Influence of antemortem medication on the determination of brain death

Post-mortem concentration of pentobarbital in the blood and brain of two deceased neurosurgical patients was determined by gas chromatography/mass spectrometry. Patients treated with barbiturate for elevated intracranial pressure after head injury may incur brain death. In the present two cases of brain death a large amount of barbiturate remained in the brain, even when the blood concentration was not detectable, possibly because the blood flow was stagnant in the brain. It is suggested that a patient under barbiturate coma should be given serious consideration as to the determination of brain death, even if barbiturate is negative in the blood.

High-performance liquid chromatographic determination of thiopentone enantiomers in sheep plasma

An HPLC method was developed to determine the plasma concentrations of R(+)- and S(-)-thiopentone for pharmacokinetic studies in sheep. The method required separation of the thiopentone enantiomers from the corresponding pentobarbitone enantiomers which are usually present as metabolites of thiopentone. Phenylbutazone was used as an internal standard. After acidification, the plasma sample were extracted with a mixture of ether and hexane (2:8). The solvent was evaporated to dryness and the residues were reconstituted with sodium hydroxide solution (pH 10). The samples were chromatographed on a 100 mm x 4 mm I.D. Chiral AGP-CSP column. The mobile phase was 4.5% 2-propanol in 0.1 M phosphate buffer (pH 6.2) with a flow-rate of 0.9 ml/min. This gave k' values of 1.92, 2.92, 5.71, 9.30 and 11.98 for R(+)-pentobarbitone, S(-)-pentobarbitone, R(+)-thiopentone, S(-)-thiopentone, and phenylbutazone, respectively. At detection wavelength of 287 nm, the limit of quantitation was 5 ng/ml for R(+)-thiopentone and 6 ng/ml for S(-)-thiopentone. The inter-day coefficients of variation at concentrations of 0.02, 0.1 and 8 micrograms/ml were, respectively, 4.8, 4.4 and 3.5% for R(+)-thiopentone and, respectively, 5.0, 4.3 and 3.9% for S(-)-thiopentone (n = 6 each enantiomer). At the same concentrations, the intra-day coefficients of variation from six sets of replicates (measured over six days) were, respectively, 8.0, 8.0 and 8.8% for R(+)-thiopentone and 8.8, 7.4 and 9.6% for S(-)-thiopentone. Linearity over the standard range, 0.01-40 micrograms/ml, was shown by correlation coefficients > 0.998. This method has proven suitable for pharmacokinetic studies of thiopentone enantiomers after administration of rac-thiopentone in human plasma also and would be suitable for pharmacokinetic studies of the pentobarbitone enantiomers.

Effects of aflatoxin B1 on the sensitivity of the rat central nervous system to pentobarbital-Na racemate

The immobility time of pentobarbital was prolonged in male rats treated with aflatoxin B1 (AFB1), 2 mg/kg, with maximum on the 3rd day after treatment. It cannot be fully explained by the pharmacokinetic mechanisms. In parallel ED50 of pentobarbital was decreased both in males and females. In males the lethal dose of pentobarbital was decreased by about 30%. The pentobarbital concentration in the brain was increased during the immobility time and at awakening after the ip administration of 40 mg/kg of the drug on the 3rd day after AFB1 treatment with doses of 1 mg/kg and 2 mg/kg po in males and females, respectively. The plasma concentration of pentobarbital was significantly increased in treated males only. The content of unchanged pentobarbital in urine within 24 h after its administration was not high (about 1% in males, 2% in females) and in the AFB1 treated animals it virtually did not change. The elevation of the brain level of barbiturate at the time of awakening in AFB1 treated animals may point to a decreased sensitivity to pentobarbital.

Pharmacokinetic and pharmacodynamic studies of centrally acting drugs in rat: effect of pentobarbital and chlorpromazine on electroencephalogram in rat

Electroencephalogram (EEG) alterations in rat after the i.v. administration of pentobarbital (PTB) and chlorpromazine (CPZ) were measured by power spectral analysis. The time courses of PTB concentrations in plasma, cerebrospinal fluid (CSF) and brain were determined after the i.v. administration of PTB (20, 40 mg/kg) by GC-MS. The PTB concentrations in plasma, CSF and brain could be described by a biexponential equation, a CSF model and a blood flow limited model, respectively. The relationship between the alteration of EEG and the PTB concentrations in the CSF or brain or the effect compartment were analyzed using the sigmoid Emax model. The alteration of EEG after PTB administration could be described by the PTB concentration in these compartments using the sigmoid Emax model. These results indicated that the site of action for the alteration of EEG after PTB administration is in instantaneous equilibrium with the CSF, the brain and the effect compartment. Thus, alterations in EEG after PTB administration can be predicted by monitoring the total PTB concentration in plasma. The alteration of EEG after i.v. administration of CPZ (4 mg/kg) showed a two-phase variation. Although the relationship between the alteration of EEG and the CPZ concentrations in CSF or the striatum or the effect compartment (total and free drug) were analyzed using the linear model, the Emax model or the sigmoid Emax model, the two-phase alteration of EEG after CPZ administration could not be described by any of these models. These results indicated that the pharmacokinetic and pharmacodynamic modeling of CPZ during the alteration of EEG may be complicated due to several pharmacokinetic and pharmacodynamic factors, such as an alteration of the free fraction of CPZ in the striatum, the formation of active metabolites, and two different intrinsic effects of CPZ on the EEG (one in an increase and the other in a decrease of the brain's electrical activity.

Identification of the diastereomers of pentobarbital N-glucosides excreted in human urine

A study was undertaken to determine if humans excreted pentobarbital N-glucosides as urinary metabolites following oral administration of pentobarbital. (1'RS,5RS)-1-(beta-D-Glucopyranosyl)pentobarbital ((1'RS,5RS)-PTBG) was isolated from the urine of one subject. The two diastereomers, (1'RS,5R)-PTBG and (1'RS,5S)-PTBG were separated and found to be identical to synthetic standards when compared using HPLC retention times coupled with UV (with and without post-column ionization) and mass spectrometry (HPLC/MS). A HPLC method was developed for detecting and quantifying (1'RS,5R)-PTBG, (1'RS,5S)-PTBG and pentobarbital in urine. Following a single oral dose of sodium pentobarbital to male subjects (n = 6), 1.6-6.2% of the pentobarbital dose was excreted as (1'RS,5S)-PTBG over 60 hours. (1'RS,5R)-PTBG was also detected in one subject and accounted for 0.3% of the pentobarbital dose. Using a modified HPLC system, the four pentobarbital N-glucosides were resolved and analysis of a partially purified pentobarbital N-glucoside extract from one subject indicated that only (1'R,5R)-PTBG and (1'S,5S)-PTBG could be detected as urinary excretion products. These results indicate that the side chain chirality of pentobarbital may influence the observed enantioselectivity for the formation and/or urinary excretion of the pentobarbital N-glucosides.

Hepatoprotective effects of artemisia scoparia against carbon tetrachloride: an environmental contaminant

The hepatoprotective activity of crude extract of artemisia scoparia (aerial parts) was investigated against experimentally produced hepatic damage using carbon tetrachloride (CCl4) as a model hepatotoxin. CCl4 at the dose of 1.5 ml/kg, produced liver damage in rats as manifested by the rise in serum levels of AST and ALT to 395 +/- 110 and 258 +/- 61 IU/l (mean +/- SEM; n = 10) respectively, compared to control values of 106 +/- 15 and 26 +/- 04. Pretreatment of rats with plant extract (150 mg/kg) significantly lowered (P < 0.01), the respective serum GOT and GPT levels to 93 +/- 05 and 27 +/- 03 IU/l, indicating hepatoprotective action. Pentobarbital sodium (75 mg/kg)-induced sleeping time in mice was found to be 140.8 +/- 1.5 min (n = 10) which was similar (P > 0.05) to that obtained in the group of animals pretreated with the plant extract (139.9 +/- 1.8 min). CCl4 treatment extended the pentobarbital sleeping time to 212.2 +/- 19.1 min and pretreatment of animals with plant extract reversed the CCl4-induced prolongation in pentobarbital sleeping time to 143.9 +/- 5.5 min (P < 0.001) which further confirms the protective action of the plant extract against CCl4-induced liver damage. These data indicate that the plant artemisia scoparia is hepatoprotective and validate the folkloric use of this plant in liver damage.

Effect of pentobarbital and gaseous anesthetics on rats selectively bred for ethanol sensitivity

Rats have been genetically selected to have a differential hypnotic response to an acute injection of ethanol. These high alcohol sensitive (HAS) and low alcohol sensitive (LAS) rats were used to investigate commonalities of the mechanism of action of several gaseous anesthetics, pentobarbital and ethanol. Similar studies have been carried out extensively with mouse lines also differentially sensitive to ethanol (short- and long-sleep mice). Like the mice, the rats are also differentially sensitive to the two gaseous anesthetics, enflurane and isoflurane. However, in contrast to results with these mice, we find that the HAS and LAS rats are differentially sensitive to halothane and pentobarbital in the same direction as their sensitivity to ethanol. In other studies, the rats also have been found to be differentially sensitive to phenobarbital as are SS and LS mice. These results show that, by the use of these anesthetics in combination with selectively bred rodent lines, many new opportunities for dissecting the molecular mechanisms of anesthetic agents present themselves.

[The prolongation effect on the duration of pentobarbital anesthesia by submaxillariectomy in male rats]

The present study was performed to investigate the effects of submaxillariectomy (Subx) on the anesthetic effect (sleeping time) of pentobarbital, the concentration-time profile of plasma pentobarbital and the hepatic drug metabolizing enzyme systems in male rats of the Donryu strain. Subx was performed when the rats were 60 days old. Subx prolonged the duration of pentobarbital (30 mg/kg, i.p.) anesthesia at 10, 23 and 43 days after the operation, respectively. At 43 days after Subx, the plasma pentobarbital concentration was higher in the Subx group until 30 min after the administration. There was no significant difference in the hepatic microsomal cytochrome P-450 content between the Subx and control groups. Cytochrome b5 content, aminopyrine N-demethylase and aniline hydroxylase activities were increased significantly in the Subx group. The activity of heme oxygenase, the rate limiting enzyme in the heme catabolic pathway, tended to increase in the Subx group. Furthermore, the activity of delta-aminolevulinic acid synthetase, the rate limiting enzyme in the heme synthetic pathway, was significantly decreased to 51 percent of the control group by Subx. These results may suggest that the prolongation of the duration of pentobarbital anesthesia is caused by Subx due to the change in the pharmacokinetics of pentobarbital, especially the inhibitory effects of the hepatic pentobarbital metabolizing enzyme system.

Region-specific changes of GABAA receptors by tolerance to and dependence upon pentobarbital

An experimental model for inducing tolerance to and dependence upon pentobarbital was characterized. Rats were infused with pentobarbital, 300 micrograms/10 microliter per h i.c.v. for 6 or 7 days, through pre-implanted cannulas by osmotic minipumps. Measurement of brain and serum levels showed that pentobarbital remained mainly inside of the brain. Measurements of sleeping time and susceptibility to convulsant-induced seizures indicated a substantial degree of tolerance and dependence (24 h after termination of infusion). Results of GABAA receptor binding assays showed marked regional variations. While [35S]t-butylbicyclophosphorothionate (TBPS) binding sites were increased in frontal cortices and striata of pentobarbital-dependent animals, KD was increased in striata of tolerant animals. Dependence upon pentobarbital was correlated with increased [3H]flunitrazepam binding sites in all three regions examined. Both high and low affinity [3H]muscimol binding sites were increased in dependent animals, but low affinity sites were decreased in frontal cortices of tolerant animals. KDs of [3H]muscimol high affinity sites were increased in cerebellum after animals developed dependence upon pentobarbital. KDs of [3H]muscimol low affinity sites were decreased in striata of pentobarbital tolerant animals. These findings further support the hypothesis that GABAA receptors in discrete areas of the brain have different subunit compositions and are regulated differentially by pharmacological modulators.

Effects of social isolation on pentobarbital activity in mice: relationship to racemate levels and enantiomer levels in brain

The effects of social isolation on hypnotic actions induced by pentobarbital (PB) were investigated pharmacokinetically in isolated and aggregated mice and rats. Animals were administered i.p. 50 mg/kg of sodium (+-)-PB, S(-)-PB or R(+)-PB. Experiments in mice indicated that the duration of sleep induced by sodium (+-)-PB was reduced in the isolated mice, while the onset of sleep or the (+-)-PB brain levels at the time of awakening did not differ significantly between isolated and aggregated mice. These results suggest that changes in pharmacokinetics of PB may underlie the difference in duration of sleep between isolated and aggregated mice. In additional experiments in mice, brain concentrations of (+-)-PB, S(-)-PB or R(+)-PB were determined at predetermined intervals after injection. These experiments demonstrated that the brain concentrations of (+-)-PB, as well as those of S(-)-PB, at each predetermined timepoint in mice sacrificed before awakening were significantly lower in the isolated mice. The brain R(+)-PB levels in the isolated mice were also significantly lower as compared with those in the aggregated mice at each timepoint after injection. Experiments in rats indicated that urinary 3'-hydroxypentobarbital (major metabolite) concentrations were higher in the isolated rats at 0 to 6 hr after injection, suggesting an increased rate of hepatic drug metabolism in the isolated rats. Take together, these findings suggest that an increased rate of metabolism of PB, especially that of the S(-)-enantiomer which is responsible for hypnotic action, in isolated rodents may be involved in the shorter duration of sleep time induced by sodium (+-)-PB.

Rate of increase of plasma drug level influences subjective response in humans

This study addressed the commonly held, but seldom tested, notion that faster rates of increase of drug effects are associated with more positive subjective effects. Sodium pentobarbital was administered to normal healthy volunteers in either a single oral dose or in a series of divided, cumulating doses, and subjective responses were monitored. Twelve subjects participated in three weekly sessions, during which they received capsules containing placebo, 150 mg pentobarbital in a single dose (SIN) or 180 mg pentobarbital administered in six divided doses (DIV) of 30 mg every 30 min. Doses of pentobarbital in the SIN and DIV were selected to produce similar peak plasma levels. Blood samples were obtained at regular intervals for plasma drug level determinations, and throughout the session subjects completed self-report mood questionnaires (e.g., Profile of Mood States, visual analog ratings of drug liking and drug "high") and psychomotor performance tests (e.g., Digit Symbol Substitution Test). As expected, the SIN and DIV conditions yielded similar peak levels of pentobarbital, but the peak was attained more rapidly in the SIN condition. Despite the similarity in peak plasma levels, subjects reached greater peaks in ratings of "high" and wanted more of the drug when they were in the SIN condition. On an end-of-session liking questionnaire they also reported significantly greater liking of the drug in the SIN condition. On other measures of drug effects (e.g., sedation and psychomotor impairment) no significant differences were observed between the conditions. Thus, the rate of increase of the drug's effects specifically influenced subjects' ratings on subjective measures (e.g., "high" and liking) that may be associated with risk for abuse.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotoninergic involvement in ethanol-induced alterations of thermoregulation in long-sleep and short-sleep mice

The effect of ethanol and pentobarbital on in vivo tryptophan hydroxylase activity and its relationship to drug-induced alterations of thermoregulation was examined in long-sleep (LS) and short-sleep (SS) mice. Serotonin function was measured in both the presence and absence of ethanol or pentobarbital in six discrete brain regions. Differences in basal levels of serotonin, 5-hydroxyindole acetic acid or in vivo tryptophan hydroxylase (TpH) activity were found only in the hypothalamus and dorsal raphe nuclei (SS slightly higher). Ethanol (4.2 g/kg i.p) caused significant reductions in in vivo TpH activity in the dorsal and pontine-medullary raphe nuclei and hypothalamus (putative thermoregulatory areas) in both LS (50-60% decrease) and SS (15-30% decrease) mice, but it had no effect on TpH activity in the striatum, cortex or hippocampus. The greater degree of ethanol-induced reduction in TpH activity in LS mice was associated with a greater degree of hypothermia (LS, 4.2 degrees C vs SS, 2.0 degrees C). Pentobarbital had equivalent effects in LS and SS mice on TpH activity in central nervous system thermoregulatory areas (decreases of 40-60%) and on body temperature (decreases of 6.8-7.5 degrees C). When the mice were given ethanol at an elevated environmental temperature (34 degrees C) the hypothermia was almost abolished completely, but depressant effects on TpH activity remained, suggesting that ethanol-induced decreases in TpH activity were direct effects and not secondary to hypothermia. Alterations in ethanol or pentobarbital elimination did not appear to account for the observed differences.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of cryogenic brain injury on the pharmacodynamics of pentobarbital. Evidence for a serotonergic mechanism

To study of the influence of brain injury on the pharmacodynamics of pentobarbital, the authors examined the effect of a focal cortical freezing lesion in rats on the brain concentration of pentobarbital associated with lack of response to tail clamp. The freezing lesion was made with a probe (-50 degrees C) applied through a craniotomy to the intact dura over the left parietal cortex. Three days after injury the rats were anesthetized with a continuous intravenous infusion of pentobarbital until they first did not respond to tail clamp stimulation. The brains were then removed for determination of pentobarbital by high-performance liquid chromatography. The brain pentobarbital concentration required to prevent response to tail clamp (EC50) was reduced from 209 +/- 39 nmol/g (mean +/- standard deviation) in rats without brain injury to 149 +/- 28 nmol/g in the injured animals (P = 0.005). The cortical serotonin (5-HT) concentration was increased from 1904 +/- 358 pmol/g in uninjured rats to 2513 +/- 598 pmol/g (P less than 0.01) in injured animals ipsilateral to the lesion. Pretreatment of the rats with p-chlorophenylalanine (PCPA, 200 mg/kg by intraperitoneal injection) to inhibit 5-HT synthesis abolished both the increase in 5-HT concentration associated with the injury (left cortex, 708 +/- 389 pmol/g; right cortex, 911 +/- 979 pmol/g) and the effect of the lesion on EC50 (uninjured, EC50 = 186 +/- 24 nmol/g; injured, EC50 = 179 +/- 47 nmol/g). Prevention of the decrease in EC50 by inhibition of 5-HT synthesis provides support for a functional role for 5-HT in the influence of cold injury on the pharmacodynamics of pentobarbital.

Stress in mice increases intrinsic pentobarbitone sensitivity by a predominantly pharmacodynamic mechanism

1. Mice were swum for 3 min at room temperature. 2. After this stress 'sleeping time' in response to pentobarbitone was increased by over 70%. 3. Loss of 'righting reflex' occurred in these stressed animals at brain concentrations of pentobarbitone which were 40% lower than those needed for 'sleep' in the unstressed mice, indicating a true increase in sensitivity to the drug. 'Waking' (the return of the righting reflex) occurred at identical levels in both groups. 4. Kinetic analysis showed that the rates of absorption, elimination and transfer between plasma and brain were slower in the swum than in the unswum mice, probably because of the reduced body temperatures produced by the swimming.

The effect of aluminium chloride upon the transition of drugs through the blood-brain barrier into the central nervous system

In order to determine the effect of Al3+ upon the transition of drugs through the blood-brain barrier into the central nervous system we examined its effect upon a drug that dissociates as a cation (quinidine) and drugs that dissociate as anions (acetylsalicylic acid and pentobarbital). The entry and exit of quinidine into and out of the brain in mice pre-treated with AlCl3 was inhibited. Al3+ did not compete with acetylsalicylic acid for the penetration through the blood-brain barrier but did slow down its elimination from the brain. Brain kinetics of the examined drugs showed good correlation with their central pharmacodynamic effects.

Pharmacokinetics of ampicillin and pentobarbital in the course of subclinical fascioliasis in sheep

Pharmacokinetics of two common veterinary drugs, ampicillin and pentobarbital, were determined in sheep before and four, eight, 12, 17 and 21 weeks after infestation of animals by an oral administration of 150 metacercariae of Fasciola hepatica. The parasite infestation was ascertained by clinical observation of the animals. The pharmacokinetics of ampicillin were not significantly affected by the liver parasitism but the disposition of pentobarbital changed. A significant increase in elimination half-life (around 180 per cent), volume of distribution (130 per cent) and mean residence time (154 to 170 per cent) was observed in sheep infected by the parasite for four to 12 weeks. In these animals, duration of narcosis caused by pentobarbital was prolonged 1.8-fold. The results suggested that both reduced elimination of pentobarbital and impaired distribution of the drug would be responsible for the prolonged duration of narcosis in infected animals.

Management of elevated intracranial pressure

The pathophysiology, clinical manifestations, monitoring techniques, and management of elevated intracranial pressure (ICP) are reviewed. The use of barbiturate coma to treat ICP is discussed in detail. Elevated ICP can be associated with severe head injuries and diseases of the central nervous system such as brain tumors and stroke. Symptoms of elevated ICP may be difficult to distinguish from symptoms of other disease states. ICP monitoring techniques such as the intraventricular catheter and the Camino fiber optic system are useful for determination of ICP elevations before any changes in vital signs or neurological status occur. Conventional treatment and control of ICP elevations includes general and physiologic management (cerebrospinal fluid removal, fluid restriction, controlled hyperventilation, sedation, and elevating the patient's head) and pharmacologic management. Osmotic diuretics, (e.g., urea, mannitol, glycerol) and loop diuretics (e.g., furosemide, ethacrynic acid) are first-line pharmacologic agents used to lower elevated ICP. Corticosteroids may be beneficial in some patients. Patients with elevated ICP refractory to conventional treatment may benefit from therapy with high-dose barbiturates. Pentobarbital has been used in the majority of the clinical studies. Pentobarbital serum concentrations should be determined every 24-48 hours when a patient is in a barbiturate coma because pentobarbital clearance increases with continued high-dose therapy. The treatment of elevated ICP requires aggressive therapy and intensive monitoring. In patients whose ICP is refractory to conventional therapies alone, survival rates have been improved by combining high-dose barbiturates with conventional therapies.

Post-mortem drug redistribution--a toxicological nightmare

Detailed human case data is presented to illustrate the dramatic extent of the phenomenon of post-mortem drug redistribution. The data suggests that there is a post-mortem diffusion of drugs along a concentration gradient, from sites of high concentration in solid organs, into the blood with resultant artefactual elevation of drug levels in blood. Highest drug levels were found in central vessels such as pulmonary artery and vein, and lowest levels were found in peripheral vessels such as subclavian and femoral veins. In individual cases, in multiple blood samples obtained from ligated vessels, concentrations of doxepin and desmethyldoxepin ranged from 3.6 to 12.5 mg/l and 1.2 to 7.5 mg/l, respectively; amobartital, secobarbital and pentobarbital from 4.3 to 25.8 mg/l, 3.9 to 25.3 mg/l and 5.1 to 31.5 mg/l respectively; clomipramine and desmethylclomipramine from 4.0 to 21.5 mg/l and 1.7 to 8.1 mg/l, respectively and flurazepam 0.15 to 0.99 mg/l; imipramine and desipramine from 4.1 to 18.1 mg/l and 1.0 to 3.6 mg/l, respectively. We conclude that this poorly studied phenomenon creates major difficulties in interpretation and undermines the reference value of data bases where the site of origin of post-mortem blood samples is unknown.

Dose-related and other effects of maternal cimetidine pretreatment during lactation on drug metabolism in mouse dams and pups

The effects of maternal cimetidine pretreatment at different dose levels during lactation, on drug metabolism, were investigated in mouse dams and recently weaned pups. Aminopyrine N-demethylase, aniline hydroxylase and pentobarbitone metabolism were inhibited in both dams and pups in a dose-dependent manner (15, 25 and 50 mg/kg/day, i.p.). Pretreatment at a dose level of 50 mg/kg/day resulted in comparable levels of inhibition of drug metabolism in dams and female pups while male pups were less affected. Of the three indices studied, aniline hydroxylase was the least influenced by cimetidine pretreatment. Thus, the effects of maternal cimetidine pretreatment on drug metabolism in the nursing pair varied with the dose, sex and substrate. The possible implications of these results for man are discussed.

N,N'-diallylpentobarbital (DAPB) metabolites and their effects on pentobarbital-induced sleep and hepatic drug-metabolizing enzymes

1. The biological half-life (t 1/2) of N,N'-diallylpentobarbital (DAPB) in brain after i.p. injection to mouse was 96 min (first phase) and 11 h (second phase). The t 1/2 values in plasma were 102 min and 9.4 h, respectively, after i.p. injection. After intracerebroventricular (i.c.v.) administration, the t 1/2 values in brain and plasma were 18 and 120 min, and 42 and 177 min, respectively. 2. Following i.p. administration of 2-14C-DAPB (80 mg/kg), 58% of the 14C was excreted in the urine in 72 h. Several urinary metabolites were identified by g.l.c.-mass spectrometry, DAPB was metabolized by three major pathways, i.e., omega-1 hydroxylation, epoxide-diol pathway and N-deallylation. 3. The effects of DAPB and its metabolites on pentobarbital (PB)-induced sleep were examined after i.p., i.v. and i.c.v. administration. Metabolite 1 [M-1; (omega-1)-hydroxy-DAPB], an active metabolite, exhibited the most potent prolonging effect. 4. M-1 and other metabolites, as well as unchanged DAPB, showed significant inhibitory effects on mouse hepatic drug-metabolizing enzymes.

Influence of nutritional status on the pharmacokinetics and pharmacodynamics of pentobarbital

The influence of dietary protein deficiency on the pharmacokinetics and pharmacodynamics of pentobarbital was investigated in male Sprague-Dawley rats fed for 4 weeks on a 23% (control) or 5% (low) protein diet ad libitum. Following a single iv dose of 40 mg/kg sodium pentobarbital, the average mean residence time (MRT) was prolonged by 144% (2.3 +/- 0.2 to 5.6 +/- 1.5 hr, mean +/- SD) in the protein-deficient rats, whereas the mean total body clearance (CL) per kilogram of body weight decreased from 0.56 +/- 0.09 to 0.22 +/- 0.06 liter/hr/kg. As a result, the terminal disposition rate constant was decreased by approximately 60% (0.398 +/- 0.037 to 0.178 +/- 0.050 hr-1 when compared to rats on a normal protein diet. No significant differences were found in the two groups of rats with respect to the apparent steady state volume of distribution (Vss). In order to investigate the effect of nutritional status on the concentration-pharmacologic activity relationship, pentobarbital was infused iv at a constant rate of 0.55 mg/min until the animals lost their righting reflex (16 +/- 3 min and 8 +/- 1 min in control and protein-deficient animals, respectively). The total dose and concentration of pentobarbital in plasma were not significantly different between the two groups of animals. However, the concentrations of pentobarbital in plasma water (unbound) and brain were appreciably higher in the rats on a low protein diet. Thus, a diet low in protein appears to be associated with a decreased sensitivity of the central nervous system to the depressant effect of pentobarbital.

Sensitivity to ethanol hypnosis and modulation of chloride channels does not cosegregate with pentobarbital sensitivity in HS mice

Several findings suggest that barbiturates and alcohol produce their sedative effects through a common neural and possibly a common genetic mechanism. We tested this hypothesis by examining the correlation between ethanol and pentobarbital sedative effects in individual animals from a genetically heterogeneous population. The duration of pentobarbital-induced hypnosis (sleep-time) was unrelated to the sleep-time produced by ethanol in heterogeneous stock (HS) mice. Therefore, the present study also examined the effect of ethanol, pentobarbital, and flunitrazepam on muscimol-stimulated chloride flux into brain membranes prepared from HS mice selected for differences in pentobarbital- and ethanol-induced sleep-time. Brain membranes from mice selected for differences in ethanol sleep-time were differentially responsive to ethanol- and flunitrazepam-, but not to pentobarbital-induced augmentation of muscimol-stimulated chloride flux. No differences in augmentation of chloride flux by ethanol, pentobarbital, or flunitrazepam were found in membranes prepared from mice differentially sensitive to pentobarbital hypnosis. The ability of muscimol to stimulate chloride uptake was not related to ethanol or pentobarbital sensitivity. These findings suggest that sensitivity to ethanol is not likely to be genetically linked to pentobarbital sensitivity.

Pulmonary densities during anaesthesia. An experimental study on lung morphology and gas exchange

The nature of dense areas in dependent lung regions regularly seen in anaesthetized humans was examined in a sheep model. During anaesthesia with muscle paralysis and mechanical ventilation dense areas in dependent lung regions could be seen by means of computerized tomography (CT). They had the same location and the same attenuation as in anaesthetized humans. Gas exchange impairment tended to increase in proportion to the size of the dense area on the CT scan. Microscopy showed that the densities in the sheep were atelectatic lung regions, with no or little interstitial oedema and only minor vascular congestion. The atelectatic lung tissue was sharply demarcated and the lung tissue in the immediate vicinity was well aerated, or even hyperinflated. Gravimetry showed the same amount of extravascular fluid and blood per unit lung weight in the atelectatic lung and in the aerated lung region. It is concluded that the densities appearing in dependent lung regions during anaesthesia are caused by atelectasis.

Oral absorption of sodium pentobarbital and effects on gastrointestinal function

An anaesthetic dose (40 mg/kg) of sodium pentobarbital (SP) was administered intragastrically to adult, fasted male rats at total dosing volumes of 1, 2, or 3 ml. Area under the plasma concentration-time curve did not differ for the various dosing volumes. During the initial (rapid) phase of gastric emptying all solutions containing drug appeared to empty at a faster rate than distilled water (2 ml). However, solutions containing drug emptied much more slowly than water during the terminal (slow) phase of gastric emptying. Drug solutions moved along the small intestine at approximately the same rate as distilled water. SP significantly lowered rectal temperature and slowed the propagation velocity of the migrating myoelectric complex (MMC) recorded from four serosal electrodes chronically implanted along the proximal small intestine. In addition, the drug significantly decreased the rate of MMC recurrence, extended the duration of MMC phases, and decreased slow wave frequency at all sites monitored. The results suggest that: 1) the relative oral bioavailability of sodium pentobarbital is not influenced by dosing volume within the range tested, 2) the various dosing volumes of SP tested moved through the gastrointestinal tract at an equal rate, and 3) orally administered SP significantly decreases the propagation velocity and periodicity of the MMC in the small intestine.

The contribution of environmental cues to cross-tolerance between ethanol and pentobarbital

The contribution of Pavlovian conditioning of environmental cues has been studied in relation to tolerance to ethanol-induced hypothermia and cross-tolerance to pentobarbital. Two groups of 12 male Sprague-Dawley rats were exposed every other day to a distinctive set of environmental cues paired with an IP injection of either ethanol 2.5 g/kg or an equivalent volume of isotonic saline. On alternating non-drug days, both groups received saline in the animal room. When they were tested for tolerance to the hypothermic effect of ethanol 2.5 g/kg and cross-tolerance to pentobarbital 25 mg/kg in each environment, tolerance and cross-tolerance in the ethanol-treated group were significantly more pronounced in the ethanol-paired environment than in the saline-paired environment. This indicates the importance of a conditional factor in tolerance and cross-tolerance in this paradigm. Determination of blood levels of ethanol and pentobarbital at various times after injection indicated that conditioned tolerance and cross-tolerance can be explained in part by dispositional factors.