Presence Of Pindolol Research Articles

Voltammetric Determination of Pindolol in Biological Fluids Using Molecularly Imprinted Polymer Based Biomimetic Sensor

A sensitive and selective electrochemical sensor for pindolol (PDL) was fabricated by embedding molecularly imprinted polymer (MIP) in graphite carbon paste. PDL imprinted polymer was prepared by free radical polymerization of itaconic acid (IA) and subsequent cross linkage with ethylene glycol dimethacrylate in the presence of PDL. The prepared MIP was subjected to extraction of template and then carbon paste electrode (CPE) was prepared by mixing optimized quantities of graphite, MIP and eicosane. The electrochemical behavior of PDL at MIP and non-imprinted polymer (NIP) modified CPEs have been investigated employing cyclic voltammetry (CV), and adsorptive stripping differential pulse voltammetry (AdSDPV). Chronocoulometry (CC) was used to approximate the surface coverage of analyte molecules which are specifically bound to MIP-CPE. Under the optimal experimental conditions, the sensor displayed linear relationship between the peak current and concentration of the PDL ranging from 0.1 μM to 50 μM, with the detection limit of 0.05 μM (S/N = 3). The presence of most common interferents and other structural analogues of PDL have no deleterious effect on the PDL anodic peak current. The fabricated sensor was successfully applied for the determination of PDL in serum and urine samples with recoveries in between 97 and 105%.

Radioligand binding analysis of knockout mice reveals 5-hydroxytryptamine 7 receptor distribution and uncovers 8-hydroxy-2-(di- n-propylamino)tetralin interaction with α 2 adrenergic receptors

In the present autoradiographic study, we took advantage of 5-hydroxytryptamine 7 (5-HT 7) receptor knockout mice to analyze the brain distribution of 5-HT 7 receptor binding sites using [ 3H]5-carboxamidotryptamine (5-CT; a 5-HT 1A/1B/1D/5/7 receptor ligand) and [ 3H]8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT; a 5-HT 1A/7 receptor ligand). Low to moderate densities of [ 3H]5-CT (2 nM) binding sites insensitive to pindolol (10 μM, for 5-HT 1A/1B receptor blockade) and GR-127935 (1 μM; for 5-HT 1D receptor blockade) were observed in wild-type mice (mainly in thalamus and hypothalamus) but not in 5-HT 7 receptor knockout mice. Surprisingly, moderate to high densities of [ 3H]8-OH-DPAT (10 nM) binding sites insensitive to pindolol (10 μM) remained in 5-HT 7 receptor knockout mouse brain. These non-5-HT 1A, non-5-HT 7 binding sites were found to be adrenergic α 2A receptor binding sites. In α 2A receptor knockout mice low to moderate densities of [ 3H]8-OH-DPAT binding sites insensitive to pindolol but sensitive to the selective 5-HT 7 receptor antagonist SB-269970 (300 nM) were observed mainly in thalamus and hypothalamus. Therefore, in addition to 5-HT 1A and 5-HT 7 binding sites, [ 3H]8-OH-DPAT also binds to α 2A receptor binding sites in wild-type mouse brain. [ 3H]8-OH-DPAT (in the presence of pindolol and 1 μM RX-821002 for α 2 receptor blockade) and [ 3H]5-CT (in the presence of pindolol and GR-127935) bind to a similar receptor binding population corresponding to 5-HT 7 binding sites. Detailed anatomical mapping of 5-HT 7 receptor binding sites in wild-type mouse brain was then performed using both radioligands in the presence of suitable pharmacological agents for non-5-HT 7 receptor binding sites blockade. The mapping revealed binding sites consistent with the mRNA distribution with the highest densities found in anterior thalamic nuclei.

Determination of bopindolol by sequential injection technique with spectrophotometric detection

In the proposed procedure, the determination of bopindolol using a sequential injection technique (SIA) with spectrophotometric detection at 560 nm is described. The new method of determination is based on the color reaction of the indole group in the molecule of bopindolol with 4-dimethylaminobenzaldehyde (Ehrlich's reagent) in acidic medium with production of a violet water-soluble complex. Due to the kinetic standpoint of reaction, the “stopped flow” technique with mixing coil between the valve and detector was tested and optimized. The proposed SIA system was used for the direct determination of bopindolol in tablets, negative effects of interfering substances (excipients of tablets) were not observed. The selectivity of the proposed method of determination was tested in the presence of seven interfering substances from the group of β-blockers with good results. The interference effect was observed only in the presence of pindolol. The sample throughput with stopped flow technique was 40 samples per hour. Bopindolol was determined in the linear range from 1 to 10 μg ml −1, RSD was less than 1% ( n=10), with limit of detection (3 σ) 0.1 μg ml −1 and limit of quantification 0.5 μg ml −1. Obtained results were compared with conventional HPLC method, both analytical techniques were in good agreement.

Pindolol-insensitive [3H]-5-hydroxytryptamine binding in the rat hypothalamus; identity with 5-hydroxytryptamine7 receptors.

Pindolol-insensitive [3H]-5-hydroxytryptamine ([3H]-5-HT) binding to rat hypothalamic membranes was pharmacologically and functionally characterized to resolve whether this procedure selectively labels 5-HT7 receptors. Consistent with a previous report, 3 microM and not 100 nM pindolol was required to occupy fully 5-HT1A and 5-HT1B receptors. Remaining [3H]-5-HT binding was saturable (KD, 1.59+/-0.21 nM; Bmax, 53.8+/-3.1 fmol x mg protein(-1)). Displacement of [3H]-5-HT with metergoline and 5-CT revealed shallow Hill slopes (<0.5) but seven other compounds had slopes >0.8 and pKi values and the rank order of affinity were significantly correlated (r = 0.81 and 0.93, respectively) with published [3H]-5-HT binding to rat recombinant 5-HT7 receptors. In the presence of pindolol, 5-HT-enhanced accumulation of [32P]-cyclic AMP was unaffected by the 5-HT4 antagonist RS39604 (0.1 microM) or the 5-ht6 antagonist Ro 04-6790 (1 microM) but significantly attenuated by mesulergine (250 nM), ritanserin (450 nM) or methiothepin (200 nM) which have high affinity for the 5-HT7 receptor. Intracerebroventricular pretreatment with the serotonergic neurotoxin 5,7-dihydroxytryptamine, 5,7-DHT, elevated the [3H]-5-HT Bmax 2 fold, indicating that the hypothalamic 5-HT7 receptor is post-synaptic to 5-HT nerve terminals and regulated by synaptic 5-HT levels. These results suggest that, in the presence of 3 microM pindolol, [3H]-5-HT selectively labels hypothalamic binding sites consistent with functional 5-HT7 receptors.

Isomeric-activity ratios of trimetoquinol enantiomers on beta-adrenergic receptor subtypes: functional and biochemical studies.

Trimetoquinol [1-(3',4',5'-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4- tetrahydroisoquinoline , TMQ] exists as two enantiomers, and the (-)-(S)-isomer is a potent beta-adrenergic receptor (beta-AR) agonist. Experiments were conducted to examine the functional and biochemical potencies of the (S)-and (R)-enantiomers of TMQ for interaction with beta-AR subtypes in tissues, membrane fractions, and cell systems. The isomeric-activity ratios (IARs) of the TMQ isomers [(S)-isomer > > (R)-isomer] for stimulation of beta 1- and beta 2-AR of guinea pig right atria and trachea were 224 and 1585, respectively; these IARs were similar to those observed on atypical beta-AR systems of rat distal colon (575), rat brown adipocytes (398), but differed from that of rat esophageal smooth muscle (2884) in the presence of pindolol. In the absence of pindolol, the potencies for the TMQ enantiomers were slightly increased; however, the IARs remained unchanged in rat distal colon, rat brown adipocytes, and rat esophageal smooth muscle. Similarly, radioligand binding studies demonstrated that the TMQ isomer beta-AR affinities were stereoselective for the (-)-(S)-isomer in membranes of guinea pig left ventricle (beta 1) and lung (beta 2) giving IARs of 115 and 389, respectively; and in E. coli expressing human beta 1- and beta 2-AR giving IARs of 661 and 724, respectively. Corresponding IARs of receptor affinities and stimulation of cAMP accumulation in Chinese hamster ovary cells expressing human beta 2-AR and rat beta 3-AR were 331 and 282, and 118 and 4678, respectively. These results indicate that the (-)-(S)-isomer of TMQ exhibits high affinity, and is a potent and highly stereoselective agonist for each beta-AR subtype, that the isomers generally fail to differentiate between the beta-AR subtypes, and that, based upon differences in IAR within beta 3-AR containing systems, subtypes of atypical beta (or beta 3)-AR may exist in adipose tissue and smooth muscle.

Buspirone affects hippocampal rhythmical slow activity through serotonin 1A rather than dopamine D 2 receptors

Buspirone reduces anxiety clinically but, unlike classical anxiolytics, is not muscle relaxant, sedative, anticonvulsant or effective in increasing GABA function. The basis for its clinical action is not known, but action at both dopamine D 2 and serotonin 1A receptors has been suggested. Buspirone, like classical anxiolytics, produces a general reduction in the frequency of hippocampal rhythmical slow activity elicited by stimulation of the midbrain in the rat. Methysergide (3 mg/kg i.p,), GR38032F (0.3 mg/kg i.p.) and haloperidol (0.2 mg/kg and 2.0 mg/kg i.p.) failed to block this effect of buspirone (10 mg/kg i.p.). Apomorphine (0.3 mg/kg i.p.) had minor effects, but did not produce a general reduction in frequency. Pindolol (2 mg/kg i.p.) produced a small reduction in frequency itself. In the presence of pindolol, buspirone was without effect, while the effect of chlordiazepoxide (5 mg/kg i.p.) was potentiated. These results show that: (a) the similar effects of buspirone and classical anxiolytics such as chlordiazepoxide on reticular-elicited hippocampal rhythmical slow activity are achieved through different mechanisms; (b) the effects of buspirone in this particular test are more likely to depend on its interaction with serotonin 1A receptors than its interaction with D 2 receptors; and (c) that, as in other tests, buspirone does not act via serotonin 2 or serotonin 3 receptors.

Do both adrenaline and noradrenaline stimulate cardiac α‐adrenoceptors to induce positive inotropy of rat atria?

1. The positive inotropic responses of rat paced left atria to adrenaline and noradrenaline were recorded. Desmethylimipramine (DMI, 1 microM) and metanephrine (10 microM) were initially present throughout. 2. The positive chronotropic responses of spontaneously beating right atria to adrenaline were used as a reference. In these, pindolol, in increasing concentrations, caused progressive shift of the concentration-response curves to the right, which yielded a pA2 value (8.15) compatible with antagonism of beta-adrenoceptors. 3. The left atrial tension responses to adrenaline showed an initial progressive displacement by pindolol (up to 3 microM) which gave an unexpectedly low pA2 value (6.48). However, with further increases in pindolol concentration there was no additional shift of the curve. In the presence of pindolol (3 microM), prazosin (0.1 microM) displaced the curve to the right but the pA2 value derived from this shift (7.75) was less than expected for alpha 1-adrenoceptor antagonism. 4. When the experiments in the presence of pindolol (3 microM) were repeated in the absence of DMI, prazosin displaced the concentration-response curves for adrenaline-induced left atrial tension to a greater extent and the pA2 value (8.76) was now compatible with adrenaline stimulating typical alpha 1-adrenoceptors. 5. The concentration-response curves for noradrenaline-induced left atrial tension were also progressively displaced to the right by pindolol (0.1, 0.3 and 1.0 microM). These concentrations yielded a Schild plot of unity slope and a pA2 value of 7.94 +/- 0.04. This was not significantly different from the pA2 value of 8.02 +/- 0.07 determined for pindolol against isoprenaline in the left atria, which indicates a normal interaction of noradrenaline with beta-adrenoceptors in the absence and presence of low concentrations of pindolol. 6. A further increase in the concentration of pindolol to 3 microM failed to induce an additional shift of the noradrenaline curves, whether a 'before and after' antagonist or a 'naïve tissue' design was adopted. Similarly, the rightwards shift of the concentration-response curves by timolol reached a limit as the concentration was increased. In all cases the limit of shift occurred at a noradrenaline EC50 value of 5-10 microM. 7. At the limit of beta-adrenoceptor antagonism, prazosin and dibenamine did not displace the noradrenaline curves further. The residual inotropic response to noradrenaline therefore appeared to be mediated via neither alpha- nor beta-adrenoceptors. 8. DMI, in the absence of beta-blockade, produced the potentiation of adrenaline and noradrenaline expected of a neuronal uptake inhibitor. However, in the presence of pindolol, there was no potentiation of the right atrial rate response to adrenaline while its left atrial tension responses were antagonized. This suggested that DMI was acting as an alpha-adrenoceptor antagonist. It also explained the less-than-expected shift by prazosin of the adrenaline responses in the presence of both pindolol and DMI, the latter drug already exerting some alpha-blocking activity. In contrast, the left atrial tension responses to noradrenaline in the presence of pindolol (1 microM) were neither potentiated nor antagonized by DMI. 9. When the effects of prazosin upon left atrial tension responses to noradrenaline in the presence of pindolol (10 microM) were examined in the presence of a lower concentration of DMI (O.1 microM) or cocaine (1O microM), again there was no further shift of the curve. However, when the effect of prazosin) The Macmillan Press Ltd 1989 598 K.L. WILLIAMSON & K.J. BROADLEY was examined in the absence of DMI, but in the presence of pindolol (1 and 1O microM) or timolol (3 microM), there was a small shift of the curves by prazosin (0.1 microM). This yielded pA2 values of 7.19, 7.34 +/- 0.1 and 7.66 +/- 0.09, which were at least one order of magnitude less than literature values and that obtained with adrenaline (8.76 +/- 0.18), and are not consistent with noradrenaline stimulating an alpha 1-adrenoreceptor in the presence of beta-adrenoceptor blockade, the increase in left atrial tension by noradrenaline does not appear to be mediated by beta l- or typical alpha-adrenoceptors. This is in contrast to adrenaline which in these conditions stimulates typical alpha 1-adrenoceptors.

Cardiovascular Effects of an ionophorous Antibiotic, Lonomycin A, in Anesthetized Dogs

-An intracoronary administration of lonomycin A, a K-selective ionophore, produced coronary vasodilatation in the presence of pindolol in anesthetized dogs. Coronary vasodilatation induced by lonomycin A, KCl and nifedipine was inhibited byo pretreatment with an intracoronary injection of ouabain. This result suggests that lonomycin A-induced coronary vasodilatation may be partly due to a stimulation of Na+, K+-ATPase as well as KCl and/or a decrease in Ca2+ influx as well as nifedipine.

Multiple effects of alpha-adrenoceptor stimulation on the action potential of the rabbit atrium.

Effects of alpha-adrenoceptor stimulation by phenylephrine (10(-7)-10(-4) mol/l) in the presence of pindolol (10(-7) mol/l) on the action potential and force of contraction were observed in the rabbit left atrium. Phenylephrine reduced resting potential, prolonged action potential duration (APD), decreased maximum rate of rise of action potential (Vmax) and increased force of contraction in a concentration-dependent manner. Effects of phenylephrine (10(-5) mol/l) were antagonized by prazosin (10(-7) mol/l) or phentolamine (10(-6) mol/l). APD which had been prolonged by phenylephrine (10(-5) mol/l) was slightly shortened by Ni2+ (0.3 mmol/l) at the level of 50% repolarization but almost unaffected at the level of 90% repolarization. TTX (10(-6) mol/l) had no effect on ADP which had been prolonged by phenylephrine (10(-5) mol/l). Cs+ (10 mmol/l), which inhibits outward current ik1, depolarized resting potential, but in contrast with phenylephrine Cs+ did not affect APD at 90% repolarization. Phenylephrine (10(-5) or 3 X 10(-5) mol/l) restored Ca2+-dependent action potential and force of contraction in 20 mmol/K+-Tyrode solution. These responses were suppressed by prazosin (10(-7) mol/l) or Ni2+ (0.3 mmol/l). Phenylephrine (10(-5) or 10(-4) mol/l) had no effect on steady-state membrane potential--Vmax relationship. It is concluded that in the rabbit left atrium phenylephrine, via alpha-adrenoceptors may suppress outward currents perhaps ik1 and ix, and might increase slow inward current.

Influence of acetylcholine on the positive inotropic effect evoked by alpha- or beta-adrenoceptor stimulation in the rabbit heart.

The influence of acetylcholine (ACh) on the positive inotropic responses to α- as well as β-adrenoceptor stimulation was investigated in the isolated electrically driven rabbit ventricular muscle. 1. Stimulation of muscarinic receptors by ACh (10−9–10−4 mol/l) reduced the positive inotropic effect evoked by isoprenaline (10−8 mol/l) via β-adrenoceptor stimulation, but enhanced the positive inotropic effect of the α-adrenoceptor stimulating agent phenylephrine (10−6 mol/l) in the presence of pindolol (3×10−8 mol/l). 2. Sodium nitroprusside (SNP) (10−6–10−3 mol/l) reduced the β-adrenoceptor-mediated positive inotropic effect but did not effect the α-adrenoceptor-mediated one. 3. The depression by ACh (10−6 mol/l) or SNP (10−4 mol/l) of the positive inotropic effects evoked by β-adrenoceptor stimulation was accompanied by a decrease of the cAMP level which has been elevated by isoprenaline. However, the enhancement of the α-adrenoceptor mediated positive inotropic effect by ACh seems to be independent of changes in cAMP- and/or cGMP-levels. 4. ACh (10−6 mol/l) diminished the shortening of the action potential duration induced by isoprenaline (10−8 mol/l) in Tyrode solution and Ca2+-dependent potential restored by β-adrenoceptor stimulation in 27 mmol/l K+ Tyrode solution. In contrast, ACh (10−6 mol/l) affected neither the prolongation of action potential duration nor the Ca2+-dependent potential caused by α-adrenoceptor stimulation. The depression by acetylcholine of the β-adrenoceptor mediated positive inotropic effect may be due to the decrease in cAMP content and to the reduction of the slow inward current while the enhancement by ACh of the α-adrenoceptor mediated positive inotropic effect is not associated with changes in cAMP- and/or cGMP-levels and in electrophysiological phenomena. It is concluded that the accentuated antagonism (Levy 1971) between sympathomimetic and parasympathomimetic agents at the postsynaptic region results mainly from the interaction between β-adrenoceptor- and muscarinic receptor-mediated responses, and that the α-adrenoceptor-mediated responses are able to counteract the accentuated antagonism.

Adenosine antagonizes the positive inotropic action mediated via β-, but not α-adrenoceptors in the rabbit papillary muscle

In the isolated rabbit papillary muscle, adenosine (1–300 μM) alone scarcely affected the basal tension developed. The positive inotropic action of isoprenaline, mediated via β-adrenoceptors, was inhibited by adenosine in a concentration-dependent manner. Atropine (0.3 μM) abolished the inhibitory action of carbachol on the isoprenaline-induced positive inotropic action but did not affect the inhibitory action of adenosine. Adenosine failed to inhibit the positive inotropic action exerted by phenylephrine via stimulation of α-adrenoceptors in the presence of pindolol (30 nM). The present results indicate that the positive inotropic action was mediated via α-adrenoceptors whose subcellular mechanism was not susceptible to the inhibitory action of adenosine as are β-adrenoceptors.

Differentiation by cholinergic stimulation of positive inotropic actions mediated [formula omitted] α- and β-adrenoceptors in the rabbit heart

In the isolated rabbit papillary muscle, experiments were carried out in order to elucidate whether or not cholinergic stimulation produces a differential antagonistic action on the positive inotropic effects mediated via β- and α-adrenoceptor stimulation. Carbachol (0.1–30 μM) alone scarcely affected the basal tension developed. The postive inotropic effects of phenylephrine (30 μM) in the presence of phentolamine and of isoprenaline, which were mediated via β-adrenoceptors, were markedly inhibited by carbachol. Carbachol (3 μM) shifted the dose-response curve for isoprenaline in a parallel manner, and that for phenylephrine with phentolamine to the right and downwards. Carbachol administered during induction of the positive inotropic effects via α-adrenoceptors by phenylephrine (30 μM) with pindolol or by methoxamine failed to inhibit these effects and increased further the tension developed. The dose-response curve for phenylephrine determined in the presence of pindolol was not affected by carbachol. The present results indicate that the cholinergic antagonism of the adrenergic action on the contractility of the mammalian ventricular myocardium is exerted specifically to the β-adrenoceptor-mediated action, but not to the α-adrenoceptor-mediated one.

Characterization of adrenoceptors mediating positive inotropic responses in the ventricular myocardium of the dog.

1 The pharmacological characteristics of adrenoceptors mediating the positive inotropic action in the dog heart were assessed by the use of blood-perfused papillary muscles and isolated strips of ventricular myocardium.2 On the blood-perfused papillary muscle driven at 2 Hz and in sinus node preparations, phenylephrine induced positive inotropic and chronotropic responses in the same dose range and was much less potent than isoprenaline. The dose-response curve for the chronotropic action of phenylephrine was parallel to that of isoprenaline, whilst the dose-response curve for the inotropic action of phenylephrine was less steep than that of isoprenaline.3 The infusion of pindolol, a beta-adrenoceptor blocking agent, at a rate of 1 mug/min, shifted the isoprenaline dose-response curves to the right, and to the same extent, in both papillary muscle and sinus node preparations. In contrast to isoprenaline, the antagonism of phenylephrine by pindolol was noncompetitive. Phentolamine did not affect the positive inotropic and chronotropic actions of phenylephrine.4 On isolated ventricular strips alpha-adrenoceptor blockade by 10(-6) M phentolamine did not affect dose-response curves to phenylephrine or dopamine. Pindolol shifted the dopamine dose-response curves to the right in a competitive manner and those of phenylephrine in a noncompetitive manner.5 On ventricular strips from reserpine-pretreated dogs phenylephrine and tyramine dose-response curves were shifted markedly to the right and downwards. Desipramine (10(-5) M) which enhanced the action of noradrenaline considerably reduced the myocardial responses of phenylephrine.6 Papaverine (10(-5) M) decreased the threshold concentration of phenylephrine required to stimulate the myocardium and shifted phenylephrine dose-response curves to the left.7 Raising the temperature from 32 degrees C to 37 degrees C shifted phenylephrine dose-response curves to the right; when the temperature was raised from 37 degrees C to 42 degrees C the affinity of the drug was not changed.8 Other alpha-adrenoceptor stimulants, methoxamine and clonidine, decreased the active tension of ventricular strips. The responses to noradrenaline and adrenaline (in the presence of pindolol; 3 x 10(-8) M) were not affected by phentolamine (10(-6) M).9 The results indicate that adrenoceptors mediating positive inotropic responses in the dog ventricle are of the beta-type and that post-synaptic alpha-adrenoceptors are not involved. Phenylephrine acts mainly by releasing noradrenaline from adrenergic nerve endings and partly by a weak direct action on beta-adrenoceptors.