Characteristics of cyanopindolol analogues active at the beta 3-adrenoceptor in rat ileum

1. Cyanopindolol (CYP) is a potent antagonist at the beta 3-adrenoceptor in rat ileum. Several analogues of CYP and pindolol were synthesized that also produced antagonist effects at the beta 3-adrenoceptor. However, at high concentrations, these compounds appear to act as "partial agonists'. This study was conducted to determine the structural requirements of CYP analogues necessary for antagonist activity and to examine the possibility that the agonist effects of CYP and its analogues may occur through a mechanism independent of beta-adrenoceptor activation. 2. Analogues of CYP and pindolol were tested for antagonist activity in rat ileum in which the beta 1- and beta 2-adrenoceptors were blocked. Fourteen compounds were tested against (-)-isoprenaline, and four of the more potent analogues were then tested against BRL 37344. The two most potent antagonists were CYP and iodocyanopindolol. The pKb values (negative log of equilibrium dissociation constant) obtained against (-)-isoprenaline were significantly higher than those obtained against BRL 37344, but the cause of this difference is not known. 3. Several structural requirements were determined for antagonist activity. Modification at the carbon atom alpha to the secondary amine caused the antagonist potency to fall as the level of saturation was reduced. Thus, a quaternary carbon group, such as t-butyl, produced the most potent antagonist. Substitution with a large moiety such as a cyclohexyl or benzyl group reduced antagonist activity, probably due to steric hindrance. Inclusion of an electron-withdrawing group, such as a cyano or ethylester moiety, alpha to the indole nitrogen, also increased the potency. Iodination of CYP and ethylesterpindolol at the 3-position of the indole ring did not increase antagonist potency. In contrast, iodination of the almost inactive analogues produced a significant increase in potency, suggesting that a beneficial electronic effect on the indole ring imparted by the iodo moiety may be able to offset partially the negative effects caused by either the steric hindrance, of lack of a quaternary carbon alpha to the secondary amine. 4. Values for pseudo-pD2 were also determined by conducting cumulative concentration-response studies up to the limit of drug solubility. For nine of the compounds tested, the pKb was significantly higher than the pseudo-pD2 value. 5. The discrepancy between the pKb and pseudo-pD2 values was examined further. The agonist effects of iodocyanopindolol, the agonist with the highest potency, were not antagonized by CYP which was the most potent antagonist of (-)-isoprenaline and BRL 37344 at the beta 3-adrenoceptor. This suggests that the agonist effects of iodoCYP were produced through a different mechanism: either via another receptor, another isoform of the rat beta 3-adrenoceptor, or through a non-receptor-mediated effect. Pseudo-pD2 values did not correlate with log P values for these compounds, indicating that their relaxant effects were not simply a function of their lipid solubility. 6. This study has highlighted several structural requirements for antagonist binding potency at the rat ileum beta 3-adrenoceptor and should assist in the development of potent selective antagonists for this receptor.

Pharmacological distribution diagrams: a tool for de novo drug design

Discriminant analysis applied to SAR studies using topological descriptors allows us to plot frequency distribution diagrams: a function of the number of drugs within an interval of values of discriminant function vs. these values. We make use of these representations, pharmacological distribution diagrams (PDDs), in structurally heterogeneous groups where generally they adopt skewed Gaussian shapes or present several maxima. The maxima afford intervals of discriminant function in which exists a good expectancy to find new active drugs. A set of beta-blockers with contrasted activity has been selected to test the ability of PDDs as a visualizing technique, for the identification of new beta-blocker active compounds.

Liquid chromatographic determination of total celiprolol or (S)-celiprolol and (R)-celiprolol simultaneously in human plasma

A method has been developed for the determination of total celiprolol (sum of enantiomers) or the enantiomers (R)-celiprolol and (S)-celiprolol in plasma by high-performance liquid chromatography with UV and fluorescence detection. After extraction from alkalinized plasma with methyl-tert.-butyl ether and back-extraction into 0.01 M HCl (for total celiprolol determination) or after evaporation of the organic phase and derivatisation with R(-)-1-(1-naphthyl)ethyl isocyanate (enantiomer determination), total celiprolol or its diastereomeric derivatives were chromatographed on a reversed-phase HPLC column with a mixture of acetonitrile and phosphate buffer pH 3.5 (+0.05% triethylamine). Acebutolol was used as internal standard. Linearity was obtained in the range of 5 to 2000 ng/ml for total and 2.5 to 500 ng/ml for enantiomer determination. Intra-day and inter-day variation was lower than 10%. The method can be applied for analysis of plasma samples obtained from patients treated with oral racemic celiprolol doses.

Comparison of the Hummel-Dreyer method in high-performance liquid chromatography and capillary electrophoresis conditions for study of the interaction of (RS)-, (R)- and (S)-carvedilol with isolated plasma proteins

The Hummel-Dreyer method in capillary zone electrophoresis was compared with the corresponding high-performance liquid chromatographic (HPLC) variant in order to study the interaction of racemic carvedilol and its individual enantiomers with isolated human plasma proteins [alpha 1-acid glycoprotein (AGP) and human serum albumin (HSA)]. The binding parameters characterizing the high-affinity binding site of AGP evaluated by using capillary electrophoresis [Ka(RS) = (3.01 +/- 1.15).10(6) l/mol; Ka(S) = (2.13 +/- 0.53).10(6) l/mol; Ka(R) = (4.88 +/- 1.57).10(6) l/mol] were in good accordance with those obtained by HPLC [Ka(RS) = (3.88 +/- 1.74).10(6) l/mol: Ka(S) = (1.80 +/- 0.53) x 10(6) l/mol; Ka(R) = (5.43 +/- 2.53).10(6) l/mol]. Relatively small quantitative differences have been observed considering the attachment of (R)-carvedilol to the secondary low-affinity binding sites on alpha 1-acid glycoprotein by comparing these two methods. In general, the Hummel-Dreyer method applied to capillary zone electrophoresis conditions was verified to be an efficient and fast technique for reliable description of quantitative binding parameters of hydrophobic drugs.

[Transdermal administration of drugs. XI. Formulation of polymeric matrices with metoprolol in transdermal therapeutic systems]

The paper is concerned with formulation studies of the transdermal therapeutic system of the matrix type with beta-adrenolytic drug metoprolol. The base of the hydrophobic matrix is the biocompatible polymer-silicone rubber, and the hydrophilic matrix was prepared from the polyacrylate polymer of the Eudragit type. The properties of the silicone matrix were modified by the additive Methocel F 4M, macrogol 600, copolymer p (HEMA) with methacrylic acid and polyacrylamide. The matrices were evaluated on the basis of the results of in vitro liberation of the drug at 32 degrees C. The liberation profiles of metoprolol were evaluated by means of the parameters of Tornquist hyperbolic function calculated by nonlinear regression. Of the composite ingredients of the silicone matrix, Methocel F 4M proved to be the best. Metoprolol was released most from the hydrophilic matrix prepared from Eudragit NE 30D. It released 12.32 mg.cm(-2).24 h-1 of metoprolol.

Preformulation studies of atenolol in oral liquid dosage form. I. Effect of pH and temperature

The stability of atenolol solutions was evaluated under accelerated isothermal degradation conditions at 90 degrees C. A specific and sensitive HPLC method was adopted to study the pH dependence of the stability. The maximum stability of atenolol was achieved at pH 4. The degradation of atenolol followed first-order kinetics at 90 degrees C, pH 4 with k value of 1.1.10(-3) hour-1.

Disposition of human drug preparations in the horse. V. Orally administered oxprenolol

Urinary concentrations of the beta-antagonist oxprenolol and some of its major human metabolites were determined following oral administration of a dose of 160 mg to five fasted horses. Quantitation was performed by gas chromatography-mass spectrometry (GC-MS) in the selected ion mode (SIM) by monitoring ion m/z 466 of the heptafluorobutyric derivatives. As early as 2 h after dosage oxprenolol could be detected in hydrolysed urine and remained detectable up to 24 h. Maximum urinary concentrations and excretion rates were obtained between 2 and 12 h. After 12 h only 2.8% of the administered dose was excreted as conjugates of oxprenolol and major human metabolites including 4-OH-oxprenolol and 5-OH-oxprenolol. These metabolites were detectable up to 48 h.

Antagonist conformations with the beta(2)-adrenergic receptor ligand binding pocket

The interactions between beta-adrenergic receptor (beta AR) antagonists and the beta(2)AR were studied with the use of photoaffinity labels. A proteolytic map of the receptor was made and confirmed through amino-terminal amino acid sequencing by locating sites of derivatization. [125I]Iodoazidothiophenylalprenolol (IAPTA) is a photoaffinity derivative of the beta AR antagonist alprenolol with a photoactivatable group on the aryloxy end of the molecule. IAPTA exclusively derivatizes a peptide consisting of transmembrane domains (TMs) 6 and 7 of the hamster lung beta(2)AR, supporting the contention that TMs 6 and 7 interact with the aryloxy portion of the beta AR antagonist pharmacophore. The beta AR antagonist photoaffinity labels [125I]iodoazidobenzylpindolol (IABP), [125I]iodoazidophenyl CGP-12177A (IAPCGP), and [125I]iodocyanopindololdiazarene (ICYPdz) are similar in that their photoactive moieties are attached to the amino end of the antagonist pharmacophore. IABP derivatized TMs 5-7 and a peptide containing TM 1 to approximately equal extents. IAPCGP derivatized Tms 6 and 7 >> TM 5 = TM 4 = TMs 2 and 3 = TM 1. ICYPdz derivatized TM 1 >> TMs 6 and 7 > Tm 4. We conclude that the aryloxy end of the beta AR antagonist pharmacophore is highly constrained within TMs 6 and 7, whereas the amino terminus is much less constrained and able to assume multiple conformations. Molecular dynamics simulations predict that IABP, IAPCGP, and ICYPdz favor a folded conformation, with both ends close together. Derivatization of TMs 6 and 7 by IABP, IAPCGP, and ICYPdz suggests the folded conformation of these compounds in the ligand binding pocket.

X-ray structure investigations of potential beta-blockers. II.6,7-Dimethoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline

The saturated part of the isoquinoline moiety in the title compound, C17H19NO2, has a twist conformation and the phenyl ring substituent is in an equatorial position. The absolute configuration of the molecule is R and molecules form infinite chains by means of weak hydrogen bonds.

Some effects of nipradilol, a beta-antagonist possessing a nitroxy group, on smooth muscle of the pig coronary artery

1. The effects of nipradilol, a beta-adrenoceptor antagonist which possesses a nitroxy group, on cytosolic Ca2+ concentration ([Ca2+]i), and on tension development were simultaneously measured by front-surface fluorometry and fura-2-loaded strips in the proximal portion of pig coronary arteries. 2. Nipradilol reduced in a concentration-dependent manner both the [Ca2+]i and tension, irrespective of whether the strips were unstimulated or exposed to either high K+ or histamine containing solutions. However, both in the case of contractions induced by high K+-depolarization and histamine stimulation, for a given [Ca2+]i elevation the tension which developed in the presence of nipradilol was smaller than that generated in its absence, so that the [Ca2+]i-tension curves during the contraction were shifted to the right. 3. In the absence of extracellular Ca2+, the [Ca2+]i elevation due to the release of Ca2+ from histamine-sensitive store was inhibited by nipradilol. Nipradilol had no effect on the [Ca2+]i elevation due to the release of Ca2+ from caffeine-sensitive stores; however, it did inhibit the caffeine-induced increase in tension. A derivative of nipradilol, which lacked a nitroxy molecule (Nip(-N)), had no effect on the [Ca2+]i and tension elevated by histamine or caffeine in the absence of extracellular Ca2+. 4. The beta-adrenoceptor agonist, isoprenaline, reduced [Ca2+]i tension when applied to steady state contractions induced by high K+, or at the peak level of tension to histamine. The reduction of [Ca2+]i and tension induced by isoprenaline was inhibited by Nip(-N) in a concentration-dependent manner and nipradilol inhibited the isoprenaline-induced relaxation with bell-shaped concentration-response curves. At lower concentrations, nipradilol acted as a beta-blocker, the IC50- value being smaller than that of Nip(-N), and at higher concentrations, it acted as a nitrovasodilator. 5. Thus, it is suggested that, at lower concentrations, nipradilol, an antianginal drug, acts as a beta-adrenoceptor antagonist. At higher concentrations, it relaxes the proximal portion of the coronary artery by directly reducing [Ca2+]i and the Ca2+-sensitivity of the myofilaments, apparently due to the presence of the nitroxy molecule.

Toxic doses of rac-, (-)-(S)- and (+)-(R)-propranolol in rats and rabbits

The contribution of the individual enantiomers ([+]-[R]- and [-]-[S]-propranolol) to rac-propranolol intoxication was studied in anaesthetized, spontaneously breathing (SB) rats and artificially ventilated (AV) rats and rabbits. In the SB rat, propranolol (30 mg.kg-1.h-1 i.v.) decreased heart rate and mean arterial blood pressure and caused hypoventilation, serious hypoxaemia, respiratory acidosis, and death by respiratory arrest. Survival time (ST) in the (+)-(R)-propranolol group (ST 91 +/- 5 min) was significantly longer than in the rac-propranolol group (ST. 68 +/- 6 min). In AV rats and rabbits toxic doses of rac-, (-)-(S)- and (+)-(R)-propranolol, 30 mg.kg-1.h-1 and 15 mg.kg-1.h-1 i.v., respectively, induced comparable effects on haemodynamic variables as in the SB rat. Artificial ventilation lengthened ST by a factor of three to four in rats. In the AV rat, ST's were not significantly different between the rac-, (-)-(S)- and (+)-(R)-propranolol groups. In the rabbit, as in the SB rat, ST in the (+)-(R)-propranolol group was significantly longer than ST's in the rac- and (-)-(S)-propranolol groups. The acute respiratory acidosis in SB rats and the prolonged ST in AV rats suggest that respiratory failure is the primary and cardiovascular failure the secondary cause of death in propranolol intoxication. The potentiation of the toxic effect of the enantiomers observed after dosing the racemate instead of the pure enantiomers could not be explained by a stereoselective difference in plasma propranolol concentration.

Timolol hemihydrate: a new formulation of timolol for the treatment of glaucoma

Timolol maleate, a non-selective beta-adrenergic blocker, has been used to treat glaucoma and ocular hypertension for almost two decades. Recently a new preparation, timolol hemihydrate, has been described which eliminates the maleate buffer and simplifies the purification step for the R-enantiomer. The ocular pharmacology of the two medicines is expected to be similar. Ocular bioavailability as well as toxicity for timolol hemihydrate is similar to that which has been shown previously for timolol maleate. In a multicenter trial in the United States, timolol hemihydrate was shown to reduce the intraocular pressure to a similar extent as timolol maleate. At the week 12 visit intraocular pressure was 19.5 and 19.5 mm Hg for the hemihydrate and maleate groups respectively for the 0.25% concentration and 18.3 and 18.6 mm Hg respectively for the 0.5% concentration. Following a nine month open-label portion where patients were treated with timolol hemihydrate only intraocular pressure was 19.9 and 19.1 mm Hg for the 0.25% and 0.5% concentrations respectively. Ocular and systemic adverse events, as well as vital signs, were similar between timolol hemihydrate and maleate. In conclusion, timolol hemihydrate appears to be a safe and effective medicine in the treatment of ocular hypertension and chronic open-angle glaucoma.

Lambda-carrageenan: a novel chiral selector for capillary electrophoresis

Lambda-carrageenan, a linear high molecular weight sulfated polysaccharide, has been employed as a chiral selector in capillary electrophoresis for the separation of enantiomers of weakly basic pharmaceutical compounds. The racemic compounds that were enantioresolved included propranolol, pindolol, tryptophanol, laudanosine and laudanosoline. In addition, the diastereomeric pair of cinchonine and cinchonidine were also resolved. Method conditions such as buffer pH, electrolyte concentration, column temperature, and chiral selector concentration were found to be important for improvement of enantioselectivity.

Correlation of drug absorption with molecular surface properties

The correlation between dynamic surface properties of drug molecules and drug absorption in two common in vitro models of the intestinal wall (Caco-2 monolayers and rat intestinal segments) has been investigated. A homologous series of beta-adrenoreceptor antagonists were used as model compounds. Dynamic molecular surface properties, considering all low-energy conformations, of the compounds were calculated. The flexibility of the molecules was studied by molecular mechanics calculations (MM2) and the van der Waals' (vdW), and water accessible surface areas were calculated and averaged according to a Boltzmann distribution. Excellent correlations were obtained between the dynamic polar vdW surface areas and cell permeabilities in Caco-2 cells and rat ileum (r2 = 0.99 and 0.92, respectively). These correlations were stronger than those between calculated octanol/buffer partition coefficients (log Doct,7.4) and permeability (r2 = 0.80 and 0.73, respectively). Moreover, the calculated log Doct,7.4 values failed to rank the permeability coefficients through Caco-2 monolayers and rat ileum in the correct order. The results indicate that dynamic polar surface area is a promising alternative model for the prediction of oral drug absorption.

Positive and negative inotropic effects of DL-sotalol and D-sotalol in failing and nonfailing human myocardium under physiological experimental conditions

BACKGROUND

DL-Sotalol has class III antiarrhythmic activity through prolongation of the repolarization phase of the action potential as well as beta-adrenoceptor-blocking properties. Although the former effect was found to exert positive inotropic effects in animal experimental studies, the latter may be detrimental in heart failure due to negative inotropism. In contrast to DL-sotalol, D-sotalol is suggested to exert only positive inotropic effects, which were never tested in isolated human myocardium.

METHODS AND RESULTS

Therefore, we investigated the effects of racemic DL-sotalol and its enantiomer D-sotalol in human right atrial muscle strip preparations and in left ventricular muscle strip preparations from nonfailing and end-stage failing human hearts. DL-sotalol and D-sotalol significantly (P < .01) increased peak developed force in atrial preparations by 14.0 +/- 3.4% and 16.7 +/- 3.8%, respectively, but had no effect in ventricular myocardium. In nonfailing ventricular myocardium, both DL-sotalol and D-sotalol shifted the dose-response curve for isoproterenol to higher concentrations (P < .01); however, DL-sotalol was 100-fold more effective than D-sotalol. In non-failing myocardium, a positive force-frequency relation was found between 30 and 120 beats per minute, but isoproterenol was much more powerful in its inotropic effects. In failing myocardium, reduction in stimulation rate from 120 to 30 beats per minute increased peak developed force more pronounced than did the application of isoproterenol.

CONCLUSIONS

(1) D-Sotalol has no relevant beta-adrenoceptor-blocking activity compared with DL-sotalol. (2) Neither DL-sotalol nor D-sotalol exhibit positive inotropic effects in human left ventricular myocardium. (3) Heart rate reduction increases contractile force in end-stage failing human myocardium due to an inverse force-frequency relation and thereby counteracts the potential negative inotropic properties of beta-blockade.

Application of intracerebral microdialysis to study regional distribution kinetics of drugs in rat brain

1. The purpose of the present study was to determine whether intracerebral microdialysis can be used for the assessment of local differences in drug concentrations within the brain. 2. Two transversal microdialysis probes were implanted in parallel into the frontal cortex of male Wistar rats, and used as a local infusion and detection device respectively. Within one rat, three different concentrations of atenolol or acetaminophen were infused in randomized order. By means of the detection probe, concentration-time profiles of the drug in the brain were measured at interprobe distances between 1 and 2 mm. 3. Drug concentrations were found to be dependent on the drug as well as on the interprobe distance. It was found that the outflow concentration from the detection probe decreased with increasing lateral spacing between the probes and this decay was much steeper for acetaminophen than for atenolol. A model was developed which allows estimation of kbp/Deff (transfer coefficient from brain to blood/effective diffusion coefficient in brain extracellular fluid), which was considerably larger for the more lipohilic drug, acetaminophen. In addition, in vivo recovery values for both drugs were determined. 4. The results show that intracerebral microdialysis is able to detect local differences in drug concentrations following infusion into the brain. Furthermore, the potential use of intracerebral microdialysis to obtain pharmacokinetic parameters of drug distribution in brain by means of monitoring local concentrations of drugs in time is demonstrated.

Enantiomeric separation of denopamine by capillary electrophoresis and high-performance liquid chromatography using cyclodextrins

Direct separation of enantiomers of denopamine was investigated by two separation methods. One is capillary zone electrophoresis (CZE) using cyclodextrins (CDs) (CD-CZE) and the other is high-performance liquid chromatography (HPLC) using CD immobilized chiral stationary phases (CD-CSPs). Enantiomers of denopamine were successfully resolved by employing heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) and acetyl-beta-cyclodextrin (AC-beta-CD), and partially resolved with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and beta-CD polymer under acidic conditions. Separation of enantiomers of denopamine by HPLC was also successful with one of the CD-CSPs, where perphenylated beta-CD (Ph beta-CD) was immobilized. In CD-CZE, some polymeric additives, such as hydroxy-propylmethylcellulose (HPMC) and polyvinylalcohol (PVA), and a coated capillary were used to improve the enantioseparation of denopamine. Method validations such as linearity, recovery and repeatability, etc., were investigated for HPLC, and the method was applied to the optical purity testing of the drug substances and in tablet form.

Determination of the optical purity of timolol maleate by proton nuclear magnetic resonance spectroscopy with a chiral Pr(III) shift reagent

A 1H NMR spectroscopic method with chiral shift chelate is presented for the determination of the optical purity of timolol maleate. Optimum experimental conditions were established by studying the interactions of solvents (CCl4, CDCl3), substrate concentration, and the type and concentration of chiral lanthanide chelate (Pr(hfc)3, Eu(hfc)3). Larger induced shift (delta delta) and enantiomeric shift difference (delta delta delta) values, and more detailed spectral differences were obtained with Pr(hfc)3 than with Eu(hfc)3. By monitoring the spectral changes of the resonance signals for the enantiomeric -C(CH3)3 protons, suitable conditions for quantitative determinations were found when 0.1 molar equivalents of Pr(hfc)3 were complexed with 0.074 M of substrate. Enantiomeric compositions were calculated from the relative intensities of the enantiomeric -C(CH3)3 proton resonances. Based on the analysis of six synthetic enantiomeric mixtures, the mean +/- SD recovery of (R)-(+)-timolol by the proposed method was 99.5 +/- 1.17% of the amount added.

Effects of the ester moiety on stereoselective hydrolysis of several propranolol prodrugs in rat tissues

The stereochemical characteristics of the hydrolysis of several ester-type prodrugs of propranolol, O-acetyl, O-propionyl, O-butyryl, O-pivaloyl and succinyl esters, were studied in phosphate buffer (pH 7.4), rat plasma and rat tissue homogenates. In phosphate buffer, no differences were observed in the hydrolysis rate between the esters of (R)- and (S)-propranolol. The effects of the ester moieties on the hydrolysis rate in phosphate buffer were in the following order: acetate > propionate > butyrate > succinate > pivalate. In rat plasma and tissue homogenates, the hydrolysis of the esters was accelerated, and stereoselective hydrolysis was observed. In plasma, the hydrolysis of the (R)-isomer was faster than that of the (S)-isomer except for the succinate ester. On the other hand, in the liver and intestine homogenates, the (S)-isomer was hydrolyzed faster than the (R)-isomer except for the succinate and pivalate esters in the liver homogenate. Also, the ratio of the hydrolysis rates (S/R) changed with the type of prodrug. As the length of the alkyl chain of the ester increased, the S/R ratio approached unity in liver and intestine homogenates but stayed almost constant in plasma. For the pivalate ester, stereoselective hydrolysis was observed in plasma and intestine homogenate but not in liver homogenate. The stereoselective hydrolysis of the succinate ester was observed only in intestine homogenate, but the S/R ratio was almost 1 in plasma, liver and intestine homogenates. No interconversion between (R)- and (S)-isomer was observed during the hydrolysis of any of the ester prodrugs. These results indicate that hydrolysis of ester-type prodrugs of propranolol occurs stereoselectively in rat tissues, and that its selectivity is dependent on the kind of tissue and prodrug.

Nebivolol vasodilates human forearm vasculature: evidence for an L-arginine/NO-dependent mechanism

Nebivolol, a beta 1 selective adrenergic receptor antagonist with additional properties, is a racemic mixture of (S,R,R,R)- and (R,S,S,S)-enantiomers. We investigated its effects on human forearm vasculature. Blood flow was measured using venous occlusion plethysmography during brachial artery infusion of drugs. Interaction between nebivolol and the L-arginine/nitric oxide pathway was investigated via comparison with carbachol (an endothelium-dependent agonist) and nitroprusside, and by coinfusion of a competitive inhibitor of nitric oxide synthase, NG-monomethyl L-arginine (LNMMA) +/- L-arginine. Nebivolol (354 micrograms/min) increased blood flow by 91 +/- 18% (mean +/- SEM, n = 8, P < .01) whereas an equimolar dose of atenolol had no significant effect. L-NMMA (1 mg/min) inhibited vasodilation to nebivolol (by 65 +/- 10%) and carbachol (by 49 +/- 8%) to a significantly greater extent than it reduced responses to nitroprusside. Inhibition of nebivolol response by L-NMMA was abolished by L-arginine (62 +/- 11% inhibition by L-NMMA, 15 +/- 17% inhibition by L-NMMA with L-arginine, 10 mg/min, n = 8). Vasodilation caused by the (S,R,R,R)- and (R,S,S,S)-enantiomers was similar. We conclude that nebivolol vasodilates human forearm vasculature via the L-arginine/nitric oxide pathway.

Conformational structure of some beta 1-blockers, their partitioning in lipid and the role of parasubstituents

The conformational structure of beta1-blockers metoprolol, atenolol and practolol has been investigated by PCILO method. The aminoalkanol moiety adopts the same conformation in all these compounds. These beta-antagonists differ only in the conformation adopted by the substituent para to the aminoalkanol moiety. The graphical representation of the B1-antagonists for the final conformation reveals that only in the S-form, three interacting sites, namely, aromatic moiety, the beta-hydroxyl group and the -NH2(+) groups of aminoalkanol moiety are available for interactions with the receptor. The interaction of the aryloxy oxygen of the beta-antagonists with water molecule has also been taken into account. A linear relationship was obtained between log K (the partitioning of the beta-blocker in DMPC and also in octanol/water) and the potencies of these beta1-antagonists. Possibly, the role of para substituent is to act as an anchor by partitioning in the lipid bilayer so that the beta1-antagonist adopts the proper orientation for binding to the receptor.

Biphasic effect of local anesthetic and beta-blocker heptacaine on fluidity of phosphatidylcholine bilayers as detected by ESR spin probe method

Heptacaine (1), the monohydrochloride of [2-(heptyl-oxy)phenyl]-2-(1-piperidinyl)ethyl ester of carbamic acid, exerts a biphasic effect on the fluidity of egg yolk phosphatidylcholine (EYPC) model membranes as detected by the methyl esters of stearic acid spin probes with the paramagnetic doxyl group bound to the C-12 or C-16. The fluidity initially increases with an increase in the molar ratio of 1:EYPC, but a molar ratios above 1:EYPC = 0.5 a decrease of fluidity has been observed.

Protective effects of beta-blockers against 2,2'-azobis(2-amidinopropane)-dihydrochloride-induced damage

The protective effects of beta-blockers against 2,2'-azobis(2- amidinopropane)-dihydrochloride (AAPH)-induced damage were investigated. With the exception of pindolol, none of the beta-blockers tested inhibited arachidonate peroxidation induced by AAPH in the absence of iron. In contrast, ADP-Fe(3+)- and NADPH-dependent microsomal lipid peroxidation was inhibited by all the beta-blockers tested, although the inhibitory effects of atenolol and metoprolol were very slight. Oxidation of tryptophan residues in bovine serum albumin (BSA) induced by AAPH was strongly inhibited by pindolol and propranolol but not by atenolol or metoprolol. All the beta-blockers tested, however, inhibited AAPH-induced carbonyl formation of BSA. Furthermore, all the beta-blockers tested also strongly inhibited the deoxyribose degradation induced by AAPH, suggesting that these agents act as hydroxyl radical scavengers to inhibit carbonyl formation. DNA strand scission was induced by AAPH in the absence or presence of O2. Only pindolol strongly inhibited the DNA damage in the absence of O2. In the presence of O2, however, all the beta-blockers tested effectively prevented the DNA damage. These results suggested that the hydroxyl radicals produced from AAPH damaged DNA and, that beta-blockers might act as hydroxyl radical scavengers to protect DNA against the AAPH-induced oxidative damage.