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B Testa

Publications and source records attributed to B Testa.

At least 55 records · Page 3Linked to original sources
PubMed1988

Modeling of beta-adrenoceptors based on molecular electrostatic potential studies of agonists and antagonists.

The molecular electrostatic potential (MEP) of 32 beta-adrenoceptor ligands, mainly antagonists, was calculated by the STO-3G ab initio quantum mechanical method. The MEP of phenylethanolamines (PEAs) features a negative minimum in the meta region (designated M1) which is topographically equivalent to a minimum (designated M2) found in the vicinity of the aromatic ring in all (aryloxy)propanolamines (AOPAs). In these compounds, a second negative zone located beyond the meta position and designated M3 is found in all beta 1-selective antagonists and in some nonselective and beta 2-selective antagonists. The beta 1-selective antagonists feature in the para position an additional zone which is positive (P4) in the full antagonists and negative (M4) in the antagonists displaying intrinsic sympathomimetic activity (ISA). The MEP-based pharmacophoric models of PEAs, AOPAs, and oxime ethers show common elements and lead to a proposed general model for beta-adrenoceptor ligands.

Adrenergic beta-Agonists↗
PubMed1988

The interaction of substituted benzamides with brain benzodiazepine binding sites in vitro.

1. The interaction of substituted benzamides with brain benzodiazepine (BDZ) binding sites was examined by their ability to displace [3H]-flunitrazepam ([3H]-FNM) from specific binding sites in bovine cortical membranes in vitro. 2. Clebopride, Delagrange 2674, Delagrange 2335 and BRL 20627 displayed concentration-dependent displacement of [3H]-FNM with IC50 values of 73 nM, 132 nM, 7.7 microM and 5.9 microM, respectively. Other substituted benzamides including metoclopramide, sulpiride, tiapride, sultopride and cisapride were inactive at 10(-5) M. 3. Inhibition by clebopride and Delagrange 2674 of [3H]-FNM binding was apparently competitive and readily reversible. 4. In the presence of gamma-aminobutyric acid (GABA), the ability of diazepam and Delagrange 2674 to displace [3H]-Ro 15-1788 binding was increased 3.6 and 1.6 fold respectively, compared to the absence of GABA, while ethyl beta-carboline-3-carboxylate (beta CCE) and clebopride were less potent in the presence of GABA. 5. Diazepam was 30 fold less potent at displacing [3H]-Ro 15-1788 in membranes that had been photoaffinity labelled with FNM than in control membranes, whereas the potency of beta CCE did not differ. Clebopride and Delagrange 2674 showed a less than two fold loss of potency in photoaffinity labelled membranes. 6. The pattern of binding of clebopride and Delagrange 2674 in these in vitro tests is similar to that found previously with partial agonists or antagonists at BDZ binding sites. 7. Clebopride and Delagrange 2674 inhibited [3H]-FNM binding with similar potency in rat cerebellar and hippocampal membranes, suggesting they have no selectivity for BDZ1 and BDZ2 binding sites. 8. Clebopride and Delagrange 2674 are structurally dissimilar to other BDZ ligands and represent another chemical structure to probe brain BDZ binding sites.

Affinity Labels↗
PubMed1988

Influence of lipophilicity and chirality on the selectivity of ligands for beta 1- and beta 2-adrenoceptors.

Eudismic and QSAR analyses are reported for the beta 1- and beta 2-adrenoceptor affinities and beta 1-selectivity of 10 enantiomeric pairs of ligands with only N-isopropyl or N-t-butyl groups. For both receptors, the eudismic index (ratio of affinity) increases with the affinity of the eutomers. However, the affinity of the distomers for the beta 2-adrenoceptor is relatively high, suggesting additional hydrophobic interactions. This is confirmed by various correlations between affinities and lipophilicities, showing that the affinity for beta 2-adrenoceptors is slightly more dependent on lipophilicity than that for beta 1-adrenoceptors. As a result, the beta 1-selectivity of the investigated beta 1-adrenoceptor ligands is strongly and negatively correlated with their lipophilicity (r = -0.942).

Adrenergic beta-Agonists↗
PubMed1988

Metabolic chiral inversion of anti-inflammatory 2-arylpropionates: lack of reaction in liver homogenates, and study of methine proton acidity.

1. Enrichment in the (S)-enantiomers for (R)-flurbiprofen, (R)-naproxen, (R)-suprofen and (R;S)-ibuprofen was investigated in various subcellular hepatic preparations containing coenzyme A. While such preparations were able to form hippuric acid from benzoic acid, the chiral inversion was never seen. 2. Using 2-dimethylaminoethanethiol 2-phenylpropionate (DEPP) as a model acyl thioester, the acidity of the methine proton was investigated by monitoring the proton/deuterium exchange occurring in deuterated solvents using high-resolution n.m.r. The compound was inert up to 22 h in D2O at 37 degrees C and pD 7.4. In pure methanol or a methanol-water mixture, only solvolysis was seen. In contrast, competitive hydrolysis (k = 0.005 h-1) and proton/deuterium exchange (k = 0.09 h-1) were seen in a CD3CN/D2O (50:50) mixture at 37 degrees C. 3. It is speculated that the failure to characterize chiral inversion of 2-arylpropionates in subcellular preparations may be due to the absence of a microenvironment of adequately moderate polarity.

Animals↗
PubMed1988

In vitro inhibition by stiripentol of rat brain cytochrome P-450-mediated naphthalene hydroxylation.

1. The formation of 1-naphthol from naphthalene was investigated in rat brain 105,000 g particulate fraction. The reaction showed NADPH dependency and was inhibited by carbon monoxide. Michaelis-Menten kinetics were apparent with Vmax = 0.264 pmol/mg protein per min and Km = 22.6 microM. 2. Stiripentol, an antiepileptic drug containing a methylenedioxybenzene moiety, proved to be a potent inhibitor of the reaction, with an IC50 value close to 1 microM under the conditions of study and without preincubation. 3. The inhibitory activity of stiripentol was seen mainly after metabolic activation of the drug. The inhibitory effect appeared progressively when substrate and inhibitor were added together to the incubates, whereas its appearance was more rapid following preincubation of stiripentol.

Animals↗
PubMed1988

[Comparison of the efficacy of two H2 antagonists of histamine in allergic rhinitis. Considerations on the mechanism of action].

A random study has been made on perennial atopic rhinitis patients divided into two homogeneous groups and treated with HH2 antagonists of different chemical structure: Cimetidine and Ranitidine. An identity of clinical and humoral results was noted in the two groups. This leads us to believe that the effects induced by the two drugs are linked to the properties of H2 antagonists and not to other potential action as hypothesised for Cimetidine by Drazen. The improvement in all subjective and objective parameters, decrease in total serum IgE, the delayed onset of clinical improvement and its duration in time, suggest that the vascular type action mechanism hypothesised by some Authors is quite secondary to the immunomodulatory one. H2 antagonists in fact induce, together with the clinical improvement and the total serum IgE decrease, a modulatory effect on the T-lymphocyte subsets with a variation in the OKT4/OKT8 ratio towards the latter subset that identifies the suppressor cells. Since lymphocyte histamine receptors are uniquely present on suppressor T-cell, it is on these the H2 antagonists would act, modulating the suppressive function positively.

Adolescent↗
PubMed1988

[Changes in serum immunoglobulins in allergic rhinitis induced by histamine H2 antagonists].

The authors discuss their double-blind experiments on 40 allergic rhinitis affected patients, aged 15 to 50 years. Twenty were treated with H2 antagonists (Cimetidine) and twenty with placebo. The clinical assessment of the effectiveness of the treatment was carried out on a range of subjective and objective parameters taken before and after treatment. The IgE, IgA, IgG and IgM serum rate was measured. An improvement in the symptomatology was noted in 15 of the 20 Cimetidine treated patients and none in the placebo group. The results have shown a significant percentage decrease in the total serum IgE values after treatment, compared to initial ones, while no significant change was observed in the values of IgA, IgG and IgM. This decrease in IgE is thus a specific class. As it has been demonstrated that a subpopulation of lymphocyte T suppressors acts selectively on IgE producing B cells, the authors believe that only on these elements, carriers of H2 membrane receptors, can Cimetidine act to induce a decrease in total serum IgE levels and therefore a reduction in degranulation processes.

Adolescent↗
PubMed1987

Analogues of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine as monoamine oxidase substrates: a second ring is not necessary.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is oxidised to a neurotoxic metabolite by monoamine oxidase B (MAO B). Using two colorimetric assays, we have examined a range of its structural analogues as possible further substrates of this enzyme in order to identify the types of environmental or endogenous compounds that might also be neurotoxic. Compounds with fully saturated or unsaturated pyridine rings were not substrates; nor were a range of tetrahydro-beta-carbolines or isoquinolines. Four substrates for MAO were found, 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'-Me-MPTP), 4-phenyl-1,2,3,6-tetrahydropyridine (PTP), 4-(p-chlorophenyl)-1,2,3,6-tetrahydropyridine (Cl-PTP) and ethyl-1-methyl-1,2,3,6-tetrahydro-4-pyridine-carboxylate (ethyl-MTP-carboxylate). Ethyl-MTP-carboxylate is of particular interest as it shows that a tetrahydropyridine without a phenyl ring can also be a substrate. Cl-PTP, PTP and ethyl-MTP-carboxylate appeared to be partially metabolised by MAO A. The inhibitor sensitivity of 2'-Me-MPTP oxidation was more complex.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1987

Quantitative structure-activity relationships and eudismic analyses of the presynaptic dopaminergic activity and dopamine D2 and sigma receptor affinities of 3-(3-hydroxyphenyl)piperidines and octahydrobenzo[f]quinolines.

Data from the preceding paper were examined by QSAR and eudismic analyses. A fair parabolic relationship was found between the lipophilicity (measured by a RP-HPLC method) and the sigma-receptor affinity of 3-(3-hydroxyphenyl)piperidines (3HPP derivatives) and octahydrobenzo[f]quinolines (OHBQ derivatives). As far as the dopamine D2 receptor is concerned, the trans-7-hydroxy-OHBQ derivatives show a 10-fold higher affinity than the eutomeric S enantiomers of 3HPP derivatives, once lipophilicity has been accounted for. This difference in affinity is suggested to correspond to the energy necessary for the 3HPP derivatives to adopt the receptor-bound conformation. The R enantiomers of 3HPP derivatives display no apparent increase in D2 affinity with increasing lipophilicity, and indeed the eudismic index in this series increases with affinity (eudismic affinity quotient = 0.70), in agreement with a recent model of the binding of N-propyl-3HPP (3PPP) enantiomers to the D2 receptor. The selectivity in sigma/D2 affinities was found to depend on both lipophilicity and configuration of the ligands; thus, the selectivity is maximal for log kw values of ca. 1.7-2.1 and is much larger for the R than for the S enantiomers of 3HPP derivatives.

Phenanthrenes↗
PubMed1987

L-dopa esters as potential prodrugs: behavioural activity in experimental models of Parkinson's disease.

Intraperitoneal administration of the 2-tetrahydropyranylmethyl, phenoxyethyl, ethyl, 2-hydroxypropyl and methyl ester prodrugs of L-dopa produced locomotor activity in reserpine-pretreated mice with equal intensity and duration to that observed following administration of L-dopa itself. Administration of the 2-(1-methoxy)propyl ester produced a more prolonged effect while the p-methoxyphenylethyl, n-propyl, phenylethyl, m-trifluoromethylbenzyl, cyclohexyl, p-chlorophenylethyl and benzyl ester prodrugs were less active than L-dopa itself. On oral administration, the ethyl and methyl ester prodrugs were more effective than L-dopa in reversing reserpine-induced akinesia in mice. The 2-tetrahydropyranylmethyl, 2-(1-methoxy)propyl, 2-hydroxypropyl, n-propyl, benzyl and phenoxyethyl ester prodrugs produced effects comparable with those of L-dopa. In contrast, the cyclohexyl, m-trifluoromethylbenzyl, phenylethyl, p-chlorophenylethyl and p-methoxyphenylethyl ester prodrugs were less effective than L-dopa on oral administration. Intraperitoneal administration of L-dopa and the ester prodrugs of L-dopa to rats with a prior 6-hydroxydopamine (6-OHDA) lesion of the medial forebrain bundle (MFB) produced contraversive circling responses. Rotation observed following administration of the n-propyl, 2-tetrahydropyranylmethyl, methyl and ethyl ester prodrugs was more intense than that observed following administration of L-dopa itself. Rotation produced by the administration of L-dopa and the cyclohexyl, 2-(1-methoxy)propyl, phenylethyl, p-chlorophenylethyl, p-methoxyphenylethyl, benzyl, 2-hydroxypropyl, phenoxyethyl and m-trifluoromethylbenzyl ester prodrugs was identical. Ester prodrugs of L-dopa may be as effective as L-dopa itself in producing motor activity but overall none of the compounds tested was markedly more potent or of longer duration than L-dopa itself.

Animals↗
PubMed1987

L-dopa esters as potential prodrugs: effect on brain concentration of dopamine metabolites in reserpinized mice.

The intraperitoneal administration of L-dopa and a series of ester prodrugs of L-dopa to reserpinized mice produced elevations of striatal and tuberculum olfactorium homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels. Differences in the pattern of change produced by individual drugs, compared with L-dopa, were observed. Only the phenoxyethyl ester caused elevations of both striatal and tuberculum olfactorium HVA and DOPAC, greater than those measured following L-dopa administration. Overall the m-trifluoromethylbenzyl, phenylethyl, p-chlorophenylethyl and p-methoxyphenylethyl ester prodrugs produced greater elevations of striatal and tuberculum olfactorium HVA, but not DOPAC, compared with L-dopa. The administration of the 2-tetrahydropyranyl-methyl derivative only enhanced striatal HVA and striatal and tuberculum olfactorium DOPAC concentrations. Changes of HVA and DOPAC tissue concentrations following administration of the 2-hydroxypropyl, n-propyl, methyl, ethyl and 2-(1-methoxy)propyl ester prodrugs were comparable with those produced by the administration of L-dopa itself. The alterations in striatal and tuberculum olfactorium HVA and DOPAC levels observed did not correlate with the ability of these compounds to elicit locomotor activity in reserpinized mice.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1987

Multivariate statistical analysis of L-dopa esters as potential anti-parkinsonian prodrugs.

This paper reports a QSAR study of thirteen L-DOPA esters previously synthesised and examined for their physicochemical, biochemical and behavioural properties. Multivariate statistical analysis (principal component analysis, cluster analysis, simple and multiple linear regression) reveals favourable and unfavourable structural features of L-DOPA prodrugs. Some of the many biochemical and behavioural activities investigated are shown to be redundant. These indications may contribute to the design of novel L-DOPA prodrugs.

Analysis of Variance↗
PubMed1986

Dual ligand binding of pyridylalkanamides to microsomal cytochrome P-450.

Twelve homologous and regioisomeric pyridylalkanamides were examined spectrally for their binding affinity to cytochrome P-450 in phenobarbital- and 3-methylcholanthrene-induced rat liver microsomes. The pKs values were calculated by the Lineweaver-Burk method and by non-linear analysis using both a one ligand-one acceptor and a one ligand-two acceptor model. The latter model best fits most of the data, confirming that two pKs values exist for most derivatives in the 3-pyridyl and 4-pyridyl series. Structure-binding relationships are discussed. The two binding constants are hypothesized to arise from a dual mode of binding to the ferric ion. At low ligand concentrations, binding to hexacoordinated cytochrome P-450 occurs and involves displacement of an endogenous 6th ligand; at higher concentrations, the ligands bind to the pentacoordinated P-450, resulting in a high-to-low spin shift.

Animals↗
PubMed1986

Histamine2 antagonists in allergic rhinitis. Possible role in the control of cellular immune reaction.

We studied effects of monoclonal antibodies on lymphocyte subpopulations in patients with allergic rhinitis treated with histamine2 antagonists. The OKT4/OKT8 ratio after treatment showed a statistically significant decrease compared with initial values, the expression of a relative increase in the OKT8 subpopulation containing the suppressor fraction. In control patients no significant variations were observed. These results confirm our hypothesis that histamine2 antagonists act in allergic rhinitis by modulating the activity of T-suppressor lymphocytes reduced in atopic patients.

Adolescent↗
PubMed1986

Molecular electrostatic potential of orthopramides: implications for their interaction with the D-2 dopamine receptor.

The electronic properties of orthopramides, a group of selective D-2 dopamine receptor antagonists, were investigated by calculating molecular electrostatic potentials (MEP) of model compounds with the ab initio STO-3G MO method. The various substitution patterns of the aromatic ring are characterized by a positive region comprising the H-bonded 2-methoxy group and ring positions 2, 3, and 4 and a negative region comprising the CONH group, 5-substituent, and ring positions 5 and 6. The regions of positive and negative potential are separated by a "curtain" running along the longitudinal axis of the molecule. At shorter distances from the plane of the aromatic ring (1.75 and 2.0 A), this "curtain" is quite sinuous, but at greater distances (2.5 and 3.0 A) it tends toward rectilinearity. We postulate that this longitudinal separation, together with the single positive maximum and the three negative minima perceptible at 3.0 A, constitute a distance pharmacophore responsible for the recognition and proper alignment of the ligand. The more complex MEP at 1.75 and 2.0 A are equated with a contact pharmacophore. Comparison of the MEP of orthopramides and dopamine reveals some analogies and suggests a possible mode of binding of these antagonists to the D-2 receptor.

Benzamides↗
PubMed1986

The influence of conformational factors on the metabolic conjugation of aryloxyacetates.

Among p-chlorophenoxyalkanoic acids, the acetate and 2-propionate are essentially inert towards metabolic conjugation, whereas the isobutyrate (clofibric acid) undergoes extensive glucuronidation, as well as amino acid conjugation in carnivores. To try to explain these differences, the conformational behaviour of three model compounds was studied by quantum mechanical calculations (PCILO method). All three compounds prefer syn (folded) conformers, but the isobutyrate, in contrast to its two lower homologues, also has anti (extended) conformers of relatively low energy. Based on these results, a hypothetical topographical model is proposed for the binding site of glucuronyltransferase.

2,4-Dichlorophenoxyacetic Acid↗