Sympathomimetic bronchodilators and animal models for assessing their potential value in asthma

Tracheal relaxing effects and beta2 adrenoceptor selectivity of S1319, a novel sponge-derived bronchodilator agent, in isolated guinea-pig tissues

1. S1319 (4-hydroxy-7-[1-(1-hydroxy-2-methylamino)ethyl]-1, 3-benzothiazol-2(3H)-one acetate), a novel non-catecholamine beta-adrenoceptor agonist, has been compared with isoprenaline, salbutamol and formoterol for activity in vitro on a range of beta-adrenoceptor containing preparations from guinea-pig. 2. S1319, like isoprenaline, salbutamol and formoterol, relaxed preparations of guinea-pig trachea (contracted by histamine) in a concentration-dependent manner. The relaxing activity of S1319 appeared to be more potent than that of isoprenaline and salbutamol, and similar to that of formoterol (pD2 values of 10.58+/-0.03 vs 7. 60+/-0.01, 7.50+/-0.01 and 10.52+/-0.04, respectively), and was blocked by the beta2-adrenoceptor selective antagonist (ICI 118,551). The intrinsic activity of S1319 was close to 1.0. 3. In the beta1-adrenoceptor containing preparations, guinea-pig right and left atria, a monophasic inotropic response of S1319 was observed. The pD2 value of S1319 for left atrial and right atrial inotropism was 6.70+/-0.15 and 7.81+/-0.01, respectively. 4. The selectivity ratio (trachea/left atrial inotropism) of S1319, formoterol, salbutamol and isoprenaline was 8523, 284, 4.8 and 0.45, respectively. The relative selectivity ratio of S1319 was 18743, 1858 and 30 times greater than that of isoprenaline, salbutamol and formoterol, respectively. 5. Relaxant responses of guinea-pig trachea to S1319 declined rapidly when the agonist was washed from the tissues, with complete recovery within 30 min. The duration of action of S1319 was similar to that of isoprenaline and less than that of salbutamol and formoterol. 6. In summary, S1319, a sponge-derived beta-adrenoceptor agonist, is a potent and selective beta2-adrenoceptor agonist with a short-duration of action in isolated guinea-pig tracheas.

Biochemical regulation of airway smooth muscle tone: current knowledge and therapeutic implications

Evidence collected during the last decade indicates that the molecular processes responsible for smooth muscle contraction are fundamentally different from those responsible for skeletal muscle contraction. Furthermore, because of the diverse functional roles of various smooth muscles, it would not be surprising if significant differences in regulatory processes also exist among different smooth muscles. Such diversity may already be exemplified by differences in cross-bridge kinetics and sources of activator Ca2+. Additional unique regulatory features of various smooth muscle types will undoubtedly be uncovered by further research. A convincing body of data suggests that activation of the adenylate cyclase/protein kinase cascade is responsible for the bronchodilation produced by beta-adrenoceptor agonists. Although the exact mechanism by which the activation of cAMP-dependent protein kinase induces relaxation is not clear, the phosphorylation of multiple substrates may be involved. Phosphorylation of these substrates can promote relaxation by decreasing the myoplasmic Ca2+ concentration, decreasing the Ca2+ sensitivity of the contractile apparatus, or both. Thus, because beta-adrenoceptor agonists act as physiologic antagonists of broncho-constriction, they should relax airway smooth muscle regardless of the mediator(s) responsible for the bronchospasm. Perhaps this is the major reason that the beta-adrenoceptor agonists have become the premier class of drugs used in the treatment of bronchial asthma. As useful as the sympathomimetic bronchodilators have been, they are not without liabilities. These liabilities include: cardiovascular and skeletal muscle side effects, an inherent subsensitivity of the asthmatic patient population to beta-adrenoceptor agonists, the development of tolerance and a loss of efficacy during severe asthmatic episodes. The fact that these drawbacks are probably shared by all sympathomimetic bronchodilators suggests that little therapeutic advantage will be gained by developing new beta-adrenoceptor agonists. The task of developing novel bronchodilators will be facilitated by an understanding at the molecular level of the diversity among smooth muscles and the processes that regulate smooth muscle tone. Hopefully, such knowledge will lead to a new generation of highly effective, tissue-selective bronchodilators with significant therapeutic advantages over those currently available.

Antagonistic effects of bisoprolol on several beta-adrenoceptor-mediated actions in anaesthetized cats

The beta-adrenoceptor antagonistic activity of i.v. administered bisoprolol ((+/-)-1-[4-(2-isopropoxyethoxymethyl)-phenoxy] -3-isopropylamino-2-propanol, hemifumarate) was studied under two different sets of experimental conditions in anaesthetized cats and compared to the activity of atenolol and propranolol. The responses of several target organs to beta 2-adrenoceptor stimulation were used: inhibition of isoprenaline effects on diastolic blood pressure, hindlimb perfusion pressure, soleus muscle contractility and histamine aerosol-induced bronchoconstriction. The inhibition of isoprenaline-induced tachycardia served as indicator of beta 1-antagonism. The slopes of agonist dose ratio vs. antagonist dose effect were close to unity for propranolol but deviated from unity for atenolol and even more so for bisoprolol. In spite of the ensuing difficulty of comparisons, bisoprolol showed the most pronounced selectivity indices (10-20), followed by atenolol (1-7.5) and propranolol (0.3-1.6). Thus, bisoprolol exhibited a higher degree of beta 1-selectivity in the cat than did atenolol, regardless of the parameter used for measurement of beta 2-antagonism. Propranolol proved to be non-selective or even had a somewhat higher affinity for beta 2- than for beta 1-adrenoceptors.

Fenoterol: a beta2-adrenergic agonist for use in asthma. Pharmacology, pharmacokinetics, clinical efficacy and adverse effects

Fenoterol (hydroxyphenylorciprenaline) is chemically closely related to metaproterenol (orciprenaline). It has a higher bronchodilating potency than metaproterenol, albuterol (salbutamol in Europe) or terbutaline. The beta 2 selectivity of fenoterol at normal oral and inhaled doses is the same as for albuterol and terbutaline. Its pharmacodynamic effects are similar to those of other selective beta 2-adrenoceptor agonists. It has a high first-pass metabolism. The long half-life previously reported in the literature (7 hours) is mainly the half-life of inactive fenoterol metabolites. The duration of action at equipotent bronchodilating doses seems to be the same as for albuterol and terbutaline, and not longer, as previously reported. Inhalation of beta-adrenoceptor agonists is the superior route of administration. Side effects do not usually occur at normal therapeutic doses. One puff of fenoterol (200 micrograms) is about equipotent to 2 puffs of albuterol (2 X 100 micrograms) or 2 puffs of terbutaline (2 X 250 micrograms) with the same duration of effect. In patients who overdose with the metered-dose inhaler (MDI), side effects occur at half the number of puffs with fenoterol. Dosage for an acute attack in children is 1 puff (200 micrograms), repeated within 5 minutes if necessary; in adults 1-3 puffs can be given. For maintenance therapy, the dose in adults is 1-2 puffs 2-4 times daily, while in children 1 puff at night and 1 in the morning may be sufficient. The usual oral dosage has been 5-10 mg 3 times daily.

The sympathomimetic activity of (+/-)-pindolol at beta 1- and beta 2-adrenoceptor sites

In isolated right atrial and stilboestrol-pretreated uterine preparations from both guinea-pigs and rats, pindolol elicited propranolol-sensitive positive chronotropic and smooth muscle relaxant actions. Although the pD2 values for pindolol (8.4-9.2) and (-)-isoprenaline (ISO, 8.4-8.7) fell within the same range in these preparations, the maximum responses to pindolol were less than 15% of those to the catecholamine. Thus, pindolol did not display any selectivity for agonistic actions at beta 1- or beta 2-adrenoceptors. In uteri taken from progesterone-pretreated rats, the pD2 value for (-)-isoprenaline was 9.5 and that of pindolol 8.5. In these preparations the maximal relaxant effect of pindolol (approximately 50% Emax ISO) was greater than that found in oestrogen-pretreated uteri. Thus, it appears that the maximal response of pindolol in vitro can be related to the pD2 value for (-)-isoprenaline. In anesthetized cats, intravenous pindolol elicited non-beta-adrenoceptor-mediated increases in heart rate and decreases in soleus muscle contractility. The mechanism(s) underlying the latter actions are unknown.

Some problems encountered in the evaluation of new bronchodilating beta-adrenoceptor agonists

A series of phenylethanolamine derivatives were examined with respect to their bronchospasmolytic effect and their ability to depress the contractions of the soleus muscle in cat and guinea-pig. One group of compounds including D2343 (1-(4-hydroxyphenyl)-2-[1,1-dimethyl-3-(2-methoxyphenyl) propylamino]-ethanol HCl), a new beta 2-adrenoceptor agonist, appeared to be more effective in combating bronchospasm induced by histamine than in depressing the contractions of the soleus muscle in anaesthetized cat. This difference disappeared when serotonin was used to induce bronchospasm. Terbutaline antagonized histamine and serotonin equally well. Experiments in vivo and in vitro with guinea-pigs gave ambiguous results. Slowly developing effects was a common feature of the compounds showing the apparent effect separation. None of the available beta-adrenoceptor agonists appears to distinguish between the adrenoceptors in the airway smooth muscle mediating bronchial relaxation and those in the skeletal muscle associated with tremor.

The adrenoceptor blocking properties of the new beta 2-selective antagonist, IPS 339 on tracheal smooth muscle and on slow contracting skeletal muscle

The beta-adrenoceptor blocking properties of IPS 339 and propranolol were studied on isolated preparations of trachea and of the slow-contracting soleus muscle from the guinea-pig. Both compounds antagonized the relaxation of the trachea and the depression of subtetanic contractions of the soleus produced by the beta2-selective agonist, terbutaline. On the soleus muscle the pA2-values for IPS 339 and propranolol were similar and close to those obtained for propranolol on the trachea. However, on the trachea the slope of the Schildplot for IPS 339 against terbutaline became less than one and a reliable pA2-value could not be calculated.

Comparison of the beta-adrenoceptor effects of soterenol and its 3-hydroxy, 4-sulphonamido isomer (MJ6987-1) in isolated tissues from the guninea-pig

1. Soterenol and its 3-hydroxy, 4-methanesulphonamido isomer (MJ6987-1) were compared with isoprenaline for beta-adrenoceptor mediated effects in guinea-pig atrial, tracheal, uterine and ileal preparations. In addition, MJ6987-1 was tested for its effects in the atria of cats, rabbits and rats. 2. Soterenol had a lower intrinsic activity and was approximately two to six times less active than isoprenaline in all preparations. 3. MJ6987-1 was a full agonist, being some 30--200 times less active than isoprenaline at beta 1-receptor sites and greater than 3000 times less active in preparations where beta 2-receptor activation was involved. 4. Change in the position of the ring substituents in soterenol leads to the production of beta 1-receptor selective agonist.

Isolated lung strips of guinea pigs: responses to beta-adrenergic agonists and antagonists

Isolated lung strips of guinea pigs were examined as an in vitro model for assessing the direct effect of beta-adrenergic drugs at the level of peripheral airways. Changes in intrinsic tone of thin strips of lung parenchyma were measured with an isometric force transducer. Isoproterenol, a nonselective beta-adrenergic agonist, and several beta-adrenergic agonists, soterenol, salbutamol, metaproterenol and ritodrine elicited a dose-related relaxation of lung strip. Responses to isoproterenol were antagonized by propranolol and the selective beta blocking agents butoxamine (beta2) and practolol (beta1). These results were compared to data obtained with the same compounds on isolated guinea pig atria. All agonists except ritodrine were full agonists in the lung strip whereas isoproterenol and metaproterenol were the only full agonists in the atrial preparation. In the atria, practolol was a more effective blocker of isoproterenol responses than butoxamine, and the reverse was true for the lung strip.

Heterogeneity of cerebral beta-adrenoceptor binding sites in various vertebrate species

[3H]-Dihydroalprenolol ([3H]-DHA) binds to cerebral membranes of the frog, chick, rat, mouse, rabbit and human with a dissociation equilibrium constant (KD) of about 1 nM and displays binding characteristics indicative of an interaction with beta-adrenoceptors. However, the maximum number of specific binding sites labelled by this beta-adrenoceptor ligand varies substantially between the species with the chick and mouse having the highest, and the frog the lowest density. The structure--activity relationships of adrenergic agents to inhibit specific [3H]-DHA binding suggests that whereas the membrane sites from all the species had similar affinities for non-selective beta-adrenergic agents, several drugs that have been reported to show selectivity for beta1-adrenoceptors demonstrated considerably higher affinities for mammalian rather than avian or amphibian membrane sites. By this pharmacological criteria it is likely that all the beta-adrenoceptor binding sites in frog and chick cerebral tissue have properties resembling beta2-receptors. However, in mammalian cerebral cortex, evidence is presented that beta1- and beta2-adrenoceptors coexist in a ratio of 70%/30% respectively.

Agonistic and antagonistic actions of 3,4-dihydroxy-substituted phenoxypropanolamines in guinea-pig atria and trachea

1. Racemic mixtures of noradrenaline, adrenaline, isoprenaline, N-t-butylnor-adrenaline and their corresponding derivatives containing an oxymethylene (OM) link between the phenyl ring and ethanolamine side-chain have been tested for their effects on beta-adrenoceptors in isolated guinea-pig atrial and tracheal preparations. 2. In atrial and in spontaneously contracted tracheal preparations both the parent catecholamines and their corresponding OM-derivatives had a similar order of potency as beta-receptor agonists. 3. In carbachol-stimulated tracheal preparations the OM-derivatives were shown to have partial agonistic actions. 4. As in other phenylethanolamines and phenoxypropanolamines, both the agonistic and antagonistic potency of the OM-derivatives increased with increasing amine substitution.

Actions of procaterol (OPC-2009), a new beta2-adrenoceptor stimulant, on pulmonary resistance, contractions of the soleus muscle, and cardiovascular system of the anaesthetized cat

The β-adrenoceptor stimulant actions of procaterol hydrochloride [5-(1-hydroxy-2-iso-propylaminobutyl)-8-hydroxycarbostyril hydrochloride hemihydrate] were compared with those of isoprenaline, orciprenaline and salbutamol on pulmonary resistance, contractions of the soleus muscle, heart rate and diastolic blood pressure in the anaesthetized cat. All four drugs reduced the 5-HT-induced increase in pulmonary resistance, decreased the tension of incomplete tetanic contractions of the soleus muscle and the diastolic blood pressure, and increased the heart rate in a dose-related manner. The duration of the bronchodilator action of procaterol was far longer than that of orciprenaline or salbutamol while isoprenaline had the shortest duration. Procaterol was about 1·5 times more potent, and orciprenaline and salbutamol about 80 and 10 times less potent than isoprenaline in reducing the 5-HT-induced increase in pulmonary resistance and in decreasing the tension of incomplete tetanic contractions of the soleus muscle. Procaterol, orciprenaline and salbutamol were 3·5, 91·9 and 43·9 times less potent than isoprenaline in increasing the heart rate. Procaterol, orciprenaline and salbutamol were 3·4, 130·2 and 12·9 times less potent than isoprenaline in decreasing the diastolic blood pressure. Calculation of selectivity for bronchial vs cardiac β-adrenoceptors indicates that procaterol and salbutamol have a similar degree of selectivity for β2-adrenoceptors mediating the bronchodilation, and that orciprenaline was an essentially unselective stimulant. Furthermore, the results support the suggestion that at present it is not possible to separate the bronchodilating and tremor-enhancing properties of β-adrenoceptor stimulants.

The beta-adrenoceptor stimulant properties of OPC-2009 on guinea-pig isolated tracheal, right atrial and left atrial preparations

1. The beta-adrenoceptor stimulant properties of 5-(1-hydroxy-2-isopropylaminobutyl)-8-hydroxy-carbostyril hydrochloride hemihydrate (OPC-2009) were compared with those of isoprenaline and salbutamol on guinea-pig isolated tissues. 2. In producing tracheal relaxation, OPC-2009 was approximately 7 times more potent and salbutamol 5 times less potent than isoprenaline. Both compounds were less potent than isoprenaline in increasing either the rate of beating of isolated right atria or the contractile force of left atria, OPC-2009 being 4 and 127 times and salbutamol being 100 and 700 times less potent on the respective preparations. 3. Selectivity calculated from EC50 ratio indicates that OPC-2009 was approximately 26 times and salbutamol approximately 21 times more selective than isoprenaline for tracheal smooth muscle as compared to right atrial muscle, whereas OPC-2009 was approximately 850 times and salbutamol 140 times more selective than isoprenaline for tracheal smooth muscle as compared to left atria. 4. The responses to OPC-2009 on trachea and right atria were not altered by treatment of animals with reserpine 24 h previously. Propranolol was a competitive antagonist of OPC-2009 on these tissues. 5. OPC-2009 at high concentrations competitively antagonized the positive chronotropic and inotropic responses to isoprenaline, indicating that OPC-2009 like salbutamol, may be classified as a partial agonist. 6. The results indicate that the action of OPC-2009 is more selective for tracheal smooth muscle than cardiac muscle and are interpreted in the light of subdivisions of beta-adrenoceptors.

Catechol-substituted phenoxypropanolamines: adrenoceptor activity in the anaesthetized cat

1 The pharmacological actions of racemic noradrenaline, adrenaline, isoprenaline and N-t-butylnoradrenaline have been compared with those of their corresponding derivatives containing an oxymethylene (OXY) link between the ring and ethanolamine side chain. 2 The compounds were tested in the anaesthetized cat for their ability to produce positive chronotropic effects, bronchodilator actions, changes in perfusion pressure in the perfused hind limb and decreases in soleus muscle contractions. 3 All the OXY-derivatives were potent beta-adrenoceptor agonists. The inclusion of the oxymethylene link promotes selectivity for beta1-as opposed to beta2-adrenoceptor activity. 4 In comparison with the parent compounds, the OXY-derivatives of adrenaline and noradrenaline had very weak alpha-adrenoceptor stimulant effects.

Isolation and study of functional mast cells from lung and mesentery of the guinea pig

A method is described for the dissociation of guinea pig lung and mesentery into their component cells. The method comprises incubation of the tissues with the enzyme pronase in Ca++- and Mg++-free saline followed by mechanical dispersion and yields on average 3-8% free mast cells. These cells are morphologically intact and viable. They retain an active sensitization or can be passively sensitized. The levels of cAMP and cGMP in the whole cell suspension respond to catecholamine, histamine or cholinergic stimulation in a way similar to that observed in the corresponding undispersed tissue. Although the separation of guinea pig mast cells from other cells proved to be more difficult than the purification of rat mast cells, an inrichment of greater than 50% has been achieved. The mast cells isolated by this method proliferate in vitro and have been cultured successfully for several months.