Population pharmacokinetics model of THC used by pulmonary route in occasional cannabis smokers.

Cannabis is the most widely used illegal drug in the world. Delta-9-tetrahydrocannabinol (THC) is the main source of the pharmacological effect. Some studies have been carried out and showed significant variability in the described models as the values of the estimated pharmacokinetic parameters. The objective of this study was to develop a population pharmacokinetic model for THC in occasional cannabis smokers. Twelve male volunteers (age: 20-28years, body weight: 62.5-91.0kg), tobacco (3-8 cigarette per day) and cannabis occasional smokers were recruited from the local community. After ad libitum smoking cannabis cigarette according a standardized procedure, 16 blood samples up to 72h were collected. Population pharmacokinetic analysis was performed using a non-linear mixed effects model, with NONMEM software. Demographic and biological data were investigated as covariates. A three-compartment model with first-order elimination fitted the data. The model was parameterized in terms of micro constants and central volume of distribution (V1). Normal ALT concentration (6.0 to 45.0IU/l) demonstrated a statistically significant correlation with k10. The mean values (%Relative Standard Error (RSE)) for k10, k12, k21, k23, k32 and V1 were 0.408h-1 (48.8%), 4.070h-1 (21.4%), 0.022h-1 (27.0%), 1.070h-1 (14.3%), 1.060h-1 (16.7%) and 19.10L (39.7%), respectively. We have developed a population pharmacokinetic model able to describe the quantitative relationship between administration of inhaled doses of THC and the observed plasma concentrations after smoking cannabis. In addition, a linear relationship between ALT concentration and value of k10 has been described and request further investigation.

Oxidative metabolism of bupivacaine into pipecolylxylidine in humans is mainly catalyzed by CYP3A.

Bupivacaine is used to provide prolonged anesthesia and postoperative analgesia. The human cytochrome P450 (CYP) involved in bupivacaine degradation into pipecolylxylidine (PPX), its major metabolite, has, to our knowledge, never been described. Microsome samples were prepared from six human livers and incubated in the presence of bupivacaine. The concentrations of PPX in the microsomal suspensions were assessed, and K(m) and V(max) values were calculated. Bupivacaine incubations were then performed with specific CYP substrates and inhibitors. For each sample of hepatic microsomes, the correlation between the rate of PPX formation and the corresponding erythromycin N-demethylase activity was analyzed. Finally, an immunoinhibition study using an anti-rabbit CYP3A6 antibody and assays with cDNA-expressed human CYP were conducted. The apparent K(m) and V(max) values of bupivacaine were, respectively, 125 microM and 4.78 nmol/min/mg of microsomal protein. The strongest inhibition of bupivacaine metabolism was obtained for troleandomycin (-95% at 50 microM), a specific CYP3A inhibitor. The correlation between PPX formation and erythromycin N-demethylase activity showed an R value of 0.99 whereas anti-rabbit CYP3A6 antibody inhibited the degradation of bupivacaine into PPX by 99%. Finally, CYP1A2 and CYP2E1 cDNA-expressed forms of human CYP did not allow PPX formation, CYP2C19 and CYP2D6 produced only small amounts whereas CYP3A4 most efficiently metabolized bupivacaine into PPX. These results demonstrated that bupivacaine degradation into PPX was mediated in humans by CYP3A.

Nicorandil affects diurnal rhythms of body temperature, heart rate and locomotor activity in rats.

The effects of nicorandil, a K+ channel opener with a potent vasodilator action, on diurnal rhythms of body temperature, heart rate and locomotor activity were assessed in rats. Transmitters were intraperitoneally implanted under ether anaesthesia. After recovery from surgery, body temperature, heart rate and locomotor activity were recorded during control, saline or nicorandil (10 mg x kg(-1) administered orally) treatment and for 5 days after treatment. For each period, Fourier analysis determined the predominant rhythmicity for body temperature, heart rate and locomotor activity while cosinor analysis assessed the corresponding mesors, acrophases and amplitudes and maxima and minima were directly plotted from raw data. The results indicated: (1) loss of the diurnal rhythmicity for all three rhythms after implantation; (2) stress-induced modifications of almost all the characteristics of the three rhythms after saline and (3) a loss of diurnal rhythmicity of heart rate after nicorandil, an effect that was not observed after saline and which was reversed when nicorandil administration was stopped. In conclusion, nicorandil perturbed the diurnal rhythmicity of heart rate while the rhythmicity of body temperature and locomotor activity was not affected.

Effects of tobacco smoke on the gene expression of the Cyp1a, Cyp2b, Cyp2e, and Cyp3a subfamilies in mouse liver and lung: relation to single strand breaks of DNA.

Cigarette smoking is a worldwide health problem and is the greatest risk factor for lung cancer. By activating procarcinogens, hepatic and extrahepatic cytochromes P450 can participate in lung carcinogenesis. Tobacco smoke contains numerous cytochrome P450 inducers, substrates, and inhibitors. In the present study we investigated, in male NMRI mice, the effects of cigarette smoke on hepatic and pulmonary cytochrome P450 expression and their possible role in the induction of DNA lesions such as DNA single strand breaks (SSB). Hepatic and pulmonary mouse cytochrome P450 isozymes involved in carcinogenesis (Cyp1a, 2b, 2e, 3a) were differently induced by cigarette smoke. Cyp2e1 mRNA was dramatically enhanced (12.7-fold increase) while Cyp2b10 mRNA remained unchanged and Cyp1a1 was decreased or not detected. Cyp3a protein and mRNA were not detected in lung, suggesting that this isozyme is not expressed in mouse pulmonary tissue. The SSB of DNA increased in lung and liver treated mice. In contrast no modification was observed in lymphocytes that barely expressed cytochromes P450. Cimetidine and propylene glycol reduced SSB of DNA induced by smoking in liver and lung cells. The inhibition (-70%) observed in lung following treatment by propylene glycol, a CYP2E1 inhibitor, suggested that this isozyme is at least in part involved in pulmonary DNA damage induced by tobacco smoke. The high concentration of CYP2E1 function and regulation in mammals suggests that this protein could be involved in pulmonary carcinogenesis in human smokers.

Effect of cigarette smoke on UDP-glucuronosyltransferase activity and cytochrome P450 content in liver, lung and kidney microsomes in mice.

The effect of cigarette smoke on the expression of several cytochromes P450 (CYP) and UDP-glucuronosyl-transferases (UGT) was studied in mice. The animals were exposed to cigarette smoke for 4 to 30 days. Enzymatic activities supported by CYP1A1, 1A2, 2B, 2E1 and the glucuronidation activity toward phenols were measured in lung, liver and kidney microsomes. Cigarette smoke induced several CYPs, especially in lung. CYP2E1 was more induced than CYP1A1 in this organ. The expression of CYP2E1 was also increased in kidney (5.6 times after 30 days). The glucuronidation in kidney was non-sensitive to the treatment whatever substrate used. In contrast, this activity was enhanced in liver and particularly in lung, in which the glucuronidation of 1-naphthol and 2-hydroxybiphenyl was increased by 122 and 180%, respectively. Interestingly, the times of induction differed according to the substrate used, thus suggesting the presence of different UGTs active toward phenols that were differentially affected by cigarette smoke. The UGT activities toward phenols were low in lung, when compared with those measured in liver or kidney. In conclusion, cigarette smoke greatly affected both glucuronidation activity and the hydroxylation reactions supported by CYPs in mouse liver and lung.

Daily rhythms of heart rate, temperature and locomotor activity are modified by anaesthetics in rats: a telemetric study.

The aim of this study was to evaluate the effect of anaesthesia (ether or ketamine) on daily rhythms of temperature (T), heart rate (H) and locomotor activity (A) in unrestrained rats by using implanted radio-telemetry transmitters. T, H and A were measured every 10 min, in Wistar male rats, and analysed using Cosinor. The mean +/- SEM days needed, after surgical implantation, to detect a daily rhythm in H, T and A were also assessed. Six rats were anaesthetized for about 50 min either by ketamine or ether in a 3 by 3 cross-over design. Mesors, amplitudes and acrophases of T, H and A were calculated three days before (D-3; D-2; D-1), the day of anaesthesia (D0) as well as the three following days (D1; D2; D3). ANOVA was performed in order to detect, firstly a possible effect due to the order of application of anaesthesia, secondly a significant difference between ether or ketamine-induced anaesthesia and finally a modification of the mesors, amplitudes and acrophases of T, H and A, induced by each anaesthesia, for D0, D1, D2 and D3 when compared to D-1. Our results indicate: (1) Alterations of the acrophases, mesors and amplitudes, except for the amplitude of A, of the daily rhythms of T, H and A on D0 of ketamine anaesthesia while regarding ether anaesthesia only amplitude of T and H and acrophase of A were modified on D0. Some of these modifications were still observed on the days following anaesthesia. A significant difference between ether and ketamine-induced anaesthesia was also observed. (2) A non-detection of T, H and A daily rhythms after surgical implantation, which was not observed after injection of either ether or ketamine alone. Almost 10 days were needed to detect a significant daily rhythm for T, H and A. The authors suggest that, the general anaesthetic agent was responsible for a perturbation of the mesors, amplitudes and acrophases of the daily rhythms of H, T and A while the non-detection of these rhythms after implantation was more due to the surgical aggression.

Kinetics of bupivacaine after levcromakalim treatment in mice.

Previous workers have reported that 0.01 mg kg-1 of levcromakalim injected intraperitoneally did not modify bupivacaine-induced neurotoxicity but increased the duration of action of bupivacaine. This study was designed to document possible changes in the pharmacokinetic behaviour of bupivacaine and its main metabolite, N-desbutylbupivacaine in mice after a single 0.01 mg kg-1 intraperitoneal injection of levcromakalim. The kinetic parameters of bupivacaine were determined after a single 20 mg kg-1 intraperitoneal injection of bupivacaine in controls and in levcromakalim-treated mice. It was found that levcromakalim did not change any kinetic parameters of bupivacaine or of its main metabolite, N-desbutylbupivacaine. The previously reported findings of the influence of the low dose (0.01 mg kg-1) of levcromakalim on bupivacaine-induced toxicity agree well with the lack of influence of 0.01 mg kg-1 of levcromakalim on bupivacaine and N-desbutylbupivacaine pharmacokinetics, although the reported increase in the duration of action of bupivacaine after levcromakalim treatment can hardly be explained by the pharmacokinetics of bupivacaine when associated with levcromakalim. We suggest that levcromakalim might interfere directly with ion-channel block caused by bupivacaine by altering conduction properties or indirectly by enhancing bupivacaine-induced voltage and time-dependent sodium-channel block.

Ketamine effects on bupivacaine local anaesthetic activity and pharmacokinetics of bupivacaine in mice.

This study was designed to document possible changes in bupivacaine (B) local anaesthetic activity and pharmacokinetics in mice after a ketamine (K) injection. In the experiments, bupivacaine (8.25 mg.kg(-1)), was injected into the popliteal space of the right posterior limb: the local anaesthetic activity was assessed according to a sciatic nerve blockade method with three different doses (2, 10 and 40 mg/kg) of ketamine and the kinetics were studied after a 10 mg/kg dose. When ketamine was associated, the local anesthetic activity of bupivacaine was significantly enhanced as well as its elimination half-life. Significantly lower levels of the main metabolite, PPX, were observed, when ketamine was associated, suggesting a metabolic inhibition phenomenon. The ketamine-induced increase in the total anaesthetic effect of bupivacaine may thus be explained by kinetic modifications i.e. a possible inhibiting effect of ketamine on the metabolism of bupivacaine.

Effects of tobacco smoke exposure on the kinetics of bupivacaine in mice.

The aim of this work was to determine the effects of different time of tobacco smoke exposure on pharmacokinetics of bupivacaine in mice. Mice were exposed to tobacco smoke during 4 days (group T4) or 8 days (group T8) using the Hamburg II smoking machine. Controls were exposed under the same experimental conditions but without tobacco smoke. Serum pharmacokinetic parameters, protein or erythrocyte binding of bupivacaine were measured on the 4th and 8th day of exposure. Furthermore the urines were kept during 24 hours and urine metabolite percentages were determined. After the short exposure (4 days), no differences between treated and control groups were reported in contrary to the longer exposure (8 days), where data showed a significantly increased metabolism and elimination of bupivacaine in the treated group compared to the controls. Our data indicate that tobacco smoke acts at different levels i.e. metabolism, elimination and binding of bupivacaine. Tobacco smoke exposure increases the metabolism of bupivacaine by activating the hydroxylation route and by inducing an important elimination of 3OH-bupivacaine. Besides, it increases the permeability of the cell membranes and facilitates the penetration of bupivacaine and desbutylbupivacaine in erythrocytes.

Tobacco smoke influence on heart rate, body temperature, and locomotor activity daily rhythms as assessed by radiotelemetry in rats.

Using radiotelemetry, this study aimed to evaluate the influence of tobacco smoke on heart rate (H), body temperature (T) and locomotor activity (A) daily rhythms in rats. The tobacco smoke intoxication was produced with a smoking apparatus. H, T, and A data were captured by radiotelemetry. The study was divided into three periods: a 1-week control period (P1), a 1-week stress period (P2), in order to evaluate the stress induced by the animals' restraint in the smoking apparatus, and a 1-week daily tobacco smoke intoxication period (P3). For P1, P2, and P3, a power spectrum analysis was applied in order to determine the dominant period of rhythmicity. Then, characteristics of the rhythms were determined by cosinor analysis. Statistical comparisons were done by ANOVA. Power spectrum analysis showed that neither stress nor tobacco suppressed the daily rhythmicity. Cosinor revealed some modifications: H amplitude was decreased during P2 and P3 with a greater reduction during P3, while T and A amplitudes were decreased during P2 and P3 without difference between P2 and P3. T acrophase was delayed during P2, while A acrophase was delayed during P2 and P3 without any difference between P2 and P3. These perturbations may reflect the effects of stress and tobacco on the suprachiasmatic nucleus by a dopaminergic mechanism.

Effects of calcium antagonists on binding of local anesthetics to plasma proteins and erythrocytes in mice.

This study was designed to document possible changes in the binding of bupivacaine (BV), lidocaine (LC) and their main metabolites desbutylbupivacaine (PPX) and monoethylglycinexylydide (MEGX), respectively, to plasma proteins and erythrocytes in mice after acute treatment with the calcium antagonists diltiazem (DZ), nicardipine (NP) and verapamil (VP). A significant plasma protein binding of BV, LC and PPX was measured, whereas no binding could be detected for MEGX. The binding of BV was not modified by DZ, NP and VP, however, the total plasma level was increased in the presence of VP. For PPX a significant increase in total and free plasma levels and a decrease in protein binding were demonstrated after DZ and VP treatment. Concerning LC, a significant increase in total and free plasma levels was documented for DZ, NP and VP suggesting an inhibition of the metabolism of LC by the calcium antagonists. An increased penetration of LC into erythrocytes was also demonstrated which is consistent with the calcium antagonist-induced increase in LC free plasma levels. These effects may contribute in part to the previously observed increase in toxicity of BV by calcium antagonists, but are not likely to be the sole mechanism.

Effects of different exposure times to tobacco smoke intoxication on carboxyhemoglobin and hepatic enzymate activities in mice.

The aim of this work was to determine the effects of different exposure times to smoke on carboxyhemoglobin (HbCO) and hepatic enzymate activities in order to adapt a tobacco smoke intoxication model in mice. Mice were exposed to tobacco smoke for various durations of either 2 (group S2), 4 (group S4), 8 (group S8), or 31 days (group S31) using the Hamburg II machine. Controls (nonexposed animals) were used under the same experimental conditions. On the 2nd, 4th, 8th, and 31st day, mice were sacrificed by decapitation, and blood carboxyhemoglobin level and hepatic enzymate activities catalysed by CYP 450 families were measured. Our data with regard to the exposed group indicated first that HbCO was significantly increased after 4 or 8 days of exposure and decreased after 31 days compared to controls (where HbCO was constant for the duration of the 31 days) and second, the enzymate activities were significantly higher during the period of exposure. In conclusion, a 4- and 8-day exposure period with eight cigarettes per day seems to be the model of tobacco smoke intoxication in mice to be chosen.

Potassium channel agonists modify the local anaesthetic activity of bupivacaine in mice.

PURPOSE: The mechanisms of action of local anaesthetics and potassium channel agonists (PCAs) may interfere by acting in a direct or indirect manner on the same ion channels. In a previously reported study, the bupivacaine-induced mortality was shown to be modified in different ways by four PCAs tested (diazoxide (D), levcromakalim (L), nicorandil (N) and pinacidil (P)) since bupivacaine-induced mortality was increased by high doses of P and L, decreased by N and stayed unchanged by D. The present study was designed to document the changes in bupivacaine (B) local anaesthetic activity in mice after a single injection of one of the four PCAs (D, L, N and P). METHODS: Each PCA was tested at three different dosages. Controls received saline. The local anaesthetic activity was evaluated using sciatic nerve blockade. After injection of bupivacaine in the region of the sciatic nerve, the local anaesthetic activity was estimated as the loss of motor control of the injected limb. RESULTS: PCA treatment increased (P = 0.0001) the time needed for recovery from bupivacaine-induced local anaesthesia. The area under the effect vs time curve, assessing the total anaesthetic effect, was greater for N (P = 0.0016) and P (P = 0.038) but not for L (P = 0.11). Compared with controls, the maximal effect (Emax) was less for D (P = 0.009) and N (P = 0.038) but not for L (P = 0.185) or P (P = 0.45) treated groups. The injection of the PCA in the region of the sciatic nerve of the right hindlimb did not induce any alteration of the motor activity of the injected limb. CONCLUSION: The four PCAs decreased the maximal local anaesthetic effect and increased the duration of action of bupivacaine.

Kinetics of bupivacaine after nicorandil treatment in mice.

Previous studies have reported interactions between potassium-channel agonists and bupivacaine. This study was designed to document possible changes in the pharmacokinetic behaviour of bupivacaine and its main metabolite, N-desbutylbupivacaine, in mice after a single 1 mg kg-1 intraperitoneal injection of nicorandil. The kinetic variables of bupivacaine were determined after a single 20 mg kg-1 intraperitoneal dose of bupivacaine in controls (group 1) and in nicorandil-treated mice (group 2). The maximal concentration in the serum (Cmax 0.618 +/- 0.051 vs 0.408 +/- 0.041 microgram mL-1 for group 1 vs 2, P = 0.01) and the area under the concentration curve (AUC 1.039 +/- 0.051 vs 0.758 +/- 0.072 microgram mL-1 h for group 1 vs 2, P = 0.013) of bupivacaine were significantly lower in nicorandil-treated mice, while CL (0.579 +/- 0.025 vs 0.815 +/- 0.079 for group 1 vs 2, P = 0.022) and Vd (0.506 +/- 0.054 vs 0.981 +/- 0.117 for group 1 vs 2, P = 0.1006) were increased in nicorandil-treated animals. The ratio of AUC for N-desbutylbupivacaine to AUC for bupivacaine, which may partially indicate the rate of metabolism, was higher in the presence of nicorandil (1.142 +/- 0.017 compared with 0.877 +/- 0.013, P = 0.0001). Our data may indicate an increased metabolism of bupivacaine in nicorandil-treated mice. These results do not explain the previously reported enhanced anaesthetic activity of bupivacaine in the presence of nicorandil, but may participate, at least in part, in the relative protective effect of nicorandil against the previously reported bupivacaine-induced toxicity.

Seasonal variations in the kinetics of bupivacaine in the mouse.

Very few studies have been devoted to the influence of the time of the year, i.e. seasonal variations, on drug kinetics. This study aims to evaluate whether or not the kinetics of bupivacaine varied according to the time of the year in mice. Eight groups of 30 animals each received bupivacaine (20 mg/kg i.p.) at a specific month of the year, i.e. February (second week), March (first week), May (fourth week), July (first week), September (fourth week), November (second and third weeks) and December (first week), at the same time of the day (10.00 h). Total bupivacaine serum concentrations were determined by using a specific gas liquid chromatographic method on blood samples collected by decapitation at 0.25, 0.5, 1, 2, 4 and 6 h after drug administration. Pharmacokinetic variables were determined, according to a non linear fitting method (two compartment open model). All data were compared by ANOVA and the influence of the month of the year was estimated by Cosinor analysis. According to the month of the year, the kinetic parameters were significantly different except for Vd: the maximal Cmax occurred in July, the highest Tmax occurred in May, the maximal T1/2 beta and the maximal AUC were observed in February. The mechanisms underlying these variations may depend on seasonal variations of resorption, distribution, metabolism and elimination.

High inducibility of mouse renal CYP2E1 gene by tobacco smoke and its possible effect on DNA single strand breaks.

Several studies have shown in humans an association between renal carcinoma and cigarette smoking. Cigarette smoke contains numerous cytochrome P450 inducers and substrates. In the present study we investigated the effect of cigarette smoke on the regulation of murine cytochrome P450 expression in kidney and its possible role in the induction of single strand breaks in DNA. Results demonstrated that CYP2E1 (activity, protein, and MRNA) was induced by tobacco smoke (2.1, 5.6 and 20.8, respectively). We did not detect any CYP1A, CYP2B, and CYP3A using Western blot and RT-PCR experiments. We have analyzed the renal single strand breaks of DNA in control and treated mice. The results indicated an increase of single strand breaks of DNA in kidney from treated mice which paralleled the high inducibility of the CYP2E1. No significant difference was observed between lymphocytes (which expressed very low or undetectable cytochrome P450 levels) of control and treated mice.

Effects of clonidine pretreatment on the local anaesthetic activity of bupivacaine in mice.

This study was designed to document possible changes in bupivacaine local anaesthetic activity in mice after a single injection of clonidine (0.1 or 1 mgkg-1, i.p.). The local anaesthetic activity was evaluated during 60 min, according to a previously reported technique, using sciatic nerve blockade by injection of bupivacaine in the area of the sciatic nerve. Clonidine pretreatment modified the local anaesthetic activity of bupivacaine dose-dependently. The time of recovery was higher for clonidine-pretreated mice (40.00 +/- 7.24 min, 0.1 mgkg-1 clonidine: 50.0 +/- 9.35 min, 1 mgkg-1 clonidine) compared with controls (27.22 +/- 1.21 min, P = 0.02). The maximal effect (Emax) was significantly lower for the pretreated group (1.15 +/- 0.13 units, 0.1 mgkg-1; 1.35 +/- 0.09 units, 1 mgkg-1) compared with the control group (1.72 +/- 0.13, P = 0.01). Our data indicate a significant decrease in the duration of anaesthetic activity of bupivacaine in clonidine-pretreated mice.

Kinetics of bupivacaine after clonidine pretreatment in mice.

Previous studies have reported that clonidine pretreatment causes an increase in the local anaesthetic activity of bupivacaine. This study was designed to document possible changes in the pharmacokinetic behaviour of bupivacaine and its main metabolite, desbutylbupivacaine, PPX, in mice after a single, 0.1 mg.kg-1, injection of clonidine. Kinetic variables of bupivacaine were determined after a single 20 mg.kg-1 ip dose of bupivacaine in controls (Group I) and in clonidine (0.1 mg.kg-1 ip) pretreated mice (Group 2). The maximal concentration in serum (Cmax, 2.553 +/- 0.862 micrograms.ml-1 versus 0.962 +/- 0.141 microgram.ml01 for Groups 2 and 1, respectively, P = 0.01) and the area under the concentration curve (AUC, 3.530 +/- 0.330 micrograms.ml-1.hr-1 versus 1.755 +/- 0.252 micrograms.ml-1.hr-1 for Groups 2 and 1, respectively, P < 0.01) of bupivacaine were higher in clonidine pretreated mice while the Clearance (Cl) was decreased in clonidine pretreated animals (0.603 +/- 0.054 micrograms.ml-1 versus 1.264 +/- 0.447 micrograms.ml-1 for Groups 2 and 1, respectively, P < 0.01). The ratio of AUC PPX/AUC bupivacaine (which may partially indicate the rate of metabolism) was lower in presence of clonidine (0.220 +/- 0.019 against 0.425 +/- 0.033 for Groups 2 and 1, respectively, P < 0.01). Our data indicate decreased metabolism in the clonidine-treated mice which suggests altered hepatic metabolism of bupivacaine by clonidine. This may explain the previously reported enhanced anaesthetic activity of bupivacaine in the presence of clonidine.

Effect of four potassium channel agonists on bupivacaine-induced toxicity in mice.

The influence of four potassium channel agonists i.e. diazoxide (D), levcromakalim (L), nicorandil (N) and pinacidil (P) on bupivacaine-induced acute toxicity was evaluated by measuring the convulsant activity, the time of latency to convulse and the mortality rate. Four different dosages (i.e. 0.1, 1, 10 and 100 mg/kg/i.p. for D, N and P and 0.01, 0.1, 1 and 5 mg/kg/i.p. for L) were injected to a total of 200 male NMRI adult mice: 16 groups of 10 mice each were previously treated by a single i.p. dose of each potassium channel agonist while controls (n = 40) received saline injection. Thus, 15 minutes later, all groups were injected with a 50 mg/kg/i.p. single dose of bupivacaine. The convulsant activity of bupivacaine was significantly modified by only high doses of L in a dose-dependent manner. Compared to the controls, the period of latency was significantly increased for most of the doses of P, N, D and L in a dose dependent manner for L and P. The anesthetic-induced mortality (47.5% for controls) was not significantly modified by D, but decreased by N and increased by high doses of L and P which is probably related to a delayed mortality.