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H Timmerman

Publications and source records attributed to H Timmerman.

At least 235 records · Page 13Linked to original sources
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

Shallow agonist competition binding curves for beta-adrenergic receptors: the role of tight agonist binding.

The beta 2-adrenergic receptors of bovine trapezius muscle membranes demonstrate tight agonist binding as a result of the formation of complexes between agonists, receptors, and Ns. Preincubation of the membranes with (-)-isoproterenol (followed by washing) causes a time- and concentration-dependent decrease in the number of radioligand-binding sites to a plateau value of 41.5 +/- 4%. The affinity of the remaining sites for the radioligand (-)-[3H]dihydroalprenolol is unchanged. This decrease is stable under radioligand binding conditions but is readily reversed in the presence of GTP. The isoproterenol/(-)-[3H]dihydroalprenolol competition binding curves are shallow. Such a phenomenon is usually interpreted in terms of two interconvertible affinity states of the receptor: the high affinity state reflecting the coupling of the agonist X receptor complex to Ns and the low affinity state not interacting with Ns. However, the competition curves undergo time-dependent shifts to the left. This apparent non-equilibrium can be explained by a model in which tight agonist binding to part of the receptor population is included. The usual computerized interpretation of the competition binding curves do not allow the correct evaluation of agonist binding parameters in the presence of tight agonist binding.

Adrenergic beta-Agonists↗
PubMed1986

The beta-adrenoceptor-adenylate cyclase complex. From model to biochemical reality.

Developments in the receptor concept have greatly influenced our current knowledge of the beta-adrenoceptor. The triad of pharmacology, organic chemistry and studies in structure-activity relationships is discussed along historical lines, as it has been and still is an impetus for progress in the biochemistry of ligand-receptor interactions. With respect to the beta-adrenoceptor complex these advances which have led to a model in which three protein structures are functionally interacting within the frame of the cell wall: the beta-adrenoceptor, the regulatory guanine nucleotide binding protein, and the enzyme adenylate cyclase, are reviewed.

Adenylyl Cyclases↗
PubMed1986

Influence of lipid peroxidation on beta-adrenoceptors.

The peroxidation of lipids in biological membranes is a destructive phenomenon that can be elicited in various ways. Surface receptor molecules that allow cells to respond to hormones are possibly inactivated during lipid peroxidation. Effects of lipid peroxidation on receptors have not been extensively examined thus far. This investigation shows that there is a decrease in beta-adrenoceptor density (measured as specific (-)-[125I]iodocyanopindolol binding) during lipid peroxidation, in both lungs and erythrocytes of the rat. To this end, lung membranes (containing both beta 1- and beta 2-adrenoceptors) and intact erythrocytes (containing a homogeneous beta 2-adrenoceptor population) were pretreated with cumene hydroperoxide (lung membranes with 0.1 mM and erythrocytes with 1 mM) and Fe2+ (1 X 10(-5) M) for 60 min which resulted in extensive lipid peroxidation measured as malondialdehyde formation. The ration beta 1-:beta 2-adrenoceptor density in lung membranes after treatment with cumene hydroperoxide did not change and remained at 30%:70%. A single injection (i.p.) with the herbicide paraquat (50 mg/kg, 24 h), which is known to cause lung damage via lipid peroxidation, resulted in similar alterations in receptor density to those caused by cumene hydroperoxide in the in vitro experiments.

Animals↗
PubMed1986

The influence of guanidino and isothiourea groups in histaminergic compounds on H2-activity.

Because in some alkylenediisothioureas replacement of one of the isothiourea groups by a guanidino group resulted in a strong increase in agonistic histamine H2-activity, while replacement of the guanidino group of a potent analogue of impromidine by an isothiourea group resulted in a complete loss of histamine H2-activity, it was concluded that guanidino and isothiourea groups are not bio-isosteric for the H2-receptor.

Animals↗
PubMed1986

Histamine H2-binding on guinea pig cerebral cortex.

The Kd-values of some histamine H2-active compounds, obtained from radio-ligand-binding studies on a homogenate of the guinea-pig cerebral cortex with 3H-tiotidine as the labelled H2-ligand, were compared with the pA2/pD2-value of these compounds on the guinea-pig right atrium and guinea-pig isolated gastric fundus. A good correlation was found between the pKd of the H2-antagonists and their pA2 on the guinea-pig right atrium. A much poorer correlation however was obtained between the pKd of the agonists on the cerebral cortex and their pD2-values on the guinea-pig right atrium and the gastric fundus. This poor correlation between true affinity and H2-activity of the agonists might be explained by spare receptors as a much better correlation was obtained between pKd and pD2 of partial agonists.

Animals↗
PubMed1986

Inhibition of complement by a series of substituted 2-aryl-1,3-indandiones: interaction with the fifth component of complement.

A series of substituted 2-aryl-1,3-indandiones were investigated for their ability to inhibit the complement system. Some of them were found to be considerably strong inhibitors. The inhibitory activity was mainly dependent on substitutions at positions 3 and 5 of the phenyl ring. 3,5-dichloro-(8), 3,5-bis(trifluoromethyl)- (7), 3,5-diisopropyl- (3) and 3,5-di-t-butyl- (5) phenylindandiones were the strongest inhibitors of the series. The generation of EAC1-5 cells from EAC1-3 cells and C5 was most strongly inhibited by these compounds although some inhibition of the interaction of EAC1-5 with C6-C9 and EAC1-6 with C7-C9 was also observed. Slight inhibition at other steps of complement activation was also seen but this was not considered to be appreciable. Dialysis of normal serum or purified C5 pre-incubated with compounds 3, 5, 7 and 8 did not cause recovery of the hemolytic activity of normal serum or purified C5. Thus, the main site of inhibition in the complement cascade appeared to be at C5. The total alternative pathway was also inhibited to some extent by these compounds, probably due to their interaction with C5.

Animals↗
PubMed1986

The effects of 4-hydroxy-2,3-trans-nonenal on beta-adrenoceptors of rat lung membranes.

Lung membranes are susceptible to oxygen radicals, formed during inflammation, redox cycling of toxic agents, exposition to ozon etc. Oxygen radicals may modify the beta-adrenergic response. However, at the same time beta-adrenoceptors of the lung are frequently addressed in therapy. We embarked upon this problem by studying the effects of the aldehyde 4-hydroxy-2,3-transnonenal (HNE), one of the major products of lipid peroxidation, on the density of beta-adrenoceptors of rat lung membranes. It is shown, that the physiological important sulfhydryl blocking agent HNE inactivates the beta-adrenoceptors in a time- and concentration dependent (0.5-2.5 mM) way, indicated by a decrease in (-)-[3H]dihydroalprenolol (DHA) binding to lung membranes. Moreover, it is shown that combined treatment of HNE with (-)-isoproterenol (0.5 microM) or 1-alprenolol (0.5-10 nM) does not influence the extent of inactivation of beta-adrenoceptors by HNE. This is in contrast with previous studies, conducted with other, synthetic, sulfhydryl blocking agents, such as N-ethylmaleimide (NEM), suggesting that an other mechanism of inactivation is involved upon HNE treatment.

Aldehydes↗
PubMed1986

Mapping the turkey erythrocyte beta receptor: a distance geometry approach.

Extensions and refinements of the receptor mapping method as originally developed by Crippen are presented. In a set of newly developed algorithms measures are taken to reduce the number of required energy parameters to a statistically acceptable degree. The most important measure is the incorporation of lipophilicity as a hydrophobic bonding parameter to describe the binding of parts of the ligands to lipophilic areas on the receptor. In order to test the applicability of our set of programs, we mapped the turkey erythrocyte beta receptor using a data set of Bilezikian. It was found that the experimentally determined free energies of binding can be reasonably described using a nine-point geometrical representation of the receptor site and only six energy parameters. The deduced model predicts that the phenyl rings of phenylethanolamines and phenoxypropanolamines occupy different parts of the receptor site.

Animals↗
PubMed1986

Quantitative evaluation of the beta 2-adrenoceptor intrinsic activity of N-tert-butylphenylethanolamines.

The extent of stimulation of the enzyme adenylate cyclase, and the concomitant production of cAMP, by a number of beta-adrenoceptor agonists, all belonging to the class of the N-tert-butylphenylethanolamines, has been determined. The results have been used as direct measures for intrinsic sympathomimetic activity (ISA) and were correlated with various physicochemical parameters of the compounds. Significant correlations were established by means of the method of multiple regression analysis, and it was demonstrated that electronic effects only govern ISA. The use of 13C NMR chemical shifts of the aromatic C atoms proved to be a valuable tool in this analysis.

Adrenergic beta-Agonists↗
PubMed1986

Binding characteristics of the regulatory guanine nucleotide binding protein, and the activation of the enzyme adenylate cyclase, present in a bovine skeletal muscle membrane preparation.

The binding of [3H]GppNHp (beta, gamma-imido[8(-3)H] guanosine 5'-triphosphate) to membrane particles of a bovine skeletal muscle preparation, the m.trapezius, and the subsequent activation of adenylate cyclase in this preparation have been studied, both in the presence and absence of (-)-isoprenaline. Specific binding of [3H]GppNHp could be best explained on the assumption of a two-sites model, in which the binding sites displaying the higher affinity, appeared to be associated with the activation of adenylate cyclase, and are likely to include the regulatory guanine nucleotide binding protein (G/F or NS). The apparent excess of high affinity [3H]GppNHp binding sites over the number of beta-adrenoceptors in this preparation with respect to its possible physiological relevance is discussed.

Adenylyl Cyclases↗
PubMed1985

Factors controlling beta 1-adrenoceptor affinity and selectivity.

A membrane preparation of the calf heart left ventricle has been used after identification and characterization, as a source of myocardial beta 1-adrenoceptor for radioligand binding studies. The displacement of specifically bound (-)-[3H]dihydroalprenolol by some beta-adrenoceptor ligands appeared to be pH-dependent, which could be related to the ionization characteristics of the compounds. Among the usually four ionic species of the ligand, present at physiological pH, the cation was shown to govern beta 1-adrenoceptor affinity. Furthermore, quantitative structure affinity relationships for the interaction with beta 1- and beta 2-adrenoceptors were established for the phenoxypropanolamines, a class of beta-adrenoceptor ligands. The N-isopropyl-oxypropanolamine side chain itself does not discriminate between beta 1- and beta 2-adrenoceptors, whereas aromatic substitution ortho to the side chain induces some beta 2-selectivity. Selectivity for myocardial beta 1-adrenoceptors is mainly obtained by aromatic substitution para to the side chain. This substitution pattern yields a decrease in beta 2-adrenoceptor affinity, far more pronounced than the decrease in beta 1-adrenoceptor affinity.

Animals↗
PubMed1985

Quantitative evaluation of the beta 2-adrenoceptor affinity of phenoxypropanolamines and phenylethanolamines.

The influence of the aromatic moiety of beta-adrenoceptor ligands on the affinity for the beta 2-adrenoceptor has been studied. Three classes of ligands have been examined, viz. N-isopropyl- and N-tert-butylphenylethanolamines and N-isopropylphenoxypropanolamines. Computer-assisted analysis of the inhibition by any of these ligands of the specific (-)-[3H]dihydroalprenolol binding to the beta 2-adrenoceptors of a bovine skeletal muscle preparation in the presence of GppNHp (10(-4) M) yielded the affinities of these ligands at pH 7.5. The obtained values were adjusted for the amounts of cations present at this pH value. A significant correlation was found between the calculated lipophilicities and the experimentally determined affinities in the three classes. Furthermore, steric factors seem to play an important role, as these correlations were improved by the introduction of steric parameters for the aromatic substituents in the regression analyses. From the established equations it is concluded that the phenoxypropanolamine derivatives bind to the beta 2-adrenoceptor in a way different from that of the ligands in both ethanolamine classes.

Animals↗
PubMed1985

Non-specific binding of the fluorescent beta-adrenergic receptor probe alprenolol-NBD.

The fluorescent beta-adrenergic receptor probe alprenolol-NBD was found to exhibit a high affinity (Kd 3.2 nM) and a low capacity (10 fmol/mg protein) for the beta 2-adrenergic receptor on living Chang liver cells but also a high affinity (Kd 320 nM) for non-beta-adrenergic receptor binding sites with a very high capacity (28,000 fmol/mg protein). Calculations are presented which make clear that less than 3% of the binding of alprenolol-NBD during visualization experiments is beta-adrenergic receptor related. Furthermore, it is shown that besides the downregulation of beta-adrenergic receptors during incubation with isoproterenol, the high-affinity non-beta-receptor binding sites are also deminishing during incubation with isoproterenol. Based on our findings it is concluded that the results of Henis et al. who claimed the visualization of the beta-adrenergic receptor population on Chang liver cells by alprenolol-NBD must be interpreted as an almost completely non-specific fluorescence.

4-Chloro-7-nitrobenzofurazan↗
PubMed1984

The relation between ionization and affinity of beta-adrenoceptor ligands.

The displacement by some beta-adrenoceptor ligands of the specific (-)-[3H]dihydroalprenolol binding to membranes of the bovine musculus trapezius, a rich and homogeneous source of beta 2-adrenoceptors, appeared to be pH-dependent. This phenomenon was in contrast to the pH-dependency of the (-)-[3H]dihydroalprenolol receptor-binding and could be related to the ionization characteristics of the compounds. It was shown quantitatively that of the four ionic species of the ligands commonly present at physiological pH, the cation governs beta 2-adrenoceptor affinity.

Animals↗
PubMed1984

Anti-complement activity in a series of substituted 2-aryl-1,3-indandiones; absence of correlation with the anti-carrageenan oedema effects.

It was found that a number of substituted 2-phenyl-1,3-indandiones possesses a considerable inhibitory effect on the classical pathway of complement. Furthermore it appeared that in this series a reasonable correlation (r = 0.86) exists between this anti-complement effect and the inhibition of the prostaglandine biosynthesis. A quantitative structure-activity relation study revealed that both the electronic sigma parameter of the substituent involved and the lipophilicity of the corresponding compound are important for anti-complement activity. Mainly the C5 step in the complement process is inhibited by these compounds. The complement-inhibiting phenylindandiones also inhibit the alternative pathway. This effect may also be due to an inhibition of C5, as C5 is common to both pathways. Remarkably, the 2-(3,5-dichlorophenyl)-1,3-indandione, which is most active in the anti-complement test, showed no reduction of the carrageenan-induced oedema in the rat after both oral and local application. Possibly the absence of this anti-inflammatory effect is caused by the pharmacokinetic profile of the compound.

Animals↗