Biomedical subjects

A Bast

Publications and source records attributed to A Bast.

At least 109 records · Page 6Linked to original sources

PubMed1995

The use of telemetry to record electrocardiogram and heart rate in freely swimming rats.

Measurement of parameters from the circulatory system of laboratory animals can play an important role in pharmacological or toxicological research. To study the mutual interaction between physical exercise and antioxidant systems in rats, we selected swimming as a model for exercise performance. Swimming belongs to the natural behavior of the rat, and under proper experimental conditions, it primarily involves physical exercise with little emotional arousal. Therefore, we developed a swimming basin in which the intensity of exercise could be manipulated through speed and duration of swimming. A laser beam interruption system enables the rat to be followed during each swimming session. A motor-controlled following device, consisting of a rail and sledge connected to a position sensor, contains an antenna mounted in a receiver board. In this way, we can record the electrocardiogram (ECG) and heart rate (HR) with a commercially available telemetry transmitter implanted in the peritoneal cavity of freely swimming rats and evaluate the physical fitness (condition) of the swim-trained rats.

Animals↗

PubMed1994

Rapid desensitization of the histamine H2 receptor on the human monocytic cell line U937.

In the present study we have subjected the histamine H2 receptor on the monocytic cell line U937 to a thorough pharmacological characterization using a series of selective histamine H1, H2 and H3 receptor agonists and antagonists. Recent reports have demonstrated the existence of a histamine H2 receptor on HL-60 and HGT-1 cells with a pharmacological profile distinct from the commonly described histamine H2 receptor. U937 cells, however, seem to express classical histamine H2 receptors. Histamine and dimaprit dose dependently induce the formation of cAMP, whereas dimaprit's inactive analogues, nordimaprit and homodimaprit, show reduced potencies. Histamine H1 and H3 receptor agonists do not show histamine H2 receptor activity. Various histamine H2 receptor antagonists are able to block the histamine induced production of cAMP with an antagonistic profile comparable to that observed in the guinea-pig right atrium. Furthermore, endogenous histamine H2 receptors in U937 cells are found to be susceptible to receptor desensitization, a mechanism which may become apparent under pathophysiological conditions or during drug therapy. A 30-min pre-exposure of U937 cells to histamine (100 microM) results in a 50% attenuation of the production of cAMP to a subsequent application of an agonist. Desensitization of the histamine H2 receptor in U937 cells is found to be homologous as the beta-adrenoceptor mediated response remained unaffected.

Cells, Cultured↗

PubMed1994

Structural characteristics of histamine H2 receptor antagonists that scavenge hypochlorous acid.

Gastric and duodenal ulcers are characterized by hypersecretion of gastric acid and pepsin, inflammation of the mucosa and an influx of neutrophils. These cells can produce reactive oxygen species after stimulation. Particularly hydroxyl radicals and hypochlorous acid (HOCl) can be cytotoxic and damage the gastroduodenal mucosa. It has been shown that histamine H2 receptor antagonists such as cimetidine, ranitidine and famotidine are good hydroxyl radical scavengers. This study was undertaken to investigate whether these agents were able to scavenge the cytotoxic HOCl, and if so, which part of the molecule could be responsible for this action. It appears that the sulfur atom in the compound is of importance for scavenging HOCl. This finding should be taken into consideration in the development of new anti ulcer drugs, as HOCl is a detrimental factor in the pathophysiology of gastroduodenal ulcers.

Cimetidine↗

PubMed1994

A method for screening hypochlorous acid scavengers by inhibition of the oxidation of 5-thio-2-nitrobenzoic acid: application to anti-asthmatic drugs.

Neutrophils use a bactericidal mechanism through the release of the enzyme myeloperoxidase which catalyzes the formation of the powerful oxidant hypochlorous acid (HOCl) from H2O2 and Cl-. HOCl can inactivate alpha 1-antiproteinase (alpha 1-AP) which causes increased proteolytic activity at sites of pulmonary inflammation. The search for possible HOCl scavengers usually involves time-consuming enzyme assays (e.g., alpha 1-AP and elastase). We developed a method in which the compound 5-thio-2-nitrobenzoic acid could easily be oxidized by HOCl. The inhibition of this oxidation by a test compound is a measurement of its HOCl scavenging activity. To illustrate the method we tested some well-known HOCl scavengers such as S-methylated glutathione and oxidized lipoate. Finally several anti-asthmatic drugs such as terbutaline, isoproterenol, salbutamol, cromoglycate, theophylline, and dexamethasone were evaluated. Only the drug terbutaline acted as a HOCl scavenger.

Bronchodilator Agents↗

PubMed1994

Lipoic acid favors thiolsulfinate formation after hypochlorous acid scavenging: a study with lipoic acid derivatives.

Lipoic acid, the oxidized form of 6,8-dimercapto-octanoic acid has a strained cyclic disulfide in a 1,2-dithiolane ring. Recently its antioxidant activity gained attention. Hypochlorous acid (HOCl) is an oxidant produced by neutrophils. A prominent effect of HOCl is the inactivation of alpha-1-antiproteinase. Due to this inactivation, the ability of alpha-1-antiproteinase to inhibit elastase is lost. The resulting higher activity of elastase is held responsible for tissue damage in lung emphysema. We studied the HOCl scavenging capability of three metabolites of lipoic acid: tetranor-, bisnor-, and beta-lipoic acid. To obtain some insight on the molecular basis of HOCl scavenging 1,2-dithiane-4,5-diol, cystine, lipoic acid methyl ester, and lipoamide were also included in the study. The extent of alpha-1-antiproteinase inactivation by HOCl in the presence of scavenger was taken as a parameter to quantify the scavenging activity. It was found that lipoic acid, tetranor- and bisnorlipoic acid, lipoic acid methyl ester, and lipoamide all showed the same activity toward HOCl. beta-Lipoic acid, 1,2-dithiane-4,5-diol and cystine were less active. The products of lipoic acid after reaction with HOCl were studied using GC/MS. Indications for thiolsulfinate formation were found by comparing these products with the GC/MS profile of beta-lipoic acid. Thiolsulfinate formation may also be suggested in the reaction of tetranor- and bisnorlipoic acid and lipoic acid methyl ester with HOCl. The present results show an antioxidant activity of the metabolites tetranor- and bisnorlipoic acid. The 1,2-dithiolane ring may enhance the reactivity toward HOCl compared to less strained disulfides, resulting in the formation a thiolsulfinate.

Free Radical Scavengers↗

PubMed1994

Comparison of different iron chelators as protective agents against acute doxorubicin-induced cardiotoxicity.

Doxorubicin (Dox) is a widely used antineoplastic agent. Irreversible cardiomyopathy is a serious and dose-limiting side effect after chronic administration. The iron chelating bispiperazinedione ICRF-187 is currently the only drug which affords protection against Dox-induced cardiotoxicity. To compare the protective value of structurally unrelated iron chelators, isolated mice atria were exposed to Dox (30 microM) and either the hydroxamate desferrioxamine (DFO, 200 and 500 microM), EDTA (200 microM) or the hydroxypridones CP44 (200 microM), CP51 (200 microM), and CP93 (200 microM) and ICRF-187 (200 and 500 microM). The nitroxide TEMPO (5 mM) lacks iron chelating properties but was used to prevent redox cycling or iron and scavenge superoxide. All iron chelators, except EDTA. CP93 and CP44, were modestly protective against a Dox-induced decrease in contractile force. As a single agent the hydroxypridones decreased atrial contractile force. At a concentration of 200 microM, DFO was the most effective protector of the chelators tested. However, this effect disappeared when a concentration of 500 microM was used. This in contrast to ICRF-187 for which a concentration-dependent inhibition of Dox-induced decrease in contractile force was observed. TEMPO exerted a biphasic response consisting of a two-fold increase in contractile force, followed by a decrease in force and irregular contractions. In this model TEMPO lacked any perspective as a cardioprotectant. We conclude that at 200 microM. DFO was the most effective agent to afford protection against Dox-mediated atrial malfunction. However, at 500 microM, DFO was not effective whereas ICRF-187 afforded partial protection. Hydroxipyridones were found to be of limited value because of a negative inotropic effect on the isolated atria.

Animals↗

PubMed1994

The involvement of nitric oxide synthase in the effect of histamine on guinea-pig airway smooth muscle in vitro.

The influence of histamine on nitric oxide synthase (NOS) in the development of airway smooth muscle hyperresponsiveness to histamine was investigated in vitro. In the absence of histamine, NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) had no significant effect on the basal tone. However, precontraction of the tissues with histamine (0.3 microM) resulted in a significant contractile response to L-NAME in the preparations with intact epithelium. Removal of the epithelial layer decreased the responses to L-NAME. L-arginine could partially reverse the contraction produced by L-NAME. L-NAME enhanced the maximal response to histamine, but the sensitivity of the tracheal smooth muscle to histamine was not affected. These results suggest that, in the airway, histamine can activate NOS, resulting in the release of nitric oxide. The latter may be regarded as a local negative modulator to maintain the tissue in a physiological homeostasis.

Amino Acid Oxidoreductases↗

PubMed1994

A new radioligand binding assay for cytochrome P450IID1 (CYP2D1) in rat liver microsomes: a tool to predict sparteine/debrisoquine type polymorphism of drugs.

[3H]-Mepyramine ([3H]-pyrilamine) has a high affinity for cytochrome P450IID1 (CYP2D1) in rat liver microsomes, the isoenzyme involved in the oxidative metabolism of debrisoquine. Drugs known to interact with this enzyme, as either substrate or inhibitor, displaced [3H]-mepyramine. Compounds specific for other P450 isoenzymes did not displace [3H]-mepyramine. Drugs that are positive in this binding assay can be either substrates or inhibitors of CYP2D1 and warrant further research to investigate possible polymorphism. Substrates could reach toxicological concentrations, and inhibitors can have drug interactions with known CYP2D6 substrates. Although care should be taken in the extrapolation from rat to human, since CYP2D1 and CYP2D6 have clear differences, this rapid, easy-to-perform and inexpensive assay has predictive value for the sparteine/debrisoquine type of polymorphic behavior of compounds and could be used at an early stage in drug development.

Animals↗

PubMed1994

Screening of cattle urine samples for the presence of beta-agonists with a functional test: some preliminary results.

A new procedure based on the measurement of biological effects has been developed for the determination of residues of beta-agonists, such as clenbuterol, in urine. A multi-chamber superfusion apparatus containing isolated trachea strips from guinea pigs was used to detect smooth muscle relaxation induced via beta 2-adrenoceptor activation. The trachea tissue was pre-contracted with metacholine. Urine samples were extracted using a solid-phase column containing reversed-phase and anion-exchange materials. Extracts were introduced into the superfusion apparatus via flow injection. The intensity and response of relaxation are dependent on the type and concentration of the beta-agonist introduced. The sensitivity of the assay for clenbuterol in calf urine is about 1 microgram l-1. This methodology in the present form is especially suitable for survey screening analysis for several types of samples. An extensive validation of the procedure is performed to determine the range of analytes that can be detected, the possibilities of analysing urine samples obtained from mature cattle or other animal species and the influence of cross-reacting substances.

Adrenergic beta-Agonists↗

PubMed1994

Characterization of the binding of the first selective radiolabelled histamine H3-receptor antagonist, [125I]-iodophenpropit, to rat brain.

1. The binding of the first selective radiolabelled histamine H3-receptor antagonist [125I]-iodophenpropit to rat cerebral cortex membranes was characterized. 2. [125I]-iodophenpropit, radiolabelled to a high specific activity of 1900 Ci mmol-1, saturably bound to a single class of sites with a KD of 0.57 +/- 0.16 nM (n = 4) and Bmax of 268 +/- 119 fmol mg-1 protein. 3. Specific binding at a concentration below 1 nM represented 50 to 60% of total binding. 4. Binding of [125I]-iodophenpropit to rat cerebral cortex membranes was readily displaced by histamine H3-agonists and antagonists. In contrast, the inhibitory potencies of selective histamine H1- and H2-receptor ligands were very low. 5. [125I]-iodophenpropit was biphasically displaced by the histamine H3-receptor antagonists, burimamide and dimaprit, which may indicate the existence of histamine H3-receptor subtypes. Other histamine H3-receptor antagonists showed a monophasic displacement. 6. Competition binding curves of H3-agonists were biphasic and showed a rightward shift upon the addition of the nonhydrolysable GTP analogue, guanosine 5'-o-(3-thio) triphosphate (GTP gamma S; 100 microM) which implicates the interaction of histamine H3-receptors with G-proteins. The affinities of the H3-receptor antagonists iodophenpropit, thioperamide and burimamide were not altered by GTP gamma S. 7. Histamine competition binding curves were shifted to the right by different nucleotides (100 microM) with a rank order of potency GTP gamma S > Gpp(NH)p, GTP. 8 In vitro autoradiographic studies revealed a heterogeneous distribution of [125I]-iodophenpropitbinding sites in rat brain, with highest densities observed in specific cerebral cortical areas and layers,the caudate-putamen complex, the olfactory tubercles, the hippocampal formation, the amygdala complex, the hypothalamic area and the mammillary bodies.9 It is concluded that the histamine H3-receptor antagonist, [125I]-iodophenpropit, meets the criteria fo ra suitable radioligand for histamine H3-receptor binding studies in rat brain.

Animals↗

PubMed1994

A functional beta-2 adrenoceptor-mediated chronotropic response in isolated guinea pig heart tissue: selectivity of the potent beta-2 adrenoceptor agonist TA 2005.

Responses were measured of the highly potent beta-2 adrenoceptor agonist TA 2005, a new bronchodilator, on isolated guinea pig right and left atria and papillary muscle. The main objectives of the study were to investigate the selectivity of the compound and to determine whether guinea pig isolated heart tissues could be used as a model for investigating mechanisms of clinical cardiac side effects. It was found that the inotropic responses in all tissues were mediated by the beta-1 adrenoceptor only. TA 2005 was a partial agonist for the inotropic response compared with I-isoprenaline. For the right atrial chronotropic response, however, TA 2005 exerted a biphasic effect and reached 84% of the I-isoprenaline response. The first phase was mediated by the beta-2 adrenoceptor, whereas the second phase was beta-1 adrenoceptor mediated. Approximately 64% of the TA 2005 chronotropic response was exerted via the beta-2 adrenoceptor. Addition of the beta-2-selective antagonist ICI 188.551 blocked the beta-2 adrenoceptor-mediated response, providing only a monophasic response. Addition of the beta-1-selective antagonist ICI 89.406 resulted in further separation of the phases. The finding that a beta-2-mediated chronotropic response exists on the right atrium of the guinea pig sheds new light on selectivity studies. It is suggested that quantification of beta-1/beta-2 selectivity of beta adrenoceptor agonists be performed not on the basis of measurement of guinea pig right atrial chronotropism but rather on the basis of measurement of guinea pig left atrial inotropism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗

PubMed1993

Extracellular ATP elevates cytoplasmatic free Ca2+ in HeLa cells by the interaction with a 5'-nucleotide receptor.

In the present study we have characterized the effects of ATP and several other nucleotides on the intracellular Ca2+ levels of HeLa cells. Using fura-2 microscopy fluorescence measurements, the ATP-mediated increase in intracellular Ca2+ was shown to consist of a rapid rise which decreased after a few seconds to a sustained elevated level. In the absence of extracellular Ca2+ or in the presence of 10 microM La3+, only a transient elevation of the Ca2+ concentration was observed. The ATP responses were not altered after treatment of HeLa cells with cholera toxin or pertussis toxin. Pharmacological analysis of this calcium response revealed that this effect was not mediated by the classical P2y purinoceptor but by a 5'-nucleotide receptor.

Adenosine Triphosphate↗

PubMed1993

Cardioprotective properties of O-(beta-hydroxyethyl)-rutosides in doxorubicin-pretreated BALB/c mice.

Chronic doxorubicin-induced cardiotoxicity is believed to be caused by the formation of oxygen free radicals. Thus O-(beta-hydroxyethyl)-rutosides, a standardized flavonoid mixture (Venoruton) with iron chelating and radical scavenging activity, might provide protection. Therefore, we investigated the (cardio)protective effect of Venoruton (1.5 g/kg injected i.p. on days 1-5, 8-12, 15-19, and 22-26) in BALB/c mice treated with doxorubicin (4 mg/kg injected i.v. on days 1, 8, 15, and 22) compared with mice treated with doxorubicin alone. Saline-treated animals served as controls. No mortality was encountered in either of the groups; weight gain data suggest little general toxicity of this dose schedule. The basal frequency of the isolated right atria was increased in doxorubicin-pretreated animals as compared to control animals (468 +/- 22 and 366 +/- 20 beats/min, respectively). Venoruton coadministration diminished this increase (373 +/- 17 beats/min). The -log of the concentration giving 50% effect of l-isoprenaline on the right atrium was changed after doxorubicin pretreatment (8.33 +/- 0.04 versus 8.86 +/- 0.06 for control animals). Venoruton coadministration resulted in a smaller shift in the -log of the concentration giving 50% effect (8.51 +/- 0.10) than with doxorubicin alone. The extent of cardiotoxicity found in the functional studies was confirmed by histological scoring of heart ventricle damage. It can be concluded that Venoruton has the potential to protect against doxorubicin-induced cardiotoxicity.

Animals↗

PubMed1993

Is there a difference in the affinity of histamine H1 receptor antagonists for CNS and peripheral receptors? An in vitro study.

An extended series of structurally different histamine H1 receptor antagonists was investigated for binding at central and peripheral histamine H1 receptors in vitro. Antagonist affinities were measured by displacements of [3H]mepyramine from both guinea-pig cerebellum and lung membrane suspensions. Single [3H]mepyramine binding sites with identical affinity for [3H]mepyramine were found in both tissues; however, the H1 receptor density was 6-fold lower in lungs than in cerebellum. None of the antagonists tested showed substantial preference for either of the receptors. It is concluded from the displacement data that there is no difference between the antagonist binding sites of cerebellum and lung H1 receptors.

Animals↗

PubMed1993

Cimetidine and other H2 receptor antagonists as powerful hydroxyl radical scavengers.

Hydroxyl radical scavengers are able to compete with deoxyribose for the hydroxyl radicals generated in a reaction mixture. We found that the H2 receptor antagonists like cimetidine, burimamide, ranitidine, famotidine and tiotidine except for being good inhibitors in histamine-stimulated gastric acid secretion, were also very powerful hydroxyl radical scavengers. Rate constants for reaction of these drugs with hydroxyl radicals ranged from 7.7 x 10(9) Ms-1 to 14.8 x 10(9) M-1 s-1. These rate constants are much higher than for the well-known hydroxyl radical scavenger mannitol (1.7 x 10(9) M-1 s-1). In this study we investigated which part of the cimetidine molecule might be responsible for its potent hydroxyl radical scavenging activity. Testing fragments of the cimetidine molecule revealed that the guanidine moiety of cimetidine had little hydroxyl radical scavenging activity. However the other part of the molecule, the methylated imidazole with a sulfur and amino group containing side chain appeared to be a powerful hydroxyl radical scavenger.

Cimetidine↗

PubMed1993

Control of physical exercise of rats in a swimming basin.

To study the mutual interaction between physical exercise and antioxidant systems in rats, we selected swimming as a model for exercise performance. Swimming belongs to the natural behavior of a rat, which under proper experimental conditions, primarily involves physical exercise with little emotional arousal. Therefore, we developed a swimming basin in which the intensity of exercise was manipulated by swimming speed and swimming duration. A laser beam interruption system enables recording of swimming patterns. For comparison we also used the basin to induce emotional arousal. Hereto the basin was transformed into a maze, in which unexpected blockade of a learned swimming route induced a panic-like emotional reaction. The antioxidant enzyme superoxide dismutase decreased in rat plasma after emotional arousal, not after physical exercise. Depletion of the antioxidant glutathione in the liver by diethyl maleate led to decrease of swimming performance. Noradrenaline but not adrenaline plasma levels increased in response to physical exercise. After emotional arousal the ratio noradrenaline/adrenaline did not change. In contrast, lactate only increased in response to emotional arousal. Plasma levels of glucose increased after both stress situations. Beta-adrenoceptor function, determined in the heart and in erythrocytes, only changed after physical exercise. The sensitivity to the beta-agonist (-)isoprenaline in the right atrium decreased and a downregulation of the beta-adrenoceptor density was observed in the erythrocyte.

Animals↗

PubMed1993

Molecular pharmacology of vitamin E: structural aspects of antioxidant activity.

In this review, the involvement of vitamin E in free radical physiology and antioxidant mechanisms is discussed. Moreover, structure-activity relationship (SAR) studies on vitamin E analogues are presented. A molecular explanation for the antioxidant activity often is based on molecular parameters, such as Hammett sigma and Brown sigma +. These parameters correlate with the activity. Using semiempirical calculations, we have found other molecular parameters related to electron distribution and structure (such as the difference in heat of formation between the compound and its radical or the energy of the highest occupied molecular orbital, HOMO) which correlate with the antioxidant action of vitamin E and its derivatives.

Antioxidants↗

PubMed1993

Use of telemetry to record electrocardiogram and heart rate in freely moving mice.

This paper describes for the first time the possibility to record the electrocardiogram (ECG) and heart rate (HR) with a commercially available telemetry and data acquisition system in freely moving mice. The system comprises a telemetry transmitter implanted in the peritoneal cavity and a receiver, placed underneath the home cage, an A/D converter (MacLab) and a Macintosh LC II 4/80 computer with software (MacLab, Chart/Scope). The raw analog ECG data are digitized within the MacLab and can be converted to HR data additionally. The effects of surgery for implanting the transmitter, handling and anesthesia by either Nembutal or a mixture of Hypnorm, Dormicum, and water, on the changes in ECG and HR were examined. The telemetry system for recording the ECG and HR provides an accurate and reliable method for monitoring the direct effects of handling on HR. By using this telemetry system, we maintain that measurements in freely moving animals are more efficient, reliable, and less labor-intensive than the measurement techniques described in the literature thus far.

Animals↗