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.