Comparative effects of β-carbolines on platelet aggregation and lipid membranes

The effects of 14 β-carbolines on human platelet aggregability were comparatively studied, and the effects on lipid membranes were determined. Several β-carbolines inhibited platelet aggregation induced by collagen, epinephrine, adenosine 5'-diphosphate, platelet-activating factor and thrombin. This activity was structure-dependent. Of all the compounds examined, 1-methyl-1,2,3,4-tetrahydro-β-carboline was the most potent. Treatment with 15-177 μM 1-methyl-1,2,3,4-tetrahydro-β-carboline inhibited the aggregation responses to different stimulants by up to 50%. Its potency was comparable to or greater than that of the antiplatelet reference, aspirin. The next most effective compound was 1-methyl-3,4-dihydro-β-carboline. The structure-antiplatelet activity relationship indicated that this activity is reduced by oxidation to 1-methyl-β-carboline, by demethylation to 1,2,3,4-tetrahydro-β-carboline and by 6-hydroxylation, 7-hydroxylation and 3-carboxylation. Active 1-methyl-1,2,3,4-tetrahydro-β-carboline fluidized biomimetic membranes at 25-250 μM which corresponded to the antiaggregatory concentrations, although relatively inactive 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-β-carboline showed no significant effects on the membranes. β-Carbolines are considered to be effective antiplatelet agents that inhibit human platelet aggregation by interacting with lipid membranes to modify fluidity.     

Effects of harmane and other β-carbolines on apomorphine-induced licking behavior in rat

Harmane, harmine and norharmane are β-carboline compounds which have been referred to as inverse agonists of benzodiazepine receptors. The effect of these compounds on apomorphine-induced licking behavior was studied in rats. Subcutaneous (s.c.) injection of apomorphine (0.5 mg/kg) induced licking. The licking behavior was counted with a hand counter and recorded for a period of 75 min by direct observation. Intraperitoneal (i.p.) injections of harmane (1.25-5 mg/kg), harmine (2.5-10 mg/kg) and norharmane (1.25-5 mg/kg) significantly reduced the licking behavior. In rats pretreated with reserpine (5 mg/kg, i.p., 18 h before the test), the effects of harmane (4 mg/kg, i.p.), harmine (7.8 mg/kg, i.p.) and norharmane (2.5 mg/kg, i.p.) were unchanged. When flumazenil (2 mg/kg, i.p.) was administered 20 min before apomorphine, it was able to antagonize the effects of harmane, harmine and norharmane. It was concluded that the β-carbolines harmane, harmine and norharmane reduce the licking behavior via an inverse agonistic mechanism located in the benzodiazepine receptors.     

Interaction of N-benzoyl-D-phenylalanine and related compounds with the sulphonylurea receptor of β-cells

1. The structure activity relationships for the insulin secretagogues N-benzoyl-D-phenylalanine (NBDP) and related compounds were examined at the sulphonylurea receptor level by use of cultured HIT-T15 and mouse pancreatic β-cells. The affinities of these compounds for the sulphonylurea receptor were compared with their potencies for K_ATP-channel inhibition. In addition, the effects of cytosolic nucleotides on K_ATP-channel inhibition by NBDP were investigated.
2. NBDP displayed a dissociation constant for binding to the sulphonylurea receptor (K_D value) of 11 μM and half-maximally effective concentrations of K_ATP-channel inhibition (EC₅₀ values) between 2 and 4 μM (in the absence of cytosolic nucleotides or presence of 0.1 mM GDP or 1 mM ADP).
3. In the absence of cytosolic nucleotides or presence of GDP (0.1 mM) maximally effective concentrations of NBDP (0.1–1 mM) reduced K_ATP-channel activity to 47% and 44% of control, respectively. In the presence of ADP (1 mM), K_ATP-channel activity was completely suppressed by 0.1 mM NBDP.
4. The L-isomer of N-benzoyl-phenylalanine displayed a 20 fold lower affinity and an 80 fold lower potency than the D-isomer.
5. Introduction of a p-nitro substituent in the D-phenylalanine moiety of NBDP did not decrease lipophilicity but lowered affinity and potency by more than 30 fold.
6. Introduction of a p-amino substituent in the D-phenylalanine moiety of NBDP (N-benzoyl-p-amino-D-phenylalanine, NBADP) reduced lipophilicity and lowered affinity and potency by about 10 fold. This loss of affinity and potency was compensated for by formation of the phenylpropionic acid derivative of NBADP. A similar difference in affinity was observed for the sulphonylurea carbutamide and its phenylpropionic acid derivative.
7. Replacing the benzene ring in the D-phenylalanine moiety of NBDP by a cyclohexyl ring increased lipophilicity, and the K_D and EC₅₀ values were slightly lower than for NBDP. Exchange of both benzene rings in NBDP by cyclohexyl rings further increased lipophilicity without altering affinity and potency.
8. This study shows that N-acylphenylalanines interact with the sulphonylurea receptor of pancreatic β-cells in a stereospecific manner. Their potency depends on lipophilic but not aromatic properties of their benzene rings. As observed for sulphonylureas, interaction of N-acylphenylalanines with the sulphonylurea receptor does not induce complete inhibition of K_ATP-channel activity in the absence of inhibitory cytosolic nucleotides.

     

Attenuation of scopolamine-induced impairment of spontaneous alternation behaviour by antagonist but not inverse agonist and agonist β-carbolines

Mice were tested in a simple automated Y-maze. Total number of arm entries and alternation behaviour were measured. The latter is thought to reflect working memory capacity at a rudimentary level. During an 8-min session, vehicle-treated mice performed 32.4±7.4 arm entries, 51.0±12.4% of which were organized in alternations (triplets). The two variables showed a negative correlation. Scopolamine (1.0 mg/kg) significantly enhanced activity, reduced alternation behaviour and diminished the correlation between the two variables. The effects of benzodiazepine receptor inverse agonist, antagonist and agonist -carbolines on this spontaneous behaviour and on the effects of scopolamine were examined. The effects of inverse agonists and agonists on locomotor activity were complex in interaction with both vehicle and scopolamine. The scopolamine-induced reduction of alternation behaviour was significantly reversed by the antagonist ZK 93426 but not by inverse agonists; furthermore, partial agonists and agonists showed no effects. It is hypothesized that the interaction of antagonist -carbolines with scopolamine is based on a direct GABA-ergic control of cholinergic neurotransmission, and suggests an ability of antagonist -carbolines to antagonize amnestic properties of scopolamine.     

Discriminative stimulus properties of β-carbolines characterized as agonists and inverse agonists at central benzodiazepine receptors

The discriminative stimulus properties of three -carboline derivatives were studied in three groups of rats trained, respectively, to discriminate diazepam (2.5 mg/kg IP), chlordiazepoxide (CDP, 5 mg/kg IP) or pentylenetetrazol (PTZ, 15 mg/kg IP) from saline in standard procedures employing two-lever operant chambers. Two -carbolines, ZK 91296 and ZK 93423, substituted for the benzodiazepines in both CDP- and diazepam-trained rats. The neutral benzodiazepine antagonist Ro 15-1788 blocked the diazepam discriminative stimulus and the ability of ZK 91296 to substitute for diazepam. A third -carboline, FG 7142, was not identified as benzodiazepine-like in generalization tests in either diazepam- or CDP-trained rats, but when administered together with CDP antagonized the benzodiazepine discriminative stimulus. In rats trained to discriminate PTZ from saline (a discrimination which is thought to depend on the anxiogenic properties of PTZ) the PTZ cue was antagonized by diazepam and ZK 93423, and partially antagonized by ZK 91296. The PTZ cue generalized to FG 7142 and this generalization was partially antagonized by Ro 15-1788. These results suggest that the three -carbolines provide more than one kind of discriminative stimulus, consistent with the classification of ZK 93423 as an agonist at central benzodiazepine receptors, with ZK 91 296 as a partial agonist, and with FG 7142 as an inverse agonist. Pharmacologically, ZK 93 423 and ZK 91 296 may exhibit anxiolytic qualities, whereas FG 7142 produces anxiogenic effects.     

Comparison of the in vitro binding characteristics of the β-carbolines harman and norharman in rat brain and liver and in bovine adrenal medulla

The in vitro binding of the naturally occurring -carbolines harman and norharman in their tritium-labelled forms to cell membranes from the rat brain and liver and from bovine adrenal medulla was investigated. Displacement of the specific [³H]harman binding in bovine adrenal medulla and rat liver by several -carbolines and monoamine oxidase (MAO) inhibitors revealed the pharmacological profile of a single, high-affinity binding site (K _D 4.92±0.43 nmol/l, B_max 8.47±0.17 pmol/mg protein; adrenal medulla) which corresponded to the active site of MAO type A (MAO-A). Similar characteristics have previously been found for brain tissue from rat, marmoset and pig. In order to determine the temperature dependence of the [³H]harman binding, the K _D and B_max values for rat cerebral cortex were calculated from the results of saturation experiments at 5 temperatures (range: 0°C–37°C). Whereas the B_max values under all conditions were – 4 pmol/mg protein, the K _D values, with increasing temperature, ranged from 3 nmol/l to 30 nmol/l. The calculated linear van't Hoff plot (-In K _D against 1/T) suggested an enthalpy-driven binding of [³H]harman to MAO-A.At least three different [³H]norharman-binding sites were detected. In the rat forebrain, 85% of the specific binding (at about 2 nmol/l of [³H]norharman) can be attributed to a MAO binding site of type B: the binding is displaceable, in nmol/l concentrations by the potent and selective MAO-B inhibitors MDL 72,974A, R(–)-deprenyl and pargyline and, in mol/l concentrations, by S(+)-deprenyl and the potent and selective MAO-A inhibitors clorgyline, harmine, harman, harmaline, brofaromine 5-F--methyltryptamine. After suppression of the MAO binding sites with 1 mol/l clorgyline and mol/l R(–)-deprenyl, a second binding site was found. However, the binding at this site was biphasically displaceable by harman and norharman (Hill-slopes about 0.5 and 0.6, curvilinear Rosenthal plots) suggesting the presence of negative co-operativity or of two binding sites (states). A similar clorgyline/R(–)-deprenyl resistent single (Hill-slopes of displacement by norharman, harman and 6-hydroxy--carboline about unity; linear Rosenthal plots) high affinity binding site (K _D 7.5±2 nmol/l, B_max 130±30 fmol/mg protein) was found in bovine adrenal medullary cell membranes. A third quite different clorgyline/R(–)-deprenyl resistent high-affinity (K _D14 nmol/l) and high-density (B_max 10–30 pmol/mg protein) binding site was detected in the liver. The specific binding at this site was not displaceable by harman or most other substituted -carbolines or by tetrahydro--carbolines, but was displaced by norharman and several newly synthesized 6-substituted aromatic -carbolines (e.g. F-, CH₃-, CH₃O-, HO-). The [³H]norharman binding site in the liver is certainly not identical with any of the binding sites for MAO-inhibitors, benzodiazepines or sigma receptor ligands and is slightly enriched in the microsomal (P₃) fraction whereas most of the specific [³H]harman binding was detected in the crude mitochondrial (P₂) fraction. Correspondence to: T. May at the above address     

Kinetic profile of N,N-dimethyltryptamine and β-carbolines in saliva and serum after oral administration of ayahuasca in a religious context

Ayahuasca is a beverage obtained from Banisteriopsis caapi plus Psychotria viridis. B. caapi contains the β-carbolines harmine, harmaline, and tetrahydroharmine that are monoamine oxidase inhibitors and P. viridis contains N,N-dimethyltryptamine (DMT) that is responsible for the visionary effects of the beverage. Ayahuasca use is becoming a global phenomenon, and the recreational use of DMT and similar alkaloids has also increased in recent years; such uncontrolled use can lead to severe intoxications. In this investigation, liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used to study the kinetics of alkaloids over a 24 h period in saliva and serum of 14 volunteers who consumed ayahuasca twice a month in a religious context. We compared the area under the curve (AUC), maximum concentration (C_max), time to reach C_max (T_max), mean residence time (MRT), and half-life (t_1/2), as well as the serum/saliva ratios of these parameters. DMT and β-carboline concentrations (C_max) and AUC were higher in saliva than in serum and the MRT was 1.5–3.0 times higher in serum. A generalized estimation equations (GEEs) model suggested that serum concentrations could be predicted by saliva concentrations, despite large individual variability in the saliva and serum alkaloid concentrations. The possibility of using saliva as a biological matrix to detect DMT, β-carbolines, and their derivatives is very interesting because it allows fast noninvasive sample collection and could be useful for detecting similar alkaloids used recreationally that have considerable potential for intoxication.     

Determination of dimethyltryptamine and β-carbolines (ayahuasca alkaloids) in plasma samples by LC-MS/MS

Background: Ayahuasca is a psychoactive plant beverage originally used by indigenous people throughout the Amazon Basin, long before its modern use by syncretic religious groups established in Brazil, the USA and European countries. The objective of this study was to develop a method for quantification of dimethyltryptamine and β-carbolines in human plasma samples. Results: The analytes were extracted by means of C18 cartridges and injected into LC-MS/MS, operated in positive ion mode and multiple reaction monitoring. The LOQs obtained for all analytes were below 0.5 ng/ml. By using the weighted least squares linear regression, the accuracy of the analytical method was improved at the lower end of the calibration curve (from 0.5 to 100 ng/ml; r(2)> 0.98). Conclusion: The method proved to be simple, rapid and useful to estimate administered doses for further pharmacological and toxicological investigations of ayahuasca exposure.     

Analytical techniques for the determination of tryptamines and β-carbolines in plant matrices and in psychoactive beverages consumed during religious ceremonies and neo-shamanic urban practices

The consumption of ayahuasca, a hallucinogenic beverage used by indigenous communities in the Amazon, is increasing worldwide due to the expansion of syncretic religions founded in the north of Brazil in the first half of the twentieth century, such as Santo Daime and Uni?o do Vegetal. Another example is the jurema wine, a drink that originated from indigenous cultures of the northeast of Brazil. It is currently used for several religious practices throughout Brazil involving urban neo-shamanic rituals and syncretic Brazilian religions, such as Catimbó and Umbanda. Both plant products contain N,N-dimethyltryptamine which requires co-administration of naturally occurring monoamine oxidase inhibitors, for example β-carboline derivatives, in order to induce its psychoactive effects in humans. This review explores the cultural use of tryptamines and β-carbolines and focuses on the analytical techniques that have been recently applied to the determination of these compounds in ayahuasca, its analogues, and the plants used during the preparation of these beverages.     

Separation of stereoisomers of sertraline and its related enantiomeric impurities on a dimethylated β-cyclodextrin stationary phase by HPLC

A reversed-phase high-performance liquid chromatographic (HPLC) method was developed and validated for evaluating the chiral discrimination ability of CYCLOBOND I 2000 DM chiral stationary phase (CSP) towards sertraline and its related enantiomers. The effect of pH, buffer concentration as well as nature of organic modifier, flow rate and temperature on enantioselectivity was investigated. The developed reversed-phase chromatographic conditions were able to separate not only the enantiomers of sertraline but also its process related chiral impurities. The method was validated for determination of enantiomeric purity of sertraline HCl in drug substances and formulations.     

Investigation of the Drug–Drug Interaction Between α-Lipoic Acid and Valproate via Mitochondrial β-oxidation

Purpose  To investigate the potential drug–drug interaction (DDI) between lipoic acid (LA) and valproate (VA) via the mitochondrial β-oxidation pathway in rats. Methods   In vitro mitochondrial assays were performed to compare the biotransformation of VA to valproyl-CoA (VA-CoA), in the absence and presence of LA. In vitro microsomal and protein binding assays were performed to elucidate their potential DDI at the microsomal metabolism and distribution levels. A pharmacokinetic study was conducted in Lister Hooded rats to ascertain the in vivo DDI between LA and VA. Results  LA was shown to decrease significantly (p < 0.05) the in vitro formation of VA-CoA in a concentration-dependent manner. Our in vitro assay results confirmed that there was minimal interaction between LA and VA in microsomal metabolism and protein binding. Based on the pharmacokinetic data, the absolute bioavailability of VA was determined to be 1.3 in the presence of LA. Conclusions  Our study demonstrated for the first time that there is a potential DDI between LA and VA at the mitochondrial β-oxidation level. While further clinical study is essential, our preliminary finding suggested that medical practitioners need to be prudent when managing epileptic patients who are co-administered with both VA and LA.     

“Anxiolytic” and “anxiogenic” benzodiazepines and β-carbolines: effects on aggressive and social behavior in rats and squirrel monkeys

Ethopharmacological studies on the behavior of socially housed rats and squirrel monkeys were conducted to explore the role of the benzodiazepine GABA_A-coupled ionophore receptor complex in aggressive and social interactions. Benzodiazepine receptor (BZR) antagonists, ZK 93426 (1–10 mg/kg) and flumazenil (3–10 mg/kg), the partial agonist, ZK 91296 (1–10 mg/kg) and the partial inverse agonists RO 15-4513 (0.3–10 mg/kg), were administered to (1) squirrel monkeys prior to 1 h focal observations within established social groups or to (2) resident male rats before confrontations with a naive male intruder in their home cage for 5 min. Aggression was modified in a similar manner in both species, although squirrel monkeys were more sensitive to BZR challenges. Specifically, resident male rats showed dose dependent reductions in attack bites directed at intruder males that were significant at the highest dose of ZK 93426 (10 mg/kg). In squirrel monkeys, ZK 93426 (3 and 10 mg/kg) reduced aggressive grasps, threats and displays, as well as reducing the duration of being the target of aggression from untreated group members (1–10 mg/kg). The BZR partial agonist, ZK 91296 and the antagonist, flumazenil produced few effects on social behavior, low and high intensity aggression and motor activity in both species. Flumazenil (10–30 mg/kg) and ZK 91296 (10 mg/kg), but not ZK 93426, produced significant increases in foraging and feeding behaviors in squirrel monkeys. The hyperphagic effects of ZK 91296 and flumazenil, that are typical of BZR agonists compounds, were not observed in rats. Similarly, the inverse agonist-like reductions in social interactions produced by ZK 93426 (3–10 mg/kg) were observed only in squirrel monkeys. The partial inverse agonist Ro 15-4513 reduced aggression in rats, but low doses (1 mg/kg) produced tremors or seizures in 80% of the monkeys tested. Decreases in aggressive and social behaviors are often interpreted to reflect anxiogenic drug properties, whereas increased feeding has been associated with anxiolytic actions. The concurrent emergence of these apparent opposites suggests independent actions on social and alimentary functions.     

Synthesis and β-Adrenergic Activities of R-Fluoronaphthyloxypropanolamine

Purpose. Many biogenic amines where an aromatic proton is substituted with fluorine have exhibited pharmacological properties that are dependent on the position of fluorine on the aromatic ring. For example, 6-fluoroepinephrine is selective for -adrenergic receptors whereas the 2-fluoroisomer is selective for -receptors. Aryloxypropanolamines are -receptor agonists or antagonists, depending on the aryl group and its substituents. We therefore hypothesized that fluorine substitution on the aromatic ring could lead to significant biological effects in this class. A target with fluorine on naphthyl group of a known -antagonist was chosen for investigation. Methods. Synthesis of the target compound began with fluoronaphthalene and involved introduction of 4-hydroxy group by Friedel-Crafts acylation followed by Baeyer Villiger oxidation. The side chain was introduced stereoselectively using the chiral synthon (2R)-glycidyl 3-nitrobenzenesulfonate, a Sharpless epoxidation technique. The epoxide was opened with t-butyl amine. HPLC methods were used to characterize %ee of the enantiomer. Results. The target compound was synthesized in several hundred milligram quantity, and in good yield and high enantiomeric excess, showing practicality of the synthetic scheme. It exhibited potent binding activities on -adrenergic receptors, and was found to be two times selective for ₂-receptors over ₁. Conclusions. The current report demonstrates that aromatic fluorine substitution on -adrenergic ligands can be achieved, and that such can be used to obtain binding selectivity between receptors.     

Effects of β2-agonist- and dexamethasone-treatment on relaxation and regulation of β-adrenoceptors in human bronchi and lung tissue

1. Long-term treatment with β₂-adrenoceptor agonists can lead to a decreased therapeutic efficacy of bronchodilatation in patients with obstructive pulmonary disease. In order to examine whether or not this is due to β-adrenoceptor desensitization, human bronchial muscle relaxation was studied in isolated bronchial rings after pretreatment with β₂-adrenoceptor agonists. Additionally, the influence of pretreatment with dexamethasone on desensitization was studied.
2. The effect of β₂-agonist incubation alone and after coincubation with dexamethasone on density and affinity of β-adrenoceptors was investigated by radioligand binding experiments.
3. In human isolated bronchi, isoprenaline induces a time- and concentration-dependent β-adrenoceptor desensitization as judged from maximal reduction in potency by a factor of 7 and reduction of 73±4% in efficacy of isoprenaline to relax human bronchial smooth muscle.
4. After an incubation period of 60 min with 100 μmol l⁻¹ terbutaline, a significant decline in its relaxing efficacy (81±8%) and potency (by a factor 5.5) occurred.
5. Incubation with 30 μmol l⁻¹ isoprenaline for 60 min did not impair the maximal effect of a subsequent aminophylline response but led to an increase in potency (factor 4.4).
6. Coincubation of dexamethasone with isoprenaline (120 min; 30 μmol l⁻¹) preserved the effect of isoprenaline on relaxation (129±15%).
7. In radioligand binding experiments, pretreatment of lung tissue for 60 min with isoprenaline (30 μmol l⁻¹) resulted in a decrease in β-adrenoceptor binding sites (B_max) to 64±1.6% (P<0.05), while the antagonist affinity (K_D) for [³H]-CGP-12177 remained unchanged.
8. In contrast, radioligand binding studies on lung tissue pretreated with either dexamethasone (30 μmol l⁻¹) or isoprenaline (30 μmol l⁻¹) plus dexamethasone (30 μmol l⁻¹) for 120 min did not lead to a significant change of B_max (160±22.1% vs 142.3±28.7%) or K_D (5.0 nmol l⁻¹ vs 3.5 nmol l⁻¹) compared to the controls.
9. In conclusion, pretreatment of human bronchi with β-adrenoceptor agonists leads to functional desensitization and, in lung tissue, to down-regulation of β-adrenoceptors. This effect can be counteracted by additional administration of dexamethasone. Our model of desensitization has proved useful for the identification of mechanisms of β-adrenoceptor desensitization and could be relevant for the evaluation of therapeutic strategies to counteract undesirable effects of long-term β-adrenoceptor stimulation.

     

Screening and identification of genes related to myasthenia gravis

Background and Purpose: Myasthenia gravis (MG) is considered as an autoimmane disease mediated by circulating antibodies against acetylcholine receptor (AChR).The thymus frequently shows abnormalities including hyperplasia and thymoma. The susceptibility to disease is likely to involve multiple genes, such as HLA haplotype, a subunit gene (CHRNA1), immunglobulin gene and T-Cell antigen receptor gene.The immunopathogenesis of MG has been clearly demonstrated by     

Different steric characteristics of β1- and β2-adrenoceptors

Summary -Adrenoceptors of lung (75% ₂) and heart (95% ₁) of calf were labelled with ³H-(–)-propranolol. The stereoisomers of 10 ligands were used to inhibit the binding of ³H-(–)-propranolol to membrane particles. The affinity ratio of sereoisomers is consistently greater for ₁-adrenoceptors than for ₂-adrenoceptors, regardless of whether the ligands are agonists, partial agonists or antagonists. The ₁-adrenoceptor appears to possess stricter steric requirements than the ₂-adrenoceptor. This property may prove helpful in differentiating the -adrenoceptor subtypes during receptor solubilization and purification.     

The effects of chronic dosing on the β1 and β2-adrenoceptor antagonism of betaxolol and atenolol

Summary Six normal subjects were given once daily treatment for 15 days with placebo (PL), betaxolol 10 mg (B10), 40 mg (B40); atenolol 100 mg (A100); and nadolol 40 mg (N40). Measurements of ₁-adrenoceptorblockade (reduction of exercise heart rate) and of ₂-adrenoceptor-blockade (attenuation of isoprenaline induced finger tremor) were made after the first, eighth and fifteenth doses of each drug.Plasma concentrations showed dose related increases between 10 mg and 40 mg doses of betaxolol, and there was significant drug accumulation at steady state compared with after single dosing. The reduction in exercise heart rate (EHR) with B10 was less in comparison with all other treatments.There were no significant differences in effects between single and chronic-dosing for any of the treatments (% reduction EHR compared with placebo, on days 1 and 15): B10 (18.2, 19.0), B40 (28.6, 26.5); A100 (22.7, 23.1); N40 (26.6, 23.8). Dose-ratios for attenuation of isoprenaline-induced finger tremor (IT₁₀₀) were significantly greater with B40 compared with B10 or A100 (no dose-ratio for finger tremor could be calculated for N40).There were no differences between single and chronic-dosing (IT₁₀₀ dose-ratios on days 1 and 15): B10 (3.0, 2.5), B40 (4.4, 5.3); A100 (3.0, 3.0). The attenuation of isoprenaline-induced chronotropic response (IH₂₅) by N40 was significantly greater in comparison with all other treatments. IH₂₅ dose-ratios (on days 1 and 15) were as follows: B10 (2.8, 3.6), B40 (5.1, 5.8); A100 (3.6, 3.6); N40 (19.0, 17.4).Thus, despite drug accumulation after chronic-dosing, there was no evidence of any increase in either ₁ or ₂-adrenoceptor antagonism at steady-state in comparison with after single-dosing. The apparent dissociation between plasma concentration and -adrenoceptor antagonism after chronic-dosing my be a consequence of -adrenoceptor up-regulation, resulting in partial attenuation of -blockade.     

Detection and quantitation of β-blockers in plasma and urine

β-blockers are a class of antihypertensive drugs that are used for the management of cardiac arrhythmias, cardioprotection after myocardial infarction (heart attack) and hypertension. They have revolutionized the medical management of angina pectoris and are recommended as first-line agents by national and international guidelines. Although β-blockers are still the cornerstone for the treatment of heart failure, some of the drugs in this category are prohibited in several sports requiring vehicle control and bodily movements as they reduce heart rate and tremors, and improve performance. As a result, urine analysis of β-blockers is mandatory in doping control and toxicological screening. The determination of plasma levels of β-blockers helps to ensure noncompliance in patients with persistent hypertonia to confirm the diagnosis of β-blocker poisoning and for therapeutic drug monitoring. This review provides a comprehensive account of various analytical methods developed for detection and quantitation of β-blockers in plasma and urine.     

Differential aversive stimulus properties of β-phenylethylamine and of d-amphetamine

In a conditioned taste-aversion experiment with male Wistar rats (two-bottle test, single pairing), the effects of -phenylethylamine (PEA 12.5, 25.0, 50.0, 100.0 mg/kg IP) and of d-amphetamine (2.5 mg/kg IP) were compared with the effect of the saline vehicle. The amphetamine-treated group exhibited a marked aversion to saccharin on each of four retention trials. A decrease in saccharin intake after PEA was limited to the highest dose group (100 mg/kg) and the first retention trial for that group. Doses of up to 50 mg/kg of PEA were also ineffective with a single-bottle conditioned taste-aversion procedure involving multiple conditioning trials, although doses of 25 and 50 mg/kg of PEA induced marked changes in spontaneous motor activity. These data demonstrate that behaviourally active doses of PEA are ineffective in inducing a conditioned taste aversion to saccharin. This result extends previous reports that structurally similar compounds may have different potencies in this paradigm. It is proposed that further studies of structureactivity relationships may help to reveal the features of drug action that are necessary for the induction of a conditioned taste aversion.     

Bioavailability of β-acetyldigoxin after single and repeated doses of tablets and solution

Summary In eight healthy volunteers the bioavailability of -acetyldigoxin solution and tablets was measured after single and multiple doses. Plasma and urine data were used to calculate bioavailability by four different methods. The differences obtained and the interindividual variations suggested that different and independent methods should be employed to assess absolute and true bioavailability. There was no significant difference between the regimens and both preparations had similar bioavailability; mean values (± SD) for the solution were 68.3 ± 8.7 % (single dose) and 68.6±5.9 % (multiple doses), and for the tablets 72.8±7.5 % and 66.1±6.0 %, respectively. For routine measurements, single dose studies with plasma and urine sampling for 24 hours and 48 hours, respectively, were an accurate and practicable procedure.