Binding of aprindine and moxaprindine to human serum, α1-acid glycoprotein and serum of healthy and diseased humans

Summary A comparison was made between the binding of the anti-arrhythmic agents aprindine and moxaprindine to human serum, to human serum albumin (HSA), to ₁-acid glycoprotein (₁-AGP) and to a mixture of HSA and ₁-AGP. In serum from healthy volunteers (n=4) the binding of aprindine-HCl 5 µg/ml (13.8 µM) was 93.8% (SD±1.0), and that of moxaprindine-HCl 5 µg/ml (12.8 µM) was 94.1% (SD±1.1). Their binding to the mixture of ₁-AGP and albumin approximated their binding to serum. For ₁-AGP, the binding was similar for both compounds, whereas for HSA the binding of aprindine was more pronounced than that of moxaprindine: for both products the affinity coefficient for binding to ₁-AGP was about 100 times greater than that for binding to albumin. In serum from rheumatoid patients and from patients with renal failure a small but significant increase in binding of aprindine and moxaprindine was observed, approximately 1%. Increased and decreased binding was seen in serum from cirrhotic patients; for example, for aprindine the range in cirrhosis was 96.7%–79.8%, and the range in controls was 95.0%–92.4%. Free drug fraction and ₁-AGP concentration were inversely correlated. The results show that ₁-AGP plays an important role in the binding of aprindine and moxaprindine, and that alteration in the binding of the two compounds in disease states to a large extent can be explained by changes in serum ₁-AGP concentration.     

Binding of perazine to α1-acid glycoprotein

Summary The high-affinity binding of perazine to human serum-protein (non-albumin binding) was previously investigated by gel-chromatography. The immunoelectrophoretic identification of the binding agent as ₁-acid glycoprotein is described here. It was demonstrated by equilibrium dialysis that the average free fraction of³H-perazine added to 22 sera from patients before neuroleptic treatment was 3.67±0.42%, and that there was a significant correlation between the ₁-acid glycoprotein content and the free fraction in these serum samples. This result is in accordance with what others have found for impramine. It is suggested that the nature of this binding should be studied in more detail, since specific binding to ₁-acid glycoprotein may be related to the receptor binding of perazine and possibly other drugs.A preliminary summary of the present findings appeared in Naunyn-Schmiedebergs Arch Pharmacol 307 (Suppl) R 70 (1979)     

Characterization of thymoquinone binding to human α₁-acid glycoprotein

Thymoquinone (TQ) is the main bioactive component isolated from Nigella sativa essential oil and seeds and has been used for the treatment of inflammations, liver disorders, arthritis, and is of great importance as a promising therapeutic drug for different diseases including cancer. This paper reports the first experimental evidence on binding of TQ to human α(1)-acid glycoprotein (AGP), an important drug-binding glycoprotein in human plasma, which affects pharmacokinetic properties of various therapeutic agents. The interaction of TQ with AGP has been characterized by Fourier transform infrared (FTIR) and fluorescence spectroscopy, as well as by molecular docking experiments. FTIR spectroscopy showed that the binding of TQ to AGP slightly increases its thermal stability and shifts the existence of a molten globule-like state observed in a previous study to higher temperature. The binding constants K(a); the number of binding sites n; and the corresponding thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated through fluorescence spectroscopy. Fluorescence quenching experiments indicated that TQ binding involves hydrophobic interactions and to a lower extent hydrogen bonds, in agreement with molecular docking experiments. The data on binding ability of TQ to AGP represent basic information for the TQ pharmacokinetics such as drug metabolism and distribution in the body.     

Binding of 16α-gitoxin and its 16-acetate to human serum albumin

Summary The binding of semi-synthetic (16-gitoxin and its 16-acetate) and naturally occurring cardioactive glycosides (digitoxin, ouabain) to human serum albumin was studied using equilibrium dialysis, ultracentrifugation and gel filtration. 16-gitoxin was 75% bound and its 16-acetate 95%. The percentage binding of digitoxin and ouabain was in good agreement with values reported in literature.     

Binding of new aminopropan-2-ol compounds to bovine serum albumin, α1 acid glycoprotein and rat serum using equilibrium dialysis and LC/MS/MS

BackgroundThe binding of three new aminopropan-2-ol compounds briefly called 2F109, ANBL and TWo8 with potential cardiovascular activity to bovine serum albumin (BSA), α₁-acid glycoprotein (AGP) and to rat serum was studied. The chemical structures of these compounds are related to carvedilol. They possess an antiarrhythmic and hypotensive activity, and β- and α-adrenolytic mechanism of action. All analogues are weak bases with pKa values 8.65,8.85 and 8.26 for 2F109, ANBL and TWo8, respectively, and they possess lipophilic character (log P > 1.9584).MethodsThe extent of protein binding was determined using equilibrium dialysis in the range 2.5 – 900 μM, and 2.5 – 300 μM for binding of investigated compounds to BSA and AGP, respectively, and the quantitative measurement was done by LC/ESI-MS/MS assay.ResultsThe studied compounds bound to a single class of binding sites on BSA which was characterized by low affinity (K_d for 2F109 = 8.49 × 10^–5 M, for ANBL = 1.92 × 10^–5 M, and for TWo8 = 1.71 × 10^–5 M) and low capacity(n = 0.53 for 2F109,0.132 for ANBL and 0.13 for TWo8). The binding of 2F109, ANBL and TWo8 to AGP revealed one class of binding sites, with moderate affinity (K_d for 2F109 = 4.67 × 10^–6 M, for ANBL = 3.48 × 10^–5 M, and for TWo8 = 1.13 × 10^–5 M) and higher capacity (n = 2.21 for 2F109, 2.76 for ANBL and 2.28 for TWo8).ConclusionThe obtained data indicate that 2F109, ANBL and TWo8 moderately bind to BSA (34.2 – 71.2%) with low capacity (K_a = 6.21 × 10³–7.61 × 10³ M^–1)and strongly bind to AGP(71.5–85.5%)with moderate affinity (K_a = 7.94 × 104⁴.73 ×10⁵ M^–1).     

How do fatty acids cause allosteric binding of drugs to human serum albumin?

Purpose. This study was undertaken to investigate how fatty acids cause the allosteric binding of drugs to human serum albumin (HSA). The influence of fatty acids on the binding of ketoprofen (KP), an NSAID, to HSA was examined by using a photoaffinity labeling technique. Methods. Ultrafiltration was performed to quantitate the concentration of free KP. HSA, photolabeled with KP in the presence of myristate (MYR), octanoate, and diazepam, was cleaved with cyanogen bromide, separated by Tricine sodium dodecyl sulfate polyacrylamide gel electrophoresis and subsequently analyzed by autoradiography. Results. The addition of MYR at molar ratios from 4 to 5, but not from 1 to 2, causes substantial increases in unbound KP for KP:HSA ratios of 0.5 and 1. The addition of two or more moles of MYR, octanoate, and diazepam per mole of HSA caused a pronounced decrease in the labeling of the 11.6- and 13.5-kDa peptides. However, only MYR showed an increase in labeling of the 20 kDa and, especially, the 9.4-kDa peptides. At MYR:HSA ratios in excess of 3, a decrease in the extent of labeling of the 9.4-kDa peptide was observed. Conclusion. Long-chain fatty acids regulate the binding properties of HSA in a complex manner, in which a simultaneous competitive and allosteric mechanism operates and which mainly involves domain I.     

Structure-activity relationships for the binding of polymyxins with human α-1-acid glycoprotein

Here, for the first time, we have characterized binding properties of the polymyxin class of antibiotics for human α-1-acid glycoprotein (AGP) using a combination of biophysical techniques. The binding affinity of colistin, polymyxin B, polymyxin B(3), colistin methansulfonate, and colistin nona-peptide was determined by isothermal titration calorimetry (ITC), surface plasma resonance (SPR) and fluorometric assay methods. All assay techniques indicated colistin, polymyxin B and polymyxin B(3) display a moderate binding affinity for AGP. ITC and SPR showed there was no detectable binding affinity for colistin methansulfonate and colistin nona-peptide, suggesting both the positive charges of the diaminobutyric acid (Dab) side chains and the N-terminal fatty acyl chain of the polymyxin molecule are required to drive binding to AGP. In addition, the ITC and fluorometric data suggested that endogenous lipidic substances bound to AGP provide part of the polymyxin binding surface. A molecular model of the polymyxin B(3)-AGP F1*S complex was presented that illustrates the pivotal role of the N-terminal fatty acyl chain and the D-Phe6-L-Leu7 hydrophobic motif of polymyxin B(3) for binding to the cleft-like ligand binding cavity of AGP F1*S variant. The model conforms with the entropy driven binding interaction characterized by ITC which suggests hydrophobic interactions coupled to desolvation events and conformational changes are the primary driving force for polymyxins binding to AGP. Collectively, the data are consistent with a role of this acute-phase reactant protein in the transport of polymyxins in plasma.     

The contribution of α 1-acid glycoprotein,lipoproteins, and albumin to the plasma binding of perazine,amitriptyline, and nortriptyline in healthy man

Summary Parameters for the binding of perazine (PER), amitriptyline (AT) and nortriptyline (NT) to plasma and to single plasma proteins were determined by equilibrium dialysis. The highest affinity (K at least 10⁵ M^–1) and lowest capacity (first site 1 mol/mol) towards all three drugs was exhibited by ₁-acid glycoprotein (₁-AGP). From the parameters, ₁-AGP was estimated to contribute 43% to total binding of PER and 49 and 31%, respectively, to AT and NT binding in samples with normal protein concentrations. Fractions bound to total lipoproteins would amount to 32% (PER), 40% (AT) and 52% (NT), respectively, while the contribution of albumin would range from 11% (AT) to 25% (PER). The extent of the binding to plasma was compared with that to single proteins and their mixtures. Binding to combinations of ₁-AGP, lipoproteins and albumin exceeded that to plasma with PER, but not with AT and NT. This leads to the assumption that additional plasma constitutents interfere with PER binding.     

Binding of diuretic antihypertensive bendroflumethiazide to human serum albumin studied by 1?F nuclear magnetic resonance method

Simultaneous specific and nonspecific binding of bendroflumethiazide (BFZ) to human serum albumin (HSA) and concentration profile of BFZ in HSA buffer (pH 7.40) solution were investigated by 1?F nuclear magnetic resonance (NMR) method. The 1?F NMR spectrum of BFZ (200 μM) in a buffer solution showed a sharp signal of its CF? group at 17.8 ppm from the reference trifluoroethanol. Addition of 0.60mM HSA to the sample solution caused the CF(3) signal splitting into three broadened peaks at 18.4 (A), 17.9 (B) and 17.4 ppm (C). By its chemical shift and spectral behavior, B was assigned to unbound BFZ. Competition experiments with Site I and II ligands lead to C being assigned to Site II bound BFZ. However, the peak intensity (areas) of A was not reduced by these ligands, suggesting that A arises from nonspecific binding. Using the peak intensities at several total concentrations of BFZ, Scatchard plot was performed. The plot for A provided a straight line parallel to the x-axis confirming nonspecific binding and that for C was consistent with specific binding. The binding constants for nonspecific and specific Site II binding were 1.02 and 1.00 × 10? (M?1) (n=1.1), respectively. The presence of 0.10 M Cl? in the sample solution affected the binding constant of Site II binding, but not that of nonspecific binding. The concentration profile of BFZ calculated using the binding constants revealed that nonspecific binding is more effective than Site II binding for the binding of BFZ to HSA. It was also confirmed that considerable amounts of BFZ liberated from Site II by the Site II ligands or Cl? ions bind again nonspecifically.     

Differential regulation of human α1-adrenoceptor subtypes

We have compared the agonist-induced downregulation of human α_1A-, α_1B- and α_1D-adrenoceptors upon stable expression in rat-1 fibroblasts. During a 24-h incubation the agonist phenylephrine downregulated α_1A- and α_1B-adrenoceptors in a concentration-dependent manner. While maximum downregulation was similar for both subtypes, the threshold concentration for significant reductions was markedly higher for α_1A- than for α_1B-adrenoceptors (10 μM vs. 100 nM). The downregulation of both subtypes by 100 μM phenylephrine was time-dependent, and significant reductions were observed already after 2– 4 h. In contrast, incubation of α_1D-adrenoceptor-expressing cells with phenylephrine increased receptor number in a time- and concentration-dependent manner. The downregulation of α_1B-adrenoceptors by 100 μM phenylephrine for 24 h was accompanied by a matching reduction in mRNA abundance, but no such reduction was seen for α_1A-adrenoceptors. These treatment conditions also caused a functional desensitization of agonist-stimulated inositol phosphate formation for α_1A- and α_1B- but not for α_1D-adrenoceptors. Treatment with the phorbol ester phorbol-12-myristate-13-acetate did not change receptor density or mRNA abundance and did not cause functional desensitization. We conclude that human α₁-adrenoceptor subtypes are differentially regulated by agonist treatment even if they are expressed in the same cell line. Received: 17 April 1998 / Accepted: 26 March 1999     

Influence of continuous ambulatory peritoneal dialysis on serumα 1-acid glycoprotein concentration and drug binding

Summary The influence of continuous ambulatory peritoneal dialysis (CAPD) on the concentrations of ₁-acid glycoprotein in serum and dialysate and on the serum binding of oxprenolol, propranolol and phenytoin has been studied.Before starting CAPD treatment, the serum binding of oxprenolol and propranolol was higher and that of phenytoin lower than in healthy volunteers, and the serum ₁-AGP concentration was higher. During the first days to weeks after starting CAPD, the serum ₁-AGP concentration rose with a concomitant increase in the binding of oxprenolol and propranolol. Subsequently, the ₁-AGP level and the binding of oxprenolol and propranolol decreased to the values found before starting CAPD. The binding of phenytoin showed little change. The concentration of ₁-AGP in dialysate was 2 to 5% of that in serum.     

Binding of 3H-clonidine to an α-adrenoceptor in membranes of guinea-pig ileum

Summary The binding of ³H-clonidine to membrane particles from guinea-pig ileum was investigated. The specific binding, i.e. the binding that could be inhibited by high concentrations of unlabeled clonidine or noradrenaline, was of high affinity, K _D3 nM. The number of sites was approximately 25 fmol/mg protein. Rate constants of association and dissociation were 5.3×10⁷ M^–1 min^–1 and 0.18 min^–1, respectively. Affinites of various drugs to the binding site were determined by measuring their effect on the binding of ³H-clonidine. The affinity of adrenergic agonists decreased in the order clonidine = tramazoline > (–)-erythro--methylnoradrenaline > (–)-noradrenaline (–)-phenylephrine. (–)-Noradrenaline had about 20 times more affinity than the (+)-isomer. The affinity of -adrenoceptor antagonists decreased in the order phentolamine > rauwolscine = yohimbine > WB 4101 > pseudoyohimbine > prazosin = corynanthine. Yohimbine and rauwolscine had about 100 times more affinity than their stereoisomer corynanthine. Serotonin 10 M and metiamide 10 M did not affect the binding, and propranolol inhibited it only at high concentrations. — The results indicate that ³H-clonidine labels an ₂-adrenoceptor in guinea-pig ileum. The orders of affinity of -adrenoceptor agonists and antagonists agree well with their orders of potency in functional tests, namely as modulators of cholinergic transmission in the guinea-pig ileum and as modulators of noradrenaline release in the rabbit pulmonary artery. An -adrenoceptor should be classified as ₂ when the affinities of clonidine, tramazoline and -methylnoradrenaline greatly exceed the affinity of phenylephrine, and when the affinities of rauwolscine and yohimbine exceed those of prazosin and corynanthine.     

Synthesis and blocking activities of a new class of α₁-adrenoceptor antagonists

Finding effective chemotherapeutic agents for clinical use is a long-lasting goal in medicinal chemistry. In this study, we report a new class of α₁-adrenoceptor (α₁-AR) antagonists. Specifically, we describe the synthesis and the blocking activities toward α₁-AR of 7-(2-hydroxypropoxy)-3,4-dihydroisoquinolin-1(2H)-one 1 and its structurally perturbed analogs 2 – 11 that were designed according to the principle of bioisosterism. Their structures were identified with IR, ¹H NMR, MS, HRMS and elemental analysis. The blocking activities of compounds 1 – 11 were evaluated on isolated rat anococcygeus muscles. The results indicated that these compounds showed moderate to good activities. Among them, compound 1 exhibited the highest activity that was comparable to those of known α₁-AR antagonists tamsulosin and DDPH (1-(2,6-dimethylphenoxy)-2-(3,4-di- methoxyphenylethylamino)propane hydrochloride) and thus may be exploitable as a lead compound for the discovery of promising α₁-AR antagonists.     

Intrinsic sympathomimetic activity ofβ-adrenoceptor blocking agents

Summary The pharmacological methods used to assess the intrinsic sympathomimetic activity (ISA) of -blockers are discussed. The clinical relevance of ISA to respiratory function, peripheral resistance and cardiac function is reviewed. It appears doubtful whether ISA is always of predominant clinical significance and an alternative explanation is offered for many clinical effects observed with certain -blockers, e.g. pindolol, oxprenolol, tolamolol, metoprolol, etc. Some effects of these -blockers resemble those of labetalol, a new drug with both - and -blocking activity. Some clinical effects of certain -blockers are more likely to be due to -blocking activity than to their ISA.     

Role of β2-adrenoceptor blockade and circulating adrenaline level for the pressor responses to β-adrenoceptor blocking drugs in rats

Summary The present experiments were designed to elucidate what mechanism(s) would be responsible for -adrenoceptor blocking drugs (-blockers)-induced pressor responses in rats. In urethane-anaesthetized rats, 6 -blockers at i.v. doses ranging from 0.3 to 300 g/kg evoked the pressor response in a dose-dependent manner. The relative potency in causing the pressor action was correlated not to their ₁-blocking activities (r=0.374, P>0.05) but to their ₂-blocking ones (r=0.856, P<0.05). In pithed or adrenalectomized rats with low levels of plasma catecholamines, however, propranolol failed to exert its sustained pressor action. Propranolol (300 g/kg i.v.) distinctly potentiated the pressor responses not to noradrenaline but to adrenaline and to electrical stimulation of the sympathetic outflow (E.S.) in pithed rats. On the contrary, there was not any potentiation of pressor response to E.S. in pithed, adrenalectomized rats treated with propranolol (300 g/kg i.v.). In rats treated with phenoxybenzamine (5 mg/kg i.v.), adrenaline was shown to have much more potent vasodilating action resulting from ₂-stimulation than noradrenaline, the dose difference for causing the diastolic blood pressure decrease by a 25 mm Hg being almost 80 times. In pithed rats, infusion of adrenaline at the rate of 0.02 g/min caused a significant increase in plasma adrenaline level from 0.02±0.01 to 0.45±0.048 ng/ml, being close to basal level obtained in urethane-anaesthetized rats. Under this situation, propranolol (1–100 g/kg i.v.) showed a distinct pressor response in a dose-dependent fashion as observed in adrenal intact rats anaesthetized with urethane. These results strongly suggest that the pressor responses to -blockers are largely due to both their inhibitory actions on the vasodilatory ₂-adrenoceptors and to their potentiating actions on the vascular response to circulating adrenaline.     

Quantification and distribution of α1-adrenoceptor subtype mRNAs in human proximal urethra

1. We performed RNase protection assays and in situ hybridization to investigate the ratio of the three α₁-adrenoceptor subtype mRNAs, α1a, α1b and α1d, in human proximal urethra, and their localization in urethral cross-sections. As revealed by the RNase protection assays, α1a was the predominant subtype mRNA in both male and female urethral samples. α1d mRNA was detected only in the female sample, and α1b mRNA was not detected in any of the samples tested. The ratio of the abundance of the subtype mRNAs, α1a : α1b : α1d, was 100 : 0 : 0 in the male urethra and 90 : 0 : 10 in the female urethra.
2. In situ hybridization studies showed no significant differences in the cross-sectional distribution of α₁-adrenoceptor subtype mRNAs between male and female urethras. Intense α1a staining was observed in the smooth muscle of the urethra, but α1b and α1d staining was much less intense.
3. Of the three cloned α1 subtypes, α1a is the most likely to be responsible for the contraction of the human urethra. Owing to the side effects of nonselective α₁ drugs, α₁-selective drugs may be clinically superior to nonselective drugs for the treatment of urethral disorders.

     

Dicentrine,an α-adrenoceptor antagonist with sodium and potassium channel blocking activities

To elucidate the electrophysological effect of dicentrine, an alkaloid isolated from Lindera megaphylla, we examined action potential and membrane currents in single cardiac cells. The tight-seal whole cell clamp technique was used. In the current clamp condition, 3M dicentrine prolonged rat ventricular action potential duration (APD₅₀) from 38.9±(SEM)9.8 ms to 147.8 ± 19.7 ms (n = 12) and reduced its maximal rate of depolarization ( _max) from 220.5±20.3 V/s to 37.0±4.0 V/s. The same concentration of quinidine increased APD₅₀from 42.5 ± 5.2 ms to 182.8 ± 15.6 ms (n = 6) and decreased the _max from 225.4± 19.5 V/s to 32.2±3.0 V/s. Voltage clamp study revealed that dicentrine (1 to 100 M) inhibited the integral of the transient outward current (I_to - I₂₀₀) dose-dependently with a K_D value of 3.0±0.5 M. At 50 mV, the suppression of I_to by 3 M dicentrine was accompanied by shortening of its inactivation timeconstant from 41.0±4.9 ms to 18.8±2.1 ms. V _0.5 for the steady state inactivation curve of I_to was shifted from -25.5±2.8 mV to –40.6±2.1 mV. Compared to dicentrine, quinidine exerted stronger but the same mode of inhibition of I_to. 4-Aminopyridine, however, blocked I_to without modification of its inactivation time constant. In addition to the inhibition of I_to, the late outward current (I_lo) was significantly reduced byt0 M eachof dicentrine and quinidine to 60.0±13.307o and 37.5±6.3070, respectively. 4-Aminopyridine (2 mM) failed to inhibit this current. The delayed rectifier (I_k) in guinea pig ventricular cells was also inhibited by dicentrine with IC₅₀ value between 3 and 10 M. Like quinidine, dicentrine exerted equipotent inhibition of sodium inward current but without inhibition of calcium inward current. These results indicate that dicentrine exerts cardiac effect by mode of action like class I and class III antiarrhythmic agents. Correspondence to: Ming-Jai Su at the above address     

Inhibition of human ether-a-go-go-related gene potassium channels by α1-adrenoceptor antagonists prazosin,doxazosin, and terazosin

Human ether-a-go-go-related gene (HERG) potassium channels are expressed in multiple tissues including the heart and adenocarcinomas. In cardiomyocytes, HERG encodes the -subunit underlying the rapid component of the delayed rectifier potassium current, I_Kr, and pharmacological reduction of HERG currents may cause acquired long QT syndrome. In addition, HERG currents have been shown to be involved in the regulation of cell proliferation and apoptosis. Selective 1-adrenoceptor antagonists are commonly used in the treatment of hypertension and benign prostatic hyperplasia. Recently, doxazosin has been associated with an increased risk of heart failure. Moreover, quinazoline-derived 1-inhibitors induce apoptosis in cardiomyocytes and prostate tumor cells independently of 1-adrenoceptor blockade. To assess the action of the effects of prazosin, doxazosin, and terazosin on HERG currents, we investigated their acute electrophysiological effects on cloned HERG potassium channels heterologously expressed in Xenopus oocytes and HEK 293 cells.Prazosin, doxazosin, and terazosin blocked HERG currents in Xenopus oocytes with IC₅₀ values of 10.1, 18.2, and 113.2 M respectively, whereas the IC₅₀ values for HERG channel inhibition in human HEK 293 cells were 1.57 µM, 585.1 nM, and 17.7 µM. Detailed biophysical studies revealed that inhibition by the prototype 1-blocker prazosin occurred in closed, open, and inactivated channels. Analysis of the voltage-dependence of block displayed a reduction of inhibition at positive membrane potentials. Frequency-dependence was not observed. Prazosin caused a negative shift in the voltage-dependence of both activation (–3.8 mV) and inactivation (–9.4 mV). The S6 mutations Y652A and F656A partially attenuated (Y652A) or abolished (F656A) HERG current blockade, indicating that prazosin binds to a common drug receptor within the pore-S6 region.In conclusion, this study demonstrates that HERG potassium channels are blocked by prazosin, doxazosin, and terazosin. These data may provide a hypothetical molecular explanation for the apoptotic effect of quinazoline-derived 1-adrenoceptor antagonists.     

Binding sites of α1- and α2-adrenoreceptors

Conclusions The models constructed for the binding sites of rat brain ₁-AR and ₂-AR satisfy all the steric requirements and energy characteristics of interaction with known ligands, cited in [5–7, 14]. The differences detected in the arrangement and orientation of the functional groups of the binding sites permit an explanation of a whole series of typical differences in the interaction of adrenoactive substances with both subtypes of-AR.Our analysis showed that the greatest contribution to the interaction with the receptor is made by ionic, donor-acceptor, and hydrophobic bonds. The role of van der Waals forces in the interactions examined is evidently extremely negligible. The most effective and specific preparations prove to be compounds that not only form the maximum number of donor-acceptor bonds with the receptor but also orient their own hydrophobic fragments in such a way that the ionic and donor-acceptor bonds formed between the molecule and the receptor are shielded from contact with the aqueous phase. The energy effects of hydrophobic interactions of this type may be rather substantial (3.9–3.12).The production of new synthetic preparations, for which the conditions of complementarity to the-AR will be most fully satisfied, can be carried out taking the requirements of structural correspondence of the topography of the binding sites into account.Translated from Khimiko-farmatsevticheskii Zhurnal, Vol. 18, No. 8, pp. 904–912, August, 1984.     

Stimulant and depressant effects ofβ-adrenoceptor blocking agents on isolated heart muscle

Summary The chronotropic and inotropic effects of fourteen -adrenoceptor blocking agents were studied in vitro on preparations of isolated heart muscle from kittens and guinea pigs. Most of the agents exert negative inotropic and chronotropic effects that increase rapidly with concentration above 10^–6 M. Exceptions are the closely related compounds practolol and atenolol, which have minimal depressant effects in concentrations as high as 2×10^–3 M. Dose-response relations for the depressant effects are similar for pacemaker frequency and for tension development in atrial and papillary muscle. The cardiodepressant effects of -blockers are non-stereospecific and are apparently unrelated to the actions of the drugs at -adrenoceptors. Many -blockers exert positive inotropic and chronotropic effects at concentrations lower than those that depress. The stimulant effects are slow in onset and do not fade. In most instances these effects are blocked by propranolol and may therefore be considered to be mediated through -adrenoceptors; (–)-enantiomers are more potent than (+)-enantiomers as adrenoceptor stimulants. Adrenoceptor-mediated inotropic effects are usually more pronounced in atrial than in ventricular muscle. Certain -blockers, notably INPEA and sotalol, exert positive inotropic effects that are not blocked by propranolol or phenoxybenzamine. The effects are very slow in onset and offset, and are accompanied by the development of contractions with a late tonic component which coincides with a greatly prolonged action potential. Unlike the adrenoceptor-mediated effect, the non-sympathomimetic inotropic effect is more pronounced in ventricular than in atrial muscle, and is not stereospecific. Pindolol also causes the development of a late tonic component, but the accompanying positive inotropic effect is overcome by the simultaneous development of the depressant action of the drug.