Tolerance to the hypnotic and electroencephalographic effect of gamma-hydroxybutyrate in the rat: pharmacokinetic and pharmacodynamic aspects

Tolerance to gamma-hydroxybutyrate (GHB) has been suggested in illicit users and has been described for the hypnotic effect in the rat. The aim of this study was to investigate whether tolerance is also observed for the EEG effect, and whether the EEG can give insight into the pharmacodynamic aspects of GHB tolerance. In three series of experiments, rats were pre-treated with either the GHB precursor gamma-butyrolactone (GBL) or saline intraperitoneally twice daily. In the first series, a reduction in sleeping time was observed in the GBL pre-treated rats compared with controls. In the second series, a fast infusion of GHB (300 mg kg(-1) over 5 min) was given after 10 days pre-treatment. The GHB plasma concentration-time curves showed a slightly faster decrease in GHB concentration in the GBL pre-treated rats, suggesting a small induction of the GHB metabolism (V(max) = 2882 +/- 457 microg min(-1) kg(-1) vs 2205 +/- 315 microg min(-1) kg(-1), P < 0.01). In contrast to controls, GBL pre-treated rats did not lose righting reflex. In the third series, a slow infusion of 480 mg kg(-1) h(-1) was given after 7 days pre-treatment, which allowed fitting a sigmoid E(max) model to the EEG amplitude versus GHB plasma concentration curve. This showed reduced end-organ sensitivity to GHB in the GBL pre-treated rats (EC50 (concentration required to obtain 50% depression of the baseline effect) = 653+/- 183 microg mL(-1) vs 323 +/- 68 microg mL(-1), P < 0.001). In conclusion, chronic pre-treatment with gamma-butyrolactone in the rat results in a reduced sleeping time and this tolerance is reflected by the EEG. This can mainly be explained by reduced end-organ sensitivity.     

The lack of effect of opioid agonists and antagonists on some acute effects of ethanol

We studied the ability of opioid antagonists: naloxone, naltrexone and diprenorphine and an opioid agonist morphine to influence the effects of ethanol on hypothermia, sleeping time and impairment of aerial righting reflex. Naltrexone (2-16 mg/kg) and naloxone (2-16 mg/kg) were not able to attenuate effects of ethanol, while diprenorphine decreased ethanol sleeping time (4 microgram/kg) and antagonized the ethanol hypothermia (8 microgram/kg). Naltrexone in a dose of 8 mg/kg sc antagonized the ethanol impairment of aerial righting reflex. The present behavioral studies did not provide any evidence for the participation of the opioid system in the mediation of acute ethanol effects in rats.     

Interaction of Sambucus nigra Flower and Berry Decoctions with the Actions of Centrally Acting Drugs in Rats

The effect of flower and berry decoctions of Sambucus nigra on the hypnotic action of phenobarbitone (30 mg/ml) and the analgesic action of morphine (5 mg/ml) in rats is described. Wistar laboratory rats received 2 ml/kg of either flower (1 : 10) or berry decoction (1 : 10) orally 2 h before and simultaneously with the investigated drugs injected subcutaneously. The hypnotic action of pentobarbitone in the animals as the onset of loss of righting reflex (sleep induction time) was assessed as the time interval between the loss and regaining of righting reflex (sleeping time). The analgesic action of morphine was measured as the reaction time to radiation heat directed onto the rat tail. Both decoctions caused a significant decrease of the sleep induction time of pentobarbitone, and increased sleeping time, compared with control (only pentobarbitone). Berry decoctions significantly decreased the analgesic action of morphine.     

Sedative and motor-impairing effects of neuropeptide Y and ethanol in selectively bred P and NP rats

Past findings suggest a positive association between endogenous neuropeptide Y (NPY) activity and ethanol-induced sedation, and there is evidence for additive effects of administered NPY with sedative-hypnotics. The present investigation examined the effects of intracerebroventricular NPY injection on ethanol-induced sedation and motor impairment in selectively bred alcohol-preferring (P) and -nonpreferring (NP) rats. In Experiment 1, P and NP rats were assessed for loss and recovery of righting reflex (RR) following infusion with either NPY (10.0 microg) or aCSF followed by ethanol injection (2.5 g/kg ip). NPY reduced time to lose RR and increased time to regain RR similarly in P and NP rats. Blood-ethanol levels (BELs) were lower at time of recovery in NPY-treated rats relative to aCSF controls. Thus, NPY enhanced ethanol-induced sedation. In Experiment 2, P and NP rats pretreated with either saline or ethanol (1.0 g/kg ip) were assessed for motor activity following infusion with either NPY (2.5, 5.0, or 10.0 microg) or aCSF. Ethanol alone and NPY alone suppressed motor activity, but there were no additive effects between the two. Taken together, these results provide partial support for past observations of additivity between NPY and drug-induced sedation, and suggest a role for NPY in the neurobehavioral effects of acute ethanol exposure.     

Gamma butyrolactone (GBL) and gamma valerolactone (GVL): similarities and differences in their effects on the acoustic startle reflex and the conditioned enhancement of startle in the rat

Gamma butyrolactone (GBL) is metabolized to gamma hydroxybutyrate (GHB) in the body. GHB is a DEA Schedule 1 compound; GBL is a DEA List 1 chemical. Gamma valerolactone (GVL) is the 4-methyl analog of GBL; GVL is metabolized to 4-methyl-GHB; GVL is NOT metabolized to GBL or GHB. The effects of GBL (18.75-150 mg/kg), GVL (200-1600 mg/kg) or vehicle on the acoustic startle reflex (ASR), and the classically-conditioned enhancement of startle, the Startle Anticipated Potentiation of Startle (SAPS) response were studied in male rats. Both compounds produced a dose-dependent reduction of ASR, with GBL 5-7 times more potent than GVL. In contrast, GBL treatment significantly reduced SAPS at doses that exerted only moderate effects on ASR, whereas GVL exerted little or no effect on the SAPS, except at doses that produced pronounced reductions in Noise Alone ASR. In a second experiment, rats were tested for Noise Alone ASR behavior following treatment with a single mid-range dose of GBL (75 mg/kg), GVL (400 mg/kg) or vehicle; immediately following startle testing the animals were sacrificed and their brains and blood were collected for determination of GHB, 4-methyl-GHB, GBL and GVL. GHB was found in measurable concentrations in all of the blood specimens and 6 (of 8) of the brain specimens from the GBL-treated subjects. 4-Methyl-GHB was found in measurable concentrations in all of the blood and brain specimens of the GVL-treated subjects; the change in startle amplitude was inversely correlated to the brain concentrations of these compounds. These findings confirm the differences in the metabolic fate of GBL and GVL as pro-drugs for the formation of GHB and 4-methyl-GHB, respectively. Moreover, the dissimilarity in effect profile for GBL and GVL on ASR versus SAPS behaviors suggests that different receptor(s) may be involved in mediating these behavioral effects.     

Kinetics of drug action in disease states. XXXVI: Effect of cyclosporine on the pharmacodynamics and pharmacokinetics of a barbiturate (heptabarbital) in rats

Pretreatment with cyclosporine reportedly prolongs the effect of certain general anesthetics in humans and the sleeping time of mice after pentobarbital administration. This investigation was designed to determine the mechanism(s) of the cyclosporine-barbiturate interaction. Adult female Wistar rats received cyclosporine (50 mg/kg im) or saline solution daily for 3 days. On the third day, they were injected with heptabarbital (45 mg/kg iv). Other cyclosporine-treated and control groups were infused with heptabarbital until they lost their righting reflex. Treatment for 3 d with cyclosporine was associated with decreased rectal temperature, decreased magnesium concentrations in serum and CSF, increased serum creatinine and urea nitrogen concentrations, elevated serum aspartate aminotransferase activity and total bilirubin concentration, decreased serum total protein concentration, and increased hematocrit. These physiologic changes are consistent with the clinically observed hypomagnesemia, nephrotoxicity, and hepatotoxicity in patients treated with cyclosporine. Control rats slept for 90 +/- 14 min (mean +/- SD, n = 9) after heptabarbital injection, whereas cyclosporine-pretreated rats slept for 154 +/- 22 min. Compared with controls, cyclosporine-pretreated rats awoke (after heptabarbital injection) and went to sleep (after heptabarbital infusion) with significantly lower barbiturate concentrations in serum and CSF. Pretreatment with a single 60-mg/kg im dose of cyclosporine 2 h before heptabarbital infusion caused no significant biochemical changes approximately 160 min later, except for elevated serum aspartate aminotransferase (which occurred also after injection of the surfactant-containing vehicle) and serum bilirubin. Again, heptabarbital concentrations at onset of sleep (loss of righting reflex) in serum, brain, and CSF of cyclosporine-treated rats were significantly lower than in saline-treated controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endogenous gamma-aminobutyric acid (GABA)(A) receptor active neurosteroids and the sedative/hypnotic action of gamma-hydroxybutyric acid (GHB): a study in GHB-S (sensitive) and GHB-R (resistant) rat lines

In the rat brain, gamma-hydroxybutyric-acid (GHB) increases the concentrations of 3alpha-hydroxy,5alpha-pregnan-20-one (allopregnanolone, 3alpha,5alpha-THP) and 3alpha,21-dihydroxy,5alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone/3alpha,5alphaTHDOC), two neurosteroids acting as positive allosteric modulators of gamma-aminobutyric acid (GABA)(A) receptors. This study was aimed at assessing whether neurosteroids play a role in GHB-induced loss of righting reflex (LORR). Basal and GHB-stimulated brain concentrations of endogenous 3alpha,5alpha-THP and 3alpha,5alpha-THDOC were analyzed in two rat lines, GHB-sensitive (GHB-S) and GHB-resistant (GHB-R), selectively bred for opposite sensitivity to GHB-induced sedation/hypnosis. Basal neurosteroid concentrations were similar in brain cortex of the two rat lines. However, in male GHB-S rats, administration of GHB (1000 mg/kg, i.p., 30 min) increased brain cortical concentrations of 3alpha,5alpha-THP and 3alpha,5alpha-THDOC 7- and 2.5-fold, respectively, whilst male GHB-R animals displayed only a 4- and 2-fold increase, respectively. In GHB-S rats this increase lasted up to 90 min and declined 180 min following GHB administration, a time course that matches LORR onset and duration. In contrast, in GHB-R rats, which failed to show GHB-induced LORR, brain cortical 3alpha,5alpha-THP and 3alpha,5alpha-THDOC had returned to control values within 90 min. At onset of LORR, a similar increase in brain cortical levels of 3alpha,5alpha-THP and 3alpha,5alpha-THDOC (2-3-fold) was observed in GHB-S female rats and in the few female GHB-R rats that lost the righting reflex after GHB administration, but not in female GHB-R rats failing to show LORR. Sub-hypnotic doses (7.5 and 12.5 mg/kg, i.p.) of pregnanolone, administered 10 min before GHB, dose-dependently facilitated the expression of GHB-induced LORR in GHB-R male rats. These results suggest that the GHB-induced increases of brain 3alpha,5alpha-THP and 3alpha,5alpha-THDOC concentrations are implicated in the eliciting of the sedative/hypnotic action of GHB.     

The interaction between ethanol and cysteine on the central depressant effects of ethanol in mice

In this study male Swiss-Webster mice were used to examine the effects of cysteine (ICV), a precursor in the biosynthesis of taurine, on ethanol-induced loss of the righting reflex. The interaction of ethanol with gamma-aminobutyric acid (GABA) and isethionic acid, a metabolite of taurine, was also investigated on ethanol-induced central nervous system depression as measured by loss of the righting reflex experiments. Immediately after the animals regained the righting reflex following ethanol injection (IP) mice received an ICV injection of saline, cysteine (1, 15 or 25 mumol/kg), GABA (1, 15 or 25 mumol/kg) or isethionic acid (25 or 50 mumol/kg). Upon ICV administration of cysteine or GABA the mice again lost the righting reflex. This effect occurred immediately and in a dose-dependent manner. The compound, isethionic acid, failed to cause a second loss of the righting reflex following ethanol administration (IP). In the absence of ethanol cysteine or GABA (25 mumol/kg, ICV) did not produce a substantial loss of the righting reflex in mice. In another experiment mice were pretreated (IP) with L-2-oxothiazolide-4-carboxylate (OTC) 2 hr prior to ethanol administration (IP). OTC is a compound which can be converted to cysteine in the body. In the presence of ethanol OTC (15 mmol/kg) caused an enhancement of ethanol-induced central nervous system depression under certain conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of combining ethanol (EtOH) with gamma-hydroxybutyrate (GHB) on the discriminative stimulus, locomotor, and motor-impairing functions of GHB in mice

Rationale Gamma-hydroxybutyrate (GHB) is a drug of abuse that is often coabused with ethanol (EtOH) and has been implicated as a date rape agent in conjunction with EtOH. Much information is lacking regarding the manner in which GHB interacts with EtOH. Objective This study was designed to further characterize the behavioral effects of GHB alone and in combination with EtOH in male Swiss–Webster mice. Methods The effects of GHB (0.1–1.0 g/kg) and EtOH (2.0–5.0 g/kg) alone, as well as the effects of GHB in combination with EtOH, were examined using an automated locomotor activity procedure, a functional observational battery (FOB) and a GHB drug discrimination procedure. Results GHB decreased, whereas EtOH had little effect on locomotor activity. In the FOB, EtOH dose-dependently decreased activity in combination with 0.3 g/kg GHB. Alone, each drug had little effect on the righting reflex, but combining ineffective doses of GHB and EtOH significantly impaired righting. GHB and EtOH decreased forelimb grip strength. Combinations of ineffective doses of GHB and EtOH decreased forelimb grip strength when given together. GHB and EtOH impaired inverted screen performance, and EtOH increased the impairing effects of low, but not high, doses of GHB. GHB and EtOH increased hind limb splay, and EtOH increased the effects of 0.1 and 0.3 g/kg GHB on splay. GHB and EtOH decreased body temperature, and EtOH augmented the temperature-decreasing effects of GHB. EtOH produced less than 50% GHB-like discriminative stimulus effects, and GHB failed to alter the GHB-like discriminative stimulus effects of EtOH. Conclusions Overall, EtOH increased the effects of GHB on several gross measures of behavior and only partially occasioned the discriminative stimulus properties of GHB.     

NMDA enhances the central depressant properties of ethanol in mice.

Male Swiss-Webster mice were used to examine the effect of NMDA on the ethanol-induced loss of the righting reflex (LORR). The LORR was used as a measure of CNS depression. Immediately after animals regained the righting reflex following ethanol injection (4.0 g/kg, IP) mice received an ICV injection of saline or NMDA (10, 50, 100, or 500 nmol/kg) in a volume of 5 microliters. Upon ICV injection of NMDA, mice again lost the righting reflex and this effect of NMDA in the presence of ethanol occurred rapidly and in a dose-dependent manner. In another experiment DL-2-amino-5-phosphonovaleric acid (APV), a competitive antagonist of NMDA, was given ICV with NMDA (50 nmol/kg) in the presence of ethanol. APV (10 and 100 nmol/kg, ICV) significantly attenuated the response of NMDA to enhance the depressant action of ethanol. When bicuculline methiodide, an antagonist of GABA, was given ICV with NMDA (50 nmol/kg), bicuculline methiodide reduced the effect of NMDA to produce a second loss of the righting reflex (return to the LORR) in the presence of ethanol. When NMDA (100 nmol/kg, ICV) was injected in the absence of ethanol into mice, NMDA by itself did not produce a loss of the righting reflex. In this investigation, the results suggest that NMDA can augment ethanol-induced depression possibly through an interaction between glutamatergic and GABAergeric systems in the CNS.     

Role of GABA(B) receptors in the sedative/hypnotic effect of gamma-hydroxybutyric acid.

The present study was aimed at identifying the receptor systems involved in the mediation of the sedative/hypnotic effect of gamma-hydroxybutyric acid (GHB) in DBA mice. Administration of the putative antagonist of the GHB binding site, 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS-382; 50-500 mg/kg, i.p.), significantly increased the duration of loss of righting reflex induced by GHB (1000 mg/kg, i.p.). In contrast, the GABA(B) receptor antagonists, (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911; 25-100 mg/kg, i.p.) and (3-aminopropyl)(cyclohexylmethyl)phosphinic acid (CGP 46381; 12.5-150 mg/kg, i.p.), completely prevented the sedative/hypnotic effect of GHB. SCH 50911 (100 and 300 mg/kg, i.p.) was also capable to readily reverse the sedative/hypnotic effect of GHB (1000 mg/kg, i.p.) in mice that had lost the righting reflex. SCH 50911 (100 mg/kg, i.p.) also completely abolished the sedative/hypnotic effect of the GABA(B) receptor agonist, baclofen. These results indicate that the sedative/hypnotic effect of GHB is mediated by the stimulation of GABA(B) receptors and add further support to the hypothesis that the GABA(B) receptor constitutes a central site of action of GHB.     

Differences in response to the aversive properties and activity effects of low dose ethanol in LAS and HAS selectively bred rats

Rats selectively bred for high alcohol sleep times (HAS) and those that are less affected (LAS) by hypnotic doses (3.0–3.6 g/kg) of ethanol were tested for differential responses to the aversive effects of 1.0 g/kg ethanol in a conditioned place preference task. Likewise, the effects of 0.3–1.0 g/kg ethanol on spontaneous locomotor activity over a 30-min period, as well as the loss of righting reflex with a higher ethanol dose (3.0 g/kg), were determined in these animals. The LAS rats reacted more aversively to 1.0 g/kg during conditioned place aversion testing than the HAS animals and also had a shorter mean sleeping time following 3.0 g/kg ethanol. Furthermore, dose-related depression of spontaneous motor activity was seen in the HAS animals and not in the LAS animals over a 30-min period using doses of 0.3, 0.6, or 1.0 g/kg (10% w/v) ethanol. Taken together, the results indicate that the intoxicating sequelae of high ethanol doses, such as ataxia and sedation, may not be correlated with the aversive effects of low ethanol doses.     

Pharmacological and Metabolic Interactions between Ethanol and Methyl n-Butyl Ketone, Methyl Isobutyl Ketone, Methyl Ethyl Ketone, or Acetone in Mice

Methyl n-butyl ketone (MnBK), methyl isobutyl ketone (MIBK),methyl ethyl ketone (MEK), and acetone are widely used industrialsolvents to which certain groups of workers are exposed. Pharmacologicaland metabolic interactions between these solvents and ethanolwere explored in male CD-1 mice. The effects of these solventson the duration of ethanol-induced loss of righting reflex andon ethanol elimination in mice were studied. The solvents weredissolved in corn oil and injected intraperitoneally 30 mm beforeethanol 4 g/kg ip. The four solvents prolonged significantlythe duration of ethanol-induced loss of righting reflex whengiven in the following doses (m mol/kg): MnBK, 3.75 and 5; MIBK,5; MEK, 5 and 10, acetone, 20 and 40. This prolongation wasdose related and increased as the dose of the solvent was increased.The concentrations of ethanol in blood or brain on return ofthe righting reflex were similar in solvent-treated and controlanimals, with the exception of the group of mice treated with40 mmol/kg acetone in which the ethanol concentrations weresignificantly lower than in control animals. The mean eliminationrate of ethanol was markedly reduced in mice treated with MnBK5 mmol/kg, MEK 15 mmol/ kg, and acetone 40 mmol/kg. All foursolvents reduced the activity of mouse liver alcohol dehy-drogenasein vitro. It is concluded that enhancement of the ethanol-inducedloss of righting reflex by these solvents in mice is well correlatedto reduced elimination rate of ethanol.     

Cysteine sulfinic acid can enhance the central depressant effect of ethanol in mice.

The interaction between ethanol and cysteine sulfinic acid was examined in male Swiss-Webster mice. The loss of the righting reflex (LORR) was used as a measurement of central nervous system depression. In addition, the interaction between ethanol and cysteic acid, a metabolite of cysteine sulfinic acid, was studied. Immediately after the animals regained the righting reflex following ethanol injection (IP), mice were given an ICV injection of saline, cysteine sulfinic acid (1, 15 or 25 mumol/kg) or cysteic acid (1, 15, or 25 mumol/kg). There occurred a return to the LORR within 30 s after the ICV injection of drugs. The return to the LORR by the administration of the amino acids in the presence of ethanol occurred in a dose-dependent fashion. When cysteine sulfinic acid or cysteic acid (25 mumol/kg, ICV) was injected in the absence of ethanol, no loss of the righting reflex occurred. In other experiments, bicuculline methiodide was given ICV with cysteine sulfinic acid (25 mumol/kg), cysteic acid (25 mumol/kg), or GABA (25 mumol/kg) in the presence of ethanol. Bicuculline methiodide, a GABA antagonist, reduced the effects of the three amino acids to produce a return to the LORR in the presence of ethanol. These results indicate that cysteine sulfinic acid, an excitatory amino acid, and cysteic acid can enhance the central depressant properties of ethanol. Since bicuculline antagonized the effects of these two amino acids, a GABAergic mechanism may be involved in the interaction between ethanol and cysteine sulfinic acid or cysteic acid.     

Acute and subchronic neurotoxicological evaluation of tetrahydrofuran by inhalation in rats.

Groups of adult male and female rats received exposure to tetrahydrofuran (THF) vapor by inhalation in acute or subchronic exposure scenarios. Acute exposure concentrations were 0, 500, 2500, or 5000 ppm for 6 hr. Evaluations conducted immediately after exposure included clinical observations, motor activity assessments (MA), and a battery of functional tests (FOB) designed to reveal nervous system dysfunction. During exposure to 2500 and 5000 ppm, rats had a diminished or absent startle response to a punctate auditory alerting stimulus. Following exposure to 5000 ppm, male and female rats were lethargic, exhibited abnormal gait or mobility, and splayed rear feet. Lethargy and splayed rear feet were also observed in females exposed to 2500 ppm. During the subsequent FOB, males exposed to 5000 ppm had a lower incidence of palpebral closure, higher incidences of slow or absent righting reflex, and a biphasic pattern of reduced motor activity followed by increased motor activity. Females exposed to 5000 ppm had increased incidences of palpebral closure in the open field, increased incidences of slow or absent righting reflex, and decreased motor activity. During the 14-week subchronic exposure series, daily THF exposure concentrations were 0, 500, 1500, or 3000 ppm, and neurobehavioral evaluations occurred on non-exposure days at approximately monthly intervals. Diminished startle responses to an auditory alerting stimulus were observed during exposure to 1500 or 3000 ppm; however, repeated exposures did not cause additional neurobehavioral or pathological effects. This pattern of effects is suggestive of transient sedation. Despite daily reinstatement of acute sedative effects during repeated exposure with up to 3000 ppm, THF did not produce any persistent or cumulative effects on nervous system structure or function. The demonstrated no-observed-effect level of THF for both acute and subchronic exposure was 500 ppm.     

ACUTE AND SUBCHRONIC NEUROTOXICOLOGICAL EVALUATION OF TETRAHYDROFURAN BY INHALATION IN RATS

Groups of adult male and female rats received exposure to tetrahydrofuran (THF) vapor by inhalation in acute or subchronic exposure scenarios. Acute exposure concentrations were 0, 500, 2500, or 5000 ppm for 6 hr. Evaluations conducted immediately after exposure included clinical observations, motor activity assessments (MA), and a battery of functional tests (FOB) designed to reveal nervous system dysfunction. During exposure to 2500 and 5000 ppm, rats had a diminished or absent startle response to a punctate auditory alerting stimulus. Following exposure to 5000 ppm, male and female rats were lethargic, exhibited abnormal gait or mobility, and splayed rear feet. Lethargy and splayed rear feet were also observed in females esposed to 2500 ppm. During the subsequent FOB, males exposed to 5000 ppm had a lower incidence of palpebral closure, higher incidences of slow or absent righting reflex, and a biphasic pattern of reduced motor activity followed by increased motor activity. Females exposed to 5000 ppm had increased incidences of palpebral closure in the open field, increased incidences of slow or absent righting reflex, and decreased motor activity.

During the 14-week subchronic exposure series, daily THF exposure concentrations were 0, 500, 1500, or 3000 ppm, and neurobehavioral evaluations occurred on non-exposure days at approximately monthly intervals. Diminished startle responses to an auditory alerting stimulus were observed during exposure to 1500 or 3000 ppm; however, repeated exposures did not cause additional neurobehavioral or pathological effects. This pattern of effects is suggestive of transient sedation. Despite daily reinstatement of acute sedative effects during repeated exposure with up to 3000 ppm, THF did not produce any persistent or cumulative effects on nervous system structure or function. The demonstrated no-observed-effect level of THF for both acute and subchronic exposure was 500 ppm.     

A comprehensive study on the variations in urinary concentrations of endogenous gamma-hydroxybutyrate (GHB)

This study was designed to supplement previous attempts to establish an accurate range of normal endogenous gamma-hydroxybutyrate (GHB) concentrations in random antemortem urine samples. Furthermore, its purpose was to ascertain the effect of gender, race, age, medications, and select medical conditions on endogenous concentrations of GHB in urine and the proposed endogenous urinary GHB cutoff of 10 microg/mL. Urine samples (n = 207) were provided by subjects who reported that they had never used GHB. As part of the collection process, subjects also completed a short survey to collect information about gender, race, age, orally ingested medications, and select medical conditions. All specimens were analyzed in duplicate for the presence of endogenous GHB using a previously reported headspace gas chromatography-mass spectrometry method. The data were analyzed for tendencies among different population groups. GHB concentrations ranged from 0.00 to 2.70 microg/mL in all specimens, with a median concentration of 0.24 microg/mL. Males (n = 130) had an average endogenous GHB concentration of 0.27 microg/mL (0.00-2.70 microg/mL), whereas females (n = 77) averaged 0.29 microg/mL (0.00-0.98 microg/mL). Select medical conditions and participants' race, age ranges, and medications that were used within 48 h prior to collection were also evaluated. We believe this to be the most comprehensive study on endogenous GHB concentrations in urine to date. The results of this study will aid the interpretation of low GHB concentrations measured in urine samples, particularly in investigations of drug-facilitated crimes.     

An evaluation of the selectivity of fenmetozole (DH-524) reversal of ethanol-induced changes in central nervous system function

The selectivity and specificity of fenmetozole (DH-524) [2(3,4-dichlorophenoxy-methy))2-imidazole HCl] as an antagonist of the actions of ethanol were examined. Fenmetozole (15–30 g/kg) reduced ethanol-induced impairment of the aerial righting reflex without changing blood or brain ethanol content, indicating that the antagonistic actions of fenmetozole were not due to change in the pharmacokinetics of ethanol. Since fenmetozole also reduced aerial righting reflex impairment due to phenobarbital, chlordiazepoxide, and halothane, this action of fenmetozole was not specific to ethanol. In mice, both the ethanolinduced increase in locomotor activity at 2.0 g/kg and the decrease caused by 4.0 g/kg were antagonized by fenmetozole. In addition, fenmetozole attenuated the ethanol-induced reduction in cerebellar cyclic guanosine monophosphate (cGMP) content, but the drug also significantly elevated cGMP levels in this tissue when given alone. Fenmetozole did not alter ethanolinduced increases in punished drinking in a conflict test, except at a high dose which alone decreased both punished and unpunished responding. Fenmetozole also failed to precipitate ethanol withdrawal-like reactions when given to physically-dependent, intoxicated rats. Thus, the antagonistic action of fenmetozole against ethanol would not seem to be related to a specific receptor interaction but rather may be the result of a physiological antagonism.