Biomedical subjects
Publications and source records attributed to H H Frey.
The influence of drugs affecting the turnover of histamine in brain and histamine antagonists on pentetrazole seizure threshold in mice was studied. A rise in histamine brain concentration as well as treatment with central acting H1-, but not H2- and H3-antagonists led to an increase of the convulsive threshold. It is therefore concluded that histamine has a certain anticonvulsant effect which is mediated through H1-receptors.
The effect of different groups of psychotropic agents on the spontaneous absence-like paroxysms in the ECoG of rats was studied in order to evaluate the specificity of the model for antiabsence drugs. Morphine-like analgesics increased the number of paroxysms, whereas this was depressed or the discharges were completely abolished by the following drugs: d-amphetamine, tricyclic antidepressants, centrally acting anticholinergics and L-DOPA, NMDA antagonists and memantine. Since the latter drugs have been reported to be effective in petit mal epilepsy, or the NMDA antagonists and memantine, have a potential anticonvulsant effect, the results are in favour of the usefulness of the model for antiabsence drugs.
Mice were treated for 14 days with clonazepam, 0.5 mg/kg i.p. twice daily, during which time partial tolerance to the anticonvulsant effect against pentetrazole developed. The development of tolerance was paralleled by a reduced turnover of noradrenaline in the whole brain, and of dopamine in the midbrain. The turnover of 5-HT was increased during the first week of treatment, but decreased thereafter. These changes in monoamine turnover, which are thought to be GABA-mediated, are consistent with an increased seizure susceptibility, and may contribute to the development of tolerance to the anticonvulsant effect of benzodiazepines.
An inquiry on the use of narcotics was carried through among practising veterinary surgeons and in animal hospitals. Of 5907 questionnaires sent out 2725 (46.1%) were returned; 86.3% of these stated the use of narcotics. There was a negative correlation between the use of narcotics and the age of the veterinary surgeons. Levomethadone, pentobarbital and fentanyl were used most often, the other narcotics were only mentioned in 1-2% of the questionnaires or not at all. Narcotics were primarily ordered for the veterinary "house pharmacy" and for use in practice, prescriptions for the individual patient being the exception.
Ethosuximide and valproic acid were tested for 4 and 2 weeks, respectively, in rats showing the spontaneous spike-wave syndrome. Ethosuximide suppressed the syndrome at plasma concentrations of 75-100 micrograms/ml. High doses of valproate (170 mg/kg i.p., t.i.d.), resulting in plasma concentrations of about 500 micrograms/ml, were necessary to suppress the syndrome, but signs of tolerance to the drug developed from day 5. Tolerance was confined to the number of spike-wave complexes, whereas the duration of the discharges was shortened to 60% of the control value, without there being signs of tolerance. It is assumed that increases in cerebral GABA, induced by the high concentration of valproate, counteracted the anti-absence effect of the drug in this model.
Apomorphine proved to be more effective as an emetic in dogs after s.c. administration than after i.m. injection with doses of 0.04 and 0.1 mg/kg. This effect is explained by an anti-emetic effect mediated by mu-receptors in the vomiting centre in the brain, which, in contrast to the chemoreceptor trigger zone, is within the blood-brain barrier. A certain delay between the stimulation of D2-receptors in the chemoreceptor trigger zone (causing emesis) and mu-receptors in the vomiting centre (producing anti-emesis) therefore results, leading to a self-limiting emesis. Blockade of the mu-receptors by naloxone increased and prolonged the effect of apomorphine. A relatively narrow range of apomorphine concentrations on s.c. administration is then effective to stimulate the chemoreceptor trigger zone, but can hardly inhibit the vomiting centre, and must therefore be considered the most suitable route for administration of apomorphine.
In testing poorly soluble substances in-vitro on isolated organs, organic solvents and solubilizers are used to increase water-solubility. To facilitate selection of appropriate substances, the effects of eleven of these chemicals have been studied in the following isolated smooth muscle preparations: guinea-pig ileum stimulated by carbachol, histamine, 5-HT or single field stimuli; rat fundus stimulated by 5-HT; and mouse vas deferens stimulated by noradrenaline or trains of field stimuli. Nine solvents (acetone, diethyleneglycol monoethylether, dimethyl sulphoxide, ethanol, glycerol, methanol, polyethylene glycol 400, 1,2-propanediol, Tetraglycol (tetrahydrofurfurylalcohol polyethyleneglycolether)) and two detergents (Triton-X 100 and Tween 80) were examined. The vas deferens proved to be most resistant, whereas rat fundus and guinea-pig ileum were more sensitive to the effects of solvent when present from 1 to 10 g L-1. Most solvents caused non-specific, concentration-dependent reversible inhibition of contractions. Dimethyl sulphoxide in high concentrations increased the contractile responses of guinea-pig ileum stimulated by 5-HT and in both experiments with electrical stimulation. Polyethylene glycol 400 augmented the response of mouse vas deferens to electrical stimulation. Overall, 1,2-propylene glycol and polyethylene glycol 400 had the least effect and can be used in a concentration of 3 g L-1, and in qualitative studies even up to 10 g L-1. Glycerol, both monohydric alcohols and dimethyl sulphoxide produced more intense effects and should not exceed concentrations of 1-3 g L-1. Stronger inhibition was caused by diethyleneglycol monoethylether, acetone and Tetraglycol, and the bath concentrations of these substances should not exceed 0.5-1g L-1. Of the detergents only Tween 80 is suitable as a solubilizer in smooth muscle preparations in-vitro, forming micelles at 10 mg L-1 a concentration tolerated by isolated organs in this study.
Abecarnil (ZK 112119; isopropyl-6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate), a novel beta-carboline with high affinity for central benzodiazepine (BZ) receptors, has been shown recently to be a potent anxiolytic and anticonvulsant in animal models whereas lacking ataxia-producing effects, a profile typical for a partial agonist at BZ receptors. In the present study abecarnil was tested in dogs after acute and chronic administration. Pharmacokinetic studies showed that abecarnil was eliminated rapidly after i.v. or p.o. administration, but elimination was delayed substantially after s.c. injection. After i.v. injection, the drug penetrated rapidly into the cerebrospinal fluid, but maximum concentrations reached in cerebrospinal fluid were only 6 to 8% of those in plasma. Anticonvulsant potency of abecarnil in dogs was studied by means of seizures induced by i.v. infusion of pentylenetetrazol. After i.v. administration of single doses, abecarnil was about half as potent as diazepam, dose-dependently increasing the pentylenetetrazol threshold by doses of 0.1-1 mg/kg. In contrast to diazepam, most dogs injected with abecarnil at anticonvulsant doses showed no ataxia. During chronic s.c. administration of abecarnil for 6 weeks, the anticonvulsant efficacy of the drug increased markedly during the first week(s) of treatment, possibly indicating drug accumulation in the brain. During the subsequent weeks of treatment, there was a slight reduction in anticonvulsant potency. No withdrawal symptoms were observed after cessation of the 6-week administration period. Furthermore, injection of the BZ antagonist Ro 15-1788 (flumazenil), 1 mg/kg i.v., after 5 weeks of treatment did not precipitate withdrawal symptoms except slight tremor in two of seven dogs studied.(ABSTRACT TRUNCATED AT 250 WORDS)
The pharmacology of the commonly used diuretic agents is reviewed, with special reference to the "high ceiling" diuretics and the benzothiadiazines, which are widely used in veterinary medicine. The different clinical indications in veterinary medicine are discussed.
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The metabolism and the anticonvulsant effect of clorazepate were followed for 2 h after its i.v. administration to mice. The ED50 of the drug was 12 mg/kg at 1 min against pentetrazole-induced convulsions (45 mg/kg i.v.), it reached a minimum at 1 h (2.0 mg/kg) and rose to 2.7 mg/kg at 2 h. The concentrations of unchanged clorazepate and its metabolites, desmethyldiazepam and oxazepam, were determined in plasma and brain after administration of the respective ED50s. Unchanged clorazepate could be detected in plasma for the first hour but never in brain, so it can be considered as inactive pro-drug. The brain concentrations of desmethyldiazepam and oxazepam after the respective ED50s of clorazepate were considerably higher at 1 and 15 min than after longer time intervals. This may be explained by a time lag needed to reach and bind to the benzodiazepine receptor.
The rate of development of tolerance to the benzodiazepines clorazepate and clonazepam against pentetrazole-induced seizures in mice was compared. Treatment with clorazepate (0.1% solution as drinking water) for 21 days led to tolerance beginning at day 7. When mice were treated with clonazepam (0.5 mg/kg twice daily intraperitoneally), tolerance was evident already at the fourth day of treatment. Twenty-four hours after cessation of treatment the seizure threshold was significantly decreased after treatment with both drugs. Clorazepate, a prodrug of the main metabolite of diazepam, desmethyldiazepam, regards further interest for anticonvulsant therapy because of a relatively slow onset of tolerance.
The effects of mu-agonists (morphine, fentanyl) and kappa-agonists (U-50,488, U-69,593, bremazocine, nalbuphine, tifluadom) on the electroconvulsive threshold were studied in mice. The threshold could be significantly elevated by all drugs tested in a dose range that was in the order of magnitude of the antinociceptive ED50. Mice tolerant to the antielectroshock effect of morphine still reacted to U-69,593. The antagonism of the anticonvulsant effect by the mu-antagonist naloxone and the kappa-antagonist MR 2266 was receptor-specific only with fentanyl and U-50,488. The other opioid agonists were either antagonized by both drugs (morphine, U-69,593, bremazocine, nalbuphine) or even by the opposite antagonist (tifluadom). A synergistic effect of mu- and kappa-stimulation is assumed for the mediation of the antielectroshock effect of opioid drugs, but drugs with high affinity and intrinsic activity at one receptor type (fentanyl, U-50,488) are obviously able to bring about their antielectroshock effect through the one respective opioid binding site.
UNLABELLED: Combinations of neuroleptic and morphine-like analgesic drugs are used alone for minor surgery or as anesthetic premedication. While morphine-like analgesics given in the therapeutic dose range show anticonvulsant properties, there is evidence indicating that neuroleptics are rather proconvulsant. This study was performed to investigate the influence of the most widely used combinations pethidine/promethazine and fentanyl/droperidol on seizure susceptibility. METHODS: Thresholds for convulsions induced by electroshock and pentetrazole infusion were used as models for seizure susceptibility. The drugs tested were injected s.c. 20-30 min before determination of the seizure threshold. RESULTS: Pethidine/promethazine and fentanyl/droperidol reduced the susceptibility to seizures induced by electroshock. Promethazine and droperidol alone elevated the threshold only at the highest doses used (2 mg/kg and 2.5 mg/kg respectively). Promethazine, whether given alone or in combination with pethidine, showed no effect on the threshold for pentetrazole-induced convulsions. Droperidol alone lowered the threshold for pentetrazole-induced clonic convulsions only at the lowest dose used (0.625 mg/kg), but lowered that for tonic convulsions at all doses studied (0.625, 1.25 and 2.5 mg/kg). The combination of fentanyl and droperidol lowered the threshold for both clonic and tonic convulsions at the two lower doses (12.5 micrograms/kg fentanyl + 0.625 mg/kg droperidol and 25 micrograms/kg fentanyl + 1.25 mg/kg droperidol). Only the highest dose studied (50 micrograms/kg fentanyl + 2.5 mg/kg droperidol) showed no significant effect. CONCLUSION: Pethidine and fentanyl show anticonvulsant properties in mice, but it is evident from our results that there is some interaction between their combinations with neuroleptics and seizure susceptibility. This is more pronounced with the combination fentanyl/droperidol in the model of pentetrazole-induced convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)
gamma-Vinyl GABA (GVG), an irreversible inhibitor of GABA degradation, was administered to seizure-susceptible gerbils at different dosage regimens. After acute i.p. administration, GVG dose dependently protected the animals against air blast-induced seizures with an ED50 of 50 mg/kg. After oral administration, GVG exerted similar anticonvulsant potency. However, during subchronic daily oral dosing of 100 mg/kg GVG, tolerance developed to the anticonvulsant effect of the treatment. No tolerance was observed with daily oral dosing of 50 mg/kg or every other day and every third day dosing of 100 mg/kg GVG. The disadvantage of the two latter dosage regimens was that no sufficient seizure control was obtained on the days between two administrations. Determination of GABA levels in 11 brain regions of gerbils after subchronic treatment with the different dosage regimens of GVG indicated that tolerance during treatment with daily administration of 100 mg/kg GVG could be the consequence of feedback reduction of GABA synthesis. The data suggest that the choice of suitable dosage regimens for chronic treatment is more critical with GVG than with other antiepileptic drugs, because compensatory mechanisms within the GABA system may develop when GVG-induced GABA accumulation is too marked.
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In gerbils, the convulsive thresholds both for electroconvulsions and for pentetrazole-induced convulsions were increased when determined 15 min after a convulsion elicited by an air blast to the back of the animals. Contrary to a recently offered hypothesis, this sign of post-ictal depression could not be reversed by pretreatment with the morphine antagonists naloxone and naltrexone. This result speaks against a mediation of post-ictal depression by endogenous opioids.
In air blast-induced seizures in gerbils, there is a relationship between the duration of the air blast and the incidence of 'major' convulsions. An ET50 of 9.6 sec was determined in untreated controls; pretreatment with anticonvulsant drugs shifted the stimulus/effect curve to the right. This 'stimulus summation' phenomenon makes a clearly defined challenge necessary when drug effects are to be evaluated.