Antifibrillatory Effect of Some β-Adrenergic Receptor Blocking Agents Determined by a New Test Procedure in Mice

Mice which were exposed to high concentrations of methylchloroform (1,1,1, trichloroethane) vapour died in cardiac fibrillation. Pretreatment 30 min. before the administration of methylchloroform gave the following antifibrillatory ED50's expressed in mg/kg intraperitoneally: β-adrenergic blocking agents: Propranolol: 1.7; (+)-propranolol: 45; (-)-propranolol 0.6; 1-(isopropylamino)-3-(o-phenoxyphenoxy)-2-propanol, HC1 (Ph QA 33): 6.5; 1-(isopropylamino)-3-(o-allylphenoxy)-2-propanol, HC1 (H 56/28 = aptin®): 19; 4-(2-isopropylamino-1-hydroxyethyl) methane sulphonanilide, HC1 (MJ 1999): 24; 2-(isopropylamino)-1-(p-nitrophenyl) ethanol, HC1 (INPEA): 50; dichloroisoprenaline (DCI): no effect; α-adrenergic blocking compounds: chlorpromazine: > 50; phenoxybenzamine, HC1 (dibenzyline®): no effect, phentolamine (regitin®): > 100. None of some commonly used antiarrhythmics: antazoline, HC1; lidocaine, HC1; phenytoin; procainamide, HC1 (pronestyl®) or quinidine sulphate had any effect. The most favourable therapeutic index (LD50/ED50) was found for (-)-propranolol ～ 200. The method appears particularly suitable for evaluation of compounds with antagonistic action on cardiac β-receptors and in this respect appears to be highly sensitive.     

α1-Adrenoceptor Blocking Activity of Some Ring-open Analogues of Prazosin

Synthesis and structural characterization of some ring-open analogues of Prazosin containing either the guanidine substructure or urea-equivalent groups are described. The opening of the pyrimidine ring in Prazosin is very important as far as the affinity for α₁-adrenoceptor is concerned. The pA₂ values of the ring-open derivatives are 10⁴–10⁵ fold lower than that of the parent. It is probable that the affinity decrease principally reflects a negative influence of the conformational factors in the interaction with the α₁-receptor. The derivative 5 containing the guanidine moiety, charged at physiological pH, is as active as the other derivatives containing the uncharged urea-equivalent groups. This behaviour indicates, in this class of compounds, the importance of H-bonding interactions with the receptor. When in the ring-open models the ethanediamino substructure is substituted for the piperazine ring additional decrease in activity occurs.     

Qualitative Differences between β-Adrenergic and α-Adrenergic Inotropic Effects in Rat Heart Muscle

Abstract If β- and α-adrenergic inotropic effects are cyclic AMP dependent and cyclic AMP independent, respectively, they may be qualitatively different. The inotropic effects of β-receptor stimulation (isoprenaline) and α-receptor stimulation (phenylephrine combined with propranolol) were characterized in isolated perfused rat hearts, rat atria and rat papillary muscles. The β-effect reached its maximum before the α-effect. The α-effect followed a three-phasic time-course indicating both stimulatory and inhibitory components. The aortic pressure wave (perfused heart) indicated a shorter contraction phase after β-stimulation than after α-stimulation. The time to peak tension (atrium, papillary muscle) was relatively shorter after isoprenaline than after α-stimulation, which tended to prolong it. The contraction-relaxation cycles (atrium, papillary muscle) were examined by recording the isometric tension (T), its first (T′) and second (T″) derivatives, α- and β-stimulation both increased T_max, T′_max (maximal rate of tension rise), T′_min, (maximal rate of tension decline) and T″_min (maximal rate of transition from rise to decline of tension). Isoprenaline increased T_min, (papillary muscle) and T″_min (atrium, papillary muscle) relatively more than did α-stimulation, i.e. the relaxing processes were activated relatively more by β-stimulation. The results indicate different mechanisms for the two adrenergic inotropic effects. The relatively larger activation of relaxation by β-stimulation is assumed to be caused by cyclic AMP.     

Differences between α-Adrenergic and β-Adrenergic Inotropic Effects in Rat Heart Papillary Muscles

Abstract: α-And β-adrenergic inotropic effects have been shown to be qualitatively different. In order to further characterize these differences we compared the mechanical responses to α- and β-adrenoceptor stimulation, respectively, in electrically driven left ventricular papillary muscles from rat heart. The muscles were stimulated by either isoprenaline (β-adrenoceptor stimulation), phenylephrine in the presence of propranolol (α-adrenoceptor stimulation) or phenylephrine alone (combined α- and β-adrenoceptor stimulation). Isometric tension (T), rate of rise and decline of tension (first derivative = T′) and rate of transition from tension rise to tension decline (negative part of second derivative = T″) were recorded. These recordings disclosed qualitative differences between the α- and β-inotropic response both in dose-response and time course experiments. Maximal β-adrenoceptor stimulation caused a small increase in T_max (18%), intermediate increases in T′_max (45%) and T′_min (68%) and a considerable increase in T″_min (145%) (“β-type” effect). Maximal α-adrenoceptor stimulation increased all qualities by about the same degree (23–24%) (“α-type” effect). While β-adrenoceptor stimulation gave a dose-dependent and pronounced increase in the ratio T″_min/T′_max (relaxation-onset index), α-adrenoceptor stimulation decreased it to subcontrol values and phenylephrine alone gave a small dose-dependent increase at higher doses. The time course of the α-adrenoceptor stimulation was characterized by a transient decrease in all qualities followed by an increase which reached maximum at 4–5 min. β-Adrenoceptor stimulation gave a monophasic response which reached maximum after 1–2 min. Phenylephrine alone gave mainly an “α-type” effect although T″_min increased significantly more in the absence than in the presence of propranolol and T″_min/T′_max showed a small increase which developed slowly. Thus β-adrenoceptor stimulation activated relaxation compared to contraction by a higher degree than did α-adrenoceptor stimulation. This probably reflects different mechanisms of action. While the α-effect may rely primarily on an increased calcium influx, the β-effect probably is the final result of several subcellular effects of cyclic AMP.     

A New β2-Adrenoceptor Agonist with α1-Adrenoceptor Blocking Properties

Abstract: The phenylethanolamine D2343 exhibits a dualistic adrenoceptormediated effect, i.e. a β-agonistic effect combined with an α-antagonistic one. Tracheal smooth muscles and heart preparations were used to gauge the agonistic effect on adrenergic β-receptors. Rabbit aorta and rat vas deferens were used to determine the α-adrenoceptor blocking activity. The β-adrenoceptor activity of D2343 was classified as β₂-type with about the same efficacy as the β₂-selective terbutaline on tracheal muscle. The effect on isolated heart preparations was greater than that produced by terbutaline. The α-receptor blocking capacity was directed against the α₁-receptor type and was of nearly the same potency as for phentolamine.     

Mechanisms of β-Adrenergic Desensitization in Rat Myometrium

Abstract: This study was performed in order to elucidate the mechanism behind the decreased responsiveness to β-adrenergic stimulation occuring in uterine muscle after prolonged treatment with isoprenaline. Pretreatment of rats with isoprenaline, 20 nmol/kg, three times daily during four days, significantly decreased the myometrial relaxing effect of the β-agonist. There was also a significant decrease of the β-receptor binding capacity of the myometrial membranes measured by the (minus;)-(³H) DHA binding technique. In the animals pretreated with isoprenaline no significant increase of the adenylate cyclase activity could be observed after isoprenaline stimulation in vitro. The uterine cAMP level was diminished in the desensitized rats. The phosphodiesterase activity was increased. Thus both decreased production and increased degradation contribute to the lower level of uterine cAMP content. The activity of cAMP dependent protein kinase was also depressed. In this work, where low concentrations of isoprenaline have been administered in vivo, several biochemical parameters have been shown to contribute to the β-adrenergic desensitization in myometrial tissue.     

Synthesis of α-, β- and cyclic spaglumic acids

A short, one-pot synthesis of α- and β-spaglumic acids (N-acetyl-L-aspartyl-L-glutamic acids, NAAGA) has been developed based on ultrasound-promoted acetylation of aspartic acid, followed by dehydration, condensation with glutamic acid dibenzyl ester and hydrogenolysis. The α- and β-peptides were separated by anion-exchange chromatography. The α-peptide shows a remarkable tendency to cyclize during methylation with diazomethane and yields cyclic N-acetylaspartylglutamic acid dimethyl ester, which could be hydrolysed to the hitherto unreported diketopiperazine dicarboxylic acid, cyclic spaglumic acid (cyclic NAAGA).     

The Effect of Genistein on the Content and Activity of α‐ and β‐Secretase and Protein Kinase C in Aβ‐Injured Hippocampal Neurons

Genistein (Gen), a derivative of soy isoflavone aglycone, has been shown to exert significant protective effect on Aβ‐induced neurotoxicity and neuroinjury. However, its underlying mechanism remains elusive. The objective was to investigate the inhibitory effect of Gen on Aβ‐induced neurotoxicity and to elucidate the underlying mechanism. Primary rat hippocampal neurons were pre‐treated with Gen for 2 hr followed by incubation with Aβ 25–35 for an additional 24 hr. The cell viability was assessed by MTT assay. The content and activity of α‐, β‐secretase and protein kinase C (PKC) were measured, and the antagonistic effect of PKC inhibitor Myr was also analysed to clarify the molecular mechanism of Gen inhibition of Aβ‐induced toxicity to hippocampal neurons. The results showed that pre‐treatment with Gen significantly increased the cell viability and presented the best effect at the final concentration of 0.375 µg/mL. Gen increases the activity of α‐secretase but down‐regulates the β‐secretase activity. It also enhances the expression and activity of PKC. Myr, a PKC inhibitor, partially blocks the activation effect of Gen. Gen exerts protective effect on Aβ‐induced neurotoxicity via activating the PKC signalling pathway, which further regulates the activities of α‐ and β‐secretase and thereby inhibits the formation and toxicity of Aβ.     

Association of β-agonists with corresponding β2- and β1-adrenergic pentapeptide sequences

Synthesized β₁- and β₂-pentapeptide sequences corresponding to published adrenoceptor transmembrane activation site subtypes were investigated in vitro for selectivity in association for drug ligands of known selectivity. Both nuclear magnetic resonance spectroscopy and molecular mechanics demonstrated that structural differences among the corresponding pentapeptide activation-site sequences can explain agonist selectivity. Results suggest the agonists bind across the activation site loop on the second transmembrane α-helix by dipole/dipole interactions between a ligand and the peptide. Since electrostatic interactions within the membrane may determine the rate of intercellular ion flux, agonist association across the activation site sequence could thereby decrease electrostatic resistance to positive ion flux into the cell. Interactions between the peptides and the ligands may provide insight into the structures and mechanisms involved in association of ligands for the identical sequences on the β-adrenoreceptors.     

β-Adrenergic Responsiveness of the Gastrointestinal Tract in Diabetic Rats

Abstract: Recently, decreased gastrointestinal β-adrenergic responses in experimental diabetes have been demonstrated. Gastrointestinal responses to β-adrenoceptor agonists are impaired in both insulin-dependent and non-insulin-dependent diabetic rat. Insulin treatment improves the impaired gastrointestinal β-adrenergic responsiveness of diabetic rats. The improvement seen with insulin treatment on β-adrenergic responsiveness is closely related to protein biosynthesis. The decreased β-adrenergic responses in diabetic rat gastrointestinal tract seem to result from a decrease in the number of β-adrenoceptors. It is most likely that the decreased gastrointestinal β-adrenergic responsiveness is related to an impairment in the turnover of β-adrenoceptors as a consequence of diabetes and that insulin has a beneficial effect on the impaired receptor turnover.     

Effects of α2-Adrenergic Drugs on the Alcohol Consumption of Alcohol-Preferring Rats

The effects of seven-day subcutaneous infusion of an α₂-adrenoceptor agonist, medetomidine, and an α₂-adrenoceptor antagonist, atipamezole, on the voluntary alcohol consumption of alcohol-preferring rats were studied. The drugs were administered by means of implanted osmotic minipumps. Sham-operated control rats had no pumps implanted. The rats had a free choice between 10% alcohol and plain water for 30 days before pump implantation and again for six days starting 24 hr after the operation. Atipamezole increased the alcohol consumption during the first day of free choice. Medetomidine had no significant effect. During the remaining period of infusion, the alcohol consumption did not differ from that preceding the pump implantation in each treatment group. Animals in the atipamezole group gained more weight during the seven-day trial than did those in the medetomidine and control groups. The amine changes in different regions of the brain were consistent with medetomidine decreasing and atipamezole increasing the noradrenaline turnover. The present results indicate that specific drugs acting on the α₂-adrenoceptors produce only minor changes in the voluntary alcohol drinking of alcohol-preferring rats.     

Effect of Different β-Adrenergic Agonists on the Intestinal Absorption of Galactose and Phenylalanine

Nutrient transport across the mammalian small intestine is regulated by several factors, including intrinsic and extrinsic neural pathways, paracrine modulators, circulating hormones and luminal agents. Because β-adrenoceptors seem to regulate gastrointestinal functions such as bicarbonate and acid secretion, intestinal motility and gastrointestinal mucosal blood flow, we have investigated the effects of different β-adrenergic agonists on nutrient absorption by the rat jejunum in-vitro. When intestinal everted sacs were used the β₂-agonist salbutamol had no effect either on galactose uptake by the tissue or mucosal-to-serosal flux whereas mixed β₁- and β₂-agonists (isoproterenol and orciprenaline) and β₃-agonists (BRL 35135, Trecadrine, ICI 198157 and ZD 7114) inhibited galactose uptake and transfer of D-galactose from the mucosal-to-serosal media across the intestinal wall (although the inhibiting effects of isoproterenol and Trecadrine were not statistically significant). In intestinal everted rings both Trecadrine and BRL 35135 clearly reduced galactose uptake, the effect being a result of inhibition of the phlorizin-sensitive component. Total uptake of phenylalanine by the intestinal rings was also reduced by those β₃-adrenergic agonists. These results suggest that β₁ and β₃-adrenergic receptors could be involved in the regulation of intestinal active transport of sugars and amino acids.     

Search for New Antiarrhythmic and Hypotensive Compounds. Synthesis,Antiarrhythmic, Antihypertensive,and α-Adrenoceptor Blocking Activity of Novel 1-[(2-Hydroxy-3-amino)]-propylpyrrolidin-2-one Derivatives

A series of the derivatives of 1-[2-hydroxy-3-(4-phenyl-1-piperazinyl)propyl]-pyrrolidin-2-one ( MG-1 ) was synthesized and tested for electrocardiographic, antiarrhythmic, and antihypertensive activity as well as for α₁- and α₂- adrenoceptors binding affinities. Some of the compounds of this series slightly decreased the heart rate, prolonged P-Q, Q-T intervals and QRS complex. Only compound 7 (1-[2-hydroxy-3-(4-phenyl-1-piperazinyl)propyl]-pyrrolidine) possesses potent antiarrhythmic and a slight hypotensive properties, and affinity for α₁- and α₂- adrenoceptor. The results suggest that the antiarrhythmic and hypotensive effect of compound 7 and MG-1 is related to their adrenolytic properties, and that those properties depend on the presence of a phenylpiperazine moiety.     

Synthesis and Antibacterial Activity of 7β-[3-(Un)substituted-2-aminopropionamido]-3-vinylcephalosporins and Related Compounds

A series of new 7β-[3-(un)substituted-alanyl]-3-vinylcephalosporins and some related compounds, 4a – 1 is described. They incorporate residues of proteinogenic L -α-aminocarboxylic acids, their antimetabolites and enantiomers as well as a dipeptide in the 7β-acylamido side chain. The acylation of diphenyl-methyl 7-amino-3-vinyl-3-cephem-4-carboxylate ( 2 : R² = DPM) with various protected α-aminocarboxylic acids 1a – k and the dipeptide 1l is carried out using TBTU as coupling reagent. The compounds, except 4f , are active in vitro against S. aureus and S. lutea, but only 4a, 4k , and 4l inhibit some of the Gram-negative strains.     

Adenylate Cyclase Modulation by Ammonium Ion: GTP-like Effect on Muscarinic and α2-Adrenergic Receptors

The stimulatory influence of ammonium sulphate on adenylate cyclase activity has been investigated. By competition binding experiments on the β-adrenergic stimulatory receptor in rat myocardial membranes, no influence could be detected of ammonium sulphate neither in receptor coupling to the stimulatory guanine nucleotide binding protein nor in the GTP-induced uncoupling. In order to detect an impaired inhibition instead of an increased stimulation of adenylate cyclase activity by ammonium sulphate the investigation was extended to inhibitory receptors. The same type of effect by ammonium sulphate was detected on both the muscarinic cholinergic receptor in rat myocardial membranes as well as on the α₂-adrenergic receptor in human platelets. The influence of ammonium sulphate noted in competition binding studies and off-kinetics experiments was GTP-like, i.e. causing a decrease in agonist-receptor affinity leaving all the inhibitory receptors in the low affinity state. In conclusion, this paper indicates that the observed stimulatory effect of ammonium sulphate is exerted by the ammonium ion on the inhibitory guanine nucleotide binding protein, impairing the negative control of adenylate cyclase activity.     

Chalcone Derivatives Inhibit Glutathione S‐Transferase P1‐1 Activity: Insights into the Interaction Mode of α, β‐Unsaturated Carbonyl Compounds

Resistance to chemotherapeutic drugs has long been a considerable barrier to successful treatment of many cancers and over‐expression of glutathione S‐transferase P1‐1 is correlated to carcinogenesis and resistance of cancer cells against chemotherapeutic agents. This study throws light on the role of chalcone derivatives, a new class of glutathione S‐transferase P1‐1 inhibitors potentially to overcome glutathione S‐transferase P1‐1‐mediated chemotherapy resistance. Nineteen α‐substituted chalcone derivatives were synthesized and their in vitro inhibitory effects on glutathione S‐transferase P1‐1 were determined. We interestingly found that most of these compounds showed inhibitory effect on glutathione S‐transferase P1‐1 activity. In addition, molecular field‐based similarity analysis provides the necessary three‐dimensional molecular field properties of α, β‐unsaturated carbonyl derivatives to inhibit glutathione S‐transferase P1‐1 activity. Thus, these compounds have great potential to be developed into novel chemotherapeutic sensitizers.