Antiarrhythmic properties of a neuroleptic butyrophenone, melperone, in acute myocardial infarction. A double-blind trial

In vitro animal studies suggest melperone, a neuroleptic butyrophenone, to be a type III antiarrhythmic drug according to the classification of Vaughan Williams. It has no negative inotropic effect on cardiac muscle. A double-blind trial of 3 hours' duration was carried out with melperone and placebo in 26 patients admitted to the CCU with suspected acute myocardial infarction (AMI) and ventricular arrhythmias. Melperone, 50 mg i.v., was superior to placebo in reducing the total number of ventricular ectopic beats (VEB) as well as the number of minutes with either frequent, multifocal, R-on-T-type or runs of VEB. The reduction became statistically significant in the second treatment hour in patients with definite AMI. Melperone induced sedation and reduction of systemic BP in most of the patients. Two patients with low initial systolic BP achieved a further reduction and had BP levels below 90 mmHg. Two patients experienced minor side-effects. In conclusion, melperone administered in large i.v. doses to patients with AMI induced sedation, acute BP reduction and some reduction of ventricular arrhythmia. X

The pharmacology and toxicology of disulfiram and its metabolites

Disulfiram (Antabuse) is one of several aldehyde dehydrogenase (ALDH) inhibitors that raise the plasma level of acetaldehyde following ethanol ingestion. The usually pleasant reaction to ethanol is thereby changed to an unpleasant one, owing to a number of bodily reactions to acetaldehyde. Populations showing genetic polymorphism with a lack of some isozymes of ALDH have exhibited an intolerance to ethanol similar to that seen with disulfiram. A normal isozyme pattern seems to be a prerequisite for the development of alcoholism, which supports the principle of disulfiram treatment. Disulfiram is an irreversible ALDH inhibitor when administered in vivo. Diethylthiomethylcarbamate (Me-DTC) is formed from disulfiram in three metabolic steps. This compound and two further oxidized metabolites appear to be active metabolites of disulfiram. Measurements of plasma Me-DTC or the reduction of leucocyte ALDH 1 activity may be valuable markers for the proper dose titration of disulfiram and the rational use of this drug. Some toxicological points are discussed.

Selective protection by adenosine receptor agonists against DMCM-induced seizures

The anticonvulsant actions of the adenosine receptor agonists, 1-phenylisopropyladenosine, 2-chloroadenosine and cyclohexyl-adenosine, against DMCM (methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate)-induced seizures in mice were studied with an infusion technique. 2-Chloroadenosine and cyclohexyladenosine were active at 1 mg/kg whereas 1-phenyl-isopropyladenosine was active at 0.03 mg/kg given i.p. At 10 mg/kg, 1-phenylisopropyladenosine was only weakly active against pentylenetetrazol-induced seizures and not active against bicuculline-induced seizures. The selective effect of 1-phenylisopropyladenosine against DMCM-induced seizures suggests that adenosine receptor agonists may allosterically counteract the negative modulating effect of DMCM on GABA coupling to the chloride channel. This indicates that adenosine receptors may have a physiological function within the GABA/benzodiazepine receptor complex in the brain.

Anticonvulsant action of the beta-carboline abecarnil: studies in rodents and baboon, Papio papio

Abecarnil (ZK 112119; isopropyl-6-benzyloxy-4-methoxymethyl-beta-carboxylate) is a metabolically stable beta-carboline derivative with potent anxiolytic and few sedative and ataxic effects in rodents. The anticonvulsant and muscle relaxant actions of abecarnil have been evaluated in mice, rats, gerbils and baboons. Abecarnil raised the threshold for tonic electroconvulsions in mice after corneal but not after auricular application, had no effect on maximal electroshock-induced tonic convulsions triggered by either method, protected mice against the tonic hindlimb extension in PTZ-, picrotoxin- and 3-mercaptopropionate-induced seizures and blocked clonus after PTZ, DMCM (methyl-4-ethyl-6,7-dimethoxy-9H-pyrido-(3,4-b)-indol-3-carboxylate) and 3-mercaptopropionate. Abecarnil had no effect on convulsions induced by bicuculline and strychnine. Furthermore, abecarnil blocked kindled seizures after chronic administration of PTZ and FG 7142 (beta-carboline-3-carboxylic acid methylamide) and protected mice and rats against limbic convulsions induced by pilocarpine. Severity and afterdischarge duration of amygdala-kindled seizures were reduced in rats treated with abecarnil. Abecarnil also antagonized selectively convulsions induced by i.c.v. administration of kainate, but not those triggered by N-methyl-D-aspartate or quisqualate. In genetic models of reflex epilepsy, abecarnil was effective against sound-induced convulsions in DBA/2 mice, against air blast-induced generalized seizures in gerbils and against myoclonus in baboons Papio papio. The anticonvulsant effect of abecornil in a PTZ seizure model in mice was potentiated by ethosuximide, whereas no significant potentiation was found with diazepam, clonazepam, diphenylhydantoin, carbamazepine and phenobarbital. Electromyographic monitoring in a etorphine model of muscle rigidity in rats showed no or little muscle relaxant effect of abecarnil.(ABSTRACT TRUNCATED AT 250 WORDS)

Abecarnil, a metabolically stable, anxioselective beta-carboline acting at benzodiazepine receptors

Abecarnil (isopropyl 6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a novel ligand for central benzodiazepine (BZ) receptors, possessing anxiolytic and anticonvulsant properties, but with considerably reduced muscle relaxant effects in comparison to diazepam (DZP). In vitro, abecarnil inhibited the binding of the BZ [3H]lormetazepam to rat cerebral cortex membranes with an IC50 value of 0.82 nM in comparison to 56 nM for DZP. The ability of abecarnil to displace [3H]lormetazepam was enhanced 1.24-fold in the presence of 30 microM gamma-aminobutyric acid; the corresponding value for DZP was 2.8-fold. DZP and abecarnil were equally effective in enhancing the binding of t-[35S]butylbicyclophosphorothionate to rat cortical membranes. In vivo, abecarnil exhibited a 3- to 6-fold higher affinity to forebrain BZ receptors than DZP. Abecarnil was from 2 to 10 times more potent than DZP in most rodent tests of anxiolytic activity, and in reducing locomotor activity in mice and rats thoroughly habituated to the test chamber. However, in rats newly exposed to a novel cage, abecarnil was less potent than DZP in reducing locomotor activity. In tests of motor coordination, abecarnil, in contrast to DZP, showed no or only weak activity, and in potentiating the effects of ethanol and hexobarbital on motor performance abecarnil was 4 to 25 times less potent than DZP. Abecarnil antagonized the effects of BZs in the chimney and loss of righting reflex tests, but not in the rotarod test.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-ischaemic effects of indomethacin and ketamine on hippocampus neurones in Mongolian gerbils

Bilateral occlusion of the carotid arteries of Mongolian gerbils for 10 min. resulted in a consistent pattern of degeneration of hippocampal CA1 neurons. Administration of the non-competitive NMDA antagonist ketamine (100 mg/kg intraperitoneally) 30 min. before the occlusion almost entirely prevented degeneration of CA1 neurones. Indomethacin 5 mg/kg intraperitoneally had no influence on the degeneration, either administered 30 min. before or 15 min. after occlusion. The production of prostaglandins from the NMDA receptor stimulation does not seem to be crucial for the development of the ischaemic lesions at least in the hours immediately following occlusion. Indomethacin did not reduce the anti-ischaemic effect of ketamine in the doses presumably necessary to reduce the increase in intracranial pressure induced by ketamine.

Pharmacological effects of diethylthiocarbamic acid methyl ester, the active metabolite of disulfiram?

A recently discovered metabolite, diethylthiocarbamic acid methyl ester (Me-DTC), has been found in the plasma of man and rats in much higher concentrations than any other described metabolite after therapeutic doses of disulfiram. Me-DTC, in contrast to other disulfiram metabolites, is a potent inhibitor of liver aldehyde dehydrogenase (ALDH) in vitro. Like disulfiram, Me-DTC had a pronounced hypothermic effect in rats. This hypothermic effect and the augmented blood pressure response to ethanol challenge in rats developed rapidly with Me-DTC but were somewhat delayed with disulfiram. The blood pressure response outlasted the presence of Me-DTC in plasma (less than 24 h); a significant effect was found 48 h after pretreatment but not 72 h after a single dose. No effect was observed when ethanol was given 15 min before Me-DTC or disulfiram. These latter two observations are consistent with a function of Me-DTC as a suicide inhibitor of ALDH. Since Me-DTC has been reported to inhibit ALDH in vitro, even under anaerobic conditions, Me-DTC may be the active metabolite of disulfiram.

Diethylthiocarbamic acid methyl ester. A potent inhibitor of aldehyde dehydrogenase found in rats treated with disulfiram or diethyldithiocarbamic acid methyl ester

Rats were treated with disulfiram (Antabuse, DSF) or its metabolite diethyldithiocarbamic acid methyl ester (Me-DDC) and challenged with ethanol. The blood pressure response to ethanol was followed and blood was analyzed for DSF, Me-DDC and diethyldithiocarbamic acid (DDC). The rat liver aldehyde dehydrogenase (ALDH) isozyme activities were measured 2 hr after the ethanol challenge. Both treatments produced a significant fall in the blood pressure when challenged with ethanol, probably caused by a marked decrease in hepatocyte low Km and high Km activities. The mean plasma concentration ranges of Me-DDC and DDC were found to be 49-1241 nmol/l and 182-841 nmol/l, respectively, whereas DSF was undetectable. In addition, it was found that inactivation of hepatocyte low Km ALDH activity was dependent on preoxidation of Me-DDC by the microsomal cytochrome P-450 mixed function oxidases. Me-DDC was found to be oxidized under aerobic conditions in the presence of NADP to form diethylthiocarbamic acid methyl ester (Me-DTC). The structure was confirmed from its MS/EI fragmentation spectrum. Me-DTC was found to be a potent inhibitor of low Km ALDH when added to rat liver homogenate. The compound was also identified as a metabolite in rat blood collected from the DSF and Me-DDC treated rats, and in blood from human alcoholics on DSF treatment. Me-DTC appears to be more selective for the low Km isozymes whereas the opposite seems to be the case for the hydrolytic product, DTC.

Lorazepam and FG 7142 induce tolerance to the DMCM antagonistic effect of benzodiazepine receptor ligands

Mice were given chronic treatment with lorazepam 10 mg/kg PO or FG 7142 40 mg/kg IP once a day for 14 days. The pretreatments with lorazepam and FG 7142 did not change the sensitivity of the mice to the convulsant effect of DMCM. Lorazepam pretreated mice showed a significantly lower sensitivity to the anticonvulsant effects of the benzodiazepine (BZ) receptor ligands lorazepam, ZK 93423, ZK 91296, Ro 15-1788 and ZK 93426 administered acutely by the IP route when challenged with DMCM 24 hr after the last dose of lorazepam. FG 7142 pretreated mice showed a significantly lower sensitivity to the anticonvulsant effect of the two agonists lorazepam and ZK 93423 and to the antagonist Ro 15-1788, whereas the effects of ZK 91296 and ZK 93426 were left unchanged. The reduced DMCM antagonistic effects of the BZ receptor ligands may indicate that these ligands may either have lost some of their affinity to those BZ receptors being responsible for the DMCM-induced seizures or they may have lost some efficacy in allosterically inhibiting DMCM binding or as a third possibility may have lost efficacy at a BZ receptor site downstream to the seizure-inducing center in the brain.

Bidirectional effects of beta-carbolines and benzodiazepines on cognitive processes

Experiments with benzodiazepine receptor ligands in two paradigms involving cognitive processing were performed in order to test whether the concept of bidirectional effects of benzodiazepine receptor ligands could also be applied to cognitive functions. Benzodiazepine receptor agonists like chlordiazepoxide, lorazepam, ZK 93423 and ZK 91296 induced amnesia in a passive avoidance paradigm. Mice treated with the benzodiazepine receptor antagonist, ZK 93426, reached a learning criterion after fewer foot-shocks than saline treated mice both in naive animals and in scopolamine pre-treated animals. Furthermore, ZK 93246, attenuated the amnesic effect of corneal electroshock. The inverse agonists FG 7142 and DMCM decreased the detrimental effect of scopolamine on retrieval. In a signal detection paradigm, chlordiazepoxide impaired signal detection. In aged rats ZK 93426, ZK 90886 and FG 7142 had no effect on signal detection but ZK 93426 and FG 7142 attenuated the impairment of signal detection induced by scopolamine. These effects of benzodiazepine receptor ligands may reflect changes in arousal/vigilance, suggesting that BZ inverse agonists may have useful properties in enhancing vigilance.

Chronic treatment with lorazepam and FG 7142 may change the effects of benzodiazepine receptor agonists, antagonists and inverse agonists by different mechanisms

Treatment of mice with lorazepam 10 mg/kg p.o. or FG 7142 40 mg/kg i.p. once a day for 14 days changed the effects of benzodiazepine (BZ) receptor ligands injected acutely on the threshold of pentylenetetrazol (PTZ)-induced seizures. The effects of the two pretreatments differed qualitatively as well as quantitatively. Lorazepam elicited a shift in the effects of all BZ receptor ligands tested, whereby the agonists lorazepam and ZK 93423 now acted like partial agonists given acutely, the partial agonist ZK 91296 acted like an antagonist and the antagonists Ro 15-1788 and ZK 93426 like partial inverse agonists. The proconvulsant effects of the partial inverse agonist FG 7142 and the full inverse agonist DMCM on the PTZ-induced seizures did not change. However, FG 7142 became a full inverse agonist i.e. became convulsant, and DMCM may have increased in potency as a convulsant. After FG 7142 pretreatment lorazepam and ZK 93423 behaved like partial agonists given acutely whereas there was no change in effect for ZK 91296, Ro 15-1788 and ZK 93426. FG 7142 became convulsant (i.e. kindling occurred) and the potency of DMCM as a convulsant was non-significantly increased, while their proconvulsant effects with respect to PTZ-induced seizures were not altered. The fact that the effects of the two very different pretreatments on the BZ receptor ligand continuum were in the same direction may be explainable by assuming two different mechanisms, both of which may involve the GABA receptors.

Bay K 8644 induces a reversible spasticity-like syndrome in rats

The dihydropyridine Bay K 8644 exerts a positive modulation of Ca2+ channels. Administration of Bay K 8644 3-5 mg/kg i.p. to rats induces within 15 min a severe spasticity syndrome consisting of stiff tail, arched back, stretching and twisting of forelimbs and hindlegs and backwards motility and rolling over. The syndrome was effectively antagonized by nifedipine 3-30 mg/kg but not by the other Ca2+ channel blockers flunarizine, diltiazem and verapamil. Diltiazem even enhanced the spasticity. Diazepam 10-30 mg/kg i.p. completely blocked the spasticity whereas the other muscle relaxants (-)-baclofen and the beta-carboline ZK 93423 were completely inactive. These findings with Bay K 8644 suggest that spasticity may be caused by changed Ca2+ homeostasis.

Evidence that the anticonflict effect of midazolam in amygdala is mediated by the specific benzodiazepine receptors

The benzodiazepine midazolam produced an anticonflict effect in rats measured in a water lick paradigm following local injection into the basolateral and lateral complex of the amygdala. This effect of midazolam seems to involve specific benzodiazepine receptors, since the systemic injection of benzodiazepine antagonists Ro 15-1788, ZK 93426, FG 7142 and CGS 8216 produced strong antagonism of the effect of midazolam in doses not affecting the non-punished drinking behaviour.

Proconflict effect of benzodiazepine receptor inverse agonists and other inhibitors of GABA function

GABA seems to be a neurotransmitter with great impact on conflict behaviour in rats. We studied the effects of different types of GABA function inhibitors on conflict behaviour in rats. Among these inhibitors, the benzodiazepine (BZ) receptor inverse agonists are a new type of compound downregulating GABA-mediated functions allosterically. The most effective proconflict inducing compounds were pentylenetetrazol and the three BZ inverse agonists beta-CCM, beta-CCE and ZK 90886. The BZ receptor inverse agonists, FG 7142, DMCM and CGS 8216, the GABA antagonist bicuculline and the GABA synthesis inhibitor isoniazid were moderately active. Only a weak effect was seen with just subconvulsive doses of picrotoxin, a chloride channel inhibitor. These results show that the mode of GABA function inhibition determines the degree to which proconflict action is elicited and that proconflict effects and proconvulsant or convulsant effects may be separated. Evidence is presented that proconflict action in rats is predictive of an anxiogenic action in man.

Antiepileptic action of the beta-carboline ZK 91296 in a genetic petit mal model in rats

The anticonvulsant action of the benzodiazepine (BZ) receptor partial agonist, ethyl 5-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate (ZK 91296) was studied in rats of Wistar origin exhibiting spontaneous bilateral cortical synchronous spike and wave discharges with a symptomatology paralleling that of human petit mal seizures. ZK 91296 1-16 mg/kg i.p.) attenuated the absence seizures without inducing signs of sedation or disorganized EEG patterns at any dose. Diazepam (1-8 mg/kg i.p.) suppressed seizures but also induced sedation and modified EEG background activity in a dose-related manner.

Evaluation of the beta-carboline ZK 93 426 as a benzodiazepine receptor antagonist

We describe here biochemical and pharmacological effects of the beta-carboline ZK 93426 was compared with Ro 15-1788 and CGS 8216, two compounds previously described as BZ receptor antagonists. Certain effects of ZK 93426, Ro 15-1788 and CGS 8216 were quite similar (e.g., 3H-FNM displacement, "GABA ratio", "photo-shift"). In most pharmacological tests ZK 93426 and Ro 15-1788 lacked overt effects; Ro 15-1788 was a weak agonist in some paradigms, while ZK 93426 exhibited a potent proconflict effect but also a weak anticonvulsant effect. This interesting finding with ZK 93426 suggests that BZ receptor ligands may possess differential efficacy at BZ receptor subtypes. In contrast, CGS 8216 exhibited potent proconvulsant effects in several paradigms in addition to proconflict and pentylenetetrazol generalizing effects. ZK 93426, Ro 15-1788 and CGS 8216 were almost equally potent as antagonists of the effects of BZ receptor agonists, such as diazepam and lorazepam. However, ZK 93426 was the most potent inhibitor of the convulsions produced by the BZ receptor inverse agonist DMCM.

ZK 91296, a partial agonist at benzodiazepine receptors

5-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a potent and selective ligand for benzodiazepine (BZ) receptors. Biochemical investigations indicate that ZK 91296 may be a partial agonist at BZ receptors. Such partial agonism may explain to some extent why ZK 91296 needs higher BZ receptor occupancy than diazepam for the same effect against chemical convulsants and for behavioural effects. The lack of sedative effects, and the very potent inhibition of reflex epilepsy, spontaneous epilepsy and DMCM-induced seizures suggest, furthermore, that ZK 91296 may possess pharmacological selectivity for a particular type of BZ receptor interaction, perhaps including topographic as well as receptor subtype differentiation.

Benzodiazepine receptor ligands with positive and negative efficacy

Recent studies have shown that benzodiazepine receptors can be affected not only by benzodiazepine agonists and antagonists but also by a new class of ligands which produce effects opposite to those of benzodiazepines, that is they produce convulsions and anxiety. These ligands can be described as having a negative efficacy at the receptor; tentatively they are named "inverse agonists". Pharmacological experiments indicate that agonists, antagonists and inverse agonists comprise a whole continuum of agents with a graduated variety of efficacy at the receptor. Biochemical studies, supported by published electrophysiological data, indicate that the benzodiazepine receptor allosterically up- or down-regulates the gain in the GABAergic system depending on the nature of the ligand.

DMCM: a potent convulsive benzodiazepine receptor ligand

DMCM (methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) is a very potent convulsant with high affinity for specific benzodiazepine binding sites. A number of compounds were compared for their ability to prevent seizures induced by DMCM and pentylenetetrazol. DMCM seizures were antagonized by benzodiazepine (BZ) receptor antagonists, such as Ro 15-1788, CGS 8216 and several beta-carboline-3-carboxylates, which all fail to inhibit pentylenetetrazol seizures. The benzodiazepines diazepam, clonazepam and lorazepam as well as valproate, ethosuximid, phenobarbital, primidone, diphenylhydantoin and carbamazepine antagonized both DMCM and pentylenetetrazol. Muscimol and gamma-vinyl-GABA did not inhibit DMCM seizures whereas THIP showed a weak and selective effect against DMCM. Valproate showed a relatively potent (60 mg/kg i.p.) and competitive antagonism of short duration. Baclofen antagonized DMCM at 3 mg/kg. Valproate and baclofen were at least 5 times more potent against DMCM-induced than against pentylenetetrazol-induced seizures. DMCM most probably induces the seizures by selective impairment of the functions mediated by the GABA/BZ receptor-chloride channel complex (inverse agonism) and therefore differs from GABA receptor blockers.

Bidirectional effects of benzodiazepine receptor ligands against picrotoxin- and pentylenetetrazol-induced seizures

The dose response curves of picrotoxin-induced seizures and pentylenetetrazol-induced seizures were shifted to the right by the benzodiazepine (BZ) receptor agonist lorazepam, and to the left by the inverse agonists, DMCM, ZK 90886, FG 7142 and CGS 8216. The BZ receptor antagonists ZK 93426 and Ro 15-1788 had no effect on the dose response curves. The anticonvulsive action of lorazepam and the proconvulsive action of DMCM against picrotoxin-induced seizures and against pentylenetetrazol-induced seizures was inhibited by low doses of ZK 93426 and Ro 15-1788. These results indicate that the bidirectional effects of benzodiazepine receptor ligands on picrotoxin and pentylenetetrazol induced seizures is actually mediated through benzodiazepine receptors.

Audiogenic seizures in DBA/2 mice discriminate sensitively between low efficacy benzodiazepine receptor agonists and inverse agonists

In experiments with audiogenic seizures in DBA/2 mice, we observed that several socalled benzodiazepine receptor antagonists exhibited either anticonvulsive (Ro 15-1788, PrCC) or proconvulsive (FG 7142, beta-CCE, CGS 8216) effects at high receptor occupancy (17-85%), as compared to benzodiazepines and DMCM which had anticonvulsive and proconvulsive actions, respectively, at very low receptor occupancy (less than 10%). Sensitive distinction between benzodiazepine receptor ligands with low anticonvulsive efficacy (partial agonists) and ligands with low proconvulsive, and maybe anxiogenic, efficacy (partial inverse agonists) can thus be obtained in sound seizure susceptible mice.

Does the reversal of the anticonflict effect of phenobarbital by beta-CCE and FG 7142 indicate benzodiazepine receptor-mediated anxiogenic properties?

In mice and rats, the high affinity ligand for brain benzodiazepine (BZ) receptors beta-CCE, and the more stable congener FG 7142, failed to exert anticonflict activity in conflict situations but instead reversed the anticonflict effect of lorazepam. In contrast to Ro 15-1788, beta-CCE and FG 7142 also antagonized the anticonflict effect of phenobarbital in rats. This effect suggests that beta-CCE and FG 7142 may produce anxiety by either inducing a conformational change in the BZ receptors which is directly opposite to that induced by the benzodiazepines, or binding to a particular subclass of BZ receptors.

Interaction of convulsive ligands with benzodiazepine receptors

The gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex, which is composed of distinct proteins embedded in the neuronal plasma membrane, is important for several effects of benzodiazepines, including protection afforded against convulsions. During structural modification of ethyl beta-carboline-3-carboxylate an agent was discovered which has high affinity for brain benzodiazepine receptors but which is a potent convulsant. Also in contrast to benzodiazepines, this type of benzodiazepine receptor ligand favors benzodiazepine receptors in the non-GABA-stimulated conformation, which may explain the convulsive properties.

Propranolol and femoxetine, a HT-uptake inhibitor, in migraine prophylaxis. A double-blind crossover study

The prophylactic effect of the 5-HT uptake inhibitor femoxetine was compared with propranolol (Frekven R) in a double-blind crossover trial of 6 months duration. Forty-nine patients commenced the trial. Twelve patients withdrew because of drug failure or failure to attend checkups (6), side effects (4) or other non-drug related causes (2). In the 37 patients who completed the trial there was no significant difference between propranolol 160 mg and femoxetine 400 mg with respect to the number of headache days or the number of migraine attacks during the last 2 months of each treatment, Propranolol, however, was superior to femoxetine when the headache index was used (P less than 0.05). The study has shown that partial depletion of thrombocyte 5-HT by a 5-HT uptake inhibitor does not lead to a marked improvement in all patients contrary to what might be expected from the 5-HT hypothesis of migraine. Nevertheless, due to the infrequent subjective side effects associated with femoxetine treatment it may be a valuable prophylactic drug to a subgroup of migraine patients.

Pre- and postsynaptic alpha-adrenoceptor antagonism by neuroleptics in vivo

Different types of neuroleptics were studied for pre- and postsynaptic alpha-adrenoceptor antagonism in pithed rats using the blood pressure effect of clonidine as a measure of postsynaptic alpha-adrenoceptor activation and the depression of the heart rate response to electrical stimulation as a measure of presynaptic alpha-adrenoceptor activation. Yohimbine (0.1 mg/kg) was more active at pre- than postsynaptic alpha-adrenoceptors while the reverse was found with prazosin (0.02-5 mg/kg). Phentolamine (1-5 mg/kg) on the other hand was very active at both receptors. Cocaine 1-5 mg/kg had no effect on these responses indicating that noradrenaline uptake inhibition presumably does not interfere with the revaluation of the alpha-adrenoceptor antagonistic effect of the neuroleptics. Melperone, haloperidol, thioridazine and flupenthixol (0.15 mg/kg) were more selective antagonists at postsynaptic alpha-adrenoceptors than prazosin. Clozapine, chlorprothixene showed preferential presynaptic (0.15 mg/kg) were antagonists at both types of receptors. Chlorprothixene showed preferential presynaptic alpha-antagonism of high potency. Chlorprothixene was the only neuroleptic drug which like phentolamine (1-5 mg/kg) gave complete presynaptic alpha-antagonism. These results indicate widely different selectivity of neuroleptics for pre- and postsynaptic alpha-adrenoceptors on peripheral sympathetic nerves. It is suggested that neuroleptics with presynaptic alpha-adrenoceptor antagonism may enhance the activity of Beta-adrenergic systems indirectly both in peripheral organs like the heart, and within the central nervous system.

A water lick conflict paradigm using drug experienced rats

A modified water-lick conflict paradigm is described, using trained rats for up to 35 weekly test sessions under 48 h of water deprivation. The rats rapidly became maximally suppressed by the punishment. This suppression was attenuated by the anxiolytics lorazepam, diazepam, phenobarbital, and meprobamate. The potentially anxiolytic drug CL 218872 and the anticonvulsant drug valproate sodium were also active. The antiserotonin drugs methysergide, cyproheptadine, cinanserin and parachlorophenylalanine were all inactive, as were several several other distinct classes of psychotropic drugs including propranolol, clonidine, THIP, theophylline, chlorpromazine, paroxetine and ethanol. The paradigm proved reliable, reproducible and useful for large scale investigations. Furthermore, it may provide means for detailed neuropharmacological and anatomical studies.

5-HT antagonism on cerebral and common carotid arteries by the 5-HT uptake inhibitors femoxetine and paroxetine

The 5-hydroxytryptamine (5-HT) antagonism of methysergide was compared with that of the phenylpiperidine 5-HT uptake inhibitors, paroxetine and femoxetine, using two different models; the isolated cat middle cerebral artery and the common carotid artery of pithed rat perfused with the rat's own blood (autoperfusion). The extracorporeal circulation consisted of about 1.5 ml blood, which was temperature regulated to 36-38 degrees at the inlet to the carotid vessel by an automatic thermistor coupled heating system. In these experiments systemic blood pressure responses and perfusion pressure responses to 5-HT were recorded simultaneously. The 5-HT induced contractile response of the middle cerebral artery was reduced in a noncompetitive way by both uptake inhibitors at concentrations above 0.3 microM which is about 100 times the concentration needed for methysergide. In autoperfusion experiments inhibition was observed only at 5 mg/kg of both drugs. However, methysergide 0.001 mg/kg totally abolished all 5-HT responses. The uptake inhibitors can therefore be described as weak 5-HT antagonists.

Clonidine increases the rate of blood pressure recovery from splanchnic nerve stimulation

Clonidine reduced both the pithed rat heart rate and blood pressure responses to low frequency sympathetic nerve stimulation. Marked shortening of the blood pressure response but not of the heart rate or of the responses to injected noradrenaline was found. This shortening effect was independent of the number of impulses in the train (4--120 impulses) and of the impulse frequency. It lasted for more than 1 hour and was found to affect only the late part of the pressor decay curve. Nerve stimulations at 2 Hz simulating bursts of different periodicity in the splanchnic nerves showed that the cumulation of the blood pressure between bursts was affected only when these were applied at intervals of more than 10 sec. The effect could not be influenced by antagonists to several known transmitters, by ligation of the renal arteries or by adrenalectomy and does not seem to be mediated by pre-or postjunctional alpha receptor stimulation.

Potent depletion of 5HT from monkey whole blood by a new 5HT uptake inhibitor, paroxetine (FG 7051)

The potent 5-hydroxytryptamine (5HT) uptake inhibitor FG 7051 (paroxetine, INN) was administered to rhesus monkeys in doses of 1.0, 2.5 or 7.5 mg/kg by oral gavage once daily for 13 weeks. Blood samples for analysis of 5HT in whole blood and paroxetine in plasma were taken prior to and after 1, 4 and 13 weeks of treatment. The lowest dose 1 mg/kg caused 30% depletion of 5HT in whole blood with a level of paroxetine in plasma below 2 ng/ml. Doses of 2.5 mg/kg produced an 85% depletion of 5HT and a steady state plasma concentration of about 5 ng paroxetine/ml, while 7.5 mg/kg caused a 93% depletion of 5HT and a steady state plasma concentration of 100--450 ng paroxetine/ml. There was no concentration-dependent 5HT reduction with the highest dose level suggesting that maximal depletion was produced by concentrations below 100 ng/ml. The results showed that paroxetine is a strong depletor of 5HT from whole blood of monkeys conceivably because it inhibits 5HT uptake inhibition. The effect of the drug reached its maximum within 1 week and no tolerance developed during 13 weeks.

Experimental anti-arrhythmic properties of melperone, a neuroleptic butyrophenone

The neuroleptic butyrophenone, melperone, has been compared with antiarrhythmics, neuroleptics, alpha-blockers and beta-blockers in various experimental arrhythmias. Melperone 0.01--1 mg/kg intravenously antagonized ouabain-induced arrhythmias in conscious rabbits to the same degree as propranolol 2 mg/kg and quinidine 10 mg/kg intravenously probably mainly via s CNS depressive effect. It was found to be considerably weaker than propranolol 2 mg/kg, when anaesthetized guinea pigs were used. Melperone 0.1--10 mg/kg was inactive against aconitine-induced arrhythmias. Melperone 1--5 mg/kg antagonized adrenaline-induced arrhythmias in halothane-sensitized guinea pigs like phentolamine 1--5 mg/kg intravenously and was more potent than chlorpromazine, propranolol and quinidine. This study and an electrophysiological study suggest that melperone might be a type III anti-arrhythmic drug, which at the same time depresses CNS and reduces afterload.

Effects of 5HT uptake inhibitors on the pressor response to 5HT in the pithed rat. The significance of the 5HT blocking property

A study was made of the effects of several serotonin (5HT) uptake inhibitors on 5HT-induced pressor responses in pithed rats, 5HT uptake into rat brain synaptosomes and 5HT-induced contractions of rat ileum in vitro. All drugs except desimipramine were potent uptake inhibitors (IC50 less than 10(-7) M), Femoxetine, chlorimipramine, imipramine and desimipramine all inhibited 5HY-induced contractions of the rat ileum in vitro and the pressor response to 5HT in vivo. FG 7051, FG 7052 and dexchlorpheniramine were weak 5HT antagonists on the rat ileum but potentiated the pressor responses to 5HT; the most potent uptake inhibitor, FG 7051, was the strongest potentiator. These results suggest that uptake inhibition is important for this potentiation. It is concluded that 5HT uptake inhibitors with potent 5HT receptor blocking properties antagonize the pressor response to 5HT and mask the potentiation due to uptake inhibition.