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Biomedical subjects

M Karobath

Publications and source records attributed to M Karobath.

At least 37 records · Page 2Linked to original sources
PubMed1982

Anion-dependent modulation of [3H]muscimol binding and of GABA-stimulated [3H]flunitrazepam binding by picrotoxin and related CNS convulsants.

Picrotoxin, isopropylbicyclophosphate (IPTBO) and related CNS-convulsants have allosteric effects on the binding of ligands to the GABA/benzodiazepine receptor complex. When binding experiments were performed at 23 degrees C and at 35 degrees C, these drugs inhibited [3H]muscimol binding and muscimol- or GABA-stimulated [3H]flunitrazepam binding, respectively. Both effects required the presence of C1-, Br-, I- but not of F- or SO4(2-). Picrotoxin and IPTBO could only partially inhibit [3H]muscimol binding. In contrast other GABA antagonists and convulsants like bicuculline, 3 alpha-hydroxy-16-imino-5 beta-17-aza-androstan-11-one (R 5135), strychnine and d-tubocurarine interferred completely with [3H]muscimol binding, also in the absence of those ions mentioned above which were essential for the effects of picrotoxin. Our results support the notion that drugs like picrotoxin and IPTBO which interfere with the GABA receptor effector system, may lead to an allosteric perturbation of GABA-recognition sites.

Animals↗
PubMed1982

Distinction of benzodiazepine agonists from antagonists by photoaffinity labelling of benzodiazepine receptors in vitro.

When membranes of rat cerebellum are exposed to UV light in the presence of flunitrazepam this ligand can be incorporated into one of the assumed 4 benzodiazepine binding sites of the GABA-benzodiazepine receptor complex. This irreversible incorporation of flunitrazepam, in contrast to reversible binding of this substance, leads to conformational changes of the remaining 3 benzodiazepine binding sites which result in a decreased affinity of benzodiazepine agonists, but not of benzodiazepine antagonists. The investigation of the affinity of drugs for [3H]benzodiazepine antagonist binding before and after photoaffinity labelling of benzodiazepine receptors with flunitrazepam can therefore be used as a sensitive and simple test to distinguish between agonists and antagonists in vitro.

Animals↗
PubMed1981

Action of pyrazolopyridines as modulators of [3H]flunitrazepam binding to the gaba/benzodiazepine receptor complex of the cerebellum.

The pyrazolopyridines etazolate (SQ 20009) and cartazolate (SQ 65396) have strong modulatory effects on the GABA/benzodiazepine receptor complex of rate cerebellum. Thus, etazolate and cartazolate directly stimulate [3H]flunitrazepam binding (with EC50 values of 1.2 microM and 0.3 microM respectively) by increasing the apparent affinity of [3H]flunitrazepam for its binding sites. Stimulation of [3H]flunitrazepam binding by pyrazolopyridines is dependent on the presence of certain anions like chloride, bromide, iodide, nitrite, nitrate but not fluoride, acetate, formate or sulfate. If is inhibited by bicuculline-methiodide, and by the "chloride channel drugs' picrotoxinin and IPTBO. isoTHAZ, a GABA analogue with GABA antagonist properties in vivo, fails to inhibit binding stimulated by etazolate but antagonizes [3H]flunitrazepam binding stimulated by GABA. The pyrazolopyridines have also indirect effects on benzodiazepine receptor binding since they enhance the apparent sensitivity of those GABA recognition sites which are coupled to benzodiazepine binding sites. Thus, in the presence of 10 microM etazolate, GABA and muscimol enhance [3H]flunitrazepam binding, with EC50 values of 109 nM and 12 nM respectively. This sensitization effect is partially dependent on the presence of chloride ions. The pyrazolopyridines facilitate also the stimulation of benzodiazepine receptor binding by beta-alanine and taurine and by the rigid and flattened GABA analogues THIP and piperidine-4-sulfonic acid. Taken together, these results suggest that the pyrazolopyridines modulate [3H]flunitrazepam binding by acting at a site closely related to GABA receptor-regulated chloride ion channels.

Animals↗
PubMed1981

Effects of antidepressant treatment with clomipramine on hormonal responses to thyrotropin-releasing hormone and insulin-induced hypoglycemia: implications for the "monoamine-hypothesis".

Neuroendocrine test were carried out to study effects of clomipramine treatment in 24 unipolar depressed women. Clomipramine (50-150 mg/day) increased the response of prolactin and thyrotropin to stimulation by thyrotropin-releasing hormone (TRH), while no response of growth hormone (HGH) to TRH was seen. Clomipramine decreased the response of HGH to insulin, while the responses of prolactin and cortisol to insulin were not affected. The findings suggest that the neuroendocrine and antidepressant effects of clomipramine cannot be accounted for entirely on the basis of monoaminergic mechanisms.

Biogenic Amines↗
PubMed1981

In vitro modulation by avermectin B1a of the GABA/benzodiazepine receptor complex of rat cerebellum.

Avermectin B1a, a macrocyclic lactone anthelmintic agent, causes a concentration-dependent increase of [3H]flunitrazepam binding to membranes from rat cerebellum by increasing the affinity and the number of binding sites. This effect appears to be independent of the concentration of chloride ions. The effects of avermectin B1a occur with high affinity (EC50 = 70 nM), and they persist after washing of the membranes with drug-free buffer. Pretreatment of the membranes with Triton X-100 completely abolishes the action of avermectin B1a. GABA and the GABA-mimetic compounds piperidine-4-sulfonic acid and THIP diminish the effects of avermectin B1a on benzodiazepine receptor binding in a bicuculline-methiodide-sensitive mode. In addition, the stimulation of [3H]flunitrazepam binding by avermectin B1a is decreased by the pyrazolopyridines etazolate and cartazolate. These observations suggest that avermectin B1a stimulates benzodiazepine receptor binding by acting on a modulatory site which is independent of the GABA recognition site and of the drug receptor for the pyrazolopyridines, but which is in functional interaction with these sites.

Animals↗
PubMed1980

The effect of temperature and chloride ions on the stimulation of [3H]flunitrazepam binding by the muscimol analogues THIP and piperidine-4-sulfonic acid.

THIP and piperidine-4-sulfonic acid (PSA) interact with [3H]GABA binding sites and have GABAmimetic efficacy in vivo, but fail to enhance benzodiazepine receptor binding performed at 0 degree C. However, when [3H]flunitrazepam binding is determined at elevated temperature (30 or 37 degrees C), THIP and PSA display potent chloride ion-dependent stimulatory effects. These results resolve apparent discrepancies between the properties of GABA receptors observed in vivo and in vitro, and they suggest that the modulation of benzodiazepine receptor binding investigated at physiological temperatures can be used as an experimental system for the characterization of GABA receptors.

Animals↗
PubMed1980

Molecular heterogeneity of benzodiazepine receptors.

Benzodiazepines exhibit reversible, stereospecific high affinity binding to mammalian brain membranes, and the respective binding sites for 3H-flunitrazepam represent pharmacologically and clinically relevant receptors for benzodiazepines. Recently it has been demonstrated that reversibly bound 3H-flunitrazepam becomes irreversibly attached to a specific membrane protein with apparent molecular weight of 50,000 when incubations are performed in the presence of UV light. Irreversible binding of 3H-flunitrazepam to this protein had pharmacological properties similar to reversible benzodiazepine receptor binding, indicating that 3H-flunitrazepam is a photoaffinity label for the benzodiazepine receptor. Using irreversible binding of 3H-flunitrazepam and subsequent electrophoretic separation of the labelled proteins in SDS-gels followed by fluorography, we found that in hippocampus and several other brain regions at least two different types of benzodiazepine receptors exist. Each seems to be associated with a gamma-aminobutyric acid (GABA) receptor.

Animals↗
PubMed1980

Simple and rapid mass fragmentographic method for the determination of glycine in brain tissue.

A method for the sensitive and selective determination of glycine in brain tissue has been developed. Small samples of brain tissue were homogenized by sonication in 0.7 N formic acid, and [1,2 13C2,15N]glycine was then added as internal standard. After centrifugation, aliquots of the supernatants were dried and the resulting residues were derivatized in a single step with heptafluorobutyric anhydride and hexafluoroisopropanol. After removal of the derivatization reagents by evaporation the residues were dissolved in ethyl acetate and an aliquot was analyzed by mass fragmentography. Quantification was performed by comparing the ratio of peak areas of glycine and its internal standard.

Animals↗
PubMed1980

In vitro modulation by SQ 20009 and SQ 65396 of GABA receptor binding in rat CNS membranes.

SQ 20009 and SQ 65396, two new pyrazolopyridines with anxiolytic properties in animals, reversibly increased Na+-independent 3H-GABA binding to rat cerabral cortex membranes in vitro. This modulation was partially chloride dependent and sensitive to Triton-X 100. Kinetic analysis of 3H-muscimol binding revealed an increase of the apparent number of binding sites. The results are compatible with a functional association between Na+-independent GABA binding sites and the GABA/benzodiazepine receptor complex.

Animals↗
PubMed1980

Interaction of SQ 20009 and GABA-like drugs as modulators of benzodiazepine receptor binding.

SQ 20009, a new anxiolytic drug structurally unrelated to GABA or benzodiazepines, has two modulatory effects on the binding of 3H-flunitrazepam to membranes from rat cerebellum. Thus, SQ 20009 has a direct and chloride ion dependent stimulatory effect on benzodiazepine receptor binding which in turn appears to be modulated by the associated GABA receptor. In addition SQ 20009 has indirect effects on benzodiazepine receptor binding since it enhances the potency of GABA and muscimol to stimulate 3H-flunitrazepam binding.

Animals↗
PubMed1980

A sensitive and specific method for the determination of chlorimipramine and desmethylchlorimipramine in plasma using selected ion monitoring with chemical ionization.

Chlorimipramine and other tricyclic antidepressant drugs are widely used for the treatment of depressive disorders. We analysed chlorimipramine and its major metabolite desmethylchlorimipramine after a two step extraction from plasma with diethylether. The underivatized samples were separated on a short (40 cm x 2 mm) silanized glass column packed with 3% OV 17 on Chromosorb HPW-DMCS, 80-100 mesh, which was directly coupled to the mass spectrometer. Detection of the tricyclic antidepressant drugs and their respective deuterium labelled internal standards was performed by chemical ionization using methanol vapour as reactant gas. The method is simple and sufficiently sensitive to permit the routine analysis of therapeutic plasma levels of tricyclic antidepressant drugs in extracts originating from 1 ml plasma.

Antidepressive Agents, Tricyclic↗
PubMed1980

Clovoxamine and fluvoxamine-2 biogenic amine re-uptake inhibiting antidepressants: quantitative EEG, psychometric and pharmacokinetic studies in man.

In a double-blind placebo-controlled study, the encephalotropic, psychotropic, pharmacodynamic and pharmacokinetic properties of 2 new substances, clovoxamine (a 5-HT and NE re-uptake inhibitor) and fluvoxamine (a selective 5-HT inhibitor) were investigated utilizing quantitative pharmaco-EEG, psychometric and blood level analyses. Ten normal volunteers received randomized and in weekly intervals oral single doses 50 mg, 75 mg and 125 mg clovoxamine, 75 mg fluvoxamine, placebo and as reference drug 75 mg imipramine. Quantitative EEG, psychometric data, pulse, blood pressure, side effects and pharmacokinetic data were studied at the hours 0, 2, 4, 6 and 8. Plasma levels of both substances peaked in the 4th to 6th hour and declined slowly thereafter. Digital computer period analysis of the EEG demonstrated after clovoxamine only minor changes characterized by an increase of fast beta-activities suggesting slight activating qualities of the drug. On the other hand 75 mg fluvoxamine and especially 75 mg imipramine produced marked CNS changes characterized by a concomitant increase of slow and fast activities and a decrease of alpha-activity. However, 75 mg fluvoxamine induced less augmentation of slow activity than imipramine indicating less sedative properties of fluvoxamine than the standard reference drug. Psychometric tests demonstrated after 50 and 75 mg clovoxamine and 75 mg fluvoxamine an increase in attention, attention variability, concentration, CFF and after-effect in the Archimedean Spiral (indicating central activation), further an improvement in mood and affectivity as compared with placebo, while 125 mg clovoxamine and 75 mg imipramine produced an increase in reaction time, deterioration of mood and affect and psychomotor activity. The latter changes were observed also after other antidepressants in normals. Pharmacodynamic investigations regarding dose-efficacy and time-efficacy relations based on both EEG and psychometric parameters revealed that 75 mg imipramine was the most effective compound, followed by 75 mg fluvoxamine and 125 mg, 75 mg and 50 mg clovoxamine. The peak effect of clovoxamine and fluvoxamine was observed around the 6th hour, while 75 mg imipramine was maximally observed around the 6th hour, while 75 mg imipramine was maximally effective between the 2nd and the 4th hours. Side effects were minimal after clovoxamine (interestingly euphoria in 3 subjects), while tiredness was seen in 5 out of 10 subjects after 75 mg fluvoxamine and in 8 out of 10 subjects after 75 mg imipramine. There were no clinically relevant changes in pulse, systolic and diastolic blood pressure.

Adult↗