Toll-Like Receptor 4 Deficiency Ameliorates Propofol-Induced Impairments of Cognitive Function and Synaptic Plasticity in Young Mice

Propofol is one of the most used intravenous anesthetic agents, which is widely used in clinical anesthesia induction and maintenance of pediatric patients. Exposure of the developing brain to propofol has been reported to lead to adverse brain changes, which in turn can induce persistent behavioral abnormalities in adulthood. However, the mechanisms by which propofol exposure in the developing brain induces cognitive impairment remain unclear. Here we report that repeated propofol exposure during the second postnatal week impairs spatial learning and memory in young mice. The reduced excitatory synaptic function and synaptogenesis in hippocampal CA1 neurons underlie this cognitive impairment. Propofol exposure specifically activates Toll-like receptor 4 (TLR4)-myeloid differentiation primary response protein 88 (MyD88)-NF-κB signaling pathway. TLR4 deficiency recues propofol exposure-induced synaptic function and cognitive deficits in young mice. Thus, we provide evidence that the activation of the TLR4-mediated pathway by propofol exposure may serve as a crucial trigger for the cognitive impairment in young adulthood caused by repeated exposure to propofol in the developing brain.

Behavioural impairments after exposure of neonatal mice to propofol are accompanied by reductions in neuronal activity in cortical circuitry

BACKGROUND

Both animal and retrospective human studies have linked extended and repeated general anaesthesia during early development with cognitive and behavioural deficits later in life. However, the neuronal circuit mechanisms underlying this anaesthesia-induced behavioural impairment are poorly understood.

METHODS

Neonatal mice were administered one or three doses of propofol, a commonly used i.v. general anaesthetic, over Postnatal days 7-11. Control mice received Intralipid® vehicle injections. At 4 months of age, the mice were subjected to a series of behavioural tests, including motor learning. During the process of motor learning, calcium activity of pyramidal neurones and three classes of inhibitory interneurones in the primary motor cortex were examined in vivo using two-photon microscopy.

RESULTS

Repeated, but not a single, exposure of neonatal mice to propofol i.p. caused motor learning impairment in adulthood, which was accompanied by a reduction of pyramidal neurone number and activity in the motor cortex. The activity of local inhibitory interneurone networks was also altered: somatostatin-expressing and parvalbumin-expressing interneurones were hypoactive, whereas vasoactive intestinal peptide-expressing interneurones were hyperactive when the mice were performing a motor learning task. Administration of low-dose pentylenetetrazol to attenuate γ-aminobutyric acid A receptor-mediated inhibition or CX546 to potentiate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-subtype glutamate receptor function during emergence from anaesthesia ameliorated neuronal dysfunction in the cortex and prevented long-term behavioural deficits.

CONCLUSIONS

Repeated exposure of neonatal mice to propofol anaesthesia during early development causes cortical circuit dysfunction and behavioural impairments in later life. Potentiation of neuronal activity during recovery from anaesthesia reduces these adverse effects of early-life anaesthesia.

Propofol induces a metabolic switch to glycolysis and cell death in a mitochondrial electron transport chain-dependent manner

The intravenous anesthetic propofol (2,6-diisopropylphenol) has been used for the induction and maintenance of anesthesia and sedation in critical patient care. However, the rare but severe complication propofol infusion syndrome (PRIS) can occur, especially in patients receiving high doses of propofol for prolonged periods. In vivo and in vitro evidence suggests that the propofol toxicity is related to the impaired mitochondrial function. However, underlying molecular mechanisms remain unknown. Therefore, we investigated effects of propofol on cell metabolism and death using a series of established cell lines of various origins, including neurons, myocytes, and trans-mitochondrial cybrids, with defined mitochondrial DNA deficits. We demonstrated that supraclinical concentrations of propofol in not less than 50 μM disturbed the mitochondrial function and induced a metabolic switch, from oxidative phosphorylation to glycolysis, by targeting mitochondrial complexes I, II and III. This disturbance in mitochondrial electron transport caused the generation of reactive oxygen species, resulting in apoptosis. We also found that a predisposition to mitochondrial dysfunction, caused by a genetic mutation or pharmacological suppression of the electron transport chain by biguanides such as metformin and phenformin, promoted propofol-induced caspase activation and cell death induced by clinical relevant concentrations of propofol in not more than 25 μM. With further experiments with appropriate in vivo model, it is possible that the processes to constitute the molecular basis of PRIS are identified.

Neurotoxicity of propofol on rat hypoglossal motoneurons in vitro

Although propofol is a widely used intravenous general anaesthetic, many studies report its toxic potential, particularly on the developing central nervous system. We investigated its action on hypoglossal motoneurons (HMs) that control two critical functions in neonates, namely tongue muscle activity and airway patency. Thus, clinically relevant concentrations of propofol (1 and 5μM) were applied (4h) to neonatal rat brainstem slices to evaluate the expression of apoptosis-inducing factor (AIF) as biomarker of toxicity. This anaesthetic strongly increased AIF in the cytoplasm and the nucleus, without early loss of HMs. Electrophysiological recordings from HMs showed that propofol (5μM) enhanced GABA- and glycine-evoked current amplitude and lengthened GABAergic current decay time. Propofol also depressed NMDA receptor-mediated responses without affecting AMPA receptors. Since GABA and glycine depolarize neonatal HMs, we propose that the damaging action by propofol on these motoneurons might arise from the facilitated action of these transmitters with subsequent cytoplasmic Ca²⁺ overload. This phenomenon, in turn, may trigger cell death mechanisms manifested as increased expression of AIF and its translocation into the nucleus. Since propofol is also employed for induction and maintenance of paediatric surgery, caution is needed because its potential neurotoxicity might negatively impact neurodevelopment.

Dexmedetomidine attenuates propofol-induce neuroapoptosis partly via the activation of the PI3k/Akt/GSK3β pathway in the hippocampus of neonatal rats

Recent studies have demonstrated that propofol causes neurodegeneration in developing brains. Evidence has shown that dexmedetomidine has neuroprotective effects. However, whether dexmedetomidine can reduce propofol-induced neuroapoptosis and by what mechanisms it acts remain unclear. We investigated whether dexmedetomidine can attenuate propofol-induced neuroapoptosis by disturbing the PI3K/Akt/GSK3β pathway during brain development. Seven-day-old rats were randomly exposed to 100mg/kg propofol and 100mg/kg propofol plus different doses of dexmedetomidine or 100mg/kg propofol and 75μg/kg dexmedetomidine plus PI3K inhibitor LY294002 or GSK3β inhibitor TDZD-8. TEM and TUNEL were used to detect neuronal structure changes and apoptosis. The expression of phospho-Akt, phospho-GSK3β, Akt and GSK3β were quantified using western blots and immunofluorescence. Pretreatment with different doses of dexmedetomidine protected against propofol-induced neuroapoptosis. Furthermore, propofol decreased the levels of phospho-Akt and phospho-GSK3β, whereas dexmedetomidine partially reversed this inhibition. In addition, treatment with LY294002 inhibited the neuroprotection of dexmedetomidine, whereas TDZD-8 enhanced neuroprotection. Our results indicate that dexmedetomidine prevents propofol-induced neuroapoptosis by increasing the levels of phospho-Akt and phospho-GSK3β.

The pituitary adenylate cyclase-activating polypeptide (PACAP) protects adrenal function in septic rats administered etomidate

BACKGROUND

Both hyperinflammation during sepsis and etomidate can suppress adrenal function. In this study, we explored whether treatment with pituitary adenylate cyclase-activating polypeptide (PACAP) relieves adrenal suppression in cecal ligation and puncture (CLP)-induced septic rats.

MATERIALS AND METHODS

Female Sprague-Dawley rats were randomly divided into five groups (n=7 per group), including the sham group, sepsis group (CLP group), sepsis and etomidate group (CLP+ETO group), PACAP group, and etomidate alone group (ETO group). Rats were sacrificed on the third day of sepsis, and blood and adrenal gland samples were obtained for further testing.

RESULTS

The PACAP reduced the apoptosis rate of adrenal cells and peripheral lymphocytes, improving adrenal function, inhibiting the secretion of interferon gamma (IFN-γ) from peripheral lymphocytes, and slightly relieving the suppression of the adrenal function induced by the injection of etomidate in sepsis.

CONCLUSION

In septic conditions, the PACAP protects the adrenal gland by regulating peripheral inflammation, which slightly relieves the toxic effects of etomidate on adrenal function.

Effects of Etomidate on the Steroidogenesis of Rat Immature Leydig Cells

BACKGROUND

Etomidate is a rapid hypnotic intravenous anesthetic agent. The major side effect of etomidate is the reduced plasma concentration of corticosteroids, leading to the abnormal reaction of adrenals. Cortisol and testosterone biosynthesis has similar biosynthetic pathway, and shares several common steroidogenic enzymes, such as P450 side chain cleavage enzyme (CYP11A1) and 3β-hydroxysteroid dehydrogenase 1 (HSD3B1). The effect of etomidate on Leydig cell steroidogenesis during the cell maturation process is not well established.

METHODOLOGY

Immature Leydig cells isolated from 35 day-old rats were cultured with 30 μM etomidate for 3 hours in combination with LH, 8Br-cAMP, 25R-OH-cholesterol, pregnenolone, progesterone, androstenedione, testosterone and dihydrotestosterone, respectively. The concentrations of 5α-androstanediol and testosterone in the media were measured by radioimmunoassay. Leydig cells were cultured with various concentrations of etomidate (0.3-30 μM) for 3 hours, and total RNAs were extracted. Q-PCR was used to measure the mRNA levels of following genes: Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Srd5a1, and Akr1c14. The testis mitochondria and microsomes from 35-day-old rat testes were prepared and used to detect the direct action of etomidate on CYP11A1 and HSD3B1 activity.

RESULTS AND CONCLUSIONS

In intact Leydig cells, 30 μM etomidate significantly inhibited androgen synthesis. Further studies showed that etomidate also inhibited the LH- stimulated androgen production. On purified testicular mitochondria and ER fractions, etomidate competitively inhibited both CYP11A1 and HSD3B1 activities, with the half maximal inhibitory concentration (IC50) values of 12.62 and 2.75 μM, respectively. In addition, etomidate inhibited steroidogenesis-related gene expression. At about 0.3 μM, etomidate significantly inhibited the expression of Akr1C14. At the higher concentration (30 μM), it also reduced the expression levels of Cyp11a1, Hsd17b3 and Srd5a1. In conclusion, etomidate directly inhibits the activities of CYP11A1 and HSD3B1, and the expression levels of Cyp11a1 and Hsd17b3, leading to the lower production of androgen by Leydig cells.

Cytotoxicity and type of cell death induced by midazolam in human oral normal and tumor cells

BACKGROUND

Intravenous anesthetics have been used during the treatment of various malignant tumors, however, their effects on oral tissues is not well-understood. In the present study, the cytotoxicity of five intravenous anesthetics towards oral tumor and normal cells was compared.

MATERIALS AND METHODS

Tumor specificity index was determined by the ratio of the mean 50% cytotoxic concentration for normal cells to that for tumor cells. Apoptosis induction was monitored by internucleosomal DNA fragmentation and caspase-3, -8, and -9 activation. Fine cell structure was observed under transmission electron microscopy.

RESULTS

Benzodiazepines (midazolam and diazepam) exhibited higher cytotoxicity than barbiturates (thiopental and thiamylal), whereas propofol had the intermediate range of cytotoxicity. Midazolam showed the highest cytotoxicity. HL-60 cells were the most sensitive to midazolam, followed by epidermal keratinocytes, oral squamous cell carcinoma (OSCC), glioblastoma and then oral normal cells. Midazolam did not induce the production of apoptosis markers such as internucleosomal DNA fragmentation and activation of caspase-3, -8 and -9, but did induce the appearance of many vacuoles, mitochondrial swelling and cell membrane rupture in OSCC cell lines (HSC-2 and HSC-4) cells. The cytotoxicity of midazolam was not reduced by pre-treatment with autophagy inhibitors (3-methyladenine and bafilomycin A1).

CONCLUSION

These results suggest that midazolam may induce necrotic cell death, rather than apoptosis or autophagy, in OSCC cell lines.

The effects of intravenous anesthetics on mouse embryonic fibroblast viability and proliferation

PURPOSE

The aim of this study is to evaluate the cytotoxic and antiproliferating effects of intravenous anesthetics on an mouse fibroblast in vitro cell culture system.

METHODS

The cells were exposed to the usual clinical plasma concentration of intravenous anesthetics, i.e., midazolam (0.15 μg/ml), propofol (2 μg/ml), remifentanil (2 μg/ml), thiopental (10 μg/ml), for 4, 8, or 24 h. Cell proliferation (n = 6 for each) under intravenous anesthetics was analyzed using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Cytotoxicity (n = 6 for each) of intravenous anesthetics was investigated using a LIVE/DEAD viability assay kit.

RESULTS

Intravenous anesthetic exposure time did not affect the proliferation rate of mouse fibroblasts. The cytotoxicity of intravenous anesthetics did not differ in accordance with exposure time.

CONCLUSION

Our results showed that intravenous anesthetics may not affect mouse fibroblast proliferation and viability.

DNA damage in patients who underwent minimally invasive surgery under inhalation or intravenous anesthesia

Recent studies have demonstrated the genotoxicity of anesthetics in patients who have undergone surgery and in personnel who are occupationally exposed to anesthetics. However, these findings are controversial. Herein, we used the comet assay (single-cell gel electrophoresis) to investigate the genotoxic effects of two volatile compounds [isoflurane (ISF) and sevoflurane (SVF)] that are used in inhalation anesthesia, and of one intravenous (iv) anesthetic compound [propofol (PF)]. The groups consisted of 45 patients who underwent minimally invasive surgery that lasted at least 2h. Patients were classified as physical status I using the criteria of the American Society of Anesthesiologists (ASA) and were randomly allocated to receive ISF, SVF or PF anesthesia. Venous blood samples were collected at three time points as follows: before the premedication and the induction of anesthesia (T(0)); 2h after the beginning of anesthesia (T(1)); and on the day following surgery (T(2)). DNA damage (strand breaks and alkali-labile sites) was evaluated in peripheral blood lymphocytes. For each patient, one hundred nucleoids were analyzed per time point using a semi-automated image system. Patients did not differ with respect to their demographic characteristics, the duration of surgery, or the total doses of intraoperative drugs. The amount of DNA damage was not different among the three groups before anesthesia (T(0)). No statistically significant (p>0.05) increase in DNA damage was detected during (T(1)) or after anesthesia (T(2)) using three different protocols (ISF, SVF or PF). In conclusion, general anesthesia with inhaled ISF and SVF or iv PF did not induce DNA strand breaks or alkali-labile sites in peripheral lymphocytes. Therefore, our results show that the genotoxic risk of these anesthetics, for healthy patients undergoing minimally invasive otorhinological surgery, is low or even absent.

[Effect of prolonged infusion of propofol on the liver mitochondria respiratory function in rabbits]

OBJECTIVE

To investigate the changes of respiratory function of liver mitochondria in rabbits induced by the general anesthetic propofol.

METHODS

Eighteen New Zealand rabbits weighted 1.5-2.5 kg were randomly divided into three groups: control group, emulsion group and propofol group. The control group received continuous infusion of 0.9% sodium chloride solution. The propofol group received continuous infusion of 1% propofol. The emulsion group received continuous infusion of 10% emulsion. The liver mitochondri of the rabbits were isolated. The carnitine acyl transferase (CPT) activity, H+ -ATPase hydrolysis activity and the content of ATP in the mitochondria were analysed.

RESULTS

The rabbits in the propofol group had lower activity of CPT than the controls (P < 0.05), while no difference was found between the control group and the emulsion group (P > 0.05). The rabbits in the propofol group had higher H+ -ATPase hydrolysis activity than the controls (P < 0.05), while no difference was found between the control group and the emulsion group (P > 0.05). No significant differences were found in the content of ATP in mitochondria between the three groups (P > 0.05).

CONCLUSION

Propofol inhibits CPT activity, which disturbs fatty acid beta-oxidation. Emulsion acted as vehicle of propofol seems to have no significant impact on mitochondria respiratory function.

Regional and temporal profiles of calpain and caspase-3 activities in postnatal rat brain following repeated propofol administration

Exposure of newborn rats to a variety of anesthetics has been shown to induce apoptotic neurodegeneration in the developing brain. We investigated the effect of the general anesthetic propofol on the brain of 7-day-old (P7) Wistar rats during the peak of synaptic growth. Caspase and calpain protease families most likely participate in neuronal cell death. Our objective was to examine regional and temporal patterns of caspase-3 and calpain activity following repeated propofol administration (20 mg/kg). P7 rats were exposed for 2, 4 or 6 h to propofol and killed 0, 4, 16 and 24 h after exposure. Relative caspase-3 and calpain activities were estimated by Western blot analysis of the proteolytic cleavage products of α-II-spectrin, protein kinase C and poly(ADP-ribose) polymerase 1. Caspase-3 activity and expression displayed a biphasic pattern of activation. Calpain activity changed in a region- and time-specific manner that was distinct from that observed for caspase-3. The time profile of calpain activity exhibited substrate specificity. Fluoro-Jade B staining revealed an immediate neurodegenerative response that was in direct relationship to the duration of anesthesia in the cortex and inversely related to the duration of anesthesia in the thalamus. At later post-treatment intervals, dead neurons were detected only in the thalamus 24 h following the 6-hour propofol exposure. Strong caspase-3 expression that was detected at 24 h was not followed by cell death after 2- and 4-hour exposures to propofol. These results revealed complex patterns of caspase-3 and calpain activities following prolonged propofol anesthesia and suggest that both are a manifestation of propofol neurotoxicity at a critical developmental stage.

Ecotoxicology of narcosis: stereoselectivity and potential target sites

The stereoselectivity of certain anesthetics is currently thought to be inconsistent with lipid theories of narcosis. The EC50-values of etomidate enantiomers for tadpole narcosis are now examined as a function of octanol/water partition coefficients, and enhancement factors for predicted over experimental EC50 values are determined from a calibration curve for non-selective narcosis. The unfavored S-(-)-enantiomers of etomidate and two analogues surprisingly still fulfill the Meyer-Overton rule. The R+-enantiomers of etomidate and four structural analogues are up to 34-fold more active than expected. The non-chiral anesthetic, propofol, is 8-fold more active than expected. It is concluded that there may be two pathways to tadpole narcosis: enhanced narcosis involving specific receptor binding sites and non-selective narcosis corresponding to the Meyer-Overton rule and operating on the lipid/protein interface.

The experimental and clinical pharmacology of propofol, an anesthetic agent with neuroprotective properties

Propofol (2,6-diisopropylphenol) is a versatile, short-acting, intravenous (i.v.) sedative-hypnotic agent initially marketed as an anesthetic, and now also widely used for the sedation of patients in the intensive care unit (ICU). At the room temperature propofol is an oil and is insoluble in water. It has a remarkable safety profile. Its most common side effects are dose-dependent hypotension and cardiorespiratory depression. Propofol is a global central nervous system (CNS) depressant. It activates gamma-aminobutyric acid (GABA A) receptors directly, inhibits the N-methyl-d-aspartate (NMDA) receptor and modulates calcium influx through slow calcium-ion channels. Furthermore, at doses that do not produce sedation, propofol has an anxiolytic effect. It has also immunomodulatory activity, and may, therefore, diminish the systemic inflammatory response believed to be responsible for organ dysfunction. Propofol has been reported to have neuroprotective effects. It reduces cerebral blood flow and intracranial pressure (ICP), is a potent antioxidant, and has anti-inflammatory properties. Laboratory investigations revealed that it might also protect brain from ischemic injury. Propofol formulations contain either disodium edetate (EDTA) or sodium metabisulfite, which have antibacterial and antifungal properties. EDTA is also a chelator of divalent ions such as calcium, magnesium, and zinc. Recently, EDTA has been reported to exert a neuroprotective effect itself by chelating surplus intracerebral zinc in an ischemia model. This article reviews the neuroprotective effects of propofol and its mechanism of action.

Propofol induces growth cone collapse and neurite retractions in chick explant culture

PURPOSE

Propofol neurotoxicity has been demonstrated in several cell culture systems. This study was undertaken to determine whether propofol has neurotoxic effects on peripheral, retinal, and autonomic neurons, and which neurons are particularly liable to injury by propofol.

METHOD

Dorsal root ganglia, retinal ganglion cell layers, and sympathetic ganglion chains were isolated from day eight chick embryos and cultured for 20 hr. Thereafter, propofol was added at various concentrations [5-300 microM (0.9-53 microg x mL(-1))] to investigate its effects on these three types of neuronal tissue. Morphological changes were examined quantitatively by growth cone collapse assay. Propofol concentrations were measured using high performance liquid chromatography.

RESULTS

Propofol induced growth cone collapse and neurite destruction. The three types of neurons tested exhibited significantly different dose-response relationships two hours after the application of propofol (P < 0.001) but not at 24 hr after application. The growth cone-collapsing effect was at least partially reversible in all three types of neurons after exposure to 100 microM propofol up to six hours, though reversibility was not observed after 24-hr exposure.

CONCLUSION

While the clinical safety profile of propofol has been well documented, at high concentrations propofol has potential neurotoxicity on growing neurons in vitro.

Clinical features of gamma-hydroxybutyrate and gamma-butyrolactone toxicity and concomitant drug and alcohol use

OBJECTIVE

To describe the clinical features of gamma-hydroxybutyrate (GHB) and gamma-butyrolactone (GBL) toxicity.

METHODS

Retrospective case-study of 65 GHB and GBL intoxications seen in an urban emergency department.

RESULTS

63% of intoxications occurred in male patients. The median age was 24 years (range 16-41 years). 65% co-ingested alcohol or illicit drugs, mostly MDMA and cocaine. 83% presented with coma. The mean+/-S.D. time to regain consciousness among comatose patients was 111+/-61 min and was significantly longer in patients who co-abused illicit drugs such as cocaine or MDMA (155+/-60 min). Bradycardia occurred in 38%, hypotension in 6% and hypothermia in 48%. Agitation was observed in 17% of all patients and was significantly more frequent in patients with alcohol co-use (29%). Vomiting occurred in 31% of all patients and tended to be more frequent in patients who co-used alcohol (39%). Management of GHB and GBL overdose was supportive. Four patients needed admission to an intensive care unit for mechanical ventilation (6%).

CONCLUSIONS

Overdosing of GHB and GBL frequently results in non-reactive coma reflecting the severity of poisoning. Multiple drug use is common and significantly influences the clinical presentation.

Succinate and artificial maintenance of normal body temperature synergistically correct lethal disorders in thiopental coma rat

Under modeling of thiopental coma influence of sodium succinate and (or) external warming for the support of normal body temperature (isothermal regimen) on the gas exchange, blood gas content, acid-base status and survival rate was studied in rats. In the absence of therapy hypothermia was developed (-9.4 degrees C), O(2) consumption decreased by a factor 5, oxygenation of arterial blood (pO(2)) did not change while that of venous blood increased, where with arteriovenous oxygen tension gradient decreased by half. Blood tension of carbon dioxide (pCO(2)) increased twice, respiratory and metabolic acidosis was developed. Survival rate under absence of a therapy was 42%, with isolated use of isothermal regimen or succinate therapy alike-50%; with their use in combination drastically increased up to 92%. Succinate increased arteriovenous gradient of pO(2), decreased deficit of buffer bases, increased bicarbonate concentration. At isothermal regimen accumulation of CO(2) in the blood was diminished, its excretion was increased, pH of blood approached normal values. Combined use of both therapy agents increased O(2) consumption and potentiated their positive influence on acid-base status. The implication is that hypothermia restrains effect of succinate in barbiturate coma; prevention of hypothermia in combination with succinate administration is highly effective method of experimental therapy of barbiturate intoxication.

A Microarray Analysis of Potential Genes Underlying the Neurosensitivity of Mice to Propofol

Establishing the mechanism of action of general anesthetics at the molecular level is difficult because of the multiple targets with which these drugs are associated. Inbred short sleep (ISS) and long sleep (ILS) mice are differentially sensitive in response to ethanol and other sedative hypnotics and contain a single quantitative trait locus (Lorp1) that accounts for the genetic variance of loss-of-righting reflex in response to propofol (LORP). In this study, we used high-density oligonucleotide microarrays to identify global gene expression and candidate genes differentially expressed within the Lorp1 region that may give insight into the molecular mechanism underlying LORP. Microarray analysis was performed using Affymetrix MG-U74Av2 Genechips and a selection of differentially expressed genes was confirmed by semiquantitative reverse transcription-polymerase chain reaction. Global expression in the brains of ILS and ISS mice revealed 3423 genes that were significantly expressed, of which 139 (4%) were differentially expressed. Analysis of genes located within the Lorp1 region showed that 26 genes were significantly expressed and that just 2 genes (7%) were differentially expressed. These genes encoded for the proteins AWP1 (associated with protein kinase 1) and "BTB (POZ) domain containing 1," whose functions are largely uncharacterized. Genes differentially expressed outside Lorp1 included seven genes with previously characterized neuronal functions and thus stand out as additional candidate genes that may be involved in mediating the neurosensitivity differences between ISS and ILS.

Characteristics of propofol-evoked vascular pain in anaesthetized rats

BACKGROUND

In this study we have assessed vascular pain caused by the i.v. anaesthetic agent, propofol, using the flexor reflex response and compared this with that of capsaicin in anaesthetized intact rats.

METHODS

Experiments were performed on 133 male Sprague-Dawley rats weighing 280-340 g. The animals were anaesthetized with urethane (1.3 g kg(-1), i.p.), and an arterial cannula was inserted to the level of the bifurcation of the femoral artery. The magnitude of the flexor reflex was examined by recording the electromyogram from the posterior biceps femoris/semitendinosus muscles.

RESULTS

Our data show that the flexor reflexes evoked by intra-arterial (i.a.) injection of propofol (1%, 25-100 microl) and capsaicin (0.05-0.2 microg) were dose dependent. An initial i.a. injection of procaine (2%, 200 microl) blocked both responses. Furthermore, the flexor reflex induced by these chemical stimuli were inhibited by morphine (5 mg kg(-1), s.c.) and restored with naloxone (1.5 mg kg(-1), s.c.). Pre-treatment with capsazepine (20 microg, i.a.), a selective VR1 antagonist, inhibited the capsaicin-evoked response, but not that of propofol. Indomethacin (10 mg kg(-1), i.p.), a non-selective cyclo-oxygenase inhibitor, inhibited only the propofol-evoked response and this recovered with arterial PGE2 (5 microg).

CONCLUSIONS

Collectively our data suggest that propofol-evoked vascular pain is mainly initiated by prostanoids.

Suppressive effects of ketamine on macrophage functions

Ketamine is an intravenous anesthetic agent. Clinically, induction of anesthesia with ketamine can cause immunosuppression. Macrophages play important roles in host defense. In this study, we attempted to evaluate the effects of ketamine on macrophage functions and its possible mechanism using mouse macrophage-like Raw 264.7 cells as the experimental model. Exposure of macrophages to 10 and 100 microM ketamine, which correspond to 0.1 and 1 times the clinically relevant concentration, for 1, 6, and 24 h had no effect on cell viability or lactate dehydrogenase release. When the administered concentration reached 1000 microM, ketamine caused a release of lactate dehydrogenase and cell death. Ketamine, at 10 and 100 microM, did not affect the chemotactic activity of macrophages. Administration of 1000 microM ketamine in macrophages resulted in a decrease in cell migration. Treatment of macrophages with ketamine reduced phagocytic activities. The oxidative ability of macrophages was suppressed by ketamine. Treatment with lipopolysaccharide induced TNF-alpha, IL-1beta, and IL-6 mRNA in macrophages. Administration of ketamine alone did not influence TNF-alpha, IL-1beta, or IL-6 mRNA production. Meanwhile, cotreatment with ketamine and lipopolysaccharide significantly inhibited lipopolysaccharide-induced TNF-alpha, IL-1beta, and IL-6 mRNA levels. Exposure to ketamine led to a decrease in the mitochondrial membrane potential. However, the activity of mitochondrial complex I NADH dehydrogenase was not affected by ketamine. This study shows that a clinically relevant concentration of ketamine (100 microM) can suppress macrophage function of phagocytosis, its oxidative ability, and inflammatory cytokine production possibly via reduction of the mitochondrial membrane potential instead of direct cellular toxicity.

Exposure to Trichloroethylene and its Metabolites Causes Impairment of Sperm Fertilizing Ability in Mice

Trichloroethylene (TCE) is a prevalent occupational and environmental contaminant that has been reported to cause a variety of toxic effects. Here, we have undertaken studies to test the hypothesis that TCE exposure adversely affects sperm function and fertilization. Sperm retrieved from mice exposed to TCE (1000 ppm) by inhalation for 1 to 6 weeks were incubated in vitro with eggs isolated from superovulated female mice. The number of sperm bound per egg was significantly decreased when mice were exposed to TCE for 2 and 6 weeks but not at exposures of 1 and 4 weeks. In vivo fertilization was also determined in superovulated female mice mated with males exposed to TCE for 2 to 6 weeks. The percentages of eggs fertilized, as assessed by the presence of two pronuclei, were significantly decreased after 2 and 6 weeks of TCE exposure. A slight but insignificant decrease was observed after 4 weeks of TCE exposure. The direct effects of TCE and its metabolites, chloral hydrate (CH) and trichloroethanol (TCOH), on in vitro sperm-egg binding were also investigated. Sperm-egg binding was significantly decreased when sperm were pretreated with CH (0.1-10 microg/mL). Significantly lower levels of sperm-egg binding were also detected with TCOH (0.1-10 microg/mL), although the decreases were not as pronounced as those for CH. These results showed that TCE exposure leads to impairment of sperm fertilizing ability, which may be attributed to TCE metabolites, CH, and TCOH.

Protection by the GABAB receptor antagonist, SCH 50911, of γ-hydroxybutyric acid-induced mortality in mice

Different effects of moderate to high doses of gamma-hydroxybutyric acid, including sedation/hypnosis, have been found to be blocked by gamma-aminobutyric acidB (GABAB) receptor antagonists. The present study investigated whether the protective effect of GABAB receptor antagonists extends also to gamma-hydroxybutyric acid-induced mortality. To this aim, the present study investigated the effect of the GABAB receptor antagonist, (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911; 100 mg/kg, ip), on mortality induced by gamma-hydroxybutyric acid (1-6 g/kg, ip) in DBA mice. Pretreatment with SCH 50911 resulted in a significant shift to the right of the dose-response curve of gamma-hydroxybutyric acid-induced mortality. Accordingly, the LD50 in SCH 50911-pretreated mice was significantly higher than that obtained in water-pretreated mice. The results of the present study support the hypothesis that (a) the GABAB receptor is a relevant site of action of gamma-hydroxybutyric acid, and (b) GABAB receptor antagonists may constitute potentially effective therapeutic interventions for gamma-hydroxybutyric acid intoxication.

Comparative effects of thiopental and propofol on atrial vulnerability: electrophysiological study in a porcine model including acute alcoholic intoxication †

BACKGROUND

Atrial tachyarrhythmias (AT) frequently complicate the perioperative period. Alcohol intoxication is a recognized causative factor for dysrrhythmias. We studied the effects of propofol and thiopental on atrial electrophysiology and vulnerability to AT in a closed-chest porcine model in which AT are facilitated by ethanol.

METHODS

Thirty-eight pigs were randomly assigned to thiopental (T-group, n=19) or propofol (P-group n=19). All animals were assigned to undergo a right atrial electrical stimulation protocol (RASP) at baseline. Thirty pigs were assigned to undergo additional RASP during ethanol infusion, while the remaining eight were assigned to undergo additional RASP during saline infusion (control group). We analysed effective refractory period (ERP), and intra-atrial conduction interval (ICI) (between atrial sites 4 cm apart), at several cycle lengths (CL).

RESULTS

There were no significant differences at baseline. During ethanol infusion, propofol produced a greater rate-dependent decrease in excitability, manifested by a longer minimum paced CL with 1:1 atrial capture: 145 (11) vs 164 (27) ms in the T- and P-group, respectively (P=0.01). Propofol was associated with a greater rate-related slowing in conduction: difference between ICI at CL of 300 ms and ICI at minimum CL: 30 ms in P-group and 22 ms in T-group (P<0.03). In the P-group we observed a longer duration of induced arrhythmias (145 (131) vs 74 (91) s, P<0.03) and a higher proportion with atrial flutter (AFl) (76 vs 19%, P<0.001).

CONCLUSIONS

Propofol in this model was more arrhythmogenic than thiopental, as manifested by a longer duration of induced arrhythmias, particularly AFI.

Isotopic effect study of propofol deuteration on the metabolism, activity, and toxicity of the anesthetic

The use of isotopic substitution to delay the oxidative metabolism of the anesthetic propofol 1 was studied. The aromatic hydrogens of propofol 1 were replaced by deuterium to produce the mono- and trideuterated derivatives 4 and 5. In vitro metabolic studies on human hepatic microsomes showed no isotopic effect in the para hydroxylation of propofol, and 1, 4, and 5 display similar hypnotic activity and toxicity in mice.

Propofol phosphate, a water-soluble propofol prodrug: in vivo evaluation

After a single IV injection of the water-soluble propofol prodrug propofol phosphate (PP) in mice, rats, rabbits, and pigs, propofol was produced rapidly (1-15 min), inducing dose-dependent sedative effects. In mice, the hypnotic dose (HD(50)), lethal dose (LD(50)), and safety index (defined as a ratio: LD(50)/HD(50)) were 165.4 mg/kg, 600.6 mg/kg, and 3.6, respectively. Propofol was produced with half-lives of 5.3 +/- 0.6 min in rats, 2.1 +/- 0.6 min in rabbits, and 4.4 +/- 2.4 min in pigs. The maximal concentration was dose and species dependent. The elimination half-life was 24 +/- 12 min in rats, 21 +/- 16 min in rabbits, and 225 +/- 56 min in pigs. Propofol generated from PP produced pharmacological effects similar to those described in the literature. We found a correlation between PP dose and duration of sedation with propofol concentrations larger than 1.0 microg/mL, which produced somnolence and sedation in rats and pigs. Adequate sedation and, at large enough doses, anesthetic-level sedation were produced after the administration of PP. Overall, PP, the water-soluble prodrug of propofol, seems to be a viable development candidate for sedative and anesthetic applications.

IMPLICATIONS

Propofol phosphate, a water-soluble prodrug of the widely used IV anesthetic propofol, was developed and evaluated in mice, rats, rabbits, and pigs after IV injection. The results of the study clearly demonstrate the feasibility of the prodrug approach to achieve sedative and anesthetic levels of propofol in laboratory animals; this warrants further evaluation in humans.

Flumazenil recovers diaphragm muscle dysfunction caused by midazolam in dogs

We studied the effects of flumazenil on diaphragm muscle dysfunction caused by midazolam in dogs. Animals were divided into three groups of eight each. In each group, anesthetic doses (0.1 mg/kg initial dose plus 0.5 mg. kg(-1). h(-1) maintenance dose) of midazolam were administered for 60 min. Immediately after the end of midazolam administration, Group 1 received no study drug; Group 2 was infused small-dose (0.004 mg. kg(-1). h(-1)) flumazenil; Group 3 was infused with large-dose (0.02 mg. kg(-1). h(-1)) flumazenil. We assessed diaphragm muscle function (contractility and electrical activity) by transdiaphragmatic pressure (Pdi) and integrated electrical activity of the diaphragm (Edi). After midazolam was administered in each group, Pdi at low-frequency (20-Hz) and high-frequency (100-Hz) stimulation decreased from baseline values (P < 0.05), and values of Edi at 100-Hz stimulation were less than those obtained during baseline (P < 0.05). In Group 1, Pdi and Edi to each stimulus did not change from midazolam-induced values. In Groups 2 and 3, with an infusion of flumazenil, Pdi at both stimuli and Edi at 100-Hz stimulation increased from midazolam-induced values (P < 0.05). The increase in Pdi and Edi was more in Group 3 than in Group 2 (P < 0.05). We conclude that flumazenil recovers the diaphragm muscle dysfunction (reduced contractility and inhibited electrical activity) caused by anesthetic doses of midazolam in dogs.

IMPLICATIONS

In dogs, flumazenil recovers diaphragm muscle dysfunction (reduced contractility and inhibited electrical activity) caused by midazolam in a dose-related manner.

Changes in effective and lethal doses of intravenous anesthetics and lidocaine when used in combination in mice

We studied the interactions between a local anesthetic agent, lidocaine, and two general anesthetic drugs, propofol and ketamine, in mice. We used two end points: hypnosis, reflected by loss of the righting reflex, and death. The ED50 for hypnosis and the LD50 were determined for each drug separately, and a dose-response curve was prepared for each drug, using combinations of propofol-lidocane and ketamine-lidocaine at three different dose ratios. Probit and isobolographic analyses revealed supra-additive (synergistic) interactions between lidocaine and each of the other anesthetic agents regarding both the effective dose and the lethal dose. No significant difference was found between propofol and ketamine regarding the supraadditive effect.

Intravenous midazolam significantly enhances the lethal effect of thiopental but not that of ketamine in mice

Intravenous (i.v.) drug combinations are used in clinical anaesthesia in order to combine the desired effects and minimize toxicity from large doses of single agents. This fundamental assumption has not been systematically evaluated. We examined its validity by testing the influence of midazolam on the lethal effect of i.v. thiopental and ketamine in mice. Dose-response curves were constructed for the lethal effect of i.v. thiopental and ketamine, and for the loss of righting reflex effect by midazolam, in sexually mature male ICR mice weighing 20-40 g. For each curve, six or seven groups of eight to 10 mice each were used. A quarter of the median effective dose (ED50) for loss of righting reflex by midazolam was combined with the two other drugs to deduce dose-response curves for the lethal effect of the combinations. The ED50 for loss of righting reflex by i.v. midazolam was 43.5 mg x kg(-1) (95% confidence interval [CI], 40.4-46.5). The median lethal dose (LD 50) of i.v. thiopental was 50.6 mg x kg(-1) (95% CI, 50.0-54.9) and that of ketamine 42.9 mg x kg(-1) (95% CI, 32.3-52). In the presence of 10 mg x kg(-1) midazolam, the LD50 of thiopental was reduced to 20 mg x kg(-1) (17.7-22.2), but that of ketamine remained 44.4 mg x kg(-1) (37.7-54.9). Midazolam increased the lethal effect of thiopental 2.5-fold, but did not affect that of ketamine. Interactions at the toxic level between commonly used anaesthetic agents may differ from those at the hypnotic or analgesic levels, which should prompt evaluation of such combinations before their introduction to routine clinical use.

Urethane anesthesia produces selective damage in the piriform cortex of the developing brain

The potential induction of neuronal death by neuroactive drugs at specific stages of embryonic or postnatal development is a serious concern in treating brain disease. Recent evidence indicates that NMDA antagonists, GABA agonists, ethanol and some anesthetics can all produce massive neuronal cell loss at critical times during development. We show here that the anesthetic urethane, once used clinically, produces a selective lesion of the piriform cortex, a region not previously implicated in such toxicity, in the developing brain. Young rats were injected with urethane at 1, 2, 3, and 4 weeks of age and brain damage was measured 1-4 days later. We found that urethane produces a large lesion in subfields of the piriform cortex and that the damage is most severe in 2 week-old animals. These data, together with other recent reports, show that there are multiple neuronal death-inducing pathways in the developing nervous system. It will be important to determine if anesthetics used in pregnant women and young children may have similar effects.

No genotoxic effect of propofol in chinese hamster ovary cells: analysis by sister chromatid exchanges

BACKGROUND

In spite of its high placental transfer, propofol is frequently used in general anesthesia and sedation during obstetric and gynecological surgery such as in vitro fertilization. This study investigated whether or not propofol has a genotoxic potential by the sister chromatid exchange assay in vitro.

METHODS

Sister chromatid exchanges induced after exposure to propofol were measured in Chinese hamster ovary cells with and without metabolic activation. After propofol (0.2-20 microg ml(-1)) diluted dimethyl sulfoxide was applied for 2 h with or without S9 mix, the cells having been incubated for two metaphases (34 h) in the presence of 5'-bromo-2-deoxyuridine. N-nitrosodimethylamine and mitomycin C were used as positive controls with and without metabolic activation. The chromosomes were stained with the fluorescence plus Giemsa method, and then sister chromatid exchanges in 50 cells were counted for each concentration.

RESULTS

Although increasing concentrations of propofol inhibited cell proliferation, no concentrations of propofol used in this study increased the sister chromatid exchange values, with and without metabolic activation.

CONCLUSION

It was concluded that there was no indication, from the sister chromatid exchange assay in mammalian cells, of a genotoxic effect of propofol and its metabolites.

[The neuroprotective effect of the glutamate antagonist acamprosate following experimental cerebral ischemia. A study with the lipid peroxidase inhibitor u-101033e]

INTRODUCTION

This study investigates the effects of acamprosate, a glutamatergic modulator, and the lipid peroxidation inhibitor U-101033E on neurological outcome following incomplete cerebral ischemia and reperfusion in rats.

MATERIAL AND METHODS

Twenty-seven male Sprague-Dawley rats were randomly assigned to one of the following treatment groups: 1 (n = 9, control, no drug treatment), 2 (n = 9, 2 x 200 mg/kg acamprosate i.p.), and 3 (n = 9, 2 x 0.3 mg/kg U-101033E i.v.). Background anesthesia was maintained using a combination of fentanyl and O2/N2O (FiO2 = 0.3). Ischemia was produced by combined unilateral common carotid artery ligation and hemorrhagic hypotension to a mean arterial blood pressure (MAP) of 35 mm Hg for 30 minutes. Functional neurological deficit was evaluated for the following 3 days after cerebral ischemia.

RESULTS

At the third postischemic day, five control animals and five animals treated with U-101033E were dead for stroke-related reasons. Surviving animals presented severe neurological deficits. In contrast, acamprosate improved neurological outcome, with stroke-related death occurring in one animal only and a minor neurological deficit in the surviving rats.

DISCUSSION

The present study demonstrates that acamprosate, in contrast to U-101033E, significantly reduces neurological deficits following transient hemispheric ischemia. The neuroprotective mechanisms of acamprosate may be related to its antiglutamatergic effect with consecutive reduction of transmembraneous Ca++ flux through NMDA-activated ion channels.

Differential neurotoxic effects of propofol on dissociated cortical cells and organotypic hippocampal cultures

BACKGROUND

Propofol is a widely used anesthetic agent for adults and children. Although extensive clinical use has demonstrated its safety, neurologic dysfunctions have been described after the use of this agent. A recent study on a model of aggregating cell cultures reported that propofol might cause irreversible lesions of gamma-aminobutyric acid-mediated (GABAergic) neurons when administered at a critical phase of brain development. We investigated this issue by comparing the effects of long-term propofol treatment on two models of brain cultures: dissociated neonatal cortical cell cultures and organotypic slice cultures.

METHODS

Survival of GABAergic neurons in dissociated cultures of newborn rat cortex (postnatal age, 1 day) treated for 3 days with different concentrations of propofol was assessed using histologic and cytochemical methods. For hippocampal organotypic slice cultures (postnatal age, 1 and 7 days), cell survival was assessed by measuring functional and morphologic parameters: extracellular and intracellular electrophysiology, propidium staining of dying cells, and light and electron microscopy.

RESULTS

In dissociated neonatal cell cultures, propofol induced dose-dependent lesions of GABAergic neurons and of glial cells. In contrast, no evidence for neurotoxic effects of propofol were found after long-term treatment of organotypic slice cultures. Excitatory transmission was not affected by propofol, and inhibitory transmission was still functional. Histologic preparations showed no evidence for cell degeneration or death.

CONCLUSION

Although long-term applications of propofol to dissociated cortical cell cultures produced degeneration and death of GABAergic neurons and glial cells, no such lesions were found when using a model of postnatal organotypic slice cultures. This conclusion is based on both functional and morphologic tests.

[Mobilization of alpha-glutathione S-transferase in the anesthetized patient]

OBJECTIVE

To measure and assess changes in plasma concentrations of alpha glutathione S-transferase (alpha-GST) during and after anesthesia with isoflurane, desflurane and propofol.

PATIENTS AND METHODS

Study of 90 ASA I and II patients scheduled for lumbar back surgery under general anesthesia assigned randomly to one of three groups to receive anesthetic maintenance with isoflurane, desflurane or propofol. We measured plasma levels of alpha-GST, aspartate aminotransferase aspartate, alanine aminotransferase, alkaline phosphatase, pseudocholinesterase, gamma glutamyltransferase and total bilirubin at baseline and several times during and after surgery.

RESULTS

Changes in plasma levels of alpha-GST were detected in all three groups, the tendency to increase reaching its peak with the sample taken at the end of anesthesia. The ranges considered normal were not exceeded in any of the patients studied.

CONCLUSIONS

By measuring alpha-GST changes in plasma, we have detected signs of disturbance in hepatocellular integrity after anesthesia with all three maintenance agents used. However, the slight and transitory nature of the events confirms the scarce hepatotoxic potential of isoflurane, desflurane and propofol.

Tiapride-induced catalepsy is potentiated by gamma-hydroxybutyric acid administration

1. The effect of administration of gammahydroxybutyrate (GHB) and tiapride, either alone or in combination, on catalepsy behavior was examined in male mice. 2. Catalepsy was measured by bar and grid tests. Two successive evaluations were carried out 30 and 60 min after injections. 3. Tiapride (175 and 200 mg/kg) and gammahydroxybutyrate (200 mg/kg) provoked an increase of catalepsy scores, exhibiting different time courses. GHB produced a marked but short lasting catalepsy with a peak of action at 30 min, while tiapride produced a catalepsy state with a peak of action at 60 min. 4. Tiapride-induced catalepsy was potentiated by gammahydroxybutyrate administration at 30 min (bar test) and 60 min (bar and grid tests). 5. These results underlie the view that GHB interacts with central dopamine D2 transmission.

Etomidate adversely alters determinants of left ventricular afterload in dogs with dilated cardiomyopathy

We tested the hypothesis that etomidate produces similar alterations in left ventricular (LV) afterload in dogs with normal LV function or dilated cardiomyopathy. Dogs were instrumented for LV and aortic pressures, and aortic blood flow. LV afterload was measured with aortic input impedance and quantified with a three-element Windkessel model. In one group of experiments, dogs (n = 6) were paced at 240 bpm for 18 +/- 2 days (mean +/- SEM). Hemodynamic data were recorded in sinus rhythm in the conscious state and during etomidate anesthesia (5, 10, and 20 mg x kg(-1) x h(-1)). Identical experiments were conducted in a separate group of chronically instrumented dogs not subjected to LV pacing (n = 6). No changes in heart rate and arterial and LV pressures were observed during etomidate anesthesia in cardiomyopathic dogs. There were decreases in arterial and LV systolic pressure during the administration of 20 mg x kg(-1) x h(-1) etomidate to dogs with normal LV function. Etomidate significantly (P < 0.05) increased total arterial resistance (R; 3220 +/- 290 dynes x s x cm(-5) during control to 6110 +/- 790 dynes x s x cm(-5) during 10 mg x kg(-1) x h(-1)) and characteristic aortic impedance (Zc; 141 +/- 22 dynes x s x cm(-5) during control to 161 +/- 23 dynes x s x cm(-5) during 20 mg x kg(-1) x h(-1)) and decreased total arterial compliance (C; 0.70 +/- 0.15 mL/mm Hg during control to 0.45 +/- 0.07 mL/mm Hg during 10 mg x kg(-1) x h(-1)) in cardiomyopathic but not healthy dogs. Etomidate markedly reduced mean aortic blood flow (2.26 +/- 0.17 L/min during control to 1.39 +/- 0.20 L/min during 10 mg x kg(-1) x h(-1)) and increased the time constant of LV relaxation (54 +/- 3 ms during control to 74 +/- 9 ms during 20 mg x kg(-1) x h(-1)) in dogs with LV failure. Arterial pressure is maintained during etomidate anesthesia in the presence of LV dysfunction as a result of increases in R and Zc and decreases in C. These deleterious increases in LV afterload further compromise LV systolic and diastolic performance in dogs with dilated cardiomyopathy.

IMPLICATIONS

The results of this investigation indicate arterial pressure is maintained during etomidate anesthesia as a consequence of increases in left ventricular (LV) afterload that further diminish LV systolic and diastolic performance in the presence of impaired LV function.

An evaluation of propofol toxicity on mouse oocytes and preimplantation embryos

Mouse biological assays were used to investigate potential adverse effects of propofol on the oocyte's competence to fuse with spermatozoa and on the embryo's ability to develop to the blastocyst stage. Cumulus-enclosed metaphase II oocytes were exposed for 1 h to 0.01, 0.1, 0.4, 1 and 10 microg/ml propofol (Diprivan) and subjected to a sperm-oocyte fusion test based on the dye (Hoechst 33342) transfer technique. Oocytes exposed to 0.4, 1 and 10 microg/ml propofol showed a significant reduction in the rate of sperm fusion and underwent pronuclei formation at a rate similar to that of sperm fusion. In a second trial, mouse 1-cell and 2-cell embryos were exposed to varying propofol concentrations for 14h and then checked for subsequent development. Although adverse effects were not observed in 2-cell embryos, treatment of 1-cell embryos with propofol concentrations ranging from 0.01 to 10 microg/ml resulted in the inhibition of cleavage to blastocyst stage. We conclude that propofol can negatively influence fertilization in the mouse by impairing the oocyte's ability to fuse with spermatozoa, without interfering with the sperm-induced activation of the cell cycle. Moreover, we document the peculiar sensitivity to propofol of mouse 1-cell embryos as compared with 2-cell embryos.

Respiratory depression and apnea induced by propofol in dogs

OBJECTIVE

To determine the maximal i.v. administered dose of propofol that would not induce a serious adverse event in nonsedated dogs.

ANIMALS

6 clinically normal dogs (3 males and 3 females) between 8 and 12 months old and weighing between 8.8 and 11.3 kg.

PROCEDURE

Propofol was administered i.v. at an initial dosage of 6.5 mg/kg of body weight at a rate of 20 mg/10 s. Subsequent doses were incrementally increased by 2.5 mg/kg (eg, second dose: 9 mg/kg) and separated by a minimum of 3 days. This procedure was repeated until a dose that induced a serious respiratory, cardiovascular, or neurologic adverse effect was determined.

RESULTS

Apnea was determined to be the serious adverse effect for all dogs. Duration of apnea varied between dogs, but increased in a dose-dependent manner at dosages > 14 mg/kg.

CONCLUSIONS

Respiratory depression and apnea are the most likely adverse effects induced by i.v. administration of propofol to dogs. Propofol administered i.v. at a rate of 20 mg/kg/10 s induces minimal cardiovascular depression at dosages in excess of the apneic dosage.

CLINICAL RELEVANCE

Respiratory depression and apnea should be expected as potential adverse effects after i.v. administration of propofol to dogs, particularly when administered at rapid rates of infusion.

Sites of action of gamma-hydroxybutyrate (GHB)--a neuroactive drug with abuse potential

OBJECTIVE

This review highlights the biochemistry, pharmacology, and toxicology of the naturally-occurring fatty acid derivative, gamma-hydroxybutyrate (GHB). GHB is derived from gamma-aminobutyric acid (GABA) and is proposed to function as an inhibitory chemical transmitter in the central nervous system.

CONTENT

When administered in pharmacological doses, its powerful central nervous system depressant effects are readily observed. Although some of the neurophysiological actions of GHB could involve alterations in dopaminergic transmission in the basal ganglia, both its physiological and pharmacological actions are probably mediated through specific brain receptors for GHB. In addition, GHB might mediate some of its effects through interaction with the GABA(B) receptor. Experimentally, GHB has been used as a model for petit mal epilepsy; clinically, it has been used as a general anesthetic and as a drug to treat certain sleep disorders and related conditions. Owing to the purported ability of GHB to induce a state of euphoria, recreational use of this substance is popular. Although no deaths or long-term problems have been associated with GHB abuse, symptoms of GHB intoxication can be severe. The continued potential for GHB abuse makes it imperative for clinical toxicologists to be aware of the effects of this agent. Future research on the mechanism of action of GHB is needed to elucidate both its central nervous system depressant properties and its ability to effect a state of well-being.

The effect of the anaesthetic, Propofol, on in-vitro oocyte maturation, fertilization and cleavage in mice

Propofol is a common anaesthetic agent used for oocyte retrieval procedures during in-vitro fertilization (IVF). The effect of Propofol in vitro on mouse oocyte maturation, fertilization and embryo cleavage was studied. In this study, 551 cumulus-free and 222 cumulus-enclosed oocytes from mice stimulated with pregnant mare's serum gonadotrophin (PMSG) were incubated for 30 min in medium containing 0, 100, 1000 or 10,000 ng/ml of Propofol prior to in-vitro maturation. Also, 325 cumulus-enclosed oocytes from mice stimulated to ovulate with PMSG/human chorionic gonadotrophin (HCG) were incubated for 30 min in similar concentrations of Propofol prior to IVF. Maturation, fertilization and cleavage rates were compared. A significant decrease in the in-vitro maturation rate was observed only when the cumulus-free and cumulus-enclosed oocytes were exposed to 10,000 ng/ml Propofol (P < 0.0074 and P < 0.0001 respectively). Fertilization and embryo cleavage rates were not significantly different compared with the controls. These findings give some reassurance with respect to human IVF. However, further studies on the potential effects of Propofol on implantation and pregnancy outcome following IVF are needed.

Propofol: pro- or anticonvulsant?

The pro- or anticonvulsant properties of propofol remain a matter of controversy. Although numerous case reports describe the appearance of abnormal movements, posturing and seizure-like activity related to the use of propofol, systematic studies in both humans and animals strongly suggest that it possesses antiepileptic properties. Propofol consistently reduces the seizure duration during electroconvulsive therapy, its use has been successful in controlling refractory status epilepticus and in animals it offers a strong protection against lignocaine- or pentylene-tetrazol-induced epilepsy. The beneficial effects of propofol may be related to its uniform depressant action on the central nervous system, to a potentialization of GABA-mediated pre- and postsynaptic inhibition, and by decreasing the release of excitatory transmitters, glutamate and aspartate.

Negative and selective effects of propofol on isolated swine myocyte contractile function in pacing-induced congestive heart failure

BACKGROUND

Although propofol (2-6 di-isopropylphenol) is commonly used to induce and maintain anesthesia and sedation for surgery, systematic hypotension and reduced cardiac output can occur in patients with or without intrinsic cardiac disease. The effect of propofol on myocyte contractility after the development of congestive heart failure (CHF) remains unknown. This study tested the hypothesis that propofol would have direct effects on myocyte contractile function in both healthy and CHF cardiac myocyte preparations.

METHODS

Isolated left ventricular (LV) myocyte contractile function (shortening velocity, micron/s) was examined in myocytes from five control pigs and in five pigs with pacing-induced CHF (240 beats/min, for 3 weeks) in the presence of propofol concentrations ranging from 1-6 micrograms/ml. In addition, myocyte contractility in response to beta-adrenergic receptor stimulation (isoproterenol, 10-50 nM) in the presence of propofol (3 micrograms/ml) was examined.

RESULTS

Three weeks of pacing caused LV dysfunction consistent with CHF as evidenced by increased LV end-diastolic diameter (control 3.3 +/- 0.1 cm vs. CHF 5.6 +/- 0.2 cm; P < 0.05) and reduced LV fractional shortening (control 34 +/- 3% vs. CHF 12 +/- 2%, P < 0.05). Propofol (6 micrograms/ml) caused a concentration-dependent negative effect on velocity of shortening from baseline in both control (67 +/- 2 microns/s vs. 27 +/- 3 microns/s; P < 0.05) and CHF myocytes (29 +/- 1 microns/s vs. 15 +/- 1 microns/s; P < 0.05). Importantly, CHF myocytes were more sensitive than control myocytes to the negative effects of propofol on velocity of shortening at the lower concentration (1 microgram/ml). beta-adrenergic responsiveness was reduced by propofol (3 micrograms/ml) in control myocytes only.

CONCLUSIONS

Propofol has a direct and negative effect on basal myocyte contractile processes in the setting of CHF, which is more pronounced than that on healthy myocytes at reduced propofol concentrations.

Influence of urethane anesthesia on neural processing in the auditory cortex analogue of a songbird

Functional maps of auditory response areas were derived from multi-unit recordings in the caudal telencephalon of the starling (Sturnus vulgaris L.). A regular grid of recording sites with distances of 200 microns horizontally and 100 microns vertically was placed over the auditory cortex analogue. Within one plane, mapping of auditory responses was first performed in the awake bird and then repeated under urethane anesthesia. The data from both experimental approaches differ considerably. Urethane reduces the spontaneous discharge rate significantly. Under anesthesia, inhibition decreases in all auditory subunits. Excitation is less affected. Eight auditory subcenters were divided into three groups according to the changes in their excitatory responses. In the first group 'on' and sustained excitation changed only weakly. These areas are thought to receive direct inputs from the diencephalon. In the second group, 'on' and sustained excitation are substantially reduced. These subcenters seem to receive projections from other forebrain areas. In subunits of the third group, an increase in sustained excitation is correlated to a decrease in inhibition. Within some specific centers, distinct natural calls, for example the bird's own song, elicit stronger responses under anesthesia than other stimuli.

Inhibitory effects of propofol on catecholamine secretion and uptake in cultured bovine adrenal medullary cells

In the central and peripheral noradrenergic neurons, the balance between noradrenaline release and reuptake determines the level of noradrenaline at the synaptic cleft or the nerve ending. In the present study, we examined the effects of propofol, an intravenous general anaesthetic, on catecholamine secretion and noradrenaline uptake in cultured bovine adrenal medullary cells and on the serum noradrenaline and blood pressure in rats. In cultured adrenal medullary cells, propofol (10-50 mumol/l) concentration-dependently inhibited catecholamine secretion stimulated by carbachol. Propofol suppressed carbachol-evoked 22Na+ influx as well as 45Ca2+ influx at concentrations similar to those which suppressed the catecholamine secretion. Propofol (10-50 mumol/l) also inhibited veratridine-evoked 22Na+ influx, 45Ca2+ influx and catecholamine secretion, whereas it had little effect on the 45Ca2+ influx and catecholamine secretion induced by 56 mmol/l K+. Cultured adrenal medullary cells show [3H] noradrenaline uptake which is sensitive to imipramine. Propofol (10-50 mumol/l) significantly inhibited the imipramine-sensitive uptake of [3H] noradrenaline. In rats, intravenous administration of propofol (2.5 mg/kg) lowered serum noradrenaline and arterial blood pressure. From these findings, in spite of inhibiting noradrenaline uptake, propofol at anaesthetic concentrations (10-30 mumol/l) seems to reduce catecholamine secretion by interfering with Na+ influx through voltage-dependent Na+ channels as well as nicotinic acetylcholine receptor-associated ion channels in the adrenal medulla and, probably, in the sympathetic nervous system. This may explain the propofol-induced hypotension during anaesthesia.

Micronuclei induced in round spermatids of mice after stem-cell treatment with chloral hydrate: evaluations with centromeric DNA probes and kinetochore antibodies

The chromosomal effects of chloral hydrate (CH) on germ cells of male mice were investigated using two methods to detect and characterize spermatid micronuclei (SMN); (a) anti-kinetochore immunofluorescence (SMN-CREST) and (b) multicolor fluorescence in situ hybridization with DNA probes for centromeric DNA and repetitive sequences on chromosome X (SMN-FISH). B6C3F1 mice received single intraperitoneal (i.p.) injections of 82.7, 165.4, or 413.5 mg/kg and round spermatids were sampled at three time intervals representing cells treated in late meiosis, early meiosis, or as spermatogonial stem cells. No increases in the frequencies of SMN were detected for cells treated during meiosis using either SMN-CREST or SMN-FISH methods. After spermatogonial stem-cell treatment, however, elevated frequencies of SMN were detected by both methods. With SMN-FISH, dose trends were observed both in the frequencies of spermatids containing micronuclei and in the frequency of spermatids carrying centromeric label. These findings corroborate the recent report by Allen and colleagues [Allen JW et al.(1994): Mutat. Res. 323:81-88] that CH treatment of spermatogenic stem cells induced SMN. Furthermore, our findings suggest that chromosomal malsegregation or loss may occur in spermatids long after CH treatment of stem cells. Further studies are needed to understand the mechanism of action of the CH effect on stem cells and to determine whether similar effects are induced in human males treated with CH.

Focal cerebral ischemia during anesthesia with etomidate, isoflurane, or thiopental: a comparison of the extent of cerebral injury

An investigation was performed to compare the cerebral protective properties of etomidate, isoflurane, and thiopental. In separate groups of spontaneously hypertensive rats, etomidate, isoflurane, or thiopental was administered to achieve and maintain burst-suppression of the electroencephalogram (3-5 bursts/min) for the duration of the experiment. A fourth group received 1.2 minimal alveolar concentration halothane. All groups underwent 3 hours of middle cerebral artery occlusion and then 2 hours of reperfusion. Thereafter, the animals were killed and the volume of injured brain was determined by staining with 2,3,5-triphenyltetrazolium. Physiological parameters did not differ among the four groups during the investigation, with the exception that hemolysis occurred in the etomidate group (free hemoglobin levels, approximately 0.4 g.dl-1). The volume of injured brain in the thiopental group (56 +/- 10 mm3) was significantly smaller than that in the halothane control group (99 +/- 13 mm3). The volumes of injured brain in the etomidate and isoflurane groups (145 +/- 11 mm3 and 139 +/- 14 mm3, respectively) were significantly larger than those in the control and thiopental groups. We speculate that the apparently detrimental effect of etomidate may be the result of the binding of nitric oxide of cerebral endothelial origin by the iron component of free hemoglobin. Intracranial pressure was not recorded, and in the isoflurane group, there may have been adverse effects on cerebral perfusion pressure associated with vasodilation caused by high concentrations of isoflurane. The results are consistent with a protective effect by barbiturates.