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Biomedical subjects

A Bast

Publications and source records attributed to A Bast.

At least 145 records · Page 8Linked to original sources
PubMed1991

Simple and sensitive quantification of anthracyclines in mouse atrial tissue using high-performance liquid chromatography and fluorescence detection.

Anthracyclines are very effective against soft tissue sarcomas, with cardiotoxicity being an important side effect after repeated administration. To estimate the relative cardiotoxicity of various anthracyclines and their metabolites, we developed an isolated mouse left atrium model. To relate an effect of doxorubicin, 4'-epidoxorubicin and their four main metabolites (doxorubicinol, epidoxorubicinol and the aglycons 7-deoxydoxorubicinon and 7-deoxydoxorubicinolon) to concentrations in the tissue instead of the incubation bath, a method of quantifying the anthracyclines in small tissue samples was developed. Atria were homogenized by sonication followed by extraction of the anthracyclines with methanol. The extract was directly analyzed by high-performance liquid chromatography with fluorescence detection. Recoveries for the six compounds tested ranged from 67.5% for 4'-epidoxorubicin to 100.6% for 7-deoxydoxorubinol aglycon with coefficients of variation of 2-3% at two spiked concentrations (0.1 and 1 nmol/mg of tissue). The calibration plots were linear (r2 greater than 0.996) over the concentration range tested (0.05-1 nmol/mg wet weight). The limits of detection (4-10 pmol/mg of tissue) were low enough to allow the determination of the anthracyclines at all relevant tissue concentrations.

Animals↗
PubMed1991

Histamine H1-receptor-mediated cyclic GMP production in guinea-pig lung tissue is an L-arginine-dependent process.

Histamine produces a rapid and massive increase of the c-GMP level of guinea-pig lung tissue. The EC50 value for this in vitro response is found to be 27 microM and the c-GMP level is maximally 9-fold elevated by 100 microM histamine. The response is stereoselectively inhibited by the enantiomers of chlorpheniramine, indicating H1-receptor involvement. Preincubation of lung tissue with 200 microM NCDC, a phospholipase C inhibitor, reduces the histamine (100 microM) responses to 16 +/- 3% (N = 6) of the control c-GMP production. Inhibition of protein kinase C by 50 microM H-7 does not significantly attenuate the H1-receptor response, whereas omittance of extracellular Ca2+ results in almost complete inhibition of the c-GMP production. The histamine-induced c-GMP response is inhibited by hemoglobin, methylene blue and the antioxidants butylated hydroxytoluene and nordihydroguaretic acid, indicating the involvement of a nitric oxide-dependent activation of soluble guanylate cyclase. This suggestion is supported by the concentration-dependent inhibition of the c-GMP production by NG-monomethyl-L-arginine (NMA). At a concentration of 20 microM NMA the histamine (100 microM) response is inhibited to 34 +/- 8% (N = 6) of the control response. This inhibition is reversed to 127 +/- 20% (N = 6) by the exogenous addition of 1 mM L-arginine. These findings show that after an initial H1-receptor-mediated, phospholipase C-dependent, Ca(2+)-mobilization the enzymatic conversion of L-arginine to nitric oxide is stimulated. This nitric oxide production is finally responsible for the activation of soluble guanylate cyclase, leading to the production of c-GMP.

Animals↗
PubMed1991

Hydrogen peroxide reduces beta-adrenoceptor function in the rat small intestine.

Incubation of isolated rat intestinal segments with hydrogen peroxide (H2O2) led to a decreased beta-adrenoceptor response. The maximal relaxation induced by isoprenaline was lowered while the EC50 remained unaffected. The effect of H2O2 in the small intestine increased slightly from duodenum to ileum. In the ileum, 10(-4) M H2O2 led to a 10% decrease of the maximal relaxation due to isoprenaline and 1 mM decreased the maximal response to about 50%. We further investigated the level at which the isoprenaline response was impaired. The relaxation caused by the stable cAMP analog, dibutyryl-cAMP, or by the adenylate cyclase activator, forskolin, was not affected or affected less than by isoprenaline. When the response to isoprenaline was expressed relative to the maximal response to dibutyryl-cAMP or forskolin, pretreatment with H2O2 led to a decreased isoprenaline response relative to the response to dibutyryl-cAMP or forskolin. This might indicate that exposure to H2O2 leads to a disturbance in receptor-mediated cAMP production. The adenylate cyclase unit is probably not affected since the response to forskolin is relatively resistant to H2O2. Our conclusion is that pretreatment of isolated intestinal segments with H2O2 leads to disturbed beta-adrenoceptor coupling, probably due to altered membrane integrity.

Animals↗
PubMed1991

Activation of the microsomal glutathione S-transferase by metabolites of alpha-methyldopa.

Rat liver microsomes contain a membrane-bound GSH S-transferase (GSH-tr), an enzyme that is involved in the detoxication of xenobiotics. Also located on rat liver microsomes is the cytochrome P450 system, an enzyme complex that catalyzes the conversion of several xenobiotics into reactive intermediates. In this study, it was demonstrated that reactive products from alpha-methyldopa formed by the cytochrome P450 system are able to stimulate microsomal GSH-tr. Also, products formed from alpha-methyldopa that are generated by H2O2-horseradish peroxidase and tyrosinase are able to stimulate the activity of microsomal GSH-tr. GSH was able to prevent the activation of microsomal GSH-tr. Our results indicate that the ortho-quinone or semi-ortho-quinone radical of alpha-methyldopa is responsible for the stimulation of microsomal GSH-tr, probably via arylation of the free sulfhydryl group of microsomal GSH-tr. This conclusion was supported by the observation that 4-methyl-ortho-quinone itself was able to stimulate microsomal GSH-tr via sulfhydryl arylation. Our results are in conformity with the hypothesis that reactive products formed by the cytochrome P450 complex are able to stimulate microsomal GSH-tr and possibly in this way enhance their detoxication.

Animals↗
PubMed1991

Homologous histamine H1 receptor desensitization results in reduction of H1 receptor agonist efficacy.

Prolonged exposure of the guinea-pig intestinal longitudinal smooth muscle to histamine caused homologous desensitization of the H1 receptor, which led to reduced H1 receptor-mediated production of [3H]inositol phosphates as well as to reduced H1 agonist-induced contractions. [3H]Mepyramine binding studies showed that desensitization affected neither the agonist affinity nor the number of H1 receptors. Combining the data from the binding studies and the contraction measurements it was found that desensitization results in a selective reduction of agonist efficacy.

Animals↗
PubMed1991

Prejunctional muscarinic receptors on cholinergic nerves in guinea pig airways are of the M2 subtype.

Prejunctional inhibitory muscarinic receptors in guinea pig tracheal strips were investigated by electrical field stimulation. Pilocarpine and methacholine caused, in a similar way, a dose-dependent increase in baseline with a concomitant decrease in twitch response. We showed by using selective muscarinic antagonists, such as pirenzepine (M1-selective), methoctramine (M2-selective), AF-DX 116 (11-[[2-[diethylamino)methyl]-1-piperidinyl]-acetyl]-5,11-dihydro- 6H-pyrido[2,3-b] [1,4]benzodiazepine-6-one, M2-selective), gallamine (M2-selective) and 4-DAMP (4-diphenylacetoxy-N- methylpiperidinemethiodide, M3-selective), that the prejunctional inhibitory muscarinic receptor is of the M2 subtype.

Animals↗
PubMed1991

Is protein kinase C involved in histamine H1-receptor desensitization?

Histamine H1-receptor mediated effects in guinea-pig lung and intestine appear to desensitize homologously rather rapidly. Within a few minutes of exposure to a high concentration of histamine (30-100 microM) the c-GMP production in guinea-pig lung and the contraction of guinea-pig jejunum are markedly attenuated. In both tissues the responses to other stimulating agents (e.g. muscarinic agent, calcium ionophore) are not affected. The protein kinase C (PKC) activating phorbolester phorbol-12,13- dibutyrate (PDB) concentration-dependently depresses H1-receptor responses in both tissues. Yet, PDB does not only attenuate the H1-receptor responses but also affects responses to other stimulating agents. In the guinea-pig ileum muscarinic receptor mediated contractions are inhibited equipotently by PDB, whereas in lung tissue the c-GMP formation after calcium-ionophore addition is affected too. In view of these findings the possible role of PKC in H1-receptor desensitization is discussed.

Animals↗
PubMed1991

Fluoride is a contractile agent of guinea pig airway smooth muscle.

1. Guinea pig parenchymal lung strips and tracheal smooth muscle contract potently after NaF-addition. Maximal contractions of lung strips and tracheal rings induced by NaF were 208 +/- 17% (n = 6) and 151 +/- 8% (n = 4) of the maximal histamine response respectively. 2. The -log EC50-value for NaF on lung strips and tracheal rings was 2.38 +/- 0.01 (n = 6) and 2.28 +/- 0.01 (n = 4) respectively. 3. Contractions induced by NaF were augmented after Al3+ pretreatment, suggesting the involvement of a G-protein. NaF responses were not affected by blockade of H1-, muscarinic-, leukotriene C4- or leukotriene D4-receptors, indicating that mast cell degranulation or nerve activation is most probably not implicated. 4. Contractions after NaF-addition were relatively insensitive to removal of extracellular calcium and were reversed via cAMP- and cGMP-mediated pathways. 5. Relaxation studies with (-)isoprenaline and 8-bromo-cGMP on lung strips, precontracted to similar levels with either a H1-agonist, KCl or NaF, showed that the level of relaxation depends on the contractile agent that is used. 6. After precontraction with KCl (-)isoprenaline relaxes lung strips only to 58 +/- 9% (n = 5) of the initial contraction, whereas lung strips precontracted with NaF or a H1-agonist relax 114 +/- 8% (n = 4) and 120 +/- 7% (n = 5) respectively with (-)isoprenaline. 7. Similar results were obtained with relaxation induced with 8-bromo-cGMP. 8. These findings suggest that NaF-induced contractions are elicited via a mechanism, that is probably similar to that of the H1-receptor. The involvement of a G-protein in the observed NaF-responses is therefore likely.

Aluminum↗
PubMed1991

Substituent effect on the stereochemistry of H2-receptor antagonists of the phenylformamidine series. A conformation-dependent mode of interaction with the H2 receptor.

The influence of alkyl substitution on the stereoisomerism of the formamidine cation (E,E vs E,Z) of several N-substituted (imidazolylphenyl)formamidines (1-10) was investigated. As (imidazolylphenyl)formamidines having alkyl substituents of more than three carbon atoms bind to H2-receptor preparations in a pseudoirreversible mode causing unsurmountable antagonism, the four isomeric butylformamidines (5-7 and 9) having comparable lipophilic character but different E,E/E,Z composition were investigated in H2-receptor assays to determine quantitatively any difference in their pseudoirreversible inhibitory pattern. It was found that the geometry of the formamidine cation is affected by the steric bulk of the substituent on the formamidine nitrogen. A relationship between the percentage of the E,E conformation of the formamidine cation and degree of pseudoirreversible antagonism was also found. The present studies support the hypothesis that bidentate hydrogen bonding plays an important role in the interaction of (imidazolylphenyl)formamidines with the H2 receptor.

Amidines↗
PubMed1991

Effects of histamine H1-, H2- and H3-receptor selective drugs on the mechanical activity of guinea-pig small and large intestine.

1. In this study we have evaluated the possible contribution of acetylcholine release in histamine-induced contractions of guinea-pig large and small intestinal smooth muscle. Moreover, the presence of the histamine receptor types involved in smooth muscle relaxations and inhibition of electrically-induced twitches was studied by use of several selective agents. 2. Histamine-induced contractions appeared to be a pure H1-receptor-mediated effect. Responses were not attenuated by the presence of 0.1 microM atropine and were competitively and stereoselectively inhibited by the two enantiomers of chlorpheniramine with pA2 values of 6.73 +/- 0.08, 7.30 +/- 0.06, 6.93 +/- 0.03 and 7.19 +/- 0.04 for the L-isomer and 8.63 +/- 0.09, 8.85 +/- 0.09, 9.01 +/- 0.16 and 0.11 for the D-isomer in the duodenum, jejunum, ileum and colon, respectively. 3. There appeared to be a marked regional difference in sensitivity to histamine. In ileal and jejunal preparations pD2 values of 6.24 +/- 0.06 (n = 22) and 6.37 +/- 0.07 (n = 22) were found, whereas the pD2 values in the duodenum and colon were 5.55 +/- 0.05 (n = 36) and 5.68 +/- 0.06 (n = 31) respectively. 4. This regional difference in sensitivity to histamine was not due to variations in receptor affinity since pA2 values for the two enantiomers of chlorpheniramine did not differ markedly among the four tested preparations. Since a similar variation in sensitivity was found for methacholine, it is likely that the signal transfer mechanism in guinea-pig ileum and jejunum is more efficient than in the duodenum and colon. 5. The H2-agonists dimaprit and impromidine relaxed methacholine-precontracted (+/- 70% of maximum contraction) intestine at high concentrations (pD2 values of 3.79 + 0.03 and 4.44 + 0.09 for the jejunum). These relaxations could not be antagonized by 0.1 microM tiotidine, famotidine or mifentidine and were observed in all parts of the intestine investigated. 6. The dimaprit analogues nordimaprit and homodimaprit (inactive at H2-receptors) were equipotent in relaxing the methacholine-precontracted smooth muscle. Since several H2-antagonists were also able to produce relaxations, we do not consider these relaxations to be mediated by a H2-receptor subtype, but to be due to some nonspecific effects at the high concentrations used. 7. The histamine receptor involved in the inhibition of electrically-induced contractions in the presence of atropine could be classified as an H3-receptor effect. In all parts of the intestine the H3-agonist R-alpha-amethylhistamine inhibited the twitches with pD2 values ranging from 8.10 + 0.06 (ileum) to 8.27 + 0.03(colon). This effect was competitively antagonized with the selective H3-antagonist thioperamine (pA2 values are 8.09 + 0.07, 8.13 + 0.05, 8.15 + 0.04 and 8.36 + 0.04 in duodenum, jejunum, ileum and colon, respectively. 8. The guinea-pig intestine is a suitable preparation for the evaluation of either H1- or H3-receptor effects. H2-receptors, causing smooth muscle relaxation appear not to be present in our preparations. At high concentrations of H2-receptor agents (agonists and antagonists) relaxations might be observed, due to unknown nonspecific effects.

Animals↗
PubMed1991

The lipid peroxidation product 4-hydroxy-2,3-trans-1 nonenal decreases rat intestinal smooth muscle function in-vitro by alkylation of sulphydryl groups.

The effects of the lipid peroxidation product 4-hydroxy-2,3-trans-1 nonenal (HNE) on intestinal smooth muscle function have been studied. Exposure of rat isolated small intestinal segments to HNE (0.1-0.5 mM) led to decreased muscarinic and beta-adrenergic responses. The maximal response to the muscarinic agonist methacholine and its pEC50 decreased in a dose dependent manner. The response to the beta-adrenoceptor agonist isoprenaline was affected in a similar manner, but at slightly higher concentrations of HNE. As HNE has been described to be sulphydryl-reactive these effects were compared with the effects of the sulphydryl-reactive agent N-ethylmaleimide (NEM). Incubation of intestinal segments with NEM had similar effects on pharmacological responses to methacholine, indicating that the effects of HNE like that of NEM are likely to be caused by alkylation of sulphydryl groups. Dithiothreitol, a compound which reduces oxidized sulphydryl groups, was unable to restore the effects of HNE or NEM, which suggests that the effects of HNE and NEM are irreversible.

Aldehydes↗
PubMed1990

Changes in inositol-1,4,5-trisphosphate binding to hepatic plasma membranes caused by temperature, N-ethylmaleimide and menadione.

We investigated the effects of the sulfhydryl-alkylating agent N-ethylmaleimide (NEM) and menadione--a sulfhydryl-arylating agent, which can undergo redox cycling--on the [3H]inositol-1,4,5-trisphosphate ([3H]IP3) binding properties of rat plasma membranes. Rat liver plasma membranes were incubated for 15 min at 37 degrees with 0.1 mM, 0.2 mM, 0.5 mM NEM or 0.3 mM menadione and subsequently diluted for use in [3H]IP3 binding studies. An incubation as such (15 min at 37 degrees) already caused the dissociation constant (Kd) of [3H]IP3 binding to increase from 1.9 +/- 0.2 nM to 3.4 +/- 0.2 nM, with only a small change in the maximal number of IP3 binding sites (Bmax-values of 401 +/- 32 and 349 +/- 13 fmol/mg protein, respectively). Incubation with NEM (0.1, 0.2 and 0.5 mM) resulted in a dose dependent decrease in the Bmax with 41, 87 and 99%, respectively, without a significant change in the Kd compared to the time matched controls. Menadione (0.3 mM) decreased the Bmax with 54% without affecting the Kd. In contrast to our findings at 37 degrees, incubation of the plasma membranes with NEM (0.5 mM) at 0 degrees for 30 min did not affect [3H]IP3 binding. In order to account for this discrepancy, the reaction rate of NEM with glutathione was examined at both 0 degrees and 37 degrees by recording the changes in the UV-spectrum of NEM (lambda max = 302 nm) after addition of 1 mM NEM to 1 mM glutathione. A similar reaction rate was observed at both temperatures. These data suggest that alkylation of a sulfhydryl-moiety in the IP3-receptor molecule causes inactivation of the receptor function. Since at 0 degrees NEM is still able to react with sulfhydryl groups, but not able to inactivate the IP3-receptor, it can be suggested that the sulfhydryl-moiety of the IP3-receptor is masked and cannot be reached by a sulfhydryl-alkylating agent at 0 degrees.

Animals↗
PubMed1990

Ebselen inhibits contractile responses of guinea-pig parenchymal lung strips.

Ebselen is a new anti-inflammatory drug with a wide spectrum of pharmacological activities. Since this compound might be useful in diseases related to airway inflammation we evaluated the effects of ebselen on the contractile responses of guinea-pig parenchymal lung strip. Ebselen and its sulfur analogue RP 62373 depressed both histamine H1-receptor-mediated and KCl-induced (50 mM) contractions of guinea-pig lung strips equipotently. The responses to histamine were only affected via depression of the maximal response; treatment with 3 microM ebselen for 30 min resulted in depression to 77 +/- 5% of the control value, whereas 10 and 30 microM inhibited the contractions to 53 +/- 4 and 52 +/- 4% of the control value respectively. The responses after membrane depolarisation (50 mM KCl) were less sensitive to ebselen pretreatment; 10 microM ebselen inhibited contractions by only 20%, whereas 30 and 100 microM depressed the response by approximately 50%. These observations were evaluated in the context of the activities of ebselen already described. The effects of lipoxygenase, cyclooxygenase, protein kinase C inhibition and thiol alkylation were studied, using established agents. However, although interaction with critical thiol groups might explain our data, the mode of action of ebselen is yet not fully elucidated.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Molecular pharmacological aspects of antiarrhythmic activity. I. Class I and class III compounds and lipid peroxidation.

The effect of nineteen antiarrhythmic agents on nonenzymatic lipid peroxidation, using rat hepatic microsomes, was studied. Lipid peroxidation was induced by Fe2(+)-ascorbic acid and assayed spectrophotometrically by measuring the 2-thiobarbituric acid reactive material. The compounds tested have various structural characteristics and represent class I and III of antiarrhythmics as classified by Vaughan Williams. The RM values, derived from reversed-phase thin-layer chromatography, were determined, and sigma f values calculated in order to correlate lipophilicity and antioxidant activity. The antiarrhythmics studied inhibited lipid peroxidation to various degrees. No apparent structural factor could definitely be attributed to this effect and antioxidants are found among both class I and class III compounds. There is a trend toward a parabolic relationship between antioxidant potency and lipophilicity. Three of the tested antiarrhythmics, namely the lipophilic amiodarone, aprindine and asocainol, were very potent antioxidants, and a further investigation of concentration and time dependency of lipid peroxidation was performed. It is suggested that, at least for some antiarrhythmic drugs, antioxidant activity may be part of their mode of action, and that it may form an additional beneficial feature for the treatment of cardiac failure.

Amiodarone↗
PubMed1990

Molecular pharmacological aspects of antiarrhythmic activity, II: Interaction of class I compounds with calmodulin.

We have tested the calmodulin (CaM) inhibitory potency of class I antiarrhythmics in the phosphodiesterase (PDE) assay. The lipophilicity of the test compounds has been quantified by two experimental (log P, RM) and two calculative (sigma f, C log P) procedures. Five antiarrhythmics (asocainol, aprindine, lorcainide, propafenone, and ethmozine) exhibit IC50 values less than 250 microM for the inhibition of the CaM-stimulated PDE activity. Lipophilicity seems to be a prime, but not the sole descriptor of CaM inhibitory potency. The functional means of CaM inhibition by the test compounds for their antiarrhythmic properties remains to be clarified in further investigations.

Anti-Arrhythmia Agents↗