A potent new beta2-adrenoceptor blocking agent

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

Synthesis, docking study and β-adrenoceptor activity of some new oxime ether derivatives

A new series of oxime ethers 4a–z was designed and synthesized to test the blocking activity against β₁ and β₂-adrenergic receptors. Docking of these ether derivatives into the active site of the identified 3D structures of β₁ and β₂-adrenergic receptors showed MolDock scores comparable to those of reference compounds. Biological results revealed that the inhibition effects on the heart rate and contractility are less than those of propranolol. Nevertheless, the two compounds 4p and 4q that displayed the highest negative MolDock score with β₂-adrenergic receptors showed β₂-antagonistic activity by decreasing salbutamol relaxation of precontracted tracheal strips, which indicates the importance of a chlorothiophene moiety in the hydrophobic region for best complementarity with β₂ receptors. On other hand, the presence of a homoveratryl moiety increases the MolDock score of the tested compounds with the β₁ receptor.

Synthesis and β-adrenergic blocking activity of oxime ether hybrids derived from a natural isochroman-4-one

AIM

In a search for new cardiovascular drug candidates, a series of novel oxime ethers derived from a natural isochroman-4-one were synthesized.

METHOD

Compounds 3 and 6, derived from the natural antihypertensive compound 7, 8-dihydroxy-3-methyl-isochroman-4-one (XJP), were designed and synthesized. Subsequently, a series of novel isochroman-4-one oxime ether hybrids were prepared by hybridizing various N-substituted isopropanolamine functionalities to isochroman-4-one oxime. Furthermore, β1-adrenergic blocking activities of the synthesized compounds were assayed using the isolated rat left atria.

RESULTS

Twenty target compounds were obtained, and the preliminary structure-activity relationships were deduced. The most promising compound Ic exhibited β1-adrenoceptor blocking activity (inhibition: 52.2%) at 10(-7) mol·L(-1), which was superior to that of propranolol (inhibition: 49.7%).

CONCLUSION

The results suggested that natural product XJP/isopropanolamine moiety hybrids may provide a promising approach for the discovery of novel cardiovascular drug candidates.

Potential hypotensive agents: synthesis and hypotensive activity of oxime ethers derived from 1-naphthoxepines and related compounds

The synthesis and pharmacological evaluation of substituted oximino-ethers 1 and 2 of naphth[1,2-b]- and naphth[2,1-b]-oxepin-5-ones (4 and 8) were carried out. The hypotensive activity of oximino-ethers 1 and 2 was evaluated on anaesthetized cats. The results indicated that 1c caused a fall of 80 mm/Hg for >100' at a dose of 5mg/kg iv in anaesthetized cats.

Effects of escapable and inescapable foot-shock on rat atrial beta-adrenoceptors

The chronotropic responsiveness to norepinephrine (NE) and isoproterenol (ISO) was determined in right atria isolated from rats submitted to repeated escapable or inescapable foot-shock. Significant postjunctional supersensitivity to ISO, but not to NE, was observed in both groups. No significant change in the pA2 value of metoprolol (a selective beta 1-adrenoceptor antagonist) was detected. However, a decrease of the maximum response to soterenol, a partial agonist at beta 1-adrenoceptors, occurred only after inescapable foot-shock. The enhanced sensitivity to ISO was abolished by butoxamine (a selective beta 2-adrenoceptor antagonist) and accompanied by a marked increase in the pA2 value of this antagonist. We conclude that the ability to control the shock prevented the down-regulation of the pacemaker beta 1-adrenoceptors but not the increased participation of beta 2-adrenoceptors in the response of the rat sinoatrial node to catecholamines after repeated foot-shock.

Studies in hypotensive agents. Synthesis and hypotensive activity of 3,4-dihydro-1(2H)-benzoxepine oxime ethers and their derivatives

Substituted oximino-ethers of 3,4-dihydro-1(2H)-benzoxepines were synthezised from 3,4-dihydro-1(2H)benzoxepin-5-ones. The hypotensive activity of these compounds was evaluated on anaesthetized cats.

Reduced immobility time in the tail suspension test (TST) by chronic immobilization stress. Role of corticosterone and brain serotonergic and adrenergic receptors

Chronically stressed adult male Balb C mice were submitted to the tail suspension test. Chronic immobilization stress (6 h/d for 14 consecutive days) induced a significant reduction in immobility time when compared to non-stressed controls. Pretreatment with LY 53857, a serotonin 5HT2 antagonist, and IPS 339, a selective beta-2 adrenoceptor blocker, reversed immobility time to the levels of non-stressed controls. Chronic administration of corticosterone (100 mg/kg for 7 d) did not modify immobility time as compared to saline treated controls. It is suggested that both serotonergic and adrenergic pathways in the brain may participate in the stress-induced changes occurring in the tail suspension test response and that corticosterone does not appear to play a role in this process.

Presynaptic beta-adrenoceptors in rat atria: evidence for the presence of stereoselective beta 1-adrenoceptors

1. Presynaptic beta-adrenoceptor activity was studied in rat isolated atria, previously loaded with [3H]-noradrenaline. The stimulation-induced release of 3H transmitter was measured in the presence of cocaine, and adrenaline was used as a facilitatory beta-adrenoceptor agonist. 2. Adrenaline (0.1 and 2 nM) increased, by about 50%, the evoked efflux of tritium. With phenoxybenzamine present, the same activity was shown with 10 nM adrenaline. 3. The beta 2-selective adrenoceptor blocking drugs: IPS 339 and ICI 118 551 caused a concentration-dependent decrease in the activity of adrenaline. Cardioselective beta-blocking drugs: acebutolol, beta-xolol, nebivolol and its isomers (R 67 138 and R 67 145) also reduced dose-dependently the agonistic action of adrenaline. The order of potency for nebivolol and its isomers was R 67 138 greater than nebivolol greater than R 67 145. The activity of pindolol was not concentration-dependent. The inhibitory effect of acebutolol was also observed in the presence of blockade of alpha-adrenoceptors. 4. The postsynaptic beta-adrenoceptor blocking activity of nebivolol and its isomers was studied in pithed rats. They reduced isoprenaline-induced tachycardia without altering hypotensive responses. The order of potency was: R 67 138 greater than nebivolol greater than R 67 145. 5. It is concluded that in rat isolated atria, presynaptic beta 2- and beta 1-adrenoceptors coexist and that facilitatory beta 1-adrenoceptors are stereospecific.

Beta-adrenoceptors in human brain labelled with [3H]dihydroalprenolol and [3H]CGP 12177

beta-Adrenoceptor binding sites were characterised and quantitated in post-mortem human brain with [3H]dihydroalprenolol ([3H]DHA) and [3H]CGP 12177. In cerebral cortex, isoprenaline and propranolol displaced both radioligands with uniform affinity. Practolol and CGP 20712A (selective beta 1-adrenoceptor antagonists) displaced with high affinity from a greater proportion of sites than ICI 118,551 and IPS 339 (selective beta 2-adrenoceptor antagonists). In cerebellum, propranolol displaced both radioligands with uniform affinity. ICI 118,551 displaced with high affinity from a greater proportion of sites than CGP 20712A. The density of total beta-adrenoceptors (defined with isoprenaline) and of beta 1- and beta 2-adrenoceptors (defined with CGP 20712A and ICI 118,551 respectively) was studied by saturation binding of both radioligands in 13 brain areas. beta-Adrenoceptor density was higher in caudate, putamen and nucleus accumbens (100-120 fmol/mg protein) than cortex (50-70 fmol/mg protein) and densities were lowest in hypothalamus and cerebellum (27-38 fmol/mg protein). The proportion of beta 1-adrenoceptors (as a % of total beta-adrenoceptors) was high in caudate (80%), putamen (80%) and cortex (60-70%) and lower in hippocampus (40%) and cerebellum (30%). Both radioligands labelled a very similar number of beta-adrenoceptors in all brain regions studied.

Peripheral mediation of effects of clenbuterol on locomotor and investigatory behavior in rats

Clenbuterol is one of the few beta adrenergic agonists that readily passes the blood-brain barrier. Hence, the behavioral effects in rats of systemic administrations of clenbuterol have been used as a reflection of the activation of central beta receptors. The present experiments were designed to test the hypothesis that the reduction in locomotor activity induced by clenbuterol is mediated by central rather than peripheral beta receptors. First, dose-dependent reductions in ambulation, holepoking, and rearing were established following intraperitoneal injections of 0.004 to 1.0 mg/kg clenbuterol. These effects were then found to be similar to those of 0.4 mg/kg isoproterenol, a mixed beta adrenergic agonist that does not enter the brain after systemic administration. The behaviorally suppressive effects of either 0.4 mg/kg isoproterenol or 0.05 mg/kg clenbuterol were found to be completely antagonized by pretreatment with a 10.0 mg/kg dose of nadolol, a beta antagonist that does not penetrate the brain when administered systemically. Nadolol itself had no significant effects on behavior. These results indicate that these behavioral effects of systemic administrations of clenbuterol are mediated by the activation of peripheral rather than central beta adrenergic receptors.

Reserpine-induced hypothermia: participation of beta 1 and beta 2 adrenergic receptors

In mice, reserpine-induced hypothermia is partly antagonized by clenbuterol, a beta-adrenergic agonist specific for beta 2 receptors, and completely antagonized by dobutamine, a beta-adrenergic agonist specific for beta 1 receptors. In addition, the effects of dobutamine and of clenbuterol are impaired by betaxolol (1 and 4 mg/kg) and unchanged by ICI 118,551 (1 and 4 mg/kg) beta-blocking drugs respectively selective for beta 1 and beta 2 receptors. These results indicate that reserpine-induced hypothermia depends on the beta 1 receptors and lend support to an indirect effect of clenbuterol. After a chronic treatment, clenbuterol-induced antagonism of reserpine hypothermia is facilitated. This facilitation is impaired by ICI 118,551 and by betaxolol but, in this last case, with high doses only. So the facilitation involves beta 2 adrenergic receptors and implies an increase in the sensitivity of beta 1 receptors.

Beta-adrenergic agonists reduce spontaneous motor activity through either beta 1 or beta 2 receptors

In mice, the clenbuterol-induced decrease in spontaneous motor activity was antagonized by IPS-339 (beta 2 antagonist) but not by betaxolol (beta 1 antagonist), whereas the isoproterenol-induced decrease in spontaneous motor activity was completely antagonized by betaxolol and only partially by IPS-339. It can be concluded that the clenbuterol-induced decrease in spontaneous motor activity is of the beta 2-type, whereas that induced by isoproterenol is essentially of the beta 1 type. In addition, chronic treatment with clenbuterol induced a tachyphylaxis to the effect of clenbuterol but not of isoproterenol. After chronic administration of tricyclic antidepressants (imipramine and desipramine) the number of cortical beta 1 adrenergic receptors decreased without impairing the clenbuterol-induced decrease in spontaneous motor activity. We conclude that beta 2 adrenergic receptors mediate the clenbuterol-induced decrease in spontaneous motor activity and the tachyphylaxis to this effect after chronic treatment.

The effect of varying carbachol concentration on the slope of Schild plots of selective beta-adrenoceptor antagonists in the carbachol-contracted guinea-pig trachea

The effect of varying the level of smooth muscle tone induced by carbachol on the Schild analysis of atenolol (beta 1-selective) and ICI 118,551 (beta 2-selective) with salbutamol as agonist, on the guinea-pig tracheal preparation has been examined. When 10(-6) M carbachol was used to induce near-maximal smooth muscle tone, Schild plot slopes for atenolol and ICI 118,551 were less than 1. Slopes of Schild plots for both drugs were equivalent to 1 when 10(-7) M carbachol was used to produce approximately half-maximal smooth muscle tone. Depletion of neuronal noradrenaline by prior treatment with reserpine had no effect on the Schild analysis. Salbutamol produced maximal relaxation and was more potent when tone was induced with 10(-7) M carbachol, but was less effective at 10(-6) M carbachol. Pretreatment with reserpine increased the potency of salbutamol at each concentration of carbachol. The results suggest that either the level of smooth muscle tone or an unknown effect associated with a high level of smooth muscle tone induced by carbachol may contribute to low slope values of Schild plots of selective beta-adrenoceptor antagonists in the carbachol-contracted guinea-pig trachea. The carbachol-contracted guinea-pig trachea can be used to determine theoretically valid pA2 values for selective beta-adrenoceptor antagonists as long as substantially less than a maximal level of smooth muscle tone is induced by carbachol.

Beta-adrenergic control of motility in the rat colon. I. Evidence for functional separation of the beta 1- and beta 2-adrenoceptor-mediated inhibition of colon activity

The beta-adrenoceptor-mediated inhibitory response in isolated rat colon strips of beta-adrenoceptor agonists (isoproterenol, terbutaline, prenalterol) in the absence and presence of the selective beta-adrenoceptor antagonists metoprolol (beta 1) and IPS 339 (beta 2) demonstrates that both beta 1- and beta 2-adrenoceptors are involved in the inhibition of colonic motility. Neuronal blockade induced by tetrodotoxin suppressed the relatively high (68%) maximal response of prenalterol (partial beta-adrenoceptor agonist) to 23%. The concentration-response curves for terbutaline (beta 2-selective agonist) and isoproterenol (nonselective agonist) were not influenced by tetrodotoxin. The results thus indicate that the beta-adrenergic inhibition of spontaneous activity in the rat colon strip may be mediated at two functional levels within the colon wall: either by beta 2-adrenoceptors in the smooth muscle layer or by beta 1-adrenoceptors in the intramural ganglionic plexuses, which by neuronal elements are coupled to the effector smooth muscle.

Further evidence of the inhibitory role of perifornical hypothalamic beta-adrenergic receptors in the feeding behaviour of hungry rats

The reduction of food intake in hungry rats induced by salbutamol (10 mg/kg/i.p.) was prevented by IPS 339 (5 mg/kg, i.p.) a selective beta 2 adrenergic antagonist, but not by metoprolol (10 mg/kg i.p.), a blocker of beta 1 adrenergic receptors. Similarly, bilateral injections of IPS 339 (32 micrograms/1 microliter) but not metoprolol (80 micrograms/1 microliter) in the perifornical hypothalamic area completely antagonized the anorectic effect of intraperitoneal salbutamol, suggesting an involvement of beta 2 adrenergic receptors in this brain area. Clenbuterol, a beta 2 adrenergic agonist which readily crosses the blood-brain barrier, was 10-100 times more potent than salbutamol in inhibiting feeding consumption of deprived rats when injected intraperitoneally and this effect was also selectively antagonized by pretreatment with IPS 339. Neither IPS 339 nor metoprolol injected in the perifornical hypothalamus significantly modified the anorectic effect of diethylpropion (5 mg/kg i.p.) whereas it was partially prevented by intraperifornical injection of 1-propranolol (52 micrograms/2 microliter), a non-selective beta antagonist, suggesting that both beta 1 and beta 2 adrenergic receptors in the hypothalamus contribute to the mechanism by which diethylpropion causes anorexia.

Biochemical and physiological effects of S-32-468, a beta-adrenoceptor antagonist with possible oculoselectivity

S-32-468, a recently synthesized aryloxymethyl beta-adrenoceptor antagonist, was tested for its ability to inhibit activation of isoproterenol-stimulated adenylate cyclase activity in rabbit and human ciliary process, heart and lung. In both species, S-32-468 was a potent inhibitor of ocular beta-adrenoceptors, with a 9-12 fold selectivity over inhibition of beta-adrenoceptors in cardiac tissue. When applied topically, S-32-468 was more effective than timolol in decreasing intraocular pressure in normal albino rabbits.

Study of beta-adrenoceptors and beta-adrenergic responsiveness in cultured "preneoplastic-like" and neoplastic rat hepatocytes

The presence of specific binding sites for tritiated CGP-12177, a beta-adrenergic antagonist, was investigated in the preneoplastic-like C1I cell-line and in Morris hepatoma MH3924 cells. It was found that C1I cells possess beta-adrenoceptors with the following characteristics: KD = 1.58 +/- 0.56 nM and Bmax = 4.41 +/- 0.88 fmol/10(6) cells. No specific binding sites could be found on MH3924 cells. Stimulation of the C1I cells beta-adrenoceptors by isoprenaline, salbutamol, adrenaline and noradrenaline induced cyclic AMP accumulation. Noradrenaline was, however, a hundred times less efficient than adrenaline, as is the case in normal rat hepatocytes. The order of potency of beta-antagonists either to displace the bound radioligand or to counteract isoprenaline induced cyclic AMP accumulation (IPS-339 greater than propranolol much greater than atenolol) indicates that the adrenoceptors present on the C1I cells are of the beta 2-subtype.

Beta adrenoceptors of human red blood cells, determination of their subtypes

The characteristics of beta adrenergic receptors of human erythrocyte membranes were investigated using (-)125iodocyanopindolol as a radioligand. Inhibition of (-)125iodocyanopindolol specific binding was checked using either atenolol and metoprolol as beta 1 selective antagonists or ICI 118551 and IPS 339 as beta 2 selective antagonists. The results showed non linear Hofstee's plots suggesting that both beta 1 and beta 2 adrenergic receptors are present. Analysis of the data yielded a beta 1/beta 2 adrenergic receptor ratio of approximately 33/67. Thus it is concluded that beta 2 subtype is predominant on human erythrocyte membranes.

ICI 118,551: an effective ocular hypotensive agent with selectivity for the ciliary process beta 2-adrenoceptor and with minimal cardiac side effects

Prior biochemical studies have shown that the ciliary process epithelium, which is involved in the secretion of aqueous humour, is rich in beta-adrenoceptors with pharmacological characteristics similar to those of the beta 2 subclass. The present experiments demonstrate that the beta-adrenoceptor antagonist, ICI 118,551, is a potent inhibitor of isoprenaline-stimulated adenylate cyclase activity measured in broken cell preparations of rabbit ciliary process. In rabbit cardiac muscle, however, ICI 118,551 is a relatively weak antagonist of isoprenaline-stimulated adenylate cyclase, being approximately 100 fold less potent than the non-selective beta-adrenoceptor antagonist, timolol. ICI 118,551 is also less potent than timolol in inhibiting isoprenaline-sensitive adenylate cyclase of rabbit lung. ICI 118,551 applied topically to eyes of unanaesthetized rabbits causes a dose-dependent decrease in intraocular pressure. Furthermore, in a blind crossover study in rabbits, topically applied ICI 118,551 decreased intraocular pressure for more than 6 h and was more effective than an identical dose of the clinically effective anti-glaucoma agent, timolol. Systemic absorption from topically-applied timolol, but not ICI 118,551, is sufficient to alter cardiac response to subcutaneous administration of isoprenaline. Furthermore, dose-response studies, using direct systemic administration of the two beta-adrenoceptor antagonists, revealed that ICI 118,551 is about 60 times less potent than timolol in blocking isoprenaline-induced cardio-acceleration. ICI 118,551, applied to one eye, causes a decrease in intraocular pressure in the contralateral eye, and systemic administration of ICI 118,551 results in decreased intraocular pressure in both eyes, data indicating that at least part of the ocular hypotensive effect of topical ICI 118,551 is mediated through systemic absorption. 8 These findings provide biochemical and physiological evidence that selective beta 2-adrenoceptor blockers such as ICI 118,551, used topically or systemically, may be useful as ocular hypotensive agents with decreased cardiac side-effects.

Regional myocardial tissue blood flow during beta-adrenergic blockade in cat hearts with acute ischaemia

Selective beta 1- or beta 2-adrenergic blockade was achieved by practolol or IPS 339, respectively, in cats with acute ligation of a coronary artery. During blockade, heart rate was kept constant by atrial pacing and blood pressure reduction was prevented by aortic clamping. Regional myocardial blood flow was measured by the distribution of 15 micron labelled microspheres. Practolol slightly reduced epicardial blood flow in ischaemic myocardium, while blood flow in border and normally perfused myocardium remained unchanged. Following IPS 339, myocardial tissue flow increased in normally perfused myocardium, on average by 37% in the endocardium and 30% in the epicardium. No changes occurred in the other regions. The flow changes brought about by IPS 339 were unrelated to haemodynamic changes, and the coronary vascular resistance was reduced. These results are indicative of coronary vasodilation related to beta 2-adrenergic receptor blockade and was confined to well-oxygenated areas surrounding the acutely ischaemic zone.

RECFIT: a microcomputer-based nonlinear regression curve-fitting package for the quantitative resolution of beta-adrenoceptor subtypes and estimation of nonspecific binding

A dedicated nonlinear regression based curve-fitting packages has been developed for quantitative analysis of beta-adrenoceptor subtypes. A feature of this package is the provision to obtain initial parameter estimates using a conversational graphical technique where the user is prompted for parameter estimates, and the resulting curve is displayed over the data. Data are then fitted to a one- or two-binding site model with user-selected weighting and constraints on the parameters. A novel feature is the provision to estimate the nonspecific binding component in the assays as a parameter in the model. The printout for each model consists of the parameters and their standard deviations, estimates of the goodness of fit, an analysis of residuals, and a graph of the data points overlayed with the fitted curve. The nonlinear regression algorithm is based on that of Gauss-Newton. When unweighted, the values determined by RECFIT are essentially the same as those found using the BMDPAR programs on an ICL 2976 mainframe computer. The implementation is reasonably efficient; a typical run for a two-site fit, using nine data points and estimating nonspecific binding, took a total time of about 8 min, excluding data entry and derivation of initial estimates, 4 min for the fitting, 30 sec for graph generation, and 2-3 min for printing of the graph and data.

Beta 2-receptors in the rat anterior pituitary mediate adrenergic stimulation of prolactin release

As previously shown, the beta-adrenergic agonists isoproterenol, epinephrine and norepinephrine stimulate prolactin (PRL) release from superfused rat anterior pituitary cell aggregates. In order to further characterize the beta-adrenergic response in this tissue preparation, the effects of various beta-adrenergic agents were investigated. The beta 2-agonist, zinterol, stimulated PRL release at concentrations more than 4 orders of magnitude lower than prenalterol, a beta 1-agonist with high potency in rat heart. The order of potency of the antagonists IPS 339 (beta 2), ICI 118.551 (beta 2), propranolol, sotalol, practolol (beta 1), metoprolol (beta 1) and H 35/25 for inhibition of beta-agonist-stimulated PRL release provided additional support for a beta 2-stimulatory effect. beta-Agonists were also capable of stimulating PRL release from superfused intact pituitaries. The beta-adrenergic response desensitized rapidly during prolonged exposure of the aggregates to beta-agonists.

Characterization of the beta-adrenergic receptor on the human platelet: a beta 2-subtype

The human platelet beta-adrenergic receptor was characterized by using the ability of different drugs to stimulate the adenylate cyclase activity and the effects of various beta-antagonists to block the isoprenaline-stimulated adenylate cyclase activity. Isoprenaline was found 10 times more potent than adrenaline and 1000 times more potent than noradrenaline in stimulating the adenylate cyclase activity in these cells. Isoprenaline-stimulated activity was blocked by the non-selective beta-antagonists propranolol and alprenolol and by the beta 2-selective antagonist IPS 339 and prenalterol. Metoprolol, a beta 1-selective blocker, was without effect on the isoprenaline-stimulated adenylate cyclase activity. We conclude from our findings that the beta-adrenergic receptor type on the human platelet is mainly of the beta 2-subtype.

Beta-adrenergic receptor subtypes in iris-ciliary body of rabbits

Direct comparison of drug interaction with intraocular relative to extraocular beta-adrenergic receptors was used to test the hypothesis that the receptors in ocular tissues are of the beta 2-subtype. Potencies for the displacement of 3H-dihydroalprenolol radioligand binding to membranes obtained from rabbit-iris ciliary bodies by beta-adrenoceptor agonists was in the order: isoproterenol greater than or equal to epinephrine greater than salbutamol greater than terbutaline greater than tazolol greater than norepinephrine. Similar radioligand displacement by beta-adrenoceptor antagonists was in the order of potency: alprenolol greater than or equal to bupranolol = oxprenolol = timolol = propranolol greater than ICI 118,551 = IPS 339 much greater than betaxolol greater than metoprolol. Finally, for the above beta-adrenoceptor antagonists, a highly significant correlation was obtained for displacement of radioligand to ocular tissues (pKi values) relative to antagonism (pA2 values) of isoproterenol-induced guinea-pig tracheal relaxation but not guinea-pig atrial chronotropic effects. Consequently, the above three observations reinforce the notion that rabbit-iris ciliary bodies contain beta-adrenergic receptors predominantly of the beta 2-subtype.

Regional myocardial tissue blood flow during sequential beta 1- and beta 2-adrenergic blockade in cat hearts with acute ischaemia

beta-Adrenergic blockade was imposed on cats with ischaemic regions of the left ventricle produced by coronary artery occlusion. Ten animals first received a beta 1-blocking agent (atenolol) followed by a beta 2-blocking agent (IPS 339). In ten more animals this sequence was reversed. Combined blockade, obtained after both agents were administered, showed clear reduction of tissue blood flow in all areas of the ventricle, except for the central ischaemic zone. The flow reduction could be ascribed to bradycardia and reduced coronary perfusion pressure. By analysing the sequential changes it was evident that blockade of beta 1-adrenergic receptors was responsible for the haemodynamic changes, and the coronary vascular resistance rose so as to match the quantity of blood flow to the functional state of the ventricle. Blockade of beta 2-receptors by IPS 339, however, showed no evidence of coronary vasoconstriction but rather maintained vascular resistance at an unchanged level despite a weak beta 1-adrenergic blocking effect.

Effect of fenoterol on immunological release of leukotrienes and histamine from human lung in vitro: selective antagonism by beta-adrenoceptor antagonists

The inhibitory effects of fenoterol, a beta 2-adrenoceptor agonist, on the release of SRS-A leukotrienes and histamine from chopped human lung tissue were measured and selective beta-adrenoceptor antagonists used to investigate the nature of the receptors involved. Fenoterol 0.01-1.0 microM inhibited the antigen-induced release of SRS-A and histamine, but not the release induced by the calcium ionophore A23187. Propranolol 0.1 and 1.0 microM and butoxamine 10 and 100 microM significantly antagonized the effects of fenoterol 0.1 microM on SRS-A and histamine at concentrations which affect (beta 2-adrenoceptors, while atenolol 0.1 to 10 microM showed no antagonism at concentrations which affect beta 1-adrenoceptors. These results suggest that adrenoceptors in human lung which modulate the immunological release of SRS-A leukotrienes are of the beta 2-subtype as for histamine release.

Effects of beta 1-adrenoceptor agonism on plasma renin activity in normal men

The contribution of beta 1-adrenoceptors to the regulation of plasma renin activity was investigated in nine healthy sodium-replete volunteers: seven subjects received a cumulative intravenous dose of 75 micrograms/kg prenalterol, a predominant beta 1-adrenoceptor agonist, and two subjects only vehiculum. In the seven actively treated subjects beta 1-adrenoceptor agonism increased (P less than 0.001) systolic intra-arterial pressure by an average of 16 +/- 4 mm Hg and heart rate by 19 +/- 3 beats min. These increases were significantly (P less than 0.04) different from the changes observed in the two control subjects (+ 3 +/- 4 mm Hg and -1 +/- 4 beats/min, respectively). Plasma renin activity, however, tended to decrease in both the actively (-38%) and saline (-28%) treated subjects. Predominant beta 1-adrenoceptor agonism, powerful enough to increase systolic pressure and heart rate does not increase plasma renin activity in supine sodium-replete normal man.

Beta 2-adrenoceptor-induced hypotension in the ganglion-blocked angiotensin II-supported rat

An in vivo method is described to demonstrate vascular beta 2-adrenoceptor agonist and antagonist activity. Agonist activity was shown by the ability of i.v. injected compounds to reduce blood pressure in ganglion-blocked, phenoxybenzamine-treated, angiotensin II-supported rats. Procaterol was employed to assess the relative beta 2 blocking activity of propranolol IPS 339 and atenolol. Arunlakshana and Schild analysis of the data revealed that all these compounds were competitively beta 2 antagonists, their relative potencies being 100 : 80 : 0.56 respectively.

Involvement of alpha- and beta 1-adrenergic mechanisms in the immobility-reducing action of desipramine in the forced swimming test

The influences of various monoaminergic agents on the immobility-reducing action of desipramine (DMI) in the forced swimming test were examined. 5-Methoxy-N,N-dimethyltryptamine and methysergide, a serotonin agonist and antagonist, respectively, did not affect the duration of immobility. Pimozide, a dopamine antagonist, prolonged the duration of immobility at a dose of 0.5 mg/kg. However, at the doses tested, these drugs had no effect on the action of desipramine. Phenoxybenzamine, an alpha-adrenergic antagonist, prolonged the duration of immobility only with the largest dose (20 mg/kg), but the action of desipramine was completely blocked by this drugs at all doses. Intracerebroventricular injection of a beta-adrenergic agonist, isoproterenol (ISO), and two selective beta 1-adrenergic antagonists, atenolol (ATE) and practolol, dose-dependently diminished and potentiated, respectively, the action of desipramine although these drugs had no effect on the duration of immobility when given alone. A beta 2-adrenergic antagonist derived from oximino-9-fluorene, (IPS 339) did not influence the duration of immobility or affect the action of desipramine. The effect of isoproterenol was almost completely blocked by the pretreatment with atenolol and practolol but not by IPS 339. Subcutaneously-injected isoproterenol did not affect the action of desipramine. Isoproterenol and atenolol had no effect on the concentration of desipramine in brain regions. Phenylephrine, a postsynaptic alpha-adrenergic agonist, reduced the duration of immobility as did desipramine, but this action was not affected by isoproterenol and atenolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic regulation of glycogenolysis in isolated guinea-pig hepatocytes: evidence that beta 2-receptors mediate catecholamine stimulation of glycogenolysis

Glycogenolysis in hepatocytes isolated from fed guinea pigs was much more enhanced by the beta-agonist, isoproterenol, than by equimolar concentrations of the alpha-agonists, phenylephrine and norepinephrine. The stimulatory effects of catecholamines occurred with the following order of potency: isoproterenol greater than epinephrine greater than norepinephrine. This order of potency is characteristic of beta 2-adrenergic receptors. That beta 2-receptors are responsible for mediating catecholamine stimulation of glycogenolysis in guinea-pig hepatocytes was further deduced from the inhibition of agonist-stimulated glycogenolysis by beta-receptor sub-type-selective antagonists. Thus, IPS 339, a beta-antagonist which has higher affinity at beta 2-sites than at beta 1-sites, was three orders of magnitude more potent in inhibiting isoproterenol-stimulated glycogenolysis than either atenolol or practolol, both of which are beta 1-selective antagonists. The beta 2-agonists zinterol and procaterol also stimulated glycogenolysis in hepatocytes and their effects were inhibited by propranolol and IPS 339, but not by practolol. Furthermore, activation of phosphorylase in these hepatocytes by isoproterenol, epinephrine, and norepinephrine also occurred with the potency order expected for beta 2-receptors. These results are in sharp contrast to those obtained with rat hepatocytes and emphasize that species differences occur in the regulation of hepatic glycogenolysis by catecholamines.

Further characterization of presynaptic beta-adrenoceptors in guinea-pig pulmonary arteries

Presynaptic beta-adrenoceptors were further characterized in spiral strips of guinea-pig pulmonary arteries preloaded with [3H]norepinephrine. l-Metoprolol (3 X 10(-6) M) inhibited isoproterenol (3 X 10(-7) M)-induced increases in 3H efflux by transmural field stimulation, whereas the d-isomer produced no inhibition. However, IPS 339, H 35/25, butoxamine and metoprolol (3 X 10(-6) M) antagonized salbutamol (3 X 10(-7) M)-induced increases in the parameter, whereas acebutolol, bevantolol and practolol (3 X 10(-6) M) produced no antagonism. Presynaptic beta-adrenoceptors in guinea-pig pulmonary arteries appear to have characteristics similar to those postsynaptic classical beta-adrenoceptors.

beta 1-and beta 2-adrenoceptor stimulatory effects of prenalterol

Prenalterol, previously characterized as a functionally cardioselective partial beta-adrenoceptor agonist, was shown to relax K+ -elicited contractures in the uterine muscle from progesterone pretreated rats (pD2 7.7) and to increase beating rate in the rat right atrium (pD2 8.0) at about the same concentrations with maximal effects corresponding to 94 and 82% respectively of those of isoproterenol. Terbutaline, with equal maximal effects as isoproterenol, was 50 times more potent in the uterus (pD2 7.8) than in the right atrium (pD2 6.1). Both tissues displayed a high sensitivity to isoproterenol (pD2 9.1 in both tissues) indicating large receptor reserves for the full agonist. The maximal relaxing effect of prenalterol in the uterus was obtained at about a three-fold increase of the cyclic AMP content, which is similar to that obtained with isoproterenol at a corresponding relaxation. The effects in the uterine muscle of all three agonists were mediated through beta 2-adrenoceptors since beta 2-adrenoceptor blockers (ICI 118, 551 and IPS 339) antagonized the effects in concentrations which had only marginal effects on the atrial responses of the agonists. The beta 1-antagonists pafenolol and pamatolol in concentrations higher than those, which blocked the effects of the agonists on beating rate, were devoid of inhibitory effects in the uterus. These results indicate that prenalterol possesses the ability to elicit a functional response by stimulation of either beta 1-or beta 2-adrenoceptors provided that the tissue has a large spare receptor reserve for full agonists.

High and low (Gpp(NH)p-sensitive) affinity sites for beta 2-adrenergic blockers as antagonists of isoproterenol in the field-stimulated rat vas deferens

Schild plots for (-)-propranolol, timolol and IPS 339, but not penbutolol or carazolol, as antagonists of isoproterenol in the isolated, field-stimulated rat vas deferens exhibited biphasic curves indicating the presence of both high and low affinity sites for these agents in this preparation. Schild plots determined for (-)-propranolol in the presence of prazosin (0.3 micron) or using the prostatic end of the rat vas deferens yielded two similar affinity sites suggesting the lack of involvement of postsynaptic alpha 1-adrenergic mechanisms in the observed response. In the presence of Gpp(NH)p(4 micron), (-)-propranolol, timolol and IPS 339 exhibited only a single affinity site which corresponded to their high affinity site in antagonizing isoproterenol in the absence of Gpp(NH)p. Similarly, only a single high affinity site was observed for (-)-propranolol when salbutamol, rather than isoproterenol, was used as the agonist. The data suggest the two affinity sites observed with some beta-adrenergic blockers in this preparation reflects a possible action of isoproterenol and the antagonists upon two subpopulations of beta 2-adrenergic receptors, one of which is sensitive to Gpp(NH)p.