking similarity between the models of the sites responsible for anesthesia and those mediating effects of the training set of propofol analogues on the GABA(A) receptor; it follows that the GABA(A) receptor is therefore the likely site of propofol's anesthetic action.

A tyrosine kinase regulates propofol-induced modulation of the beta-subunit of the GABA(A) receptor and release of intracellular calcium in cortical rat neurones

Propofol, an intravenous anaesthetic, has been shown to interact with the beta-subunit of the gamma-amino butyric acid(A) (GABA(A)) receptor and also to cause changes in [Ca2+]i. The GABA(A) receptor, a suggested target for anaesthetics, is known to be regulated by kinases. We have investigated if tyrosine kinase is involved in the intracellular signal system used by propofol to cause anaesthesia. We used primary cell cultured neurones from newborn rats, pre-incubated with or without a tyrosine kinase inhibitor before propofol stimulation. The effect of propofol on tyrosine phosphorylation and changes in [Ca2+]i were investigated. Propofol (3 microg mL(-1), 16.8 microM) increased intracellular calcium levels by 122 +/- 34% (mean +/- SEM) when applied to neurones in calcium free medium. This rise in [Ca2+]i was lowered by 68% when the cells were pre-incubated with the tyrosine kinase inhibitor herbimycin A before exposure to propofol (P < 0.05). Propofol caused an increase (33 +/- 10%) in tyrosine phosphorylation, with maximum at 120 s, of the beta-subunit of the GABA(A)-receptor. This tyrosine phosphorylation was decreased after pre-treatment with herbimycin A (44 +/- 7%, P < 0.05), and was not affected by the absence of exogenous calcium in the medium. Tyrosine kinase participates in the propofol signalling system by inducing the release of calcium from intracellular stores and by modulating the beta-subunit of the GABA(A)-receptor.

Inhibitory effects of tramadol on nicotinic acetylcholine receptors in adrenal chromaffin cells and in Xenopus oocytes expressing alpha 7 receptors

1. Tramadol has been used clinically as an analgesic; however, the mechanism of its analgesic effects is still unknown. 2. We used bovine adrenal chromaffin cells to investigate effects of tramadol on catecholamine secretion, nicotine-induced cytosolic Ca(2+) concentration ([Ca(2+)](i)) increases and membrane current changes. We also investigated effects of tramadol on alpha7 nicotinic acetylcholine receptors (AChRs) expressed in Xenopus oocytes. 3. Tramadol concentration-dependently suppressed carbachol-induced catecholamine secretion to 60% and 27% of the control at the concentration of 10 and 100 microM, respectively, whereas it had little effect on veratridine- or high K(+)-induced catecholamine secretion. 4. Tramadol also suppressed nicotine-induced ([Ca(2+)](i)) increases in a concentration-dependent manner. Tramadol inhibited nicotine-induced inward currents, and the inhibition was unaffected by the opioid receptor antagonist naloxone. 5. Tramadol inhibited nicotinic currents carried by alpha7 receptors expressed in Xenopus oocytes. 6. Tramadol inhibited both alpha-bungarotoxin-sensitive and -insensitive nicotinic currents in bovine adrenal chromaffin cells. 7. In conclusion, tramadol inhibits catecholamine secretion partly by inhibiting nicotinic AChR functions in a naloxone-insensitive manner and alpha7 receptors are one of those inhibited by tramadol.

Interscalene and infraclavicular block for bilateral distal radius fracture

Brachial plexus blockade is a suitable technique for surgery of the forearm, because it provides good intraoperative anesthesia as well as prolonged postoperative analgesia when long-acting local anesthetics are used. However, simultaneous blockade of both upper extremities has rarely been performed (1), because local anesthetic toxicity caused by the amount of drug needed to achieve an efficient block on both sides may be a problem. We report a case of successful bilateral brachial plexus block with ropivacaine in a patient with bilateral distal radius fracture, with each fracture requiring an open osteosynthesis.

IMPLICATIONS

This case report presents the performance of a simultaneous blockade of both upper extremities in a patient who sustained a bilateral distal radius fracture. The patient was known to be difficult to intubate and to have a severe hypersensitivity to opioids.

Anesthetic protocol: propofol use in Rhesus macaques (Macaca mulatta) during magnetic resonance imaging with stereotactic head frame application

Magnetic resonance image (MRI) guidance is often necessary for accurate targeting for stereotactic intracranial surgery in animals used for experimental research studies. The magnetic field created by the MR imaging equipment, logistics of the use of stereotactic head frame in confined space and the need to limit movement of the subject during the imaging creates unique challenges. We demonstrate in this study the usefulness of intravenous propofol to anesthetize adult Rhesus monkeys to obtain high resolution 3D MR images immediately followed by conversion to inhalation anesthesia and stereotactic intracranial surgery with the head frame 'in situ.' There was minimal morbidity with achieving a high degree of precision for the stereotactic targeting.

Correlating in vivo anaesthetic effects with ex vivo receptor density data supports a GABAergic mechanism of action for propofol, but not for isoflurane

If the in vivo effects of anaesthesia are mediated through a specific receptor system, then a relationship could exist between the regional changes in brain metabolism caused by a particular agent and the underlying regional distribution of the specific receptors affected by that agent. Positron emission tomography data from volunteers studied while unconscious during propofol (n=8) or isoflurane (n=5) anaesthesia were used retrospectively to explore for evidence of relationships between regional anaesthetic effects on brain glucose metabolism and known (ex vivo) regional distribution patterns of human receptor binding sites. The regional metabolic reductions caused by propofol differed significantly from those of isoflurane. Propofol's reductions negatively correlated most significantly with the regional distribution of [3H]diazepam and [3H]flunitrazepam (benzodiazepine) binding site densities (r=-0.86, P<0.0005; r=-0.79, P<0.005, respectively) and less strongly with [3H]naloxone (opioid) binding density (r=-0.69, P<0.05). Isoflurane's reductions positively correlated only with muscarinic (acetylcholine) binding density (r=0.85, P<0.05). These findings are consistent with the hypothesis that some of propofol's in vivo anaesthetic effects may be mediated through a GABAergic mechanism and suggest some of isoflurane's in vivo effects might involve antagonism of central acetylcholine functioning.

Water-soluble propofol analogues with intravenous anaesthetic activity

Propofol (2,6-diisopropylphenol) is a widely used intravenous anaesthetic that is formulated as an emulsion since it lacks water solubility. We report a range of water-soluble analogues of propofol, containing a para-alkylamino substituent, which retain good intravenous anaesthetic activity in rodents.

The effects of propofol in the area postrema of rats

Propofol has an antiemetic effect that may be mediated by gamma-aminobutyric acid (GABA) influences on the serotonin system, the mechanism of which is not known. We used three techniques, immunohistochemistry, High Performance Liquid Chromatography, and electrophysiology, to define propofol's effects on the rat's brainstem. Paired male Wistar rats received propofol, 20 mg/kg/hr, or Intralipid for 6 h. The brains were then subjected to immunohistochemical analysis of serotonin. In a separate experiment after a propofol or Intralipid infusion, cerebrospinal fluid (CSF) was extracted from the fourth ventricle and analyzed for the amount of serotonin and 5-hydroxyindoleacetic acid. Electrophysiological neuronal recordings were made in the area postrema (AP) in response to propofol with and without a GABA or serotonin antagonist. Results showed that immunohistochemical staining for serotonin in the propofol rats was significantly increased (28 +/- 12%) in the dorsal raphe and decreased in the AP (17 +/- 6%) compared with control. There were no significant changes in the isoflurane-anesthetized animals. Both serotonin and 5-hydroxyindoleacetic acid in the CSF of the fourth ventricle at the level of the AP were significantly reduced by 63% and 36%, respectively. Both propofol and pentobarbital injections reduce AP neuronal activity, but only the propofol response was blocked by bicuculline, a GABA antagonist. We conclude that the reduced levels of serotonin in the AP and the CSF may explain the antiemetic property of propofol. Propofol may also directly act on AP neurons via a GABA(A) receptor to reduce their activity.

IMPLICATIONS

Propofol may produce its antiemetic effect by depleting the area postrema of serotonin as well as by a direct gamma-aminobutyric acid-mediated inhibition.

Premedication modifies the quality of sedation with propofol during regional anesthesia

PURPOSE

To determine the effects of diazepam or clonidine on the quality of sedation with propofol during regional anesthesia.

METHODS

In a prospective randomised, controlled, double-blinded study, 60 patients undergoing elective gynecological surgery were studied. They were given premedication with 0.15-mg clonidine (Group-CL, n=20), 5-mg diazepam (Group-DZ, n = 20), or placebo (Group-P, n = 20) po. After spinal anesthesia was established, sedation was provided with propofol and controlled using a five-point sedation score at 3, "eyes closed but rousable to command", and 4, "eyes closed but rousable to mild physical stimulation". During sedation, blinded anesthesiologist recorded occurrence of complications. At two hours after end of sedation, patients were asked if they had intraoperative dream and memory.

RESULTS

The loading dose, steady-state infusion rate, and overall mean infusion rate in Group-CL were 0.80 mg x kg(-1), 2.35 mg x kg(-1) x hr(-1) and 2.89 mg x kg(-1) x hr(-1), compared with 0.97 mg x kg(-1), 3.13 mg x kg(-1) x hr(-1) and 3.59 mg x kg(-1) x hr(-1) in Group-DZ, and 1.38 mg x kg(-1), 4.10 mg x kg(-1) x hr(-1) and 4.36 mg x kg(-1) x hr(-1) in Group-P, respectively. Indices of both Group-CL (P < 0.001) and Group-DZ (P < 0.05) were smaller than those of Group-P Moreover, clonidine reduced the incidence of uncontrolled movement (P < 0.01), while diazepam reduced the incidence of intraoperative memory and increased the incidence of dream (P < 0.05). Premedication did not affect the incidence of other complications.

CONCLUSION

Both premedicants reduced propofol requirements and exerted beneficial effects on the incidence of some complications during sedation with propofol as an adjunct to regional anesthesia.

Transformations of 2,6-diisopropylphenol by NO-derived nitrogen oxides, particularly peroxynitrite

To investigate the protective effect of the anesthetic 2, 6-diisopropylphenol, or propofol, in oxidative processes in which (*)NO and peroxynitrite are involved, direct interactions were explored. The reactions of the highly lipophilic propofol with (*)NO in methanolic or aqueous buffered solutions under air were shown to produce the same compounds as those detected with peroxynitrite, but with very low yields and slow rates. In aqueous neutral medium, peroxynitrite (ONOO(-), ONOOCO(-)(2), ONOOH) was able to nitrate and oxidize propofol: In addition to oxidation products, quinone and quinone dimer, the formation of the 4-nitropropofol derivative was detected, increasing with peroxynitrite or CO(2) concentrations. Nitration reached 20% after the addition of 25 mM bicarbonate to an equimolecular mixture of peroxynitrite and propofol in methanol/phosphate-buffered solution (1/4,v/v) at pH 7.4. However, peroxynitrite either in methanol or in alkaline-buffered mixture (optimum pH 10-12) resulted in the rapid and almost complete transformation of propofol to an intermediate compound 1, which further decomposed to 4-nitrosopropofol. The transient compound 1 was obtained from either peroxynitrite or (*)NO in the presence of oxygen. From mass spectrometry determination of compound 1 we propose the involvement of the nitrosodioxyl radical ONOO(*), forming an adduct with the propofoxyl radical, to yield 4-nitrosodioxypropofol and finally 4-nitrosopropofol.

Age-related modifications of effects of ketamine and propofol on rat hippocampal acetylcholine release studied by in vivo brain microdialysis

BACKGROUND

We sometimes encounter impairment of learning and memory after general anesthesia in elderly patients. The aim of this study was to examine age-related modifications of the effects of ketamine and propofol on rat hippocampal acetylcholine (ACh) release because hippocampal cholinergic neurons are supposed to be involved in learning and memory.

METHODS

The experiments were performed on male Wistar young rats (2 months old) and old rats (18 months old), using in vivo brain microdialysis technique under freely moving condition. After initial sampling of three collections, test drugs were administered. The ACh release was determined by the HPLC-ECD method.

RESULTS

In old rats, the hippocampal basal ACh release was significantly lower than in young rats. Ketamine (25 and 50 mg kg(-1) i.p.) increased and propofol (25 and 50 mg kg(-1) i.p.) decreased the hippocampal ACh release in both young and old rats. Furthermore, ketamine 50 mg kg(-1) i.p. (anesthetic dose) produced facilitatory effects on the hippocampal ACh release in young rats (193% of the basal release), while in old rats the same dose of ketamine i.p. produced more pronounced facilitatory effects on the hippocampal ACh release (317% of the basal release). On the other hand, propofol 50 mg kg(-1) i.p. (anesthetic dose) produced inhibitory effects on the hippocampal ACh release in young rats (56% of control) and in old rats (77% of control). Although the maximal inhibitory peak effects of propofol 50 mg kg(-1) i.p. did not differ significantly between young rats and old rats, decrease of the hippocampal ACh release in old rats persisted longer than in young rats.

CONCLUSION

Ketamine produced more pronounced facilitatory effects on the hippocampal ACh release in old rats, as compared with young rats. On the other hand, propofol has inhibitory effects on the hippocampal ACh release in young and old rats. The aging process may suppress the ability to recover from the inhibitory anesthetic state induced by propofol.

Comparison of the intravenous reinforcing effects of propofol and methohexital in baboons

Propofol is a widely used intravenous anesthetic that can directly activate and positively modulate the GABA(A)-receptor. Propofol is not currently regulated under the USA Controlled Substances Act. The present study evaluated the intravenous reinforcing effects of propofol compared to the intravenous barbiturate anesthetic methohexital in baboons using a procedure in which doses of the test drug were substituted for a standard cocaine dose. Drug or vehicle was available for self-injection during daily 5.5-h sessions under a fixed-ratio 120 or 160 schedule of reinforcement. A 40-min timeout after each injection limited the maximum of injections per session to eight. Food pellets were available continuously during the session under a fixed ratio 10 schedule of reinforcement. Self-injection of cocaine (0.001-0.32 mg/kg/injection) and vehicle was characterized first. Cocaine maintained self-injection in a dose-dependent manner, with peak injections maintained by 0.32 mg/kg. Vehicle and each dose of propofol (0.1-1.0 mg/kg/injection) and methohexital (0.01-1.0 mg/kg/injection) were substituted for 0.32 mg/kg cocaine for at least 10 sessions. Propofol and methohexital maintained self-injection greater than vehicle in all three baboons, and these effects were dose dependent. Methohexital maintained peak mean levels of self-injection that were >6 injections/day at doses of 0.56 and 1.0 mg/kg, and did not alter food intake systematically. Propofol maintained peak mean levels of self-injection at 1.0 mg/kg that ranged from 2.2 to >6 injections/day across the baboons. Food intake was increased slightly above vehicle levels by propofol self-injection in two baboons, and was decreased in the third baboon. These data indicate that propofol, like methohexital, can function as a positive reinforcer.

Propofol's biphasic effect on GABA(A)-receptor-mediated response of the isolated guinea pig ileum

This study examines the effect of the anaesthetic agent propofol on the guinea pig ileum and whether this effect derives from an interaction of the drug with GABA receptors. Propofol produced a biphasic effect consisting of a dose-dependent contractile effect (EC(50)=2.2x10(-5)m) followed by an 'after relaxation'. This propofol effect was similar to the one produced by GABA and was bicuculline-sensitive (ID(50)=3.2x10(-7)m). Propofol, at concentrations of 10(-7)and 10(-6)m, potentiated the ileum contractile responses to GABA, but only at the lower dose range of applied GABA, while at a concentration of 10(-5)m, it inhibited the contractile effect over the entire dose range of applied GABA. In addition, while the contractile response of the ileum to exogenously applied acetylcholine was not influenced by propofol at concentrations of up to 7x10(-6)m, it was antagonised by higher concentrations of propofol. In conclusion, the above data permit us to suggest that propofol's contractile effect on the guinea pig ileum is mediated by an interaction of the drug with GABA(A)-receptors.

Modification of the effect of diazepam on the propofol-induced loss of the righting reflex in mice by diabetes

The effect of diabetes on the effect of diazepam on the propofol-induced loss of the righting reflex was investigated. There was no significant difference in the duration of the propofol-induced loss of the righting reflex between non-diabetic and diabetic mice. Diazepam increased the duration of the propofol-induced loss of the righting reflex in both diabetic and non-diabetic mice. The diazepam-induced enhancement of the effect of propofol was significantly lower in diabetic mice than that in non-diabetic mice. These effects were antagonized by the pretreatment with flumazenil. Pretreatment with FG7142, a benzodiazepine receptor inverse agonist, attenuated the duration of the propofol-induced loss of the righting reflex in non-diabetic mice, but not in diabetic mice. These results suggest that the attenuation of the diazepam-induced enhancement of the duration of the propofol-induced loss of the righting reflex in diabetic mice may be due to the dysfunction of benzodiazepine receptors.

Propofol anesthesia

Although questions may still remain regarding the use of this unique sedative-hypnotic drug with anesthetic properties in high-risk patients, our studies have provided cardiopulmonary and neurological evidence of the efficacy and safety of propofol when used as an anesthetic under normal and selected impaired conditions in the dog. 1. Propofol can be safely and effectively used for the induction and maintenance of anesthesia in normal healthy dogs. Propofol is also a reliable and safe anesthetic agent when used during induced cardiovascular and pulmonary-impaired conditions without surgery. The propofol requirements to induce the safe and prompt induction of anesthesia prior to inhalant anesthesia with and without surgery have been determined. 2. The favorable recovery profile associated with propofol offers advantages over traditional anesthetics in clinical situations in which rapid recovery is important. Also, propofol compatibility with a large variety of preanesthetics may increase its use as a safe and reliable i.v. anesthetic for the induction and maintenance of general anesthesia and sedation in small animal veterinary practice. Although propofol has proven to be a valuable adjuvant during short ambulatory procedures, its use for the maintenance of general anesthesia has been questioned for surgery lasting more than 1 hour because of increased cost and marginal differences in recovery times compared with those of standard inhalant or balanced anesthetic techniques. When propofol is used for the maintenance of anesthesia in combination with a sedative/analgesic, the quality of anesthesia is improved as well as the ease with which the practitioner can titrate propofol; therefore, practitioners are able to use i.v. anesthetic techniques more effectively in their clinical practices. 3. Propofol can induce significant depression of respiratory function, characterized by a reduction in the rate of respiration. Potent alpha 2 sedative/analgesics (e.g., xylazine, medetomidine) or opioids (e.g., oxymorphone, butorphanol) increase the probability of respiratory depression during anesthesia. Appropriate consideration of dose reduction and speed of administration of propofol reduces the degree of depression. Cardiovascular changes induced by propofol administration consist of a slight decrease in arterial blood pressures (systolic, mean, diastolic) without a compensatory increase in heart rate. Selective premedicants markedly modify this characteristic response. 4. When coupled with subjective responses to painful stimuli, EEG responses during propofol anesthesia provide clear evidence that satisfactory anesthesia has been achieved in experimental dogs. When propofol is used as the only anesthetic agent, a higher dose is required to induce an equipotent level of CNS depression compared with the situation when dogs are premedicated. 5. The propofol induction dose requirement should be appropriately decreased by 20% to 80% when propofol is administered in combination with sedative or analgesic agents as part of a balanced technique as well as in elderly and debilitated patients. As a general recommendation, the dose of propofol should always be carefully titrated against the needs and responses of the individual patient, as there is considerable variability in anesthetic requirements among patients. Because propofol does not have marked analgesic effects and its metabolism is rapid, the use of local anesthetics, nonsteroidal anti-inflammatory agents, and opioids to provide postoperative analgesia improves the quality of recovery after propofol anesthesia. 6. The cardiovascular depressant effects of propofol are well tolerated in healthy animals, but these effects may be more problematic in high-risk patients with intrinsic cardiac disease as well as in those with systemic disease. In hypovolemic patients and those with limited cardiac reserve, even small induction doses of propofol (0.75-1.5 mg/kg i.v.) can produce profound hypotens

Propofol inhibits muscarinic acetylcholine receptor-mediated signal transduction in Xenopus Oocytes expressing the rat M1 receptor

The effects of propofol, 2,6-diisopropylphenol, an intravenous general anesthetic, on signal transduction mediated by the rat M1 muscarinic acetylcholine (ACh) receptor (M1 receptor) were examined in electrophysiological studies by analyzing receptor-stimulated, Ca2+-activated Cl--current responses in the Xenopus oocyte expression system. In oocytes expressing the M1 receptor, ACh induced the Ca2+-activated C1- current, in a dose-dependent manner (EC50= 114 nM). Propofol (5-50 microM) reversibly and dose-dependently inhibited induction of the Ca2+-activated Cl- current by ACh (100 nM) (IC50=5.6 microM). To determine a possible site affected by propofol in this signal transduction, we tested the effects of this anesthetic (10 microM) on the activation of current by injection of CaCl2 and aluminum fluoride (AlF4-). Propofol did not affect activation of the current by the intracellular injected Ca2+, or activation of the current by the intracellular injected AlF4-. These results indicate that propofol does not affect G protein, the inositol phosphate turnover, release of Ca2+ from Ca2+ store or the Ca2+-activated Cl- channel. Propofol apparently inhibits the M1 receptor-mediated signal transduction at the receptor site and/or the site of interaction between the receptor and associated G protein.

Characterization of the electrophysiological and pharmacological effects of 4-iodo-2,6-diisopropylphenol, a propofol analogue devoid of sedative-anaesthetic properties

1. Several derivatives and analogues of the general anaesthetic 2,6-diisopropylphenol (propofol) have been recently synthesised with the aim of exploring the structure-activity relationships. 2. In the present study, the effects of one such compound, 4-iodo-2,6-diisopropylphenol (4-I-Pro), on gamma-aminobutyric acid type A (GABA(A)) receptors in vitro were compared with its in vivo effects in rodents. Human GABA(A) receptors were expressed in Xenopus oocytes, and the actions of 4-I-Pro on receptor function were compared with those of propofol by two-electrode voltage-clamp recording. 3. Similar to propofol, 4-I-Pro directly activated Cl- currents in the absence of GABA at all combinations of receptor subunits tested. However, the efficacy of 4-I-Pro in inducing direct activation of alpha1beta2gamma2S receptors was markedly less than that of propofol. 4. Similarly to propofol, 4-I-Pro potentiated in a concentration-dependent manner GABA-evoked Cl- currents measured at different GABA(A) receptor constructs. 5. As expected, intraperitoneal injection of propofol induced sedation, ataxia, and loss of the righting reflex in rats. In contrast, administration of 4-I-Pro failed to produce any of these behavioural effects. 6. Administration of 4-I-Pro to rats reduced in a dose-dependent manner the incidence of tonic-clonic seizures induced by pentylenetetrazol and induced an anticonflict effect as measured in the Vogel test. 7. Microdialysis revealed that, like propofol, administration of 4-I-Pro reduced acetylcholine release in the hippocampus of freely moving rats. 8. These results demonstrate that para-substitution of the phenol ring of propofol with iodine yields a compound that exhibits anticonvulsant and anticonflict effects, but is devoid of sedative-hypnotic and anaesthetic properties. Thus, 4-I-Pro possesses pharmacological characteristics more similar to anxiolytic and anticonvulsant drugs than to general anaesthetics.