Babao Dan Alleviates 5-Fluorouracil-Induced Intestinal Damage via Wnt/β-Catenin Pathway

OBJECTIVE

To evaluate the protective function of Babao Dan (BBD) on 5-flurouracil (5-FU)-induced intestinal mucositis (IM) and uncover the underlying mechanism.

METHODS

A total of 18 male mice were randomly divided into 3 groups by a random number table, including control, 5-FU and 5-FU combined BBD groups, 6 mice in each group. A single intraperitoneal injection of 5-FU (150 mg/kg) was performed in 5-FU and 5-FU combined BBD groups on day 0. Mice in 5-FU combined BBD group were gavaged with BBD (250 mg/kg) daily from day 1 to 6. Mice in the control group were gavaged with saline solution for 6 days. The body weight and diarrhea index of mice were recorded daily. On the 7th day, the blood from the heart of mice was collected to analyze the proportional changes of immunological cells, and the mice were subsequently euthanized by mild anesthesia with 2% pentobarbital sodium. Colorectal lengths and villus heights were measured. Intestinal-cellular apoptosis and proliferation were evaluated by Tunel assay and immunohistochemical staining of proliferating cell nuclear antigen, respectively. Immunohistochemistry and Western blot were performed to investigate the expressions of components in Wnt/β-catenin pathway (Wnt3, LRP5, β-catenin, c-Myc, LRG5 and CD44).

RESULTS

BBD obviously alleviated 5-FU-induced body weight loss and diarrhea, and reversed the decrease in the number of white blood cells, including monocyte, granulocyte and lymphocyte, and platelet (P<0.01). The shortening of colon caused by 5-FU was also reversed by BBD (P<0.01). Moreover, BBD inhibited apoptosis and promoted proliferation in jejunum tissues so as to reduce the intestinal mucosal damage and improve the integrity of villus and crypts. Mechanically, the expression levels of Wnt/β -catenin mediators such as Wnt3, LRP5, β-catenin were upregulated by BBD, activating the transcription of c-Myc, LRG5 and CD44 (P<0.01).

CONCLUSIONS

BBD attenuates the adverse effects induced by 5-FU via Wnt/β-catenin pathway, suggesting it may act as a potential agent against chemotherapy-induced intestinal mucositis.

The distribution and chemical coding of urinary bladder trigone-projecting neurons in testicular and aorticorenal ganglia in male pigs

Combined retrograde tracing and double-labelling immunofluorescence were used to investigate the distribution and chemical coding of neurons in testicular (TG) and aorticoerenal (ARG) ganglia supplying the urinary bladder trigone (UBT) in juvenile male pigs (n=4, 12 kg. of body weight). Retrograde fluorescent tracer Fast Blue (FB) was injected into the wall of the bladder trigone under pentobarbital anesthesia. After three weeks all the pigs were deeply anesthetized and transcardially perfused with 4% buffered paraformaldehyde. TG and ARG, were collected and processed for double-labelling immunofluorescence. The expression of tyrosine hydroxylase (TH) or dopamine beta-hydroxylase (DBH), neuropeptide Y (NPY), somatostatin (SOM), galanin (GAL), nitric oxide synthase (NOS) and vesicular acetylcholine transporter (VAChT) were investigated. The cryostat sections were examined with a Zeiss LSM 710 confocal microscope equipped with adequate filter blocks. The TG and ARG were found to contain many FB-positive neurons projecting to the UBT (UBT-PN). The UBT-PN were distributed in both TG and ARG. The majority of them were found in the right ganglia, mostly in TG. Immunohistochemistry disclosed that the vast majority of UBT-PN were noradrenergic (TH- and/or DBH-positive). Many noradrenergic neurons contained also immunoreactivity to NPY, SOM or GAL. Most of the UBT-PN were supplied with VAChT-, or NOS- IR (immunoreactive) varicose nerve fibres. This study has revealed a relatively large population of differently coded prevertebral neurons projecting to the porcine urinary bladder. As judged from their neurochemical organization these nerve cells constitute an important element of the complex neuro-endocrine system involved in the regulation of the porcine urogenital organ function.

Effect of calcium hypochlorite and chloramine on blood biochemistry and sodium pentobarbital induced sleeping time in mice

Disinfectants are chemical agents used to eradicate, deactivate or kill microorganisms. Chemical disinfectants especially chlorine compound are extensively used for water sanitization. Among these calcium hypochlorite and chloramines are commonly used now a day. Large number of chemical compounds, drugs and endogenous substances are metabolized by hepatic enzymes known as cytochrome P450 enzyme system. Many chemicals are capable of enzyme induction. Enzyme induction may change the metabolism of other drugs and endogenous substances which may alter the plasma concentration of these chemicals. To evaluate the enzyme inducing ability of calcium hypochlorite and chloramine, sleeping time induced by sodium pentobarbital was noted in mice. Normal saline was taken as negative control. Rifampicin, chloramphenicol and grapefruit juice were taken as positive control group. On completion of dosing after 4 weeks, alteration in sleep induction and recovery times was noted and compared. Histological evaluation of liver was observed. A significant decrease in sleeping time was observed in calcium hypochlorite and chloramine treated groups. Both calcium hypochlorite and chloramine caused a significant change in liver enzymes and in the values of complete blood count. In histological evaluation both caused fat deposition in the hepatocytes. It was concluded from the study that both calcium hypochlorite and chloramine were hepatic microsomal enzyme inducer.

A study of the in vitro interaction between lidocaine and premedications using human liver microsomes*

OBJECTIVE

To investigate potential interactions between lidocaine (lignocaine) metabolism and premedication drugs, i.e. psychotropic and antianxiety agents (diazepam, midazolam), hypnotics (pentobarbital, thiamylal), depolarizing neuromuscular blocking agents (vecuronium, pancuronium and suxamethonium), an antihypertensive agent (clonidine) and an H2-receptor blocking agent (cimetidine) using human liver microsomes in vitro.

METHODS

The interaction effects between lidocaine and premedication were examined using human liver microsomal preparations and monitored for enzyme activity. The lidocaine and its main metabolite (monoethylglycinexylide) were measured by HPLC/UV.

RESULTS

Lidocaine metabolism was non-competitively inhibited by midazolam (Ki = 77.6 microM). Thiamylal was a competitive inhibitor of lidocaine metabolism (Ki = 885 microM). Cimethidine, pancuronium and vecuronium weakly inhibited lidocaine metabolism in a concentration-depend manner over the therapeutic range in human liver microsomes. On the contrary, suxamethonium, pentobarbital and clonidine did not inhibit lidocaine metabolism over the therapeutic range in human liver microsomes.

CONCLUSION

These results show that the interactions between lidocaine and midazolam and thiamylal are of potential toxicological and clinical significance.

Genetic determinants of sensitivity to pentobarbital in inbred mice

RATIONALE

We postulated that genetic determinants of different responses to pentobarbital (PB) in mice would differ from response to response.

OBJECTIVES

Mice from 14 standard inbred strains were tested for sensitivity to several effects of acute PB.

METHODS

Strains were tested for sensitivity to PB-induced low-dose stimulation and high-dose depression of locomotor activity, reduced rearing, hypothermia, and ataxia assessed on a rotarod, using four doses of PB or saline.

RESULTS

Strains differed in sensitivity to PB for all responses. Correlations among strain means indicated that strain sensitivity to a particular effect of PB generalized rather well across doses. Sensitivities to some of the different behavioral responses were also significantly correlated. For example, strains less sensitive to PB-induced enhanced locomotor activity were also significantly more sensitive to the drug's hypothermic effects. Some responses were genetically independent. Brain PB concentrations were also determined, and appeared to be unrelated to inbred strain drug sensitivities.

CONCLUSIONS

Overall, these results suggest that there are multiple genetic determinants of behavioral sensitivity to PB effects. That is, genetically influenced sensitivity to PB is not monolithic, but is somewhat specific to the particular response variable studied, a result that also characterizes genetic control of responses to other drugs.

Changes of the level of G protein alpha-subunit mRNA by tolerance to and withdrawal from pentobarbital in rats

Pentobarbital was continuously infused intracerebroventricularly (i.c.v.) at the rate of 300 micrograms/10 microliters/h for 7 days, and withdrawal from pentobarbital was rendered 24 h after the stopping of the infusion. To eliminate the induction of hepatic metabolism by systemic administration of pentobarbital, an i.c.v. infusion model of tolerance to and withdrawal from pentobarbital was used. Little is known about the functional modulation of the G protein alpha-subunits at the molecular level. The effects of continuous infusion of pentobarbital on the modulation of G protein alpha-subunits mRNA were investigated by using in situ hybridization study. In situ hybridization showed that the level of G alpha s mRNA was increased in the septum and brainstem, and the level of G alpha o mRNA was elevated in the cortex during the pentobarbital withdrawal. The level of G alpha i mRNA was significantly elevated in almost all area of brain during the pentobarbital withdrawal. These results suggest that region-specific changes of G protein alpha-subunit mRNA were involved in the withdrawal from pentobarbital, whereas alpha-subunit is not so highly involved in the pentobarbital tolerance.

Pressure-sensitive and -insensitive coupling in gamma-aminobutyric acid(A) receptors

RATIONALE

Previous behavioral and biochemical studies suggest that allosteric coupling processes initiated by benzodiazepines, barbiturates and neuroactive steroids can be sub-categorized on the basis of their sensitivities to antagonism by increased atmospheric pressure. However, biochemical evidence supporting this hypothesis was limited to single concentration studies in long sleep (LS) mice.

OBJECTIVE

The present paper addresses these issues by extending biochemical investigation of pressure effects on allosteric modulators across a range of concentrations that allosterically enhance gamma-aminobutyric acid (GABA)A receptor function and alter behavior using two mouse genotypes. In addition, the effects of pressure on ligand binding were explored to further investigate the mechanism of pressure antagonism of allosteric modulation.

METHODS

The effects of 12 times normal atmospheric pressure (ATA) of helium-oxygen gas (heliox) on allosteric modulation of GABA(A) receptor function and [3H]flunitrazepam binding was tested in LS and C57BL mouse brain membranes (microsacs) using chloride flux and high-affinity binding assays.

RESULTS

In both genotypes, exposure to 12 ATA heliox antagonized the allosteric enhancement of GABA(A) receptor function by flunitrazepam (0.1-10 microM) and pentobarbital (0.1-50 microM) but did not affect allosteric modulation by 3alpha-hydroxy-5beta-pregnan-20-one (0.1-1 microM). Pressure did not affect benzodiazepine receptor affinity (Kd) or the number of benzodiazepine receptors (Bmax).

THE RESULTS

(1) confirm that there are differences in sensitivity to pressure antagonism of allosteric coupling among GABA(A) allosteric modulators; (2) demonstrate that these differences are not concentration or genotype dependent; (3) add evidence that pressure antagonizes allosteric modulation by uncoupling the receptor and (4) support the hypothesis that allosteric modulation of receptor function can be sub-categorized on the basis of sensitivity to pressure antagonism.

A new goldfish model to evaluate pharmacokinetic and pharmacodynamic effects of drugs used for motion sickness in different gravity loads

This paper proposes a new goldfish model to predict pharmacodynamic/pharmacokinetic effects of drugs used to treat motion sickness administered in differing gravity loads. The assumption of these experiments is that the vestibular system is dominant in producing motion sickness and that the visual system is secondary or of small import in the production of motion sickness. Studies will evaluate the parameter of gravity and the contribution of vision to the role of the neurovestibular system in the initiation of motion sickness with and without pharmacologic agents. Promethazine will be studied first. A comparison of data obtained in different groups of goldfish will be done (normal vs. acutely and chronically bilaterally blinded vs. sham operated). Some fish will be bilaterally blinded 10 months prior to initiation of the experiment (designated the chronically bilaterally blinded group of goldfish) to evaluate the neuroplasticity of the nervous system and the associated return of neurovestibular function. Data will be obtained under differing gravity loads with and without a pharmacological agent for motion sickness. Experiments will differentiate pharmacological effects on vision vs. neurovestibular input to motion sickness. Comparison of data obtained in the normal fish and in acutely and chronically bilaterally blinded fish with those obtained in fish with intact and denervated otoliths will differentiate if the visual or neurovestibular system is dominant in response to altered gravity and/or drugs. Experiments will contribute to validation of the goldfish as a model for humans since plasticity of the central nervous system allows astronauts to adapt to the altered visual stimulus conditions of 0-g. Space motion sickness may occur until such an adaptation is achieved.

Prolonged exposure to hypobaric hypoxia transiently reduces GABA(A) receptor number in mice cerebral cortex

The central nervous system is severely affected by hypoxic conditions, which produce alterations in neural cytoarchitecture and neurotransmission, resulting in a variety of neuropathological conditions such as convulsive states, neurobehavioral impairment and motor CNS alterations. Some of the neuropathologies observed in hypobaric hypoxia, corresponding to high altitude conditions, have been correlated with a loss of balance between excitatory and inhibitory neurotransmission, produced by alterations in glutamatergic and GABAergic receptors. In the present work, we have studied the effect of chronic hypobaric hypoxia (506 hPa, 18 h/day x 21 days) applied to adult male mice on GABA(A) receptors from cerebral cortex, to determine whether hypoxic exposure may irreversibly affect central inhibitory neurotransmission. Saturation curves for [3H]GABA specifically bound to GABA(A) receptors in isolated synaptic membranes showed a 30% decrease in maximal binding capacity after hypoxic exposure (Bmax control, 4.70+/-0.19, hypoxic, 3.33+/-0.10 pmol/mg protein), with no effect on GABA binding sites affinity (Kd control: 159.3+/-13.3 nM, hypoxic: 164.2+/-15.1 nM). Decreased B(max) values were observed up to the 10th post-hypoxic day, returning to control values by the 15th post-hypoxic day. Pharmacological properties of GABA(A) receptor were also affected by hypoxic exposure, with a 45 to 51% increase in the maximal effect by positive allosteric modulators (pentobarbital and 5alpha-pregnan-3alpha-ol-20-one). We conclude that long-term hypoxia produces a significant but reversible reduction on GABA binding to GABA(A) receptor sites in cerebral cortex, which may reflect an adaptive response to this sustained pathophysiological state.

Baculovirus vectors repress phenobarbital-mediated gene induction and stimulate cytokine expression in primary cultures of rat hepatocytes

Baculovirus transfection strategies have proven successful at transferring foreign DNA into hepatoma cells and primary hepatocytes. When testing the utility of these methodologies in cultured hepatocytes, we discovered that the presence of baculovirus disrupts the phenobarbital (PB) gene induction process, a potent transcriptional activation event characteristic of highly differentiated hepatocytes, and repressed expression of the albumin gene. In concert with previous reports from our laboratory demonstrating that increased cAMP levels can completely repress the induction of specific cytochrome P450 (CYP) genes, cAMP concentrations and PKA activities were measured in the primary hepatocytes subsequent to baculovirus exposure. However, neither parameter was affected by the presence of the virus. To evaluate whether immune response modulation was triggered by baculovirus exposure, RNase protection assays were performed and demonstrated that baculovirus infection activates TNF-alpha, IL-1alpha and IL-1beta expression in the primary hepatocyte cultures. Immunocytochemical experiments indicated that the production of cytokines was likely due to the presence of small numbers of Kupffer cells present in the culture populations. Exogenously added TNF-alpha was also effective in repressing PB induction, consistent with other reports indicating that inflammatory cytokines are capable of suppressing expression of biotransformation enzyme systems. Comparative studies demonstrated the specificity of these effects since exposures of hepatocytes to adenoviral vectors did not result in down-regulation of hepatic gene responsiveness. These results indicate that baculovirus vectors enhance the expression of inflammatory cytokines in primary hepatocyte cultures, raising concerns as to whether these properties will compromise the use of baculovirus vectors for study of cytochrome P450 gene regulation, as well as for liver-directed gene therapy in humans.

Synthesis and hypnotic activity of new 4-thiazolidinone and 2-thioxo-4,5-imidazolidinedione derivatives

Conveniently accessible 4-[(2-(3,4-dimethoxyphenyl)ethyl]-3-thiosemicarbazide (2) was converted to new 1-substituted benzylidene/furfurylidene-4- [2-(3,4-dimethoxyphenyl)ethyl]-3-thiosemicarbazides (3) which furnished 2-(substituted benzylidene/furfurylidene) hydrazono-3-[2-(3,4-dimethoxyphenyl)ethyl]thiazolidin-4-ones (4) and 1-(substituted benzylidene/furfurylidene)-amino -3-[2-(3,4-dimethoxyphenyl)ethyl]-2-thioxo-4,5-imidazolidinedio nes (5) on reaction with chloroacetic acid and oxalyl chloride, respectively. The structure of 5 was confirmed by X-ray diffraction studies performed on 5a. 4 and 5 were evaluated for their potentiating effects on pentobarbital induced hypnosis. Most of the compounds caused remarkable increases in pentobarbital sleeping time.

Stereoselective interaction of thiopentone enantiomers with the GABA(A) receptor

1. As pharmacokinetic differences between the thiopentone enantiomers seem insufficient to explain the approximately 2 fold greater potency for CNS effects of (-)-S- over (+)-R-thiopentone, this study was performed to determine any enantioselectivity of thiopentone at the GABA(A) receptor, the primary receptor for barbiturate hypnotic effects. 2. Two electrode voltage clamp recording was performed on Xenopus laevis oocytes expressing human GABA(A) receptor subtype alpha1beta2gamma2 to determine relative differences in potentiation of the GABA response by rac-, (+)-R- and (-)-S-thiopentone, and rac-pentobarbitone. Changes in the cellular environment pH and in GABA concentrations were also evaluated. 3. With 3 microM GABA, the EC50 values were (-)-S-thiopentone (mean 26.0+/-s.e.mean 3.2 microM, n=9 cells) >rac-thiopentone (35.9+/-4.2 microM, n=6, P=0.1) >(+)-R-thiopentone (52.5+/-5.0 microM, n=8, P<0.02) >rac-pentobarbitone (97.0+/-11.2 microM, n=11, P<0.01). Adjustment of environment pH to 7.0 or 8.0 did not alter the EC50 values for (+)-R- or (-)-S-thiopentone. 4 Uninjected oocytes responded to >100 microM (-)-S- and R-thiopentone. This direct response was abolished by intracellular oocyte injection of 1,2-bis(2-aminophenoxy)ethane-N, N,N1,N1-tetraacetic acid (BAPTA), a Ca2+ chelating agent. With BAPTA, the EC50 values were (-)-S-thiopentone (20.6+/-3.2 microM, n=8) <(+)-R-thiopentone (36.2+/-3.2 microM, n=9, P<0.005). 5 (-)-S-thiopentone was found to be approximately 2 fold more potent than (+)-R-thiopentone in the potentiation of GABA at GABA(A) receptors expressed on Xenopus oocytes. This is consistent with the differences in potency for CNS depressant effects found in vivo.

Multivariate non-parametric methods for Mann-Whitney statistics to analyse cross-over studies with two treatment sequences

A non-parametric strategy for the analysis of ordinal data from cross-over studies with two treatment sequences and d(> or = 2) periods is examined through Mann-Whitney rank measures of association. For each period, these statistics estimate the probability of larger response for a randomly selected patient in one group relative to a randomly selected patient in the other group. Such estimates are as well formed for comparisons between groups for u pairs of periods with the same treatment. Methods for U-statistics are used to produce a consistent estimate of the covariance matrix for the (d + u) Mann-Whitney estimates. The effects of periods and treatments on the respective Mann-Whitney estimates are evaluated through linear (or log-linear) models. For estimation of the parameters in these models, a modified weighted least squares method is applied through a (2d - 1) < or = (d + u) dimensional basis which effectively addresses potentially near singularities in the estimated covariance matrix of the Mann-Whitney estimates. The proposed methods are applicable to response variables with an interval or an ordered categorical scale. Their scope additionally has capabilities for controlling strata in the design of a cross-over study or concomitant variables for which covariance adjustment is of interest for reduction of variance. Applications of the methods are illustrated through three cross-over studies with different specifications for the two sequences of two treatments during two to four periods.

Increase of pentobarbitone metabolism induced in rats pretreated with some centrally acting compounds

Rats treated with phenobarbitone, phenaglycodol, glutethimide, nikethamide, meprobamate, chlorbutol and chlorpromazine showed an increased metabolism of pentobarbitone and, at the same time, a diminished sleeping-time after pentobarbitone. This effect developed 24 hr after treatment, the maximum increase in metabolism occurring after about 48 hr. The increased pentobarbitone metabolism was inhibited by ethionine injected shortly before treatment. Using a liver slice preparation, increased pentobarbitone metabolism was also observed in vitro. These results are in accord with the view that the capacity of compounds to increase pentobarbitone metabolism may be related to their ability to act directly on microsomal enzyme systems.

Anesthetic effects on the glycerol model of rhabdomyolysis-induced acute renal failure in rats

Isoflurane, the most widely used inhalational anesthetic, releases inorganic fluoride during its metabolism by the cytochrome P450 system. Recent experimental data indicate that when cultured proximal tubular cells are exposed to inorganic fluoride, they become relatively resistant to myoglobin- and ATP depletion-mediated attack. The present study was undertaken to assess whether isoflurane anesthesia might confer in vivo cytoprotection, possibly by causing renal tubular inorganic fluoride exposure, thereby mitigating a combined myoglobin/ATP depletion model of acute renal failure (glycerol-induced ARF). Rats were injected with hypertonic glycerol (50%; 9 ml/kg, intramuscularly) while undergoing 4 h of isoflurane anesthesia. Glycerol-injected rats anesthetized with a virtually nondefluorinated inhalational anesthetic (desflurane) or with a nonfluorinated anesthetic (pentobarbital) served as controls. The severity of ARF was assessed 24 h later (blood urea nitrogen, plasma creatinine [Cr], and renal histology). Anesthetic effects on extrarenal injury (plasma creatine phosphokinase, lactate dehydrogenase, and hematocrit levels), acute intrarenal heme loading (cast formation), and BP during the initiation phase of renal injury (0 to 4 h after glycerol injection) were also assessed. Glycerol induced severe ARF under pentobarbital anesthesia (Cr, 2.8 +/- 0.3 mg/dl; severe tubular necrosis). Somewhat worse azotemia, but comparable tubular necrosis, resulted with desflurane use. Conversely, glycerol plus isoflurane anesthesia induced only mild renal damage (Cr, 0.9 +/- 0.1, minimal tubular necrosis; P < 0.01). This reduction apparently was not due to differences in degrees of muscle necrosis, hemolysis, acute renal heme loading, or BP during the initiation phase of ARF, suggesting that a direct renal mechanism was operative. These results: (1) underscore that differing anesthetics can profoundly alter the expression of experimental renal injury; (2) raise the intriguing possibility that isoflurane could potentially protect surgical/trauma patients from rhabdomyolysis-induced ARF; and (3) further support the concept that renal fluoride exposure may confer proximal tubular cytoprotective effects.

The interaction of general anaesthetics with recombinant GABAA and glycine receptors expressed in Xenopus laevis oocytes: a comparative study

1. The effects of five structurally dissimilar general anaesthetics were examined in voltage-clamp recordings of agonist-evoked currents mediated by recombinant gamma-aminobutyric acid (GABA)A receptors composed of human alpha 1 beta 1 and gamma 2L subunits expressed in Xenopus laevis oocytes. A quantitative comparison of the effects of these agents was made upon recombinant glycine receptors expressed as a homo-oligomer of human alpha 1 subunits, or as a hetero-oligomer of human alpha 1 and rat beta subunits. 2. Complementary RNA-injected oocytes expressing GABAA receptors responded to bath applied GABA with an EC50 of 158 +/- 34 microM. Oocytes expressing alpha 1 and alpha 1 beta glycine receptors subsequent to cDNA injection displayed EC50 values of 76 +/- 2 microM and 66 +/- 2 microM, respectively, in response to bath applied glycine. 3. Picrotoxin antagonized responses mediated by homo-oligomeric alpha 1 glycine receptors with an IC50 of 4.2 +/- 0.8 microM. Hetero-oligomeric alpha 1 beta glycine receptors were at least 100-fold less sensitive to blockade by picrotoxin. 4. With the appropriate agonist EC10, propofol enhanced GABA and glycine-evoked currents to approximately the maximal response produced by a saturating concentration of either agonist (i.e. Imax). The calculated EC50 values were 2.3 +/- 0.2 microM, 16 +/- 3 microM and 27 +/- 2 microM, for GABAA alpha 1 beta 1 gamma 2L, glycine alpha 1 and alpha 1 beta receptors, respectively. At relatively high concentrations, propofol was observed to activate directly both GABAA and glycine receptors. 5. Pentobarbitone potentiated GABA-evoked currents to 117 +/- 8.5% of Imax with an EC50 of 65 +/- 3 microM. The barbiturate also produced a substantial enhancement of the glycine-evoked currents, Imax and EC50 values being 71 +/- 2% and 845 +/- 66 microM and 51 +/- 10% and 757 +/- 30 microM for homomeric alpha 1 and heteromeric alpha 1 beta glycine receptors respectively. At high concentrations, pentobarbitone directly activated GABAA, but not glycine, receptors. 6. The potentiation by propofol or pentobarbitone of currents mediated by alpha 1 homo-oligomeric glycine receptors was in both cases associated with a parallel sinistral shift of the glycine concentration-effect curve. The effects of binary combinations of pentobarbitone and propofol at maximally effective concentrations were mutually occlusive suggesting a common site, or mechanism, of action. 7. GABA-evoked currents were maximally potentiated by etomidate to 79 +/- 2% of Imax (EC50 of 8.1 +/- 0.9 microM). By contrast, glycine-induced currents mediated by alpha 1 and alpha 1 beta glycine receptor isoforms were enhanced only to 29 +/- 4% and 28 +/- 3% of Imax. Limited solubility precluded the calculation of EC50 values for the effect of etomidate at glycine receptors. None of the receptor isoforms examined were directly activated by etomidate. 8. The neurosteroid 5 alpha-pregnan-3 alpha-ol-20-one potentiated GABA-evoked currents to 69 +/- 4% of Imax, with an EC50 value of 89 +/- 6 nM. In contrast, both alpha 1 homo-oligomeric and alpha 1 beta hetero-oligomeric glycine receptors were insensitive to the action of this steroid. A direct agonist action of the steroid was discernible at GABAA, but not glycine, receptors. 9. Trichloroethanol, the active metabolite of the general anaesthetic chloral hydrate, enhanced glycine-evoked currents to 77 +/- 10% and 94 +/- 4% of Imax on alpha 1 and alpha 1 beta glycine receptors, with EC50 values of 3.5 +/- 0.1 mM and 5.9 +/- 0.3 mM respectively. On GABAA receptors, trichloroethanol had a lower maximum enhancement (52 +/- 5% of Imax), but a slightly higher potency (EC50 1.0 +/- 0.1 mM). Trichloroethanol activated neither GABAA, nor glycine, receptors. 10. The data demonstrate a variety of intravenous general anaesthetic agents, at clinically relevant concentrations, to augment preferentially GABA-evoked currents mediated by the alpha1beta1upsilon2L receptor subunit combination as compared to their effects on both alpha1 and alpha1beta glycine receptors. However, the presence on glycine receptors of lower affinity modulatory binding sites for pentobarbitone, propofol and trichloroethanol may aid in the identification of the molecular determinants of the CNS actions of these anaesthetics.

Bicuculline and gabazine are allosteric inhibitors of channel opening of the GABAA receptor

Anesthetic drugs are known to interact with GABAA receptors, both to potentiate the effects of low concentrations of GABA and to directly gate open the ion channel in the absence of GABA; however, the site(s) involved in direct gating by these drugs is not known. We have studied the ability of alphaxalone (an anesthetic steroid) and pentobarbital (an anesthetic barbiturate) to directly activate recombinant GABAA receptors containing the alpha 1, beta 2, and gamma 2L subunits. Steroid gating was not affected when either of two mutated beta 2 subunits [beta 2 (Y157S) and beta 2 (Y205S)] are incorporated into the receptors, although these subunits greatly reduce the affinity of GABA binding. These observations indicate that steroid binding and subsequent channel gating do not require these particular residues, as already shown for barbiturates. Bicuculline or gabazine (two competitive antagonists of GABA binding) reduced the currents elicited by alphaxalone and pentobarbital from wild-type GABAA receptors; however, gabazine produced only a partial block of response pentobarbital or alphaxalone, and bicuculline only partially blocked responses to pentobarbital. These observations indicate that the blockers do not compete with alphaxalone or pentobarbital for a single class of sites on the GABAA receptor. Finally, at receptors containing alpha 1 beta 2 (Y157S) gamma 2L subunits, both bicuculline and gabazine showed weak agonist activity and actually potentiated responses to alphaxalone. These observations indicate that the blocking drugs can produce allosteric changes in GABAA receptors, at least those containing this mutated beta 2 subunit. We conclude that the sites for binding steroids and barbiturates do not overlap with the GABA-binding site. Furthermore, neither gabazine nor bicuculline competes for binding at the steroid or barbiturate sites. The data are consistent with a model in which both gabazine and bicuculline act as allosteric inhibitors of channel opening for the GABAA receptor after binding to the GABA-binding site.

Longitudinal studies on the interaction of perfluorochemicals with liver cytochromes P-450 by means of testing the rate of detoxification of pentobarbital

Four perfluorochemicals, Bis-[F-butyl]ethene, perfluorocyclohexylmorpholine, perfluorodecalin and perfluorooctylbromide were compared by their influence on the liver cytochrome P-450 system, measuring the pentobarbital sleeping time as defined by the time of loss of the righting reflex in rats. In all experiments first a prolongation of barbital detoxification was observed, which lasted at least 2-4 days. Thereafter a very long extended period of abbreviated sleeping time followed which was only missed after perfluoroctylbromide. Thus substrate competition, uncoupling of monooxygenation and enzyme induction determine the detoxifying processes in the liver that follow the administration of perfluorochemicals.

The effect of furazolidone and furaltadone on drug metabolism in rats

This work examines the effect of oral treatment of rats with the nitrofuran drugs furazolidone (FZ) and furaltadone (F) at doses of 100, 200 and 400 mg/kg for 4 days, or F in the drinking water at concentrations of 0.1, 0.2 and 0.4% w/v for 14 days, on drug metabolism in vivo. FZ at doses of 200 and 400 mg/kg, and F at a dose of 400 mg/kg or at a concentration of 0.4% w/v in water depressed growth and prolonged pentobarbitone-induced sleeping time. Treatment also significantly increased the blood concentration of metronidazole when measured 30 and 40 min after metronidazole administration. Administration of tremorine (25 mg/kg, i.p.) to control vehicle-treated rats produced within 2-3 min tremors, piloerection, profuse salivation, defecation urination and chromodacryorrhesis (red tears). The onset of appearance of these signs was delayed to 7-12 min in rats pretreated with FZ or F (100 mg/kg, 4 days) or cimetidine (50 mg/kg, i.p.) given 45 min earlier. Taken together, these results suggest that FZ and F inhibit drug metabolism in rats. Treatment with these nitrofuran drugs may alter the disposition of certain drugs which may be given concomitantly with them.

Mechanism of prolongation of pentobarbital-induced sleeping time by empenthrin in mice

The effect of empenthrin, a synthetic pyrethroid, on pentobarbital (PTB)-induced sleeping time was examined in mice and rats. In mice, pretreatment with empenthrin prolonged PTB-induced sleeping time in a dose-dependent manner. The maximum effect on PTB-sleeping time was noted when mice were pretreated orally with empenthrin 2-4 h before PTB injection. However, empenthrin did not change the sleeping time induced by diethyl ether which is hardly metabolized in liver. Empenthrin inhibited the clearance of serum PTB in mic, but did not change the PTB concentration in serum at which animals recovered from sleeping. To examine the effect of PTB on metabolic enzymes in mouse liver, PTB was incubated aerobically with a hepatic microsomal fraction in the presence of NADPH at 37 degrees C. Empenthrin inhibited the vitro metabolism of PTB dose-dependently. In rats, empenthrin neither changed the PTB sleeping time, nor inhibited the clearance of serum PTB. No inhibitory effect of empenthrin was observed on the in vitro metabolism of PTB using rat hepatic microsomal fraction. These findings indicate that empenthrin prolongs PTB-sleeping time in mice through an inhibition of the PTB-metabolizing enzyme(s) in the liver , an effect that does not occur in rats. Also, there is a clear species-specificity in the inhibitory effect of empenthrin on the PTB-metabolizing enzyme(s).

Homomeric beta 1 gamma-aminobutyric acid A receptor-ion channels: evaluation of pharmacological and physiological properties

The ubiquitous distribution of gamma-aminobutyric acid A (GABAA) receptor beta subunits throughout the central nervous system is in accord with a vital role in receptor structure and function. Homomeric beta subunits have been reported to be either GABA-gated or capable of forming anion-selective channels that lacked GABA-gating properties. With electrophysiological recording techniques, we examined the properties of the murine Beta 1 subunit, addressed whether the homomeric receptor is expressed independently from the host cell's genome, and investigated whether these channels can open spontaneously. Murine beta 1 subunits, expressed in Xenopus oocytes or A293 cells, were unaffected by GABA or bicuculline; however, the resting membrane conductances were reduced by picrotoxin, zinc, or penicillin-G. In comparison, the expression of bovine beta1 subunits formed GABA-gated C1- channels. For murine beta 1 subunits, both pentobarbitone and propofol increased the membrane conductance, although the benzodiazepine ligands flurazepam, flumazenil, and methyl-6,7-dimethoxy-4 ethyl-beta-carboline-3-carboxylate were inactive. Oocytes injected with murine beta 1 cRNA in the presence of actinomycin D (to block host cell DNA transcription) expressed beta1 channels that were indistinguishable from those derived from previous cDNA injections in cells capable of normal transcription. Single-channel recording from murin beta 1 cDNA-injected oocytes revealed spontaneously opening channels with a main state conductance of 18 pS. Picrotoxin inhibited the channel openings by reducing the probability of opening. We concluded that murine beta 1 subunits can form functional ion channels that are not gated by GABA but can be closed by some noncompetitive GABA antagonists. Interestingly, previous observations of spontaneously opening ion channels with properties similar to those found for the murine beta 1 receptor suggest that a limited expression of homomeric beta subunit-ion channels may exist in vivo.

[Hormones, growth factors, and drugs in metabolism and nutrition]

The manipulation of the inflammatory and hormonal responses may produce, on one hand, positive effects, and, on the other hand, potentially negative effects. The modification of the neuro-endocrine-humoral pattern may become more important and effective than the supply of nutrients. In this article we bring an up date of the role of insulin, anabolic steroids, blocking the catabolic hormones, phenobarbital, somatostatin, clenbuterol and metaprorenol, growth factors: GH and IGF-1, cytokines, and anti-cytokines sera. The use of GH, IGF-1, and of the epidermal and or colonic growth factors, along with a blocking of the cytokines, the manipulation of the lipidic mediators, and the supply of classical nutrients, specific to the aggression situation, may improve the protein synthesis and tissue repair. It may at the same time both decrease the loss of body proteins as well as promoting and acceleration of the recovery, shortening the hospital stay and reducing the convalescence time. The future seems to point towards molecular and cellular biotechnology and towards "nutritional" pharmacology, which contemplates the effects of growth factors, the recent advances in the field of cytokine modulation, and the manipulation of the binomer nutrient-medication.

Effect of grapefruit juice on drug metabolism in rats

The effect of grapefruit juice on in vivo drug metabolism was investigated in rats. The juice (4 ml or 8 ml/kg) was given orally once daily for 2 consecutive days and its effect on theophylline metabolism, pentobarbitone sleeping time and the tremorgenic action of tremorine was studied. The effect of grapefruit juice on some of these parameters was compared with that of the known drug metabolism inhibitor cimetidine given ip. Grapefruit juice at 4 ml and 8 ml/kg produced significant increases in pentobarbitone sleeping time that reached 46 and 79%, respectively, compared with 107% produced by cimetidine (50 mg/kg, ip). The juice at 4 ml/kg also significantly increased plasma theophylline concentration when measured 15, 30, 60 and 90 min after ip theophylline administration (10 mg/kg). Thereafter, no significant differences were detected in plasma drug concentrations between juice- and saline-treated animals. Administration of tremorine (25 mg/kg, ip) to saline-treated controls produced, within 2 or 3 min, tremors, piloerection, profuse salivation, defaecation, urination and chromodacryorrhesis (red tears). The onset of appearance of these signs was delayed to about 7 min in rats pretreated 1 hr earlier with either grapefruit juice (4 ml/kg, orally) or cimetidine (50 mg/kg, ip). The severity of the above signs was markedly reduced to a similar extent in both the juice- and cimetidine-treated rats. These results suggest that grapefruit juice may act as an inhibitor of drug metabolism in rats, and that its consumption may alter the disposition of certain concomitantly administered drugs.

The effect of parenteral nutrition on hepatic cytochrome P-450

BACKGROUND

Total parenteral nutrition (TPN) has been shown to affect liver function tests. Additional investigations in animals and humans have demonstrated that hepatic cytochrome P-450 content and enzyme activity are also affected.

METHODS

To review the literature on the effect of TPN on hepatic cytochrome P-450, an English-language literature search was performed using MEDLINE (1966 through 1993).

RESULTS

Studies in laboratory rats show that administration of dextrose, with or without amino acids, decreases the cytochrome P-450 content and the in vitro or in vivo microsomal oxidation rates of various drugs. The addition of lipid emulsions to TPN decreases oxidation rates for meperidine demethylase but does not affect ethoxyresorufin deethylase. Using immunoquantitation, it was shown that the components of TPN selectively affect specific hepatic P-450 enzymes. In humans, dextrose decreases antipyrine clearance, whereas amino acids and possibly lipids increase antipyrine clearance. However, the effects of protein-calorie malnutrition in these studies obscure the results.

CONCLUSIONS

Possible mechanisms for the reduction of hepatic cytochrome P-450 seen during TPN administration include altered gastrointestinal hormone response, mucosal barrier, and the effect of sepsis. Additional studies are needed to determine the actual mechanisms of hepatic cytochrome P-450 reduction observed during TPN.

Dual action of the cyclodiene insecticide dieldrin on the gamma-aminobutyric acid receptor-chloride channel complex of rat dorsal root ganglion neurons

The gamma-aminobutyric acidA (GABAA) receptor-chloride channel complex is known to be the target site of dieldrin, a cyclodiene insecticide, and lindane. In order to elucidate the mechanisms of dieldrin interaction with the GABA system, whole-cell patch clamp experiments were performed with rat dorsal root ganglion neurons in primary culture. When co-applied with GABA, dieldrin exerted a dual effect on the GABA-induced chloride current. The chloride current induced by 10 microM GABA was greatly enhanced by the first 20-sec co-application with 1 microM dieldrin, but the enhancement subsided during repeated co-applications, and the current was eventually suppressed below the control level. No recovery occurred after a prolonged washing with dieldrin-free solution. Desensitization of the chloride current was accelerated by dieldrin. However, when the period of co-application was limited to 2 sec, which was short enought to avoid desensitization, no suppression of current was observed during repeated co-applications and recovery occurred after washing. The desensitization and suppression occurred with an EC50 of 92 nM, whereas the enhancement required a higher EC50 at 754 nM. The GABA-induced chloride current comprised two components, one with a high sensitivity to dieldrin suppression with an EC50 of 5 nM and the other with a lower sensitivity with an EC50 of 92 nM. Dieldrin exerted its inhibitory effect on the GABA-induced current regardless of the presence or absence of pentobarbital and chlordiazepoxide. However, its effect was attenuated by the presence of picrotoxin. Furthermore, dieldrin suppressed the GABA-induced chloride current in a noncompetitive manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of beta-myrcene on pentobarbital sleeping time

Evidence that beta-myrcene (MYR) interferes with the metabolic activation of premutagens has been provided by in vitro studies. In order to determine whether MYR also interferes with the in vivo metabolism of xenobiotics, thereby modifying pharmacological responses to drugs, we investigated the effects of this monoterpene on pentobarbital (PT) sleeping time in rats. Two experiments were carried out. In the first, a single dose of MYR (0.25, 0.5 or 1.0 g/kg po) was given 1 h before PT (40 mg/kg ip). No effect was observed with the two lowest doses, but the highest MYR dose given 1 h before PT increased the PT-induced sleeping time (131 +/- 15 min vs 64 +/- 15 min for controls, mean +/- SD). In the second experiment, male rats were treated with MYR (1.0 g/kg po once a day) for 14 days and injected with PT (40 mg/kg ip) 24 h after the last dose of MYR. Repeated treatment with MYR markedly reduced PT sleeping time compared to the vehicle-treated control group (21 +/- 13 min vs 35 +/- 19 min for controls, mean +/- SD). These results indicate that MYR interferes with the in vivo barbiturate metabolism and support the view that MYR induces the phenobarbital-inducible cytochrome P-450 (P-450 2B subfamily) enzymes in the rat.

Effects of pentobarbital tolerance and dependence on convulsant and GABAA receptor antagonist binding

Experiments were performed which examined the effects of pentobarbital tolerance and dependence on GABAA receptor antagonist binding. In rats implanted with pentobarbital pellets for 7 days, followed by 24 hours of withdrawal, there was a significant decrease in the latency of TBPS-induced seizures and an increase in [35S]TBPS binding in the frontal cortex. The pentobarbital tolerant rats had a significant increase in the low affinity KD of [3H]SR95531 binding. Removal of the pellets for 24 hours caused a reversal of the effect on the low affinity KD and caused a decrease in the number of low affinity binding sites. In vitro addition of pentobarbital to binding assays produced a decrease in the number of high affinity [3H]SR95531 binding sites without changing low affinity binding. In the cerebellum, the binding in none of the treatment groups was significantly different from placebo. These observations suggest that pentobarbital tolerance and withdrawal cause changes in the properties of the GABAA receptor antagonist binding site which are different from those caused by in vitro exposure to the drug.

Interaction of doxapram and pentobarbital in mice

We found a statistically significant increase in duration of pentobarbital-induced narcosis in doxapram-treated mice. The influence of doxapram (a respiratory stimulant) pretreatment on pentobarbital metabolism in mice was assessed by measurements of sleeping times, hypothermia, LD50 values, hepatic microsomal metabolism and relative plasma and brain levels of pentobarbital. When doxapram was given intraperitoneally 60 min. prior to administration of pentobarbital, doxapram potentiated pentobarbital-induced narcosis in a dose- and time-dependent manner, but had no effect on onset time. Doxapram potentiated hypothermia, increased acute toxicity, and prolonged the pentobarbital half-life in brain and plasma, but measurement of the concentration of pentobarbital in the brain and plasma immediately upon recovery from narcosis showed that there were no differences in any of the groups examined. Also, brain-to-plasma ratios of pentobarbital did not differ between the control and doxapram-treated groups. Doxapram competitively inhibited the hepatic metabolism of pentobarbital in 9000 x g supernatant incubation mixtures. The results obtained from these experiments indicate that inhibition of drug-metabolizing enzymes by doxapram may account for its enhancement of the duration of pentobarbital-induced narcosis.

Metabolic aspects of the toxicology of mixtures of parathion, toxaphene and/or 2,4-D in mice

The effects of mixtures of parathion (PA;5 mg kg-1), toxaphene (TOX; 50 mg kg-1)and/or 2,4-dichlorophenoxyacetic acid (2,4-D; 50 mg kg-1) on the hepatic mixed-function oxygenase (MFO) system were studied in ICR male mice (21-24 g) by oral intubation daily for 7 days. In general, TOX and TOX-containing mixtures were found to induce the metabolism of amidopyrine (21-52%), aniline (58-72%), phenacetin (239-307%), pentobarbital (104-148%) and benzo[a]pyrene (143-304%) in the 9000 g liver supernatants and to increase the hepatic cytochrome P-450 contents (57-80%). Furthermore, the TOX pretreatment was effective in enhancing the biotransformation of PA or paraoxon (PO) in the supernatants. This enhancement was not altered significantly by 5 mM EDTA. Although TOX increased the aliesterase activity in the serum and liver homogenates and supernatants by 31-158%, the activity of paraoxonase was not affected in these preparations. The TOX-induced increase in the metabolism of PA or PO was, at least in part, associated with the MFO system, and paraoxonase did not have significant involvement in the increase. These findings suggest that the toxicity of the PA + TOX mixture would be lower than that of PA, as TOX has the ability to increase the biotransformation of PA, as well as of PO, and the levels of aliesterase, thereby providing a pool of noncritical enzymes for the binding of PO. Because of these properties of TOX, it is anticipated that the toxicity of the PA + TOX + 2,4-D mixture also would be lower than that of PA.

Tolerance to ethanol and cross-tolerance to pentobarbital and barbital in four rat strains

Chronic ethanol treatment by gastric intubation conferred tolerance to ethanol-induced motor impairment and hypnosis in four different rat strains: Fischer 344, Long-Evans, Sprague-Dawley, and Wistar. Cross-tolerance to barbital was also observed in all strains after chronic treatment with ethanol. However, chronic ethanol treatment failed to produce cross-tolerance to pentobarbital-induced motor impairment and hypnosis in any of the four strains. The demonstration of cross-tolerance to barbital and the lack of it to pentobarbital after chronic ethanol treatment confirms and extends recent observations on the specificity of the site and/or mechanism of action of sedative-hypnotic drugs that differ in lipid solubility.

Cellular and learned tolerances for pentobarbital hypothermia

The development of behavioral tolerance to pentobarbital-induced hypothermia, as separable from cellular and metabolic tolerance, was established. Pentobarbital (PB) was administered to 4 groups of rats, 2 groups of which received intermittent (INT) IP PB treatment. One of these groups, INT/EXP, experienced the hypothermic (measured as rectal body temperature) drug effect after PB injection. The other group, INT/NONEXP, was monitored for body temperature functions (room temperature) before receiving PB (vehicle administration) and then prevented from experiencing PB-induced hypothermia by maintenance of body temperature with a towel wrap restraint and a heating lamp. The INT/EXP group also received equivalent exposure to this towel wrap after vehicle administration. Two other groups received chronic PB treatment (IP and in ground chow), one with experience for hypothermia after injections (CHR/EXP) and one prevented from experiencing the hypothermia (CHR/NONEXP). These groups also received equivalent exposure to the body temperature (at room temperature) testing and towel wrap restraint, EXP rats after vehicle injections and NONEXP after drug injections. A postchronic test of all groups compared the extent of PB hypothermia to prechronic test effects to assess the degree of tolerance. The INT/EXP group demonstrated behavioral tolerance for PB-induced hypothermia, as contrasted with the INT/NONEXP group which demonstrated little or no tolerance. Prominent tolerance was noted in both chronic groups for PB hypothermia, without a significant difference between them. After the postchronic test, chronic treatment was discontinued for 9 days (withdrawal) followed by 9 days of extinction training (vehicle behavioral testing). The two intermittent groups demonstrated no change in the hypothermic drug response during the postwithdrawal and postextinction drug tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular and learned tolerance to pentobarbital ataxia

Pentobarbital was administered to 4 groups of rats: 1) intermittently before testing on the rotarod (RR) (experienced, EXP), 2) chronically (CHR) before testing on the RR (EXP), 3) intermittently (INT) after being tested on the RR (NONEXP), and 4) chronically (CHR) after being tested on the RR (NONEXP). On postchronic testing, Group 1 (INT/EXP) failed to show tolerance to the RR decrement, related to prechronic scores, while Group 3 (INT/NONEXP) actually showed an enhanced RR decrement. Group 2 (CHR/EXP) and Group 4 (CHR/NONEXP) both exhibited prominent tolerance to RR impairment at the postchronic test, with a nonsignificant trend for greater tolerance in Group 2. The lack of an expressed behavioral tolerance in INT/EXP rats and the enhanced RR decrement in INT/NONEXP subjects at the postchronic test was attributed to repeated use of a towel wrap restraint during the chronic treatment period. When the prechronic tests for INT/EXP animals were separated into the first 3 and last 3 days, pentobarbital impairment of RR during days 4-6 was significantly less than during days 1-3. This tolerance in INT/EXP rats was lost at the postchronic testing, while INT/NONEXP subjects had by then developed an enhanced RR impairment to pentobarbital. Following postchronic testing, chronic pentobarbital (CHR/EXP and CHR/NONEXP groups) and chronic vehicle (INT/EXP and INT/NONEXP groups) were discontinued for 9 days (withdrawal), after which an intermediate dose of the drug was tested on RR performance. Next, 9 days of extinction training involved vehicle injection daily before testing RR performance, after which the intermediate drug dose was again tested. INT/EXP and INT/NONEXP groups showed no change in RR impairment at the postwithdrawal and postextinction tests. However, in CHR/EXP rats pentobarbital tolerance was partly lost at the postwithdrawal test, with a significantly greater loss at the postextinction test.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cimetidine on drug metabolism in rat pups

The effects of cimetidine on drug metabolism were studied in male and female rat pups and compared to similar effects in adult rats. As in adult rats, cimetidine 50 mg/kg/day i.p. for 7 days in the 2nd, 3rd, 4th or 5th weeks of life resulted in prolonged pentobarbitone sleeping times (diminished pentobarbitone hydroxylase activities), particularly when administered during the 3rd week. These effects of cimetidine were reversible since they continued only up to 2 weeks in males and 4 weeks in females, but by the 6th week were no longer observed. Pretreatment with cimetidine 15, 25 and 50 mg/kg/day i.p. for 7 days, resulted in a dose-dependent inhibition of aminopyrine N-demethylase and aniline hydroxylase as well as a prolongation of pentobarbitone sleeping time in both pups and adults, aniline hydroxylase being the least affected. In general, female pups were more adversely affected than male pups and adults. The therapeutic and toxicological relevance of these results in man are discussed.

Effects of formula composition on hepatic and intestinal drug metabolism during enteral nutrition

Significant compositional differences in protein and lipid content are present in currently available enteral nutrition preparations. Since variations in dietary protein and/or lipid have previously been shown to produce alterations in liver and gut drug metabolism, effects of five commonly used enteral nutrition regimens on several drug metabolic parameters were assessed in rats. Study formulations included: 1) Vivonex: low protein -no lipid; 2) High Protein Vivonex: normal protein -no lipid; 3) Vital: normal protein -normal lipid; 4) Sustacal: high protein -high lipid; 5) Isocal: normal protein -high lipid. Hepatic and intestinal microsomes were prepared after a continuous 7-day intragastric infusion of one of the formulations, and measurements of cytochrome P-450 content and assays of drug metabolizing activity were performed. No differences in intestinal microsomal cytochrome P-450 content or meperidine demethylase activity were seen among the various alimentation groups. However, significantly decreased amounts of cytochrome P-450 and reduced meperidine demethylase and pentobarbital hydroxylase activity were present in hepatic microsomes of animals receiving the lipid-poor Vivonex and High Nitrogen Vivonex preparations compared to the other alimentation groups. These data suggest that the composition of enteral nutrition formulations may significantly impact on hepatic function and specifically that the presence of lipid in such preparations may be important for maintaining normal levels of hepatic drug metabolism.

Actions of pentobarbital enantiomers on nicotinic cholinergic receptors

The enantiomers of pentobarbital had four different actions on the nicotinic receptor-rich membranes from Torpedo electroplaques. (i) Both inhibited cholinergically stimulated cation flux through the receptor's channel, with IC50 values of approximately 25 microM and extremely weak stereoselectivity. (ii) (R)-(+)-[14C]Pentobarbital bound to a saturable site with an apparent dissociation constant of 100 microM, a Hill coefficient of 1.2, and a stoichiometry of 1:1 with the acetylcholine binding sites. (S)-(-)-Pentobarbital also displaced (+)-[14C]pentobarbital but its IC50 was 4-fold higher than that of the (+)-enantiomer under the same conditions. (iii) Both enantiomers caused a stereoselective allosteric inhibition of [3H]acetylcholine binding, which occurred over the same concentration range and with the same stereoselectivity as barbiturate binding. (iv) Above 1 mM, pentobarbital caused an unexpected and sudden increase in [3H]acetylcholine binding, which lacked significant stereoselectivity. These results are consistent with a model where low concentrations of pentobarbital act on the receptor by binding to allosteric sites that have higher affinity but lower stereoselectivity for the open channel conformation than for the resting conformation, whereas the highest concentrations of pentobarbital act by nonspecific mechanisms mediated by general membrane perturbations.

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.

Identification of cannabielsoin, a new metabolite of cannabidiol formed by guinea-pig hepatic microsomal enzymes, and its pharmacological activity in mice

Metabolism of cannabidiol (CBD), one of the major components of marihuana, was studied in the guinea pig both in vitro and in vivo. Analyses of metabolites by gas chromatography and gas chromatography-mass spectrometry proved that cannabielsoin (CBE) was formed from CBD as a novel metabolite, and that the amount was about one-sixth of 7-hydroxy-CBD, which was the most abundant metabolite under in vitro conditions in the presence of microsomal monooxygenase (cytochrome P-450). CBE was also found in the liver of the guinea pig that was given CBD (100 mg/kg) intraperitoneally 1 h before sacrifice. The effects of CBE on pentobarbital-induced sleep and body temperature were assessed in the mouse; CBE possessed little activity in either case.

Effects of antimycotics on hepatic steroid metabolism

When male ddY mice were treated with consecutive doses of 10 and 100 mg/kg of miconazole (MCZ) or ketoconazole (KCZ), imidazole-containing antimycotics, once a day for 3 d, a dose-dependent shortening of pentobarbital sleeping time was observed for MCZ, while no change in the sleeping time was observed for KCZ. Even at a low dose (10 mg/kg), MCZ significantly increased cytochrome P-450 content and reduced nicotinamide adenine dinucleotide phosphate cytochrome c reductase activity. Simultaneously, hydroxylase activities of testosterone as a model of endogenous steroids, and aminopyrine N-demethylase and 7-ethoxycoumarin O-deethylase activities were increased, while KCZ lacked inducing properties even at a high dose (100 mg/kg). The change in hepatic oxidative metabolism of cortisol (F) in a patient before, during and after treatment with progressively increasing doses of 2-10 mg/kg/d of MCZ for 14 d was examined by monitoring urinary 6 beta-hydroxycortisol (6 beta-OHF), an oxidative metabolite of F. The ratio of 6 beta-OHF to F in 24-h urine decreased by 15% from the original level on day 1, and then it began to increase on day 7 to reach 2.4 times the original level on day 14. These results suggest that MCZ, but not KCZ, has inducing activity for hepatic cytochrome P-450-dependent oxidative metabolism of steroids and xenobiotics, in addition to its known inhibitory activity.

Barbiturate anesthesia and alcohol tolerance in a rat model

Anesthetic responses to a variety of barbiturates were examined in adult male rats rendered alcohol-tolerant by administration of an ethanol-containing balanced liquid diet for 3 weeks. Within 9 hours of withdrawing the diets, groups of 10-15 ethanol-fed rats and pair-fed controls were injected intraperitoneally with one of the following drug/dose combinations: thiamylal 20, 40, or 60 mg/kg; methohexital 10, 20, or 40 mg/kg; secobarbital 20, 30, or 40 mg/kg; pentobarbital 10, 20, or 40 mg/kg; or phenobarbital 80, 120, or 160 mg/kg. Each animal was monitored for time to loss of righting reflex (onset of anesthesia), absence of response to a painful stimulus (analgesia), and sleeping time (duration of anesthesia). None of these three anesthetic responses differed significantly in ethanol-fed and control rats with any dose of thiamylal, methohexital, or secobarbital. In contrast, all three responses were significantly less in rats given the middle dose of pentobarbital (20 mg/kg) than they were in control rats. Onset and duration of anesthesia were also shorter with the middle dose of phenobarbital (120 mg/kg), but analgesia was not. The results of this study, in combination with others, suggest that 1) cross-tolerance to anesthetic effects of barbiturates in ethanol-tolerant rats is not uniform with all barbiturates: and 2) because shorter-acting barbiturates show negligible cross-tolerance with alcohol, higher doses of these agents may not be required for satisfactory anesthesia in chronically alcoholic humans.

Characterization and identification of an indirect cytochrome P-450-initiated denitrosation of 2,6-dichloro-4-nitroaniline in rat hepatic microsomes

The metabolism of 2,6-dichloro-4-nitroaniline (DCNA) to a unique denitrosated product, 3,5-dichloro-p-aminophenol (DCAP), was investigated in rat hepatic microsomes using an HPLC system containing a reverse-phase column and an electrochemical detector. The parent compound appears to induce its own metabolism. The characterization of this induction was studied by polyacrylamide gel electrophoresis, catalytic enzymatic activity, and immunochemistry. The in vitro microsomal aerobic production of DCAP was increased 4- to 6.5-fold with respect to controls after animals were treated with DCNA. The microsomal production of DCAP can be inhibited by the addition of specific antibodies to cytochrome P-450d, thus indicating that the removal of the nitro group and subsequent replacement with a hydroxyl group was initiated by cytochrome P-450d in the mixed-function oxidase system. Finally, it was demonstrated by the addition of H218O to the assay that this hydroxyl group came from H2O and not molecular oxygen. It is concluded that cytochrome P-450 initiated this novel reaction by the formation of an N-hydroxylamine, followed by a non-P-450-mediated attack of water causing the removal of nitrous acid and the formation of the phenol.

Interaction between phencyclidine and its pyrolysis product, 1-phenylcyclohexene

The interaction between phencyclidine (PCP) and its pyrolysis product, 1-phenylcyclohexene (PC), at metabolic level was evaluated in Swiss male mice (21-24 g). PC (1.1, 2.2 and 4.4 mmol/kg/day for 4 days, IP, in corn oil) treatment to mice induced the in vitro metabolism (p less than 0.05) of amidopyrine (17%), aniline (12%), phenacetin (62-100%), pentobarbital (20-26%), PCP (25-80%) and benzo[a]pyrene (81-147%) in the 9000 g liver fraction and the hepatic microsomal contents of cytochrome P-450 (18-42%). The induction of the mixed function oxygenase (MFO) system was consistent with the decreases in the concentrations of IP administered pentobarbital (0.27 mmol/kg, in saline) and PCP (16.4, 32.8 and 65.6 mumol/kg, in saline) in the serum, brain, liver and kidneys of PC pretreated mice. At 1 hr after the above doses of PC, the in vitro metabolism of amidopyrine, aniline, or phenacetin was not inhibited. However, the biotransformation of benzo[a]pyrene was inhibited by 33 to 45%. Though PC after a single dose did not alter the tissue concentrations of PCP, it increased the pentobarbital concentrations in the tissues studied (p less than 0.05). These results indicate that PC has a potential to induce the MFO system after the 4-day treatment. This property of PC plays an important role in the reduction of the action of PCP by enhancing its metabolism, thereby decreasing its tissue levels.

Chronic ethanol administration alters gamma-aminobutyric acid, pentobarbital and ethanol-mediated 36Cl- uptake in cerebral cortical synaptoneurosomes

The effect of chronic ethanol exposure on the function of the gamma-aminobutyric acid (GABA) receptor-coupled chloride ion channel was studied in synaptoneurosomes from rat cerebral cortex. Ethanol was administered to rats by inhalation resulting in high blood ethanol levels which have previously been shown to produce tolerance and dependence. After 14 days of ethanol exposure, the stimulation (apparent Vmax) of 36Cl- uptake by the GABA agonist muscimol was decreased by approximately 26%. Similarly, stimulation of 36Cl- uptake by the barbiturate pentobarbital was also reduced to the same extent and there was an increase in the apparent EC50 concentration. Direct stimulation of 36Cl- uptake by ethanol was unchanged after chronic ethanol exposure when measured in the same membrane preparations in which a decrease in muscimol and pentobarbital-stimulated 36Cl- uptake were observed. However, ethanol's ability to potentiate muscimol-stimulated 36Cl- uptake was abolished completely in synaptoneurosomes from ethanol-treated rats. The decrease in GABA receptor-coupled chloride ion channel function observed after chronic ethanol administration was observed only in animals where the mean blood ethanol concentration was greater than or equal to 150 mg%. These blood levels have previously been shown to be associated with ethanol withdrawal after ethanol discontinuation in this rat strain. Four days after ethanol administration, after all signs of ethanol withdrawal had subsided, the decrease in muscimol and pentobarbital-stimulated 36Cl- uptake was reversed. These data suggest that subsensitivity of the GABA receptor-coupled chloride ion channel after chronic ethanol administration may contribute to ethanol tolerance and the ethanol withdrawal syndrome.

Effects of the calcium channel activator Bay K 8644 on general anaesthetic potency in mice

1. The effects of the calcium channel activator, Bay K 8644, on the anaesthetic potencies of ethanol, argon and pentobarbitone were examined in mice. 2. Bay K 8644, at 1 mg kg-1 i.p., significantly antagonized the general anaesthetic potencies of ethanol and argon, but at 5 and 10 mg kg-1 this compound increased the general anaesthetic potency of these drugs. 3. At doses of 1, 5 and 10 mg kg-1 Bay K 8644 antagonized the anaesthetic effects of pentobarbitone. Bay K 8644, at the highest dose used, did not alter the brain concentrations of pentobarbitone or the blood concentrations of ethanol. 5. The effects of the different doses of Bay K 8644 on the actions of ethanol and of argon are compatible with the known partial agonist properties of this compound on calcium channels in vitro. 6. The actions of Bay K 8644 on the anaesthetic effects of pentobarbitone suggests that specific interactions may be involved in the anaesthetic actions of this compound.

The effect of H2-receptor antagonists on antipyrine and pentobarbital metabolism in male and female rats

Pretreatment of male and female rats with cimetidine decreased the amount of 3-hydroxymethylantipyrine in the 24-hr urine, but urinary antipyrine and 4-hydroxyantipyrine were increased compared to that of the corresponding control rats. On the other hand, the amount of norantipyrine and the total amount of antipyrine and its metabolites were not changed by cimetidine, ranitidine and famotidine. These data suggest that ranitidine and famotidine have little effect on the microsomal mixed function oxidase system in male and female rats.

[Changes in pentobarbital hypnosis and hepatic metabolism in streptozotocin-diabetic mice]

The present study deals with the hypnotic effect of pentobarbital (Pento) in relation to its metabolism in hepatic microsomes in streptozotocin (STZ, 170 mg/kg, i.p.) injected mice. Liver weight (mg/10 g body wt.) of STZ-treated mice was larger than that of the controls throughout the experimental period. Although the shortening of sleeping time induced by Pento (60 mg/kg, i.p.) was always observed, Pento-metabolizing enzyme activity (by the method of Kato et al., 1964) increased in mice with diabetes for 2 and 4 weeks but decreased in mice with diabetes for 8 weeks. Induction following phenobarbital (100 mg/kg, s.c.) and inhibition by SKF 525-A (10 mg/kg, i.p.) of hepatic metabolizing enzyme were found in both control and mice with diabetes for 2, 4 and 8 weeks, but these were not definitely correlated to their hepatic Pento-metabolizing enzyme activities. STZ-induced hyperglycemia and shortening of sleeping time by Pento were completely prevented by the pretreatment with nicotinamide (500 mg/kg, i.p.). NPH-insulin injection partially decreased hyperglycemia in STZ-diabetic mice, but sleeping time by Pento was not significantly affected. These results suggest that the hyposensitivity to Pento in STZ-diabetic mice is partially related to an abnormality of metabolism in liver such as the hyperglycemic state.

Mechanism of N,N'-diallylpentobarbital potentiation of pentobarbital-induced sleep in mice

Potentiation mechanism of pentobarbital (PB)-induced sleep by N,N'-diallylpentobarbital (DAPB) was studied in mice. DAPB significantly prolonged the PB [40 mg/kg, intraperitoneal (i.p.)]-induced sleeping time by two routes of administration [intravenous (i.v.) and intracerebroventricular (i.c.v.)], nevertheless DAPB alone was devoid of hypnotic activity even by both routes of administration (i.v. and i.c.v.). In addition, DAPB (160 and 320 mg/kg, i.p.) significantly prolonged the sleeping time induced by i.c.v. injection of PB (200 micrograms/mouse). The brain PB half-life (T1/2) of DAPB (80 mg/kg, i.p.) treated group (9.0 h) was 13-fold longer than that of the control (0.7 h). The plasma PB half-life (T1/2) of DAPB treated group (15.2 h) was longer than that of the control (0.6 h). Moreover, DAPB significantly decreased the activities of ethylmorphine (EM) N-demethylase and aniline hydroxylase, and the content of cytochrome P-450 in mouse liver microsomes. The inhibitory effect of DAPB (40 mg/kg, i.p.) on the mouse hepatic drug-metabolizing enzymes was shown til 6 h after administration. DAPB exhibited non-competitive inhibition on the EM N-demethylase activity in vitro. These results indicate that DAPB prolongs the PB-induced sleeping time by both its depressant action to the central nervous system (CNS) and inhibitory effect on the hepatic drug-metabolizing enzymes.