Plasmodium yoelii nigeriensis (MDR)-efficacy of oral pyronaridine against multidrug-resistant malaria in Swiss mice

A multidrug-resistant strain of Plasmodium yoelii nigeriensis (MDR) showing a wide spectrum of resistance to chloroquine, amodiaquine, mepacrine, mefloquine, halofantrine, quinine, and quinidine was used in this study for in vivo evaluation of the blood schizontocidal activity of pyronaridine, a topoisomerase II inhibitor, in Swiss mice. The parasite produces 100% lethal infection in mice. The drug was administered orally once a day from day 0 onward. The initial studies showed that low doses of pyronaridine (0.625 to 5.0 mg base/kg x9 days) did not completely control blood-induced P. yoelii nigeriensis infection. Finally a series of doses of pyronaridine ranging from 1.25 to 30.0 mg/kg administered orally for 7 consecutive days were evaluated and in spite of high level of resistance to standard antimalarials, the parasite P. yoelii nigeriensis has shown complete susceptibility to pyronaridine (15 mg/kg dose x7 days). The present paper also compares the merits of a single MDR strain vs a battery of different resistant lines for quick antimalarials screening.     

In vivo postirradiation protection by a vitamin E analog, alpha-TMG

The water-soluble vitamin E derivative alpha-TMG is an excellent radical scavenger. A dose of 600 mg/kg TMG significantly reduced radiation clastogenicity in mouse bone marrow when administered after irradiation. The present study was aimed at investigating the radioprotective effect of postirradiation treatment with alpha-TMG against a range of whole-body lethal (8.5-12 Gy) and sublethal (1-5 Gy) doses of radiation in adult Swiss albino mice. Protection against lethal irradiation was evaluated from 30-day mouse survival and against sublethal doses was assessed from micronuclei and chromosomal aberrations in the bone marrow 24 h after irradiation. An intraperitoneal injection of 600 mg/kg TMG within 10 min of lethal irradiation increased survival, giving a dose modification factor (DMF) of 1.09. TMG at doses of 400 mg/kg and 600 mg/kg significantly reduced the percentage of aberrant metaphases, the different types of aberrations, and the number of micronucleated erythrocytes. DMFs of 1.22 and 1.48 for percentage aberrant metaphases and 1.6 and 1.98 for micronuclei were obtained for 400 mg/kg and 600 mg/kg TMG, respectively. No drug toxicity was observed at these doses. The effectiveness of TMG when administered postirradiation suggests its possible utility for protection against unplanned radiation exposures.     

Flunarizine and verapamil: Effects on central nervous system and peripheral consequences of cytotoxic hypoxia in rats

Flunarizine is a calcium entry blocking drug possessing antihypoxic activity in animal models of cerebral and peripheral ischemia-anoxia and has clinical usefulness in circulatory disorders of both central and peripheral origin. This report compares the activity of flunarizine and verapamil, another calcium entry blocking drug, on the central nervous system (CNS) and peripheral consequences of cytotoxic hypoxia induced by high and low doses of KCN. The lethal effect of KCN (6 mg/kg, i.p.) in rats was prevented by orally administered flunarizine (ED₅₀ = 12 mg/kg with four-hr pretreatment) but not by verapamil (at oral doses up to 80 mg.kg with one-hr pretreatment). Since the lethal effect of KCN involves failure of respiration at the CNS level, these results suggest that flunarizine protects against the hypoxic effect of the cyanide ion by an action in brain tissue. We found also that the stimulant effect of low intravenous doses (0.5 mg/kg/min) of KCN upon respiration rate was not altered in pentobarbital- and chloralose-anesthetized rats treated with oral doses of flunarizine up to 80 mg/kg (with four hr pretreatment). In contrast, KCN-stimulated respiration rate in pentobarbital anesthetized rats was significantly attenuated by verapamil (20 and 40 mg/kg, p.o. with one hr pretreatment). Since low doses of the cyanide ion render respiration quicker and deeper by an action on chemoreceptive cells in peripheral arteries, the effect of verapamil against the hypoxic effect of KCN is mediated by an action in the periphery. In summary, we have shown that the physiological consequences of cytotoxic hypoxia can be affected by calcium entry blocking drugs having site-specific activities. Based on our results, flunarizine is more effective than verapamil against cellular anoxia involving the CNS.     

Effect of chronic D-fenfluramine administration on rat hypothalamic serotonin levels and release

D-fenfluramine, an anorectic agent in rats and man, was administered daily at doses 1.25, 2.5, 5 or 10 mg/kg/day for 10 days, and sacrificed 6 days later. Hypothalamic serotonin (5-HT) levels were unchanged in rats receiving 1.25-5 mg/kg/day of d-fenfluramine but reduced by 22% (p less than 0.01) at the highest drug dose (10 mg/kg/day); hypothalamic 5-hydroxyindole acetic acid (5-HIAA) levels were reduced by 15% (p less than 0.05) or 28% (p less than 0.01) in rats receiving 5 or 10 mg/kg/day of the drug, respectively. Hypothalamic slices prepared from rats which were previously treated with any of the drug doses spontaneously released endogenous 5-HT at rates that did not differ from those of vehicle-treated rats. 5-HT released with electrical field-stimulation was unaffected by prior d-fenfluramine treatment at doses of 1.25-5 mg/kg/day, and was reduced by 20% (p less than 0.05) from slices prepared from rats which received 10 mg/kg/day. 5-HIAA efflux was also attenuated by the highest drug dose. These data indicate that chronic administration to rats of customary anorectic doses of d-fenfluramine (i.e. 0.06-1.25 mg/kg) fail to cause long-lasting reductions in brain 5-HT release.     

The dominant lethal effect of dietary triethylenemelamine.

Triethylenemelamine (TEM) was administered in the diet to adult male mice at doses of 0.1, 0.3, 1, 10 or 50 mg/kg body weight for 45 days or at doses of 0.1 or 0.3 mg/kg b.w. for 10 days. As a comparison, male mice were treated intraperitoneally with 5 daily doses of 0.25 or 0.5 mg TEM/kg b.w. At the end of the treatment period, males were mated sequentially with 2 untreated virgin females each for 2 or 3 weeks. Near mid-pregnancy the number of implantation sites and fetal deaths were determined. TEM, administered in the diet at 10 or 50 mg/kg b.w. for 45 dyas, was lethal to male mice. Surviving males from the 1 mg/kg level failed to impregnate any females during the two matings. TEM, given in the diet at 0.1 or 0.3 mg/kg for 10 or 45 dyas, decreased fertility and increased dominant lethal mutations in a dose and time dependent manner. These results were comparable to those obtained from males treated i.p. with TEM at 0.25 or 0.5 mg/kg b.w.     

In vivo radioprotection by 5-aminosalicylic acid

The radioprotective effect of 5-aminosalicylic acid (5ASA) was investigated in mouse bone marrow. The present study was aimed at investigating the radioprotective effect of pre-irradiation treatment with 5ASA against a range of whole-body lethal (8-11 Gy) and sublethal (1-4 Gy) doses of gamma-radiation (RT) in adult Swiss albino mice. Protection against lethal irradiation was evaluated from 30-day mouse survival and against sublethal doses was assessed from chromosomal aberrations in the bone marrow 24 h after irradiation. An intraperitoneal injection of 5ASA at a dose of 25mg/kg body weight (b. wt.) 30 min before lethal RT increased survival, giving a dose modification factor (DMF) of 1.08. Injection of 5ASA (25 mg/kg b. wt.) 60 or 30 min before or within 15 min after 3 Gy whole body RT resulted in a significant decrease in the radiation-induced aberrant metaphases, at 24 h post-irradiation. Maximum effect was seen when the drug was administered 30 min before irradiation. 5ASA (25 mg/kg b. wt.) significantly reduced the number of aberrant metaphases and the different types of aberrations at all the radiation doses (1-4 Gy) tested, giving a DMFs of 1.43 for number of aberrant metaphases. 5ASA pretreatment also significantly enhanced the endogenous spleen colonies in mouse exposed to 11 Gy RT. Pretreatment with 5ASA, protected plasmid DNA (pGEM-7Zf) against breakage induced by RT and Fenton reactants. Using nanosecond pulse radiolysis technique, the bimolecular rate constant of the reaction of 5ASA with hydroxyl radical was found to be 6.7x10(9)M(-1)s(-1). The p53 and p21 protein levels of bone marrow and spleen were evaluated to identify the specific molecular mechanisms. Both p53 and p21 increased 24h after 6 Gy irradiation, while treatment with 5ASA inhibited this RT-induced increase. Therefore, the present data suggest that 5ASA pretreatment decreases death caused by RT-induced gastrointestinal and hemopoeitic syndromes. The proposed mechanism of radioprotection by 5ASA is through the inhibition of damage to DNA, lipids, and proteins; and prevention of RT-induced increased expression of p53 and p21.     

Nitrendipine: an antidote to cardiac and lethal toxicity of cocaine

Nitrendipine, a Ca2+ modulator was tested in the rat as an antagonist to the cardiac toxicity of cocaine and as an antidote to the acute lethal effects of this drug. In a first series of experiments, nitrendipine (1.46 X 10(-3) mg/kg/min) when simultaneously administered intraarterially with cocaine (2 mg/kg/min) suppresses the arrhythmias induced by cocaine and increases survival time from 73 +/- 33 min to 309 +/- 118 min and the lethal dose of cocaine from 146 +/- 66 mg/kg to 618 +/- 236 mg/kg (p less than 0.003). Nitrendipine also protects the heart from the acute morphological lesions induced by cocaine administration and antagonizes some of the central effects of cocaine. In a second series, 5 rats administered 60 mg/kg of cocaine intraperitoneally had a survival time of 8'06 +/- 5'20. Death was attributed to convulsions and respiratory arrest. Animals treated with nitrendipine (129 +/- 23 mg/kg) 4'30" after cocaine administration survived. Nitrendipine appears to have general protective effects against cocaine cardiac toxicity and the acute lethal effects of this alkaloid.     

Genetic effects of the new pesticide rovicurt

Administration of rovicoort, a new pesticide, in various single doses (75, 150, 380 mg/kg) to mongrel white male rats intragastrically on empty stomach showed that the doses of 75 and 150 mg/kg stimulated adaptive mechanisms of the organism resulting in the increase of diameter of both seminiferous tubules and the number of Sertoli cells as well as fertilizing capacity of spermatozoa. Dominant lethal mutation in early postmeiotic cells was induced after the drug exposure of 150 and 380 mg/kg doses.     

Gametocytocidal activity of pyronaridine and DNA topoisomerase II inhibitors against multidrug-resistant Plasmodium falciparum in vitro

Gametocytocidal activities of pyronaridine and DNA topoisomerase II inhibitors against two isolates of multidrug-resistant Plasmodium falciparum, KT1 and KT3 were determined. After sorbitol treatment, pure gametocyte cultures of Plasmodium falciparum containing mostly young gametocytes (stage II and III) obtained on day 11 were exposed to the drugs for 48 h. The effect of the drugs on gametocyte development was assessed by counting gametocytes on day 15 of culture. Pyronaridine was the most effective gametocytocidal drug against P. falciparum isolates KT1 and KT3 with 50% inhibitory concentration of 6 and 20 nM, respectively. Moreover, the 50% inhibitory concentration of pyronaridine was lower than that of primaquine which is the only drug used to treat malaria patients harboring gametocytes. Prokaryotic (norfloxacin) and eukaryotic (amsacrine and etoposide) DNA topoisomerase II inhibitors were only effective against asexual but not sexual stages of the malaria parasites. Pyronaridine has both schizontocidal and gametocytocidal activities against the human malaria parasite, P. falciparum.     

Effect of artemether on pentobarbitone sleep and electrical activity in rats

Artemether (AM), a highly effective treatment for multidrug-resistant malaria and a component of artemisinin combination therapy, has been associated with some neurotoxicity following repeated high doses. This study was aimed at investigating the effect of AM on pentobarbitone sleep and electrical activities in rats. Wistar rats received AM i.p. at 3 dose levels: 1.5, 7.5, and 15 mg/kg, whereas control rats received 0.2 mL of the vehicle (3% v/v Tween 80). AM administered 20 min before pentobarbitone had no significant effect on the onset and duration of sleep. However, after a 7-day pretreatment, AM dose-dependently prolonged pentobarbitone sleep, as did chloramphenicol. Electroencephalogram and electromyogram recordings 20 min after pretreatment showed that AM (15 mg/kg) exhibited inhibitory activity similar to chlorpromazine as opposed to the excitatory effect of amphetamine. When pretreated for 7 days, rats receiving 1.5 mg/kg AM also showed inhibitory activity of the cortical centres, whereas desynchronization of the optic tectum and reticular formation was observed in rats pretreated with 7.5 and 15 mg/kg AM. The present data suggest that although the therapeutic equivalent dose of 1.5 mg/kg AM had no appreciable effects on pentobarbitone sleep but caused reduced electrical activity in rats, higher doses have more profound effects on both indices.     

Measurements of brain amobarbital concentrations in rats anesthetized and overdosed by amobarbital and treated centrally with dibutyryl cyclic AMP.

Three doses of amobarbital, an anesthetic dose (80 mg/kg), a minimum lethal dose (130 mg/kg), and a high lethal dose (180 mg/ kg) were administered intraperitoneally to groups of rats. All rats were injected intracerebroventricularly with 0.9% saline or dibutyryl cyclic AMP, 200 μg/rat. While those rats treated with saline solution were still sleeping at decapitation and those treated with dibutyryl cyclic AMP were awake, there were no significant differences in their brain concentrations of amobarbital.     

In vivo antiplasmodial activity of 11(13)-dehydroivaxillin from Carpesium ceruum

The whole plants of Carpesium genus are used in traditional medicine as anti-pyretic, analgesic and vermifugic, including a topical application for sores and inflammation. A previous study on Carpesium genus suggested that the antiplasmodial activity against Plasmodium falciparum was due to the existence of 11(13)- dehydroivaxillin (DDV) from EtOAc extracts of C. ceruum (Compositae). Here, the antimalarial activity of DDV was evaluated against Plasmodium berghei in mice. The LD(50) of the compound was determined as 51.2 mg/kg, while doses of 124 mg/kg and above were found to be lethal to mice. DDV (2, 5, 10 mg/kg/day) exhibited a significant blood schizontocidal activity in 4-day early infection, repository evaluation and in an established infection with a significant mean survival time comparable to that of the standard drug, chloroquine, 5 mg/kg/day. DDV possesses a promising antiplasmodial activity, which can be exploited in malaria therapy.     

Discriminative stimulus,antagonist, and rate-decreasing effects of cyclorphan: Multiple modes of action

The discriminative effects of cyclorphan were studied in pigeons trained to discriminate 0.32 mg/kg ethylketazocine, 1.8 mg/kg cyclazocine, or 32 mg/kg naltrexone from saline. A fourth group of pigeons was administered 100 mg/kg/day morphine and trained to discriminate 0.1 mg/kg naltrexone from saline. Cyclorphan produced dose-related ethylketazocine-appropriate responding that reached a maximum of 83% of the total session responses at 0.3 mg/kg. Higher cyclorphan doses produced less ethylketazocine-appropriate responding. In pigeons trained to discriminate cyclazocine from saline, maximum drug-appropriate responding of greater than 90% occured at 5.6–10.0 mg/kg cyclorphan. In narcotic-naive pigeons trained to discriminate 32 mg/kg naltrexone from saline, cyclorphan produced a maximum of less than 50% drug-appropriate responding. In contrast, in pigeons chronically administered morphine and trained to discriminate 0.1 mg/kg naltrexone from saline, 1.0 mg/kg cyclorphan resulted in 100% drug-appropriate responding. In pigeons responding under a multiple fixed-interval, fixed-ratio schedule of food delivery, cyclorphan produced a complete dose-related reversal of the rate-decreasing effects of 10 mg/kg morphine, the maximally effective antagonist doses being 1.0–3.2 mg/kg. Higher cyclorphan doses (10 mg/kg) resulted in response rate decreases that were not reversed by naloxone (1 mg/kg). Thus, cyclorphan has discriminative effects that are similar to those of both ethylketazocine and, at 20-fold higher doses, cyclazocine. In addition, in morphine-treated pigeons, cyclorphan, across the same range of doses that produce ethylketazocine-appropriate responding, has discriminative effects that are similar to those of naltrexone, an effect that is probably related to the antagonist action of the drug.     

Treatment of experimental Pneumocystis carinii pneumonia with 1,3-di(4-imidazolino-2-methoxyphenoxy)propane lactate.

An analogue of pentamidine, 1,3-di(4-imidazolino-2-methoxyphenoxy)propane (DMP) lactate, was tested against rat Pneumocystis carinii pneumonia (PCP). The drug was found to be highly active in the treatment of rat PCP at a dose of 1.75 mg/kg (parent molecule) when administered by intravenous (i.v.) injection (daily for 2 wk). The compound was also active against PCP when given orally, however, significantly higher doses of DMP were necessary when compared to the i.v. dosing regimen. Prophylactic doses (i.v.) of the drug also proved highly effective in preventing PCP.     

Anti-inflammatory activity of hydroxydihydrocarvone

Hydroxydihydrocarvone (HC) is a synthetic intermediate obtained by hydration of the natural compound (R)-(-)-carvone. The aim of the present study was to investigate the possible anti-inflammatory activity of orally administered HC. Toxicity, motor coordination, tail immersion test, as well as carrageenan-induced paw edema and myeloperoxidase (MPO) activity or peritonitis were all evaluated in rodents. HC was force-fed to the animals 1 h before the stimulus. The lethal dose 50% (LD50) of orally administered HC was 1259 mg/kg. No changes in motor coordination were recorded in HC-treated mice in the rotarod test. The time of response to the thermoceptive stimulus in the tail immersion test was longer in HC-treated animals (50, 100, and 200 mg/kg) than in the vehicle-treated group. HC also significantly decreased the area under curve of carrageenan-induced rat paw edema at 100 and 200 mg/kg and MPO activity at 200 mg/kg. Carrageenan-induced neutrophil recruitment to the peritoneal cavity was significantly reduced by HC at doses of 100 or 200 mg/kg, but not 50 mg/kg. These findings demonstrate that orally administered HC exerts antinociceptive and anti-inflammatory activities in rats and mice.     

Induction of lethal infection with indigenous Escherichia coli in mice by fluorouracil

A single administration of fluorouracil (5-FU), a well-used cancer chemotherapeutic agent, at high doses (338-800 mg/kg) to specific pathogen free mice induced a lethal infection with Escherichia coli. The infection was manifested in all the mice treated with 5-FU 7-14 days after administration of the drug, when the number of E. coli in liver reached levels ranging from 10(8) to 10(10) colony-forming units, and the type of the infecting bacteria was limited to E. coli. The infection was accompanied with the increase in the population levels of E. coli in the intestinal tract which reached levels about 10(3) to 10(4) times as high as those of normal mice. Administration of tegafur, a less toxic derivative of 5-FU, to mice at a lethal dose of 1280 mg/kg induced infection with E. coli similar to that induced by 5-FU. Multiple administration of both streptomycin sulfate and cephalothin to mice after treatment with 5-FU protected the mice completely from the lethal infection induced by 5-FU, suggesting that the lethality of 5-FU was due to indigenous bacterial infection.     

Retinoid teratogenicity in the macaque: verification of dosing regimen

To further define teratogenicity associated with 13-cis-retinoic acid (13-cis-RA) in the cynomolgus monkey, the drug was orally administered on three different treatment regimens. Experiment (Exp.) 1 (2.5 mg/kg/day, gestational day [GD] 12-27, n = 11) investigated the teratogenicity of a single daily dose of 13-cis-RA administered shortly after embryo implantation. Pharmacokinetic sampling was done to determine retinoid profiles on the first (GD12) and last (GD27) days of treatment. Exposure to 13-cis-RA during early organogenesis in Exp. 2 (2.5 mg/kg/day, GD20-27, and 2 x 2.5 mg/kg/day, GD28-30, n = 5) investigated the potential adverse effects of 13-cis-RA on the developing limb. The use of multiple doses of 13-cis-RA in Exp. 3 (2 x 2.5 mg/kg/day, GD26-27, n = 5) investigated the necessity of double dosing on the induction of retinoid embryopathy in the macaque. Malformations of retinoid target organs as well as embryolethality were most prevalent when single daily doses of 13-cis-RA were administered during pre- and early organogenesis in Exp. 1. Moreover, multiple doses on GD26-27 failed to induce any manifestation of abnormal development in Exp. 3. These results confirm that the lowest observed adverse effect level (LOAEL) in macaques is 2.5 rather than 5.0 times greater than that observed in human pregnancies. Exposure during forelimb development (GD20-30) in Exp. 2 was unsuccessful in inducing defects of this skeletal region, although defects in several retinoid target organs (i.e., cerebellum and internal ear) were present, indicating that a teratogenic threshold was achieved. Pharmacokinetic analysis of 13-cis-RA and its metabolites on GD12 and 27 in Exp. 1 showed considerable exposure to the administered drug and its 4-oxo-metabolite. In contrast, the exposure to all-trans-RA was negligible. The results support the use of a specific treatment schedule in early gestation in the macaque as the most appropriate model for characterizing the teratogenic potential of retinoids in humans.     

Chemoprotective effects of recombinant human IL-1 alpha in cyclophosphamide-treated normal and tumor-bearing mice. Protection from acute toxicity, hematologic effects, development of late mortality, and enhanced therapeutic efficacy

In this study, recombinant human IL-1 alpha (rhIL-1 alpha) was used to protect normal and tumor-bearing BALB/c mice from the acute toxicity caused by lethal doses of cyclophosphamide (Cy) and 5-fluorouracil. Pretreatment of mice for 7 days with 10,000 U/day of rhIL-1 alpha protected 70 to 100% of mice from the acute death induced by lethal doses of both Cy (380 mg/kg) and 5-fluorouracil (250 mg/kg). In contrast, post-treatment of mice with single or multiple doses of rhIL-1 alpha was not chemoprotective. Pretreatment of mice with rhIL-1 alpha increased the acute LD90 of Cy from 380 mg/kg to greater than 500 mg/kg in normal mice, an LD90 dose-modifying effect of at least 1.25, was accompanied by a more rapid recovery from neutropenia and a less severe reduction in the number of bone marrow single lineage monocyte, myeloid, or myelomonocytic colonies. Some of the mice (10 to 50%) that were successfully protected by pretreatment with rhIL-1 alpha died after day 50. These mice consistently presented with extensive pulmonary inflammation and fibrosis at death. Mice bearing murine renal cancer (Renca) were also protected from the acute toxic effects of Cy (450 mg/kg) by pretreatment with rhIL-1 alpha. Renca-bearing mice pretreated with rhIL-1 alpha and either sublethal (300 mg/kg) or lethal (450 mg/kg) doses of Cy exhibited enhanced survival times over those of untreated Renca-bearing mice. Interestingly, the cause of death in Renca-bearing mice that ultimately failed treatment with rhIL-1 alpha plus 300 mg/kg Cy was recurrent tumor, whereas most mice treated with rhIL-1 alpha plus 450 mg/kg Cy had no detectable tumor, although several died from late pulmonary inflammation and fibrosis. Thus, the dose escalation of Cy in rhIL-1 alpha-pretreated mice results in greater antitumor effects of Cy. However, the dose escalation of some cytotoxic agents allowed by the use of myelostimulatory agents can result in late fatal complications not detected in acute toxicity testing.     

Caffeine potentiates the enhancement by choline of striatal acetylcholine release.

We investigated the effect of peripherally administered caffeine (50 mg/kg), choline (30, 60, or 120 mg/kg) or combinations of both drugs on the spontaneous release of acetylcholine (ACh) from the corpus striatum of anesthetized rats using in vivo microdialysis. Caffeine alone or choline in the 30 or 60 mg/kg dose failed to increase ACh in microdialysis samples; the 120 mg/kg choline dose significantly enhanced ACh during the 80 min following drug administration. Coadministration of caffeine with choline significantly increased ACh release after each of the choline doses tested. Peak microdialysate levels with the 120 mg/kg dose were increased 112% when caffeine was additionally administered, as compared with 54% without caffeine. These results indicate that choline administration can enhance spontaneous ACh release from neurons, and that caffeine, a drug known to block adenosine receptors on these neurons, can amplify the choline effect.     

The comparative effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol seizure threshold in the rabbit.

The anticonvulsant effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol (PTZ) seizure threshold were studied and compared in the rabbit. The PTZ seizure threshold determined in various rabbit groups during the control phase of conducted experiments, was found to be in the range of 10.1 +/- 2.0 to 13.5 +/- 3.7 mg/kg. Intravenous administration of comparable doses of propofol, thiopental, and diazepam resulted in marked and significant increases in PTZ seizure threshold. At all administered doses (1.25-10.0 mg/kg), propofol was found to be more effective than thiopental in increasing the PTZ threshold dose. However, the anticonvulsant effects of diazepam were more marked than those of propofol, except at a dose of 10 mg/kg where both agents exhibited equipotent activities. These data demonstrate that propofol enjoys a considerable degree of anticonvulsant activity in the rabbit. This anticonvulsant action is greater than that of thiopental at doses ranging from 2.5 to 10 mg/kg and equipotent with diazepam at the 10 mg/kg dose.