Biomedical subjects

A Bast

Publications and source records attributed to A Bast.

At least 199 records · Page 11Linked to original sources

PubMed1988

The effects of beta-adrenergic receptor agonists on the H2O2 formation in alveolar macrophage suspensions are not mediated by beta-receptors.

In the present study, the effects of beta-adrenergic receptor agonists on the hydrogen peroxide (H2O2) production in phorbol myristate acetate stimulated guinea pig alveolar macrophage suspensions have been investigated. In contrast to suggestions described in literature, our results indicate that the H2O2 production in alveolar macrophage suspensions is not mediated by beta-adrenergic receptors. Rather, it is suggested that the inhibitory effect of catecholamines in the H2O2 formation which is found after 5 minutes is the result of inhibition of the horseradish peroxidase catalysed phenol red oxidation, used as H2O2 measurement, by the catecholamines.

Adrenergic beta-Agonists↗

PubMed1988

Identification of structural characteristics of some potential H2-receptor antagonists that determine the interaction with rat hepatic P-450.

Several potential H2-receptor antagonists have been tested in vitro, using liver microsomal preparations from untreated rats, in order to study their interaction with P-450. The aim of this investigation was to establish structure-activity relationships for the P-450-inhibition developed by cimetidine and related drugs. Most of the compounds tested demonstrate an inhibitory activity and a binding ability to P-450, via type II (ligand type) binding. Our results strongly indicate that the cyano-guanidine moiety is an essential structural feature for both the inhibition of a ferrocytochrome P-450-metabolic intermediate complex formation occurring during the metabolism of tofenacine, and the binding of the compounds to the heme iron of P-450. The presence of an imidazole group is not necessary for these activities. Furthermore, it is pointed out that the lipophilic character of the cyano-guanidine side chain contributes to the interaction of the test compounds with P-450, since a trend for a parabolic relationship between lipophilicity and inhibitory activity or binding ability is observed. Finally, under the experimental conditions used, no increase of the inhibitory activity of cimetidine on the metabolism of tofenacine and 7-ethylresorufin is observed after preincubation of rat liver microsomes with cimetidine, confirming earlier results in similar studies.

Animals↗

PubMed1988

Frequency-dependent autoinhibition of histamine release from rat cortical slices: a possible role for H3 receptor reserve.

The inhibition of histamine release after depolarization of rat cerebral cortex slices by electrical stimulation and mediated by the postulated presynaptic autoreceptor (H3) depends strongly on the conditions of stimulation. Using electrically stimulated slices of the cortex a rightwards shift of the concentration-response curve of histamine (an H3 agonist) was observed on increasing the frequency of stimulation. The pA2 value of the H3 antagonist impromidine was, however, not altered at different stimulation frequencies; for a partial agonist only the maximal effect was influenced. These results indicate the existence of a receptor reserve at the H3 autoreceptor.

Animals↗

PubMed1988

The effect of hydrogen peroxide on beta-adrenoceptor function in the heart.

A membrane preparation of calf heart left ventricle has been used to study the effect of radical stress on the beta-adrenoceptor complex. To this end the membranes were incubated for 30 minutes with several concentrations of hydrogen peroxide. This resulted in a dose dependent peroxidation of the membrane lipids. Preincubation with hydrogen peroxide in the concentration range 10(-7)-10(-3) M caused an increase in specific (-)-[125I]-Iodocyanopindolol binding, possibly due to a decrease in membrane fluidity as a result of lipid peroxidation, thus making the receptor protein more accessible. Higher concentrations H2O2 reduced the specific (-)-[125I]-Iodocyanopindolol binding, which is most likely the effect of deterioration of the receptor protein by the more pronounced radical stress induced by these higher concentrations. Also adenylate cyclase activity was affected by radical stress. Basal cyclic-AMP production and cyclic-AMP production induced by NaF (10(-2) M) or guanylylimidodiphosphate (10(-4) M), was suppressed after pretreatment with concentrations of H2O2 above 10(-4) M. This indicates a higher sensitivity of the adenylate cyclase toward radical stress when compared to the receptor protein. Our results show that radical stress can perturb beta-adrenoceptor function considerably in the heart.

Adenylyl Cyclases↗

PubMed1988

Irreversible binding of the fluorescent beta-adrenoceptor probes alprenolol-NBD and pindolol-NBD to specific and non-specific binding sites.

The fluorescent 4-nitrobenzo-2-oxa-1,3-diazolyl (NBD) derivatives of alprenolol and pindolol bind irreversible to beta-adrenoceptors and non-receptor binding sites. This was established in functional experiments on the guinea pig right atrium and trachea smooth muscle, and by radioligand binding assay of beta-adrenoceptors on Chang liver cells in culture. The pD2'-values of alprenolol-NBD and pindolol-NBD for the beta-adrenoceptors on the right atrium were: 8.3 +/- 0.1 and 8.5 +/- 0.1; on the tracheal smooth muscle strip: 8.2 +/- 0.1 and 8.8 +/- 0.1; and its pKd on Chang liver cells: 8.5 +/- 0.1 and 8.9 +/- 0.1 respectively. The results indicated that no selectivity for the beta-adrenoceptor subtypes was introduced by the addition of NBD. The irreversible binding characteristic to beta-adrenoceptors and non-receptor binding sites of the fluorescent NBD derivatives of alprenolol and pindolol makes these drugs unsuitable to label beta-adrenoceptors specifically. As the irreversible binding is introduced by the coupling of the drug with NBD, it is concluded that NBD derivatives of beta-adrenoceptor antagonists are not suitable to visualize the two-dimensional motion of beta-adrenoceptors during challenge with agonists.

4-Chloro-7-nitrobenzofurazan↗

PubMed1987

The effect of ischemia and recirculation, hypoxia and recovery on anti-oxidant factors and beta-adrenoceptor density. Is the damage in the erythrocytes a reflection of brain damage caused by complete cerebral ischemia and by hypoxia?

This investigation was focussed on the gravity of tissue injury caused by complete ischemia (for five min) and hypoxia (for three weeks) in the cerebral cortex (homogenate) and the erythrocyte lysate or the erythrocyte membrane of the rat in order to investigate if the changes that occur in brain tissue are reflected in the erythrocyte. To this end, glutathione (GSH), superoxide dismutase (SOD) and catalase were measured, also alterations in beta-adrenoceptor density under these two conditions were examined. It was found that in ischemia partial parallelism in changes that occur in the central nervous system (cerebral cortex) and the erythrocyte exists. The SOD activity became higher and the beta-adrenoceptor density (measured as specific (-)-[125I] iodocyanopindolol binding) was decreased in both tissues. However after the hypoxic condition we established a decrease in the number of beta-adrenoceptors in the cerebral cortex but an increase in beta-adrenoceptor density in the erythrocyte.

Animals↗

PubMed1987

HA autoreceptor assay with superfused slices of rat brain cortex and electrical stimulation.

Slices of rat brain cortex previously loaded with [3H]histamine ([3H]HA) via de novo synthesis from [3H]histidine released tritiated histamine ([3H]HA) Ca2+ dependently in a superfused system. Both electrical field stimulation and high levels of K+ ions elicited this release. The extent of release depended on stimulation intensity. Rather strong stimuli, either by high frequency or longer stimulation, were required to elicit sufficient HA release for proper assessment of the concentration-dependence of release inhibition by drugs. The system showed marked depletion (less response per pulse) upon long-continued or successive stimulations. HA added to the superfusion medium inhibited the release evoked by stimulation at frequencies up to 10 Hz or with 30 mM K+ but not the release at higher frequencies or with 45 mM K+. The inhibition was mediated by H3 receptors, was concentration-dependent (pD2 = 7.4) and was complete at 10(-6) M. The H2 agonist impromidine antagonized the inhibition competitively (pA2 = 7.1). It is concluded that this assay in a superfusion system with electrical stimulation is suitable for the assessment of H3 receptor activity of drugs.

Animals↗

PubMed1987

A disbalance between beta-adrenergic and muscarinic responses caused by hydrogen peroxide in rat airways in vitro.

The effect of hydrogen peroxide on adrenergic and muscarinic responses of rat airway smooth muscle was studied. The trachea muscle and the lung parenchymal strip were contracted with methacholine and relaxed with (-)-isoprenaline. Recording of three (-)-isoprenaline curves on the trachea muscle and the lung parenchymal strip was followed by treatment for 30 min with hydrogen peroxide (H2O2) (1mM) after which a new dose response curve for (-)-isoprenaline was constructed. Using the trachea muscle this treatment with H2O2 resulted in a decrease of 61% of the maximum contraction by methacholine compared with the control and a complete inhibition of the relaxation by (-)-isoprenaline. In the lung parenchymal strip preparation we found, after the same treatment no reduction of the contraction by methacholine and 61% reduction of the relaxation by (-)-isoprenaline, compared with the control. The results demonstrate that the adrenergic response in rat airways is more susceptible to hydrogen peroxide than the muscarinic response.

Animals↗

PubMed1987

Experimental conditions influence [3H]-dihydroalprenolol binding characteristics to living HeLa cells due to morphological changes: a warning.

Harvesting of plated growing HeLa cells, followed by incubation of these cells without any addition at 37 degrees C was found to cause changes in the cell shape. This phenomenon is accompanied by a diminished binding of the beta-adrenergic antagonist [3H]-dihydroalprenolol and the alpha-adrenergic antagonist phentolamine to a binding compartment not representing beta-adrenergic receptors. These binding sites have a high affinity for hydrophobic agents and most probably represent lipophilic structures in the cellular membrane. Changes in the cell shape obviously cause alterations in the physical properties of the plasma membrane. This might lead to misinterpretations of the results from experiments in which the redistribution of beta-adrenergic receptors is followed during incubation with agonists, as receptor occupation with subsequent receptor redistribution is possibly accompanied by effects on the membrane microviscosity. It is concluded that investigations performed in order to follow physiological events like receptor redistribution and desensitization processes, may be obfuscated by changes in the normal physical state of the living cells.

Adrenergic beta-Agonists↗

PubMed1987

Relation between pharmacological response and receptor binding with histamine blocking drugs. Irreversible antagonism of three analogues of mifentidine on right atrium and cerebral cortex of the guinea-pig.

The effects of the H2-receptor antagonists cimetidine, ranitidine, mifentidine and three analogues of mifentidine, were studied on the spontaneously beating right atrium (H2-antagonism) and membranes of the cerebral cortex (displacement of 3H-tiotidine), both obtained from the male guinea-pig. The choice of these compounds was based on preliminary experiments in which some mifentidine analogues were shown to displace tiotidine from the H2-receptor in a deviant manner. In the present study we investigated the relation between pharmacological response and receptor binding, also testing the degree of irreversible antagonism of these compounds in the atrium (functional) and cerebral cortex (binding) model. Our data indicate that a relation between the two different approaches for measuring the effect on the H2-receptor can be found, although some differences emerged as well.

Animals↗

PubMed1987

H3 receptor assay in electrically-stimulated superfused slices of rat brain cortex; effects of N alpha-alkylated histamines and impromidine analogues.

The release of the putative neurotransmitter histamine (HA) from rat brain cortex slices is under negative feedback control by an HA autoreceptor. This autoreceptor has been postulated to belong to a new class of HA receptors, H3. To verify this hypothesis we have developed an assay using superfused rat brain cortex slices. The HA transmitter pool is labelled by incubation of the slices with the precursor 3H-histidine; 3H-HA is estimated after separation by column chromatography. Release of HA was found both after K+-induced depolarization and electrical field stimulation. The latter resulted in higher and more reproducible HA release. Electrically induced HA release could be fully inhibited in a concentration dependent way by exogenous HA in the superfusion buffer. N alpha-alkylated histamines also showed agonistic activity. The action of exogenous HA was totally blocked by the potent H2 agonist impromidine and some of its analogues.

Animals↗

PubMed1987

4-Hydroxy-2,3-trans-nonenal stimulates microsomal lipid peroxidation by reducing the glutathione-dependent protection.

Glutathione (GSH) protects liver microsomes against lipid peroxidation. This is probably due to the reduction of vitamin E radicals by GSH, a reaction catalyzed by a membrane-bound protein. Pretreatment of liver microsomes with 0.1 or 1mM 4-hydroxy-2,3-trans-nonenal (HNE), a major product of lipid peroxidation, reduces the GSH-dependent protection. GSH and vitamin E concentrations are not affected by this pretreatment. Pretreatment with 0.1 mM N-ethyl maleimide (NEM), a synthetic sulfhydryl reagent, resulted in a reduction similar to that with HNE of the GSH-dependent protection against lipid peroxidation. The reduction of the GSH-dependent protection by HNE and NEM is probably the result of inactivation of the membrane-bound protein by covalent binding to an essential SH group on the protein. If the GSH-dependent protection would proceed via the microsomal GSH transferase, pretreatment with NEM, which activates the microsomal GSH transferase, should enhance the GSH-dependent protection. Actually a decrease in the GSH-dependent protection is found. Apparently the GSH-dependent protection does not proceed via the microsomal GSH transferase. Also the microsomal phospholipase A2 is not involved, since addition of 0.1 mM mepacrine, an inhibitor of phospholipase A2, did not preclude the GSH-dependent protection. Once the process of lipid peroxidation, either in vivo or in vitro, has started, the protection of liver microsomes by GSH is less effective. This might be the result of formed HNE. In this way an endproduct of lipid peroxidation stimulates the process that generates this product.

Aldehydes↗

PubMed1987

Studies on the active molecular species of the H2 receptor antagonists cimetidine and mifentidine.

The N'-(4-1H-imidazol-4-ylphenyl)formamidines were recently introduced as a new class of active H2 antagonists; the authors of the compounds (Donetti et al. of de Angeli, Italy) have suggested that these compounds interact with the H2 receptor through their monocations. This is at variance with the model proposed for cimetidine by the SK&F (Smith Kline & French, UK) group who proposed the neutral molecule as the species active at the H2 receptor. In the present study we have investigated the issue whether the neutral or charged species is the active one by measuring the pA2 values of mifentidine and cimetidine at different pH values. Changing the pH will influence the species equilibria of both compounds and thereby affect their activity. The activity changes measured for both compounds are consistent with the proposition that cimetidine as well as mifentidine elicit their activity through their neutral species.

Animals↗

PubMed1987

Cytochrome P450 metabolic intermediate complex of nefopam.

NADPH-catalysed biotransformation of nefopam in liver microsomes obtained from phenobarbitone-pretreated rats leads to the formation of an inactive cytochrome P450 metabolic intermediate (MI) complex. This complex can be detected spectrophotometrically by an absorbance maximum at 459 nm. The extent of the in-vitro MI complexation of 33 microM nefopam, a cyclic analogue of orphenadrine, was almost equal to the extent of the in-vitro MI complexation of 33 microM tofenacine, the mono-N-demethylated metabolite of orphenadrine. The time course of the MI complexation of nefopam and studies with two of its major metabolites suggest an initial biotransformation, which has to occur before MI complexation can take place. Maximal MI complexation of nefopam occurred at approximately 25 microM, whereas the MI complexation could not be detected at 100 microM nefopam.

Animals↗

PubMed1987

Cyclandelate as a calcium modulating agent in rat cerebral cortex.

Cyclandelate is clinically effective in a variety of cerebrovascular indications, but its precise mode of action is unclear. Hence, this study investigated the interaction of cyclandelate, cyclandelate alcohol and cyclandelate acid with the binding sites for radioactively labelled 3H-nitrendipine, a Ca++ entry blocker of the 1,4-dihydropyridine type, on rat cerebral cortex membranes. Cyclandelate showed a dissociation constant (Kd) of 7.1 +/- 1.4 X 10(-5) mol/L (35% inhibition of 3H-nitrendipine binding at 2 X 10(-4) mol/L cyclandelate), cyclandelate alcohol had a Kd value of 1.7 +/- 0.1 X 10(-4) mol/L (maximal 70% inhibition of 3H-nitrendipine binding) whereas cyclandelate acid was inactive. For comparison, nifedipine (Kd of 2.6 +/- 0.3 X 10(-9) mol/L inhibition of 68% of 3H-nitrendipine binding), d-cis diltiazem (Kd of 1.1 +/- 0.1 X 10(-7) mol/L enhancement of 39% of 3H nitrendipine binding) and +/- -verapamil [Kd values of 1.4 +/- 0.4 X 10(-7) mol/L (38% inhibition) and 5.3 +/- 1.7 X 10(-4) mol/L (62% inhibition)] were used. Thus, cyclandelate may exert its clinical activity in cerebral ischaemia or hypoxia at least in part through a calcium modulatory effect.

Animals↗

PubMed1987

Red blood cell anti-oxidant parameters in healthy elderly subjects versus silicosis patients.

The anti-oxidant phenotype was determined in red blood cell haemolysates of 62 healthy elderly persons (Mean age: 56) and a number of male silicosis patients (Mean age: 65, n = 19). Moreover, analysis of water-soluble fluorescent substances in plasma, recently introduced as a new test for in vivo lipid-peroxidation, was included. Within the control group results were analyzed on the effect of smoking (no effect), use of medication (lowered GSH-content) or gender (no differences apart from haemoglobin content). No simple relationship between any pair of the measured parameters in erythrocytes was present. When comparing the male control persons with the silicosis group a significantly higher red blood cell GSH-level was observed in the latter. Moreover, some factors of the anti-oxidant system are strongly correlated in the diseased, but not in the healthy subjects.

Aged↗

PubMed1987

Inhibition of rat hepatic microsomal lipid peroxidation by mesna via glutathione.

Glutathione (GSH, 1 mmol/l) inhibits Fe2+/ascorbic acid induced liver microsomal lipid peroxidation. Oxidized GSH (GSSG, 1 mmol/l) did not affect rate or extent of lipid peroxidation. The inhibition by GSH seems specific since the sulfhydryl agent sodium 2-mercaptoethanesulfonate (mesna) gave a slight stimulation of lipid peroxidation. This stimulation is probably explained by a reduction by mesna of dehydroascorbic acid which is formed during the incubation, into ascorbic acid. Remarkably, mesna (1 mmol/l) added together with GSSG (1 mmol/l) produced the same inhibition as with 1 mmol/l GSH alone. This can be explained by direct reduction of GSSG to GSH by mesna. This is corroborated in experiments in which GSH is measured directly. Dimesna did not show an effect on lipid peroxidation. In the protective action of mesna against reactive substances its ability to reduce GSSG should be appreciated.

Animals↗

PubMed1986

Hydroxyl radicals are not involved in NADPH dependent microsomal lipid peroxidation.

NADPH dependent H2O2 formation in microsomes in the presence of chelated iron leads to formation of hydroxyl radicals. Enhancement of hydroxyl radical generation (via ferric-EDTA or sodium azide) did not result in a concomitant increase in lipid peroxidation; rather, a decrease was observed. Moreover, the hydroxyl radical scavenger DMSO did not inhibit lipid peroxidation. This comparison of hydroxyl radical formation with lipid peroxidation suggests that hydroxyl radicals do not play a part in NADPH-dependent lipid peroxidation.

Animals↗