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

Asthma and COPD: A Focus on β-Agonists - Past, Present and Future

Asthma has been recognised as a respiratory disorder for millennia and the focus of targeted drug development for the last 120 years. Asthma is one of the most common chronic non-communicable diseases worldwide. Chronic obstructive pulmonary disease (COPD), a leading cause of morbidity and mortality worldwide, is caused by exposure to tobacco smoke and other noxious particles and exerts a substantial economic and social burden. This chapter reviews the development of the treatments of asthma and COPD particularly focussing on the β-agonists, from the isolation of adrenaline, through the development of generations of short- and long-acting β-agonists. It reviews asthma death epidemics, considers the intrinsic efficacy of clinical compounds, and charts the improvement in selectivity and duration of action that has led to our current medications. Important β2-agonist compounds no longer used are considered, including some with additional properties, and how the different pharmacological properties of current β2-agonists underpin their different places in treatment guidelines. Finally, it concludes with a look forward to future developments that could improve the β-agonists still further, including extending their availability to areas of the world with less readily accessible healthcare.

Association between Selective Beta-adrenergic Drugs and Blood Pressure Elevation: Data Mining of the Japanese Adverse Drug Event Report (JADER) Database

Selective beta-adrenergic drugs are used clinically to treat various diseases. Because of imperfect receptor selectivity, beta-adrenergic drugs cause some adverse drug events by stimulating other adrenergic receptors. To examine the association between selective beta-adrenergic drugs and blood pressure elevation, we reviewed the Japanese Adverse Drug Event Reports (JADERs) submitted to the Japan Pharmaceuticals and Medical Devices Agency. We used the Medical Dictionary for Regulatory Activities (MedDRA) Preferred Terms extracted from Standardized MedDRA queries for hypertension to identify events related to blood pressure elevation. Spontaneous adverse event reports from April 2004 through May 2015 in JADERs, a data mining algorithm, and the reporting odds ratio (ROR) were used for quantitative signal detection, and assessed by the case/non-case method. Safety signals are considered significant if the ROR estimates and lower bound of the 95% confidence interval (CI) exceed 1. A total of 2021 reports were included in this study. Among the nine drugs examined, significant signals were found, based on the 95%CI for salbutamol (ROR: 9.94, 95%CI: 3.09-31.93) and mirabegron (ROR: 7.52, 95%CI: 4.89-11.55). The results of this study indicate that some selective beta-adrenergic drugs are associated with blood pressure elevation. Considering the frequency of their indications, attention should be paid to their use in elderly patients to avoid adverse events.

Adrenal influences on the inhibitory effects of procaterol, a selective Beta-two-adrenoceptor agonist, on antigen-induced airway microvascular leakage and bronchoconstriction in Guinea pigs

While the guinea pig has been the preferred choice for use as a model of allergic bronchial asthma in the evaluation of anti-asthmatic drugs, it has been shown that antigen-induced bronchoconstriction in guinea pigs is attenuated by epinephrine released from the adrenal gland. In order to investigate the possible influence of the adrenal gland on the effects of antiexudative and bronchodilative drugs on antigen-induced airway responses, we examined the inhibitory effects of procaterol, a selective beta(2)-adrenoceptor agonist, on antigen-induced airway microvascular leakage and bronchoconstriction in adrenalectomized guinea pigs and compared them with the drug's effects in sham-operated animals. Guinea pigs sensitized passively with anti-ovalbumin (OA) guinea-pig serum were adrenalectomized or sham-operated under urethane anesthesia and examined 30 min after surgery in the following experiments. (1) Animals were intravenously administered Evans blue dye to quantify airway plasma exudation, and then OA was inhaled for 10 min while measuring pulmonary inflation pressure, a parameter of bronchoconstriction. Procaterol (1, 3, 10, or 30 microg/kg) or saline (control) was administered into the airways 10 min prior to OA inhalation. The amount of extravasated Evans blue dye in the airways was calculated. (2) Venous blood samples were collected during OA or saline inhalation and plasma catecholamine levels were compared. In control animals, OA-induced increases in both the amount of Evans blue dye and in pulmonary inflation pressure were markedly greater in adrenalectomized animals than in sham-operated animals. Procaterol dose-dependently inhibited OA-induced airway microvascular leakage and bronchoconstriction, and its effects were more potent in adrenalectomized animals (significant at 1 microg/kg and higher) than in sham-operated animals (significant at 10 microg/kg and higher). Although the plasma concentration of epinephrine during OA inhalation was approximately 3 times higher than that during saline inhalation in sham-operated animals, no difference was seen in adrenalectomized animals. In conclusion, while procaterol essentially possesses pronounced inhibitory effects on antigen-induced airway microvascular leakage and bronchoconstriction in guinea pigs, the effects are considerably masked by epinephrine released from the adrenal gland.

Different effects of beta-adrenoceptor desensitization on inhibitory actions in guinea-pig trachealis

1. To determine the inhibitory effects of agents that pass through and bypass beta-adrenoceptors under conditions of tolerance to beta-adrenoceptor agonists, we examined the inhibition by the beta-adrenoceptor agonists forskolin and theophylline against contraction induced by methacholine (MCh) after exposure to higher concentrations of a beta-adrenoceptor agonist for a long time in guinea-pig tracheal smooth muscle, using isometric tension records. 2. After exposure to procaterol (0.0003-3 micromol/L) for 45 min, the inhibitory effect of 0.03 micromol/L procaterol on 1 micromol/L MCh-induced contraction was attenuated in a concentration-dependent manner, whereas after exposure to isoprenaline (0.0003-3 micromol/L) for an equivalent time, the inhibitory effect of isoprenaline was markedly attenuated at each concentration. However, after exposure to 3 micromol/L procaterol for 45 min, the inhibitory actions of forskolin and theophylline were, conversely, augmented. 3. These phenomena were observed under conditions whereby the response to MCh returned to control levels 6 h after removal of 3 micromol/L procaterol. The percentage inhibition produced by 0.1 micromol/L forskolin against 1 micromol/L MCh after exposure to normal bathing solution or 3 micromol/L procaterol for 45 min was 9.8 +/- 5.5 and 82.8 +/- 6.5%, respectively (P < 0.001). These values for 100 micromol/L (18 microg/mL) theophylline on MCh resposnes were 9.9 +/- 8.5 and 88.0 +/- 4.4% (n = 6 for both), respectively (P < 0.001). 4. The inhibitory action of agents that bypass beta-adrenoceptors was markedly augmented under conditions of beta-adrenoceptor desensitization in airway smooth muscle. 5. In conclusion, procaterol is less potent in causing desensitization of beta-adrenoceptors than isoprenaline. The activity of adenylyl cyclase may be enhanced after exposure to a high concentration of beta-adrenoceptor agonists.

Beta-adrenoceptor agonists and asthma--100 years of development

Inhaled beta(2)-adrenoceptor agonists are by far the most effective and safe bronchodilators currently available. They have not been surpassed by any other bronchodilating principle. The way to this position has been long and started with the first successful treatment of acute, severe asthma with s.c. injections of adrenaline 100 years ago. Over the years, synthetic congeners of adrenaline have been produced and tested for their pharmacological properties. During the first decades, little attention was given airway smooth muscle. The discovery of isoprenaline in 1940 was the first major step towards selective bronchodilation. This compound became a key tool for the classification of adrenoceptors into alpha and beta. Salbutamol and terbutaline were the first to show a significant attenuation of the cardiostimulant effect and confirmed the subdivision of beta-adrenoceptors into beta(1) and beta(2). Much effort was made to eliminate the next dose-limiting side effect, skeletal muscle tremor but in vain. Prolonged duration of action was achieved in three ways: with bambuterol, an orally active carbamate ester prodrug of terbutaline, salmeterol, an inhaled beta(2)-adrenoceptor agonist emerging from a purposeful research project, and formoterol which was found, accidentally, to have a long duration of action when inhaled. Throughout the 20th century, beta-adrenoceptor agonists have been developed and marketed as racemates. The pharmacological activity usually resides in the (R)-enantiomer. Despite claims for the opposite, there is so far no compelling evidence that the presence of the less active (S)-enantiomer is of any harm to the patient. One hundred years of experience of structural modifications of adrenaline has shown that the possibilities to modify the properties of this endogenous prototype appear to be unlimited.

Vascular responses to beta-adrenoceptor subtype-selective agonists with and without endothelium in rat common carotid arteries

1. Using the cannula inserting method, vasodilator responses to beta-adrenoceptor agonists (isoprenaline, denopamine and procaterol) were investigated in isolated and perfused rat common carotid arteries. 2. Each beta-adrenoceptor agonist induced a vasodilation in preparations preconstricted by phenylephrine in a dose-related manner. The potencies were in the order of isoprenaline > procaterol >> denopamine. 3. Denopamine-induced dilations were significantly inhibited by 1 nmol betaxolol (a selective beta1-adrenoceptor antagonist), but it was not influenced by 1 nmol ICI 118,551 (a selective beta2-adrenoceptor antagonist). On the other hand, procaterol-induced vasodilations were significantly inhibited by 1 nmol ICI 118,551 but not modified by 10 nmol betaxolol. 4. ACh-induced vasodilations disappeared after intraluminal saponin injection to remove endothelium, but procaterol- and denopamine-induced dilations were not modified by removal of the endothelium. 5. Pretreatment with L-NG-nitroarginine methyl ester (L-NAME) readily inhibited ACh-induced vasodilations. However, neither procaterol- or denopamine-induced vasodilation was modified by L-NAME treatment. 6. From these results, it is concluded that in the rat common carotid arteries (1) there are abundant beta2- and a few beta1-adrenoceptors, and (2) there is no participation of the endothelium-dependent mechanism in beta-adrenoceptor mediated vasodilations.

Synthesis and biodistribution of [11c]procaterol, a beta2-adrenoceptor agonist for positron emission tomography

The potent, subtype-selective radioligand (+/-)-erythro-5-(1-hydroxy-2-[11C]isopropyl-aminobutyl)-8-hydroxy-car bostyril ([11C]procaterol) was synthesized and evaluated for visualization of pulmonary beta2-adrenoceptors with positron emission tomography (PET). Procaterol was labelled by reductive alkylation of the desisopropyl precursor with [11C]acetone under the influence of NaCNBH3 and acetic acid. Synthesis and HPLC purification were performed in 34 min. Specific activities ranged from 26.5-39.3 TBq (about 700-1000 Ci)/mmol and the radiochemical yield was 2.4-8.6% (corrected for decay). Biodistribution studies were performed in male Wistar rats which were either untreated or predosed with (D,L)-propranolol hydrochloride (beta-adrenoceptor antagonist, 2.5 mg/kg), ICI 118551 (beta2-adrenoceptor antagonist, 0.15 mg/kg), CGP 20712A (beta1-adrenoceptor antagonist, 0.15 mg/kg) or isoprenaline (beta1-adrenoceptor agonist, 15 mg/kg). Specific binding was observed in lungs, spleen and red blood cells, tissues known to contain beta2-adrenoceptors. Pulmonary binding was blocked by propranolol, ICI 118551 and isoprenaline, but not by CGP 20712A. This binding pattern is consistent with the beta2 selectivity of the radioligand. The clearance of [11C]procaterol was biphasic, with a rapid distribution phase (t1/2 0.17 min) representing 90% of the injected dose followed by an elimination phase (t1/2 18.1 min). About 45% of the plasma radioactivity was unmetabolized procaterol at 15 min postinjection. In a dynamic PET-study, the lungs of untreated control rats could barely be detected and total/non-specific binding ratios rose to only 1.2 at 20 min postinjection. Although labelling and administration of (-) erythroprocaterol, the most active of 4 stereoisomers, may produce better results, [11C]procaterol seems unsuitable for beta-adrenoceptor imaging.

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.

S1319: a novel beta2-andrenoceptor agonist from a marine sponge Dysidea sp

In the course of screening of potential leads for beta2-receptor agonists, we found a novel beta2-adrenoceptor selective agonist, S1319, from a marine sponge Dysidea sp. The active compound was isolated and structurally characterized as 4-hydroxy-7-[1-(1-hydroxy-2-methylamino)ethyl]-1,3-benzothiazole-2(3H)-o ne, a new member of the beta2-adrenoceptor agonist. This is the first example of a sponge-derived beta2-adrenoceptor agonist.

Relaxation of equine tracheal muscle in vitro by different adrenoceptor drugs

Strips of tracheal smooth muscle from 12 horses were contracted by carbachol in tissue baths under isometric conditions. This contraction (approximately 50% of maximum: EC50) was relaxed completely with adrenoceptor drugs. The only exception was clenbuterol, where the degree of relaxation was approximately 90%. In all horses the EC50-value for isoprenaline (mean 1.6 x 10(-8) M) was less than that for adrenaline (mean 9.6 x 10(-8) M) and noradrenaline (mean 1.8 x 10(-6) M). The potency ratio was 1 < 6 < 110 which indicates that the beta 2-subtype dominates among the beta-adrenoceptors of equine airways. All preparations were also very sensitive to the specific and potent beta 2-receptor agonists clenbuterol (mean 5.7 x 10(-9) M) and procaterol (mean 3.6 x 10(-10) M). No differences in EC50-values due to age, sex and breed were observed in this material. The standard deviation of the mean EC50-values seems to be larger for the specific beta 2-adrenoceptor agonists than for the unspecific. A reason for this could be differences in the pattern of the beta-adrenoceptor population.

Beta-adrenoceptor subtype expression and function in rat white adipocytes

1. The pharmacological features of rat white adipocyte beta-adrenoceptor subtypes were investigated by saturation and beta-agonist competition studies with [3H]-CGP 12177 and by lipolysis induced by beta-agonists as well as their inhibition by CGP 20712A (selective beta 1-antagonist) and ICI 118551 (selective beta 2-antagonist) in an attempt to establish a relationship between the functionality and binding capacity of beta-adrenoceptor subtypes. 2. Two populations of binding sites were identified on adipocyte membranes, one with high affinity (0.22 +/- 0.07 nM) and the other with low affinity (23 +/- 7 nM). The low affinity binding sites constituted 90% of the total binding sites. 3. The competition curves, with 15 nM [3H]-CGP 12177, for the beta-agonists, isoprenaline (Iso), noradrenaline (NA) and adrenaline (Ad), and the selective beta 3-agonist, BRL 37344 (BRL), were clearly biphasic (P < 0.001). The rank orders of agonist potency (pKi) in competing for [3H]-CGP 12177 high affinity and low affinity binding sites, respectively, were Iso (9.28 +/- 0.24) > NA (8.90 +/- 0.12) > Ad (8.65 +/- 0.12) > > BRL (4.53 +/- 0.17) and BRL (7.38 +/- 0.19) > > Iso (2.96 +/- 0.26) > or = NA (2.80 +/- 0.17) > Ad (2.10 +/- 0.11) indicating the expression of beta 1- and beta 3-adrenoceptor subtypes on rat white adipocytes, respectively. Inversely, competition studies with the selective beta 1-agonist, xamoterol (Xam), provided evidence for a single homogeneous population of binding sites with low density (81 +/- 9 fmol mg-1) and high pKi value (7.23 +/- 0.26) confirming the presence of beta 1-adrenoceptors. 4. To assess a possible contribution of the beta 2-subtype, procaterol (Proc), a selective beta 2-agonist, was used to compete with 2 nM [3H]-CGP 12177. A single low affinity (4.61 +/- 0.07) population of binding sites was identified. The density of these sites (71 +/- 12 fmol mg-1) was similar to the one obtained with Xam, suggesting that Proc displaced [3H]-CGP 12177 from the beta 1-subtype. 5. The functional potency (pD2) order with BRL (9.07 +/- 0.20) and catecholamines (Iso: 7.26 +/- 0.06, NA: 6.89 +/- 0.02 and Ad: 6.32 +/- 0.07) was the same as that found for the low affinity binding sites in competition studies. Xam induced lipolysis with greater potency than dobutamine (Dob), 6.31 +/- 0.06 and 5.66 +/- 0.10, respectively. Proc stimulated lipolysis with a low potency (5.59 +/- 0.21). 6. The lipolytic response to 0.001 microM BRL was inhibited by both, selective beta 1- and beta 2-antagonist, in a monophasic manner with low potencies (CGP 20712A pKi: < 4.5 and ICI 118551 pKi: 5.57 +/- 0.13). Similar monophasic profiles were obtained for inhibition of Xam- and Dob-induced lipolysis. In this case, CGP 20712A was more potent (> 10 times) than ICI 118551. The monophasic inhibition was also observed with ICI 118551 in the presence of 0.05 microM Iso or 0.13 microM NA. In contrast, two populations of sites were identified with CGP 20712A in the presence of Iso as well as NA. The pKi values for the first sites were 8.41 +/- 0.09 and 8.58 +/- 0.17, respectively, and for the second population of sites 4.73 +/- 0.22 and 4.27 +/- 0.27, respectively. The proportion of the first sites was low: 19 +/- 4 and 22 +/- 5%, respectively. Biphasic curves were obtained with both antagonists using 2.5 microM Proc (CGP 20712A: pKi1: 8.17 +/- 0.08, site1: 23 +/- 6%, pKi2: 4.77 +/- 0.14; ICI 118551: pKi1: 7.78 +/- 0.03, site1: 37 +/- 2%, pKi2: 5.35 +/- 0.25). 7. Our results show that the radioligand [3H]-CGP 12177 allows the characterization of beta 1- and beta 3-adrenoceptor subtypes on rat white adipocytes. Lipolysis is highly dependent on beta 1- and beta 3-adrenoceptors. Finally, binding and functional studies confirm that lipolysis is mainly driven by the beta 3-subtype.

Regulation of the expression of the proenkephalin gene in cultured meningeal fibroblasts: opposite effects of alpha 1- and beta 2-adrenoceptors

Meningeal fibroblasts express the proenkephalin gene during embryonal development but terminate the expression shortly before birth. When brought into primary culture at postnatal day 1, the fibroblasts again express the gene. Activation of protein kinase A reduces this expression and thus may contribute to its prenatal termination. Since the noradrenergic innervation of the meninges begins around the time of birth, it was investigated in the present study, how adrenergic agonists affected the levels of proenkephalin mRNA in cultured fibroblasts. The beta 2-adrenoceptor agonists salbutamol and procaterol increased the levels of endogenous cAMP and diminished the concentration of proenkephalin mRNA indicating that the cultured fibroblasts possessed this beta-subtype. In contrast, noradrenaline increased the level of proenkephalin mRNA in a concentration-dependent manner. This effect was independent of endogenous cAMP and was mediated by alpha 1-adrenoceptors. The data indicate that the noradrenergic innervation of the meninges at the time of birth is not responsible for the termination of the proenkephalin gene expression.

Antibronchospasmic, tachycardiac, and hypokalaemic effects of L-isoproterenol in guinea-pigs

The relationship between antibronchospasmic, tachycardiac, or hypokalaemic effects and plasma concentration of L-isoproterenol (ISP) hydrochloride was investigated in guinea-pigs in vivo. ISP was infused at the rate of 10, 30, 50, 100, and 300 ng kg-1 min-1. The antibronchospasmic effect was expressed as the attenuation of methacholine-induced bronchospasm. The EC50 values of ISP for antibronchospasmic and tachycardiac effects were 5.12 nM and 3.95 nM, respectively. Although they were comparable to the values reported in vitro (7.23-0.358 nM, 1.77 nM), the concentration response relationship of ISP for antibronchospasmic effect was quite steep with a slope factor of more than six. Moreover, a decrease in plasma potassium level was not clearly detected. The experimental procedure in our present study was useful for evaluating antibronchospasmic and tachycardiac effects of beta-agonists.

Comparison of the attenuating effects of four beta-adrenoceptor agonists on rat isolated uterus and aorta

1. The ability of four beta-adrenoceptor agonists to attenuate oxytocin (0.2, 2 and 20 nmol/L) or KCl (20, 40 and 80 mmol/L)-induced contractions of the uterus (n = 5-8 for each agonist) and the KCl (18 mmol/L)-induced contractions of the aorta (n = 9 for each agonist) from rats, pretreated with oestradiol has been compared. 2. Isoprenaline, salbutamol, terbutaline and procaterol (0.1-10 mumol/L) attenuated the contractions of the uterus and the aorta. All four agonists had similar attenuating potencies on the uterus. 3. Procaterol caused the same maximal attenuation (33%) on the aorta as the other beta-adrenoceptor agonists and is thus acting as a full beta 2-adrenoceptor agonist under these experimental conditions. Isoprenaline and procaterol were much more potent than salbutamol and terbutaline in attenuating the aorta responses. 4. This study showed that isoprenaline and procaterol were potent attenuants on both the uterus and aorta whereas salbutamol and terbutaline were potent uterine but only modest aorta attenuants. This preliminary study indicates that the responsiveness of uterine and vascular tissue to certain beta 2-adrenoceptors differs.

Determination of beta-adrenoceptor subtype on rat isolated ventricular myocytes by use of highly selective beta-antagonists

1. The relative proportions of beta 1- and beta 2-adrenoceptors were determined by radioligand binding studies in three different rat myocardial preparations: membranes prepared from rat ventricle (ventricular membranes), membranes prepared from rat isolated ventricular myocytes (myocyte membranes), and myocytes isolated from rat ventricle (myocytes). 2. Competition experiments using CGP 20712A or ICI 118,551 with [125I]-iodocyanopindolol ([125I]-ICYP) revealed high- and low-affinity binding sites in ventricular membranes. The concentration at which each beta-antagonist occupied 100% of its high-affinity binding sites was 300 nM for CGP 20712A (beta 1-adrenoceptor) and 50 nM for ICI 118,551 (beta 2-adrenoceptor). 3. The density of high-affinity (beta 1-adrenoceptor) and low-affinity (beta 2-adrenoceptor) binding sites for CGP 20712A was measured by a saturation experiment using [125I]-ICYP in the presence and absence of 300 nM CGP 20712A. In ventricular membranes, the proportions of high-affinity and low-affinity binding sites for CGP 20712A were 73% and 27%, respectively, whereas in myocyte membranes, the corresponding figures were 90% and 10%, respectively. The density of low-affinity binding sites for CGP 20712A in ventricular membranes, defined as [125I]-ICYP-specific binding in the presence of 300 nM CGP 20712A, was decreased by addition of 50 nM ICI 118,551, whereas that in myocyte membranes was not affected. 4. In myocytes, specific binding of [125I]-ICYP and [3H]-CGP 12177 was not detected by saturation experiments performed in the presence of 300 nM CGP 20712A. 5 In myocytes, the activation of adenylate cyclase caused by beta2-adrenoceptors was not detected in the presence of 10 nM, 100 nM or 1000 nM CGP 20712A, which selectively antagonized beta1-adrenoceptors.Furthermore, the concentration-response curve for isoprenaline-stimulated cyclic AMP accumulation was not shifted by 10 nm or 100 nM ICI 118,551, which selectively antagonized beta2-adrenoceptors, but was shifted to the right by 1000 nM ICI 118,551.6 These results indicate that beta2-adrenoceptors are not present on rat ventricular myocytes and that beta2-adrenoceptor stimulation does not cause any detectable production of cyclic AMP. We conclude that only beta1-adrenoceptors exist on rat ventricular myocytes.

The interaction between salmeterol and beta 2-adrenoceptor agonists with higher efficacy on guinea-pig trachea and human bronchus in vitro

1. In guinea-pig tracheal preparations precontracted with 1 mumol l-1 carbachol, formoterol, procaterol, fenoterol, salmefamol, salbutamol and terbutaline (in that order of potency) caused a concentration-dependent and almost complete, relaxation. However, under these conditions, the maximum relaxation by salmeterol was approximately 30% of the maximum attainable relaxation. 2. We have therefore explored the ability of salmeterol to inhibit the relaxant response to beta 2-adrenoceptor agonists of different chemical structure and relatively higher efficacy in smooth muscle preparations from guinea-pig trachea and human bronchus. 3. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curves for the other agonists were shifted to the right in a variable way by 1.8-2.8 log units, fenoterol and salbutamol being the extremes. 4. When 20 mumol l-1 sulfonterol, another low efficacy beta 2-adrenoceptor agonist, was substituted for salmeterol, the difference in the magnitude of the rightward shift between fenoterol and salbutamol was eliminated. 5. In the human bronchus, formoterol and terbutaline had a higher apparent efficacy than salmeterol. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curve for formoterol was shifted 2.7 log units to the right. 6. Salmeterol inhibits, competitively, relaxant responses to beta 2-adrenoceptor agonists with higher efficacy. The degree of inhibition seems to be dependent on the agonist used. This contrasts with results obtained with sulfonterol and suggests that salmeterol interacts with the beta 2-adrenoceptor in a complex way.

Pharmacological characterization and anatomical localization of prejunctional beta-adrenoceptors in the rat kidney

1. The subtype and anatomical localization of beta-adrenoceptors mediating facilitation of stimulus-induced overflow of noradrenaline ('prejunctional beta-adrenoceptors') are not conclusively known to date. The present study was undertaken to characterize these receptors by use of pharmacological methods as well as to define their localization (prejunctional or postjunctional) with radio-ligand binding and autoradiography techniques combined with surgical denervation of the sympathetic innervation to the rat kidney. 2. Exposure of the kidney to (-)-isoprenaline, the nonselective beta-adrenoceptor agonist, resulted in a dose-dependent facilitation of stimulus-induced neurotransmitter overflow. This response was inhibited by propranolol, the beta 1- and beta 2-adrenoceptor antagonist, with a pA2 of 9.20 suggesting that the prejunctional beta-adrenoceptors are not of the beta 3-subtype. 3. The rank order of potency and potency ratios of beta-adrenoceptor agonists at renal prejunctional beta-adrenoceptors (EC50 for agonist/EC50 for (-)-isoprenaline) were: (-)-isoprenaline (1) > procaterol (2) > salbutamol (3) > adrenaline (10) > (+)-isoprenaline (25). However, dobutamine, the beta 1-adrenoceptor agonist, failed to enhance stimulus-induced overflow of noradrenaline. These results are indicative of the presence of beta 2-adrenoceptors as prejunctional beta-adrenoceptors. 4. Facilitation elicited by (-)-isoprenaline and procaterol, the selective beta 2-adrenoceptor agonist, was inhibited by ICI 118,551, the selective beta 2-adrenoceptor antagonist, with pKb values of 9.20 and 9.35, respectively at renal prejunctional beta-adrenoceptors. Similarly, the pKb values of metoprolol, the selective beta 1-adrenoceptor antagonist, at renal prejunctional beta-adrenoceptors were determined to be 6.25 and 6.18 against (-)-isoprenaline and procaterol, respectively. These results suggest the presence of a homogeneous population of beta 2-adrenoceptors as prejunctional beta-adrenoceptors. 5. Radio-ligand binding analysis of renal beta-adrenoceptors revealed the prevalence of the beta 1-subtype as compared to the beta 2-subtype (63% vs 37%). However, surgical denervation of the rat kidney, resulting in more than 90% reduction in renal noradrenaline content, selectively reduced the beta 2-adrenoceptor population by 80%, implying the presence of beta 2-adrenoceptors on renal sympathetic nerve terminals. 6. Autoradiographic analysis demonstrated the presence of beta 1-adrenoceptors on cortical structures such as glomeruli and tubules. beta-Adrenoceptors were found to be present on tubules (minor population), collecting tubules in outer medulla and the adventitia and adventitial-medial border of intraparenchymal branches of the renal artery. Surgical denervation of the rat kidney resulted in the disappearance of Beta2-adrenoceptors associated with the intraparenchymal branches, without affecting the Beta-adrenoceptor populations at other sites. These results support the notion that the Beta2-subtype is present on renal sympathetic nerve terminals and demonstrate that these prejunctional Beta2-adrenoceptors are associated with the renal vasculature and not with renal tubules.7. The results of the present investigation demonstrate that renal prejunctional Beta-adrenoceptors are of the Beta2-subtype in nature. These receptors are present on sympathetic nerve terminals which are associated with the renal vasculature.

Receptor for catecholamines responding to catechol which potentiates voltage-dependent calcium current in single cells from guinea-pig taenia caeci

1. Single isolated cells were obtained from the taenia of the guinea-pig's caecum by enzymic digestion and held under voltage clamp. The effects of various catecholamines, sympathomimetics and related compounds were tested for their ability to potentiate the voltage-dependent calcium current (ICa) evoked in these cells by a depolarizing step. 2. ICa was potentiated by up to 60% by isoprenaline, adrenaline, and noradrenaline which were equipotent. The EC50 for isoprenaline was about 40 nM. 3. The racemic mixtures of the optical isomers of isoprenaline, adrenaline, and noradrenaline, and (+)-isoprenaline, were equipotent with the (-)-isomers of these drugs. Dopamine, L-dopa, and catechol were equipotent with these catecholamines. 4. Removal or substitution of one or more of the hydroxy groups of the catechol moiety, as in phenylephrine, salbutamol, procaterol, methoxamine, terbutaline, BRL 37344, ICI 215001 or tyramine substantially reduced efficacy and/or potency. 5. The adrenoceptor blockers propranolol, phentolamine, dihydroergotamine, atenolol, CGP 20712A and ICI 118551, or the dopamine receptor blockers, haloperidol or flupenthixol, did not block the potentiating action of catechol or the catecholamines. 6. The receptor activated by catecholamines to increase ICa we suggest should be called a C-receptor in view of its sensitivity to catechol. It may arise by enzymic modification of a conventional adrenoceptor but its transduction also involves a novel mechanism which might indicate that it is present in the muscle cells before enzyme treatment.

Beta-adrenoceptor subtypes and the opening of plasmalemmal K(+)-channels in bovine trachealis muscle: studies of mechanical activity and ion fluxes

1. Studies of mechanical activity and 86Rb+ efflux have been made in bovine isolated trachealis with the objectives of: (a) identifying which of the beta-adrenoceptor subtypes mediates the opening of plasmalemmal K(+)-channels, (b) gaining further insight into the properties of the novel, long-acting beta 2-adrenoceptor agonist, salmeterol and (c) clarifying the role of K(+)-channel opening in mediating the mechano-inhibitory actions of agonists at beta-adrenoceptors. 2. In bovine trachealis muscle strips precontracted with histamine (460 microM), isoprenaline (0.1 nM-1 microM), procaterol (0.1-10 nM) and salmeterol (0.1-10 nM) each caused concentration-dependent relaxation. 3. ICI 118551 (10 nM-1 microM) antagonized isoprenaline, procaterol and salmeterol in suppressing histamine-induced tone of the isolated trachealis muscle. The antagonism was concentration-dependent. In contrast, CGP 20712A (10 nM-1 microM) failed to antagonize isoprenaline, procaterol or salmeterol. 4. Salmeterol (1-10 microM) antagonized isoprenaline in relaxing strips of bovine trachea which had been precontracted with carbachol (1 microM). 5. Cromakalim (10 microM), isoprenaline (100 nM-10 microM), procaterol (10 nM-1 microM) and salbutamol (100 nM-10 microM) each promoted the efflux of 86Rb+ from strips of bovine trachealis muscle preloaded with the radiotracer. In contrast, salmeterol (100 nM-10 microM) failed to promote 86Rb+ efflux. 6. CGP 201712A (1 microM), ICI 118551 (100 nM) and salmeterol (1 microM) did not themselves modify 86Rb+ efflux from trachealis muscle strips, nor did they affect the promotion of 86Rb+ efflux induced by cromakalim (10 microM). In contrast, CGP 20712A (1 microM) and ICI 118551 (100nM) were each able to inhibit the promotion of 86Rb+ efflux induced by isoprenaline (1 microM) or procaterol (100 nM). Furthermore,salmeterol (10 microM) inhibited isoprenaline (1 microM)-induced promotion of 86Rb+ efflux.7. It is concluded that, in bovine trachealis, activation of either beta l- or beta 2-adrenoceptors can promote the opening of 86Rb+-permeable K+-channels in the plasmalemma. The failure of salmeterol to promote plasmalemmal K+-channel opening may reflect, not its selectivity in activating beta 2- as opposed to beta 1-adrenoceptors, but rather its low intrinsic efficacy at beta 2-adrenoceptors. The opening of plasmalemmal K+-channels plays a supportive rather than a crucial role in mediating the mechano-inhibitory effects of agonists at beta-adrenoceptors acting on trachealis muscle.

Prediction of the therapeutic dose for beta-stimulants based on preclinical data: application of oral dosage forms and aerosols to asthmatic patients

The therapeutic doses of beta-stimulants in the treatment of bronchial asthma show wide variation among the drugs. In the present study, we tried to construct a system for prediction of the optimum clinical dose of beta-stimulants as oral dosage forms and aerosols using the data from preclinical pharmacological studies and pharmacokinetic data in humans. Values of EC50 (drug concentration that gives the half-maximum bronchodilator effect) in the in vitro studies based on isolated trachea of guinea pigs were collected from the literature. The ratios of the EC50 value of each drug to that of isoproterenol were used as the indicator of in vitro pharmacological activity. There were significant correlations between the EC50 ratios and the oral dose or the maximum plasma concentration after single oral administration, but the correlation coefficients were relatively small (r < .9). On the other hand, a linear log-log relationship was observed between the EC50 ratio and the maximum plasma unbound concentration (Cu(max)) (slope = 0.907, r = .955, p < 0.001). In the case of aerosols, a good correlation was observed between the EC50 ratio and the dose (slope = 0.770, r = .900, p < 0.01). The predicted concentration of beta-stimulants in the lung after aerosol administration tended to be higher than the Cu(max) after oral administration, suggesting the contribution of nonspecific binding in the lung tissue. These findings indicate the possibility of predicting the appropriate dose of beta-stimulants based on the preclinical pharmacological data and the pharmacokinetic data in humans.

Selective and full beta 1-adrenoceptor agonist action of a catechol derivative of denopamine (T-0509) in the guinea-pig cardiac muscle and trachea: comparison with denopamine, xamoterol and isoprenaline

1. The pharmacological actions of T-0509, a 3-hydroxy derivative of denopamine, were studied in various guinea-pig tissues; these effects were compared with those of isoprenaline, denopamine and xamoterol. 2. The intrinsic activities of the positive inotropic actions of T-0509, denopamine and xamoterol compared with isoprenaline (= 100%) in the papillary muscle were 99%, 83% and 28%, respectively, while their relative potencies (EC50 agonist EC50 isoprenaline) were 0.23, 33 and 1.4, respectively. The intrinsic activities of T-0509, denopamine and xamoterol as positive chronotropic agents in the right atria were 98%, 69% and 48%, respectively, and their equipotent concentrations (isoprenaline = 1) were 0.24, 50 and 4, respectively. 3. The positive chronotropic actions of T-0509 and denopamine were antagonized by bisoprolol (3 x 10(-8) M), but not by ICI 118,551 (3 x 10(-8) M). 4. The intrinsic activity of T-0509 in histamine-contracted tracheae was similar to that of isoprenaline, but its equipotent concentration was 38; the effects of both agents were antagonized by ICI 118,551 (3 x 10(-8) M), but not by bisoprolol (3 x 10(-8) M). Denopamine and xamoterol did not show any agonist activity on guinea-pig trachea. 5. Denopamine and xamoterol antagonized the positive chronotropic (pA2, denopamine: 6.98, xamoterol: 7.75) and tracheal relaxant (pA2, denopamine: 5.39, xamoterol: 6.25) effects of isoprenaline. 6. Isoprenaline, T-0509 and denopamine, but not xamoterol, contracted the guinea-pig aorta in a decreasing order in the presence of propranolol (10(-6) M).7. Based on the above studies, T-0509 appears to be a highly selective betaI-adrenoceptor agonist with full agonist properties, while denopamine and xamoterol appear to be selective, but partial betaI-adrenoceptor agonists.

Tracheal relaxing effects and beta 2-selectivity of TA-2005, a newly developed bronchodilating agent, in isolated guinea pig tissues

Tracheal relaxing effects and beta 2-selectivity of TA-2005 were investigated by functional experiments and radioligand binding assay in guinea pigs in comparison with those of other beta-agonists, isoproterenol, procaterol, formoterol and salbutamol. The relaxing activity of TA-2005 on histamine-induced contraction in the isolated trachea was most potent among the five agonists, and it was blocked by a beta 2-selective antagonist (ICI 118,551) but not by a beta 1-selective antagonist (bisoprolol). The potency of the relaxing effect was in the order of TA-2005 (pD2 = 9.79) greater than formoterol greater than procaterol greater than isoproterenol greater than or equal to salbutamol. The positive chronotropic effect of TA-2005 was similar to that of isoproterenol; and it was more potent than those of formoterol, procaterol and salbutamol in the isolated atria. The selectivity for tracheal muscle to atria of these agonists were in the order of procaterol greater than greater than or equal to formoterol greater than TA-2005 greater than salbutamol much greater than isoproterenol. A radioligand binding experiment using guinea pig lung and cardiac ventricle as beta 2- and beta 1-adrenoceptor sources, respectively, has also demonstrated that TA-2005 possesses extremely high affinity (IC50 = 1.04 nM) and selectivity (38-fold) to beta 2-adrenoceptors. By addition of GTP, the competition curve of [125I]iodocyanopindolol shifted rightward, indicating the agonist property. These results confirmed that TA-2005 is a highly beta 2-selective agonist that exerts a potent tracheal relaxing effect.

Evidence for the existence of postsynaptic beta-1 and beta-2 adrenoceptors in isolated simian facial veins

With the use of a steel cannula inserting method, the actions of the beta-adrenoceptor agonists, noradrenaline (NA, a mixed agonist), isoprenaline (a mixed agonist), dobutamine (a selective beta-1 agonist), salbutamol, and procaterol (selective beta-2 agonists), were investigated on isolated and perfused simian facial veins. Each beta-agonist usually induced a vasodilation in a dose-related manner in non-preconstricted vessel preparations. The rank order of potency was isoprenaline much greater than NA greater than dobutamine greater than salbutamol greater than procaterol. NA- and isoprenaline-induced vasodilations were inhibited by either metoprolol (a selective beta-1 adrenoceptor antagonist) or ICI 118,551 (a selective beta-2 antagonist). After beta-1 blockade, NA produced a vasoconstriction which was readily blocked by bunazosin (an alpha-1 antagonist). Dobutamine-induced vasodilations were strongly suppressed by metoprolol and slightly blocked by ICI 118,551. Salbutamol-induced vasodilations were blocked by metoprolol, while ICI 118,551 more markedly inhibited these dilations. From these results, it was concluded that there are abundant beta-adrenoceptors and predominantly beta-1 adrenoceptors in isolated simian facial veins.

Beta- and alpha-adrenoceptor-agonists and -antagonists in chronic heart failure

In patients with chronic heart failure, cardiac beta-adrenoceptor function is decreased, and this decrease is related to the degree of heart failure. Under these conditions, treatment with beta-adrenoceptor agonists seems to be of limited value as it might further down-regulate cardiac beta-adrenoceptors, resulting, finally, in a loss of therapeutic efficacy. However, beta-adrenoceptor antagonists might have beneficial effects, because they can protect the myocardium from the deleterious effects of elevated endogenous catecholamines and can, simultaneously, restore the previously down-regulated beta-adrenoceptor function. Stimulation of cardiac alpha-adrenoceptors, however, seems not to be of any therapeutic value in patients with chronic heart failure, because a) the number of alpha-adrenoceptors in the human heart is very low and its function is not completely understood, and b) no alpha-adrenoceptor agonist is presently available that selectively stimulates cardiac alpha-adrenoceptors without concomitantly activating vascular alpha-adrenoceptors. In acute myocardial ischemia, cardiac beta-adrenoceptors increase; this increase is--at least in early acute myocardial ischemia--accompanied by an increased beta-adrenoceptor functional responsiveness; thus, under these conditions, beta-adrenoceptor agonists again might not be of clinical value, while beta-adrenoceptor antagonists may exert beneficial effects, because they can block (over)activation of the sensitized beta-adrenoceptors by elevated endogenous catecholamines.

Steric aspects of agonism and antagonism at beta-adrenoceptors: synthesis of and pharmacological experiments with the enantiomers of formoterol and their diastereomers

The enantiomers of formoterol (R;R and S;S) and their diastereomers (R;S and S;R) were synthesized and purified using a new procedure which required the preparation of the (R;R)- and (S;S)-forms of N-(1-phenylethyl)-N-(1-(p-methoxyphenyl)-2-propyl)-amine as important intermediates. The enantiomeric purity obtained was greater than 99.3%, usually greater than 99.7%. The four stereoisomers were examined with respect to their ability to interact in vitro with beta-adrenoceptors in tissues isolated from guinea pig. The effects measured were (1) relaxation of the tracheal smooth muscle (mostly beta 2), (2) depression of subtetanic contractions of the soleus muscle (beta 2), and (3) increase in the force of the papillary muscle of the left ventricle of the heart (beta 1). All enantiomers caused a concentration-dependent and complete relaxation of the tracheal smooth muscle which was inhibited by propranolol. The order of potency was (R;R) much greater than (R;S) = (S;R) greater than (S;S). There was a 1,000-fold difference in potency between the most and the least potent isomer. The presence of the (S;S)-isomer did not affect the activity of the (R;R)-isomer on the tracheal smooth muscle. Also on the skeletal and cardiac muscles (R;R)-formoterol was more potent than its (R;S)-isomer. The selectivity for beta 2-adrenoceptors appeared to be slightly higher for the (R;R)-isomer than for the (R;S)-isomer. The potency of the (S;R)- and (S;S)-isomers on the papillary muscle was too low to be determined accurately.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonist-induced desensitization of beta-adrenoceptor function in humans. Subtype-selective reduction in beta 1- or beta 2-adrenoceptor-mediated physiological effects by xamoterol or procaterol

We investigated the effects of beta 2- (procaterol 2 x 50 micrograms/day for 9 days) and beta 1- (xamoterol 2 x 200 mg/day for 14 days) adrenoceptor agonists on lymphocyte beta 2-adrenoceptor density and beta 1- and beta 2-adrenoceptor in vivo function (assessed as isoprenaline-infusion-evoked hemodynamic effects and exercise-induced tachycardia) in healthy volunteers. Procaterol decreased lymphocyte beta 2-adrenoceptor density and all beta 2-adrenoceptor-mediated in vivo effects but did not affect beta 1-adrenoceptor-mediated in vivo effects. In contrast, xamoterol neither affected lymphocyte beta 2-adrenoceptors nor beta 2-adrenoceptor-mediated in vivo effects but decreased beta 1-adrenoceptor-mediated in vivo effects. It is concluded that in humans, generally long-term application of beta 1- or beta 2-adrenoceptor agonists causes desensitization of beta-adrenoceptor function but in a beta-adrenoceptor subtype-selective fashion.

Lipomobilizing effects of procaterol and yohimbine in the conscious dog: comparison of endocrinological, metabolic and cardiovascular effects

1. Lipid mobilization during a hypocaloric diet may be enhanced by a pharmacological approach using beta 2-adrenoceptor agonists or alpha 2-adrenoceptor antagonists. Studies were undertaken in the dog, an animal model presenting fat cell antilipolytic alpha 2- and lipolytic beta-adrenoceptors, in order, firstly, to demonstrate the presence of beta 2 subtype adrenoceptors on adipocytes and, secondly, to compare the effects of procaterol (beta 2-adrenoceptor agonist) and of yohimbine (alpha 2-adrenoceptor antagonist) on metabolic, endocrinological and cardiovascular parameters. 2. Procaterol strongly stimulates lipolysis in dog adipocytes in vitro. The utilisation of selective beta 1- and beta 2-adrenoceptor antagonists (bisoprolol and ICI 118,551) in both lipolysis and binding studies (displacement of [3H]-dihydroalprenolol binding) demonstrated the presence of the two beta-adrenoceptor subtypes in dog fat cells. 3. Infusion of either yohimbine or procaterol (10 and 0.4 nmol min-1 kg-1, respectively for 30 min), provoked an equivalent increase in plasma non-esterified fatty acids (+100%). Procaterol, but not yohimbine, induced hyperglycaemia (+120%). Plasma insulin was weakly enhanced by yohimbine (+120%) as compared to the increase given by procaterol (+500%). 4. Both drugs stimulated sympathetic nervous system activity, as indicated by the increased plasma noradrenaline concentration, but only yohimbine increased the plasma adrenaline level. 5. Cardiovascular measurements indicated that procaterol strongly enhances heart rate and transiently decreases mean blood pressure. Yohimbine exhibits a weaker effect on heart rate and slightly increases mean blood pressure. 6. The present work clearly indicates that lipid mobilization is enhanced during fasting in the dog by selective beta 2-adrenoceptor stimulation or by alpha 2-adrenoceptor blockade. This enhanced lipolytic effect may result either from a direct action of the drugs on the adrenoceptors of fat cells or from an activation of the sympathetic nervous system. Procaterol suffers major limitations since it strongly increases heart rate, immunoreactive insulin and glycaemia. On the other hand, yohimbine induces only minor modifications both in cardiovascular and endocrinological parameters.

Classification of beta-adrenoceptors in ferret tracheal smooth muscle by pharmacological responses

Beta-adrenoceptors in ferret tracheal smooth muscle were classified into beta 1 or beta 2 by determination of (i) the potency rank order for isoprenaline, noradrenaline and adrenaline, and (ii) apparent pA2-values for a specific beta 1-antagonist (practolol) and a specific beta 2-antagonist (ICI 118.551) and (iii) concentration-inhibition curves for procaterol, a beta-agonist showing a biphasic concentration-response curve in organs with a mixed beta 1 and beta 2 adrenoceptor population. We used in vitro tracheal rings and assessed the responses to beta-adrenoceptor agonists as inhibition of phasic contractions elicited by electrical field stimulation (2 Hz for 20 s) or relaxation of tonic contractions elicited by acetylcholine (0.5 microM). The potency rank order for the agonists was isoprenaline greater than noradrenaline approximately adrenaline indicating action through beta 1-receptors. Apparent pA2-values for the antagonists were for 1, 3 and 10 microM practolol 6.0 (SE 0.27), 6.1 (SE 0.21) and 6.3 (SE 0.03), respectively. Apparent pA2 for 0.1, 1 and 10 microM ICI 118.551 were 6.8 (SE 0.25), 6.7 (SE 0.12) and 6.1 (SE 0.14), respectively. These values agree well with published pA2-values for the action of these drugs on beta 1-adrenoceptors. However, the Schild plot for ICI 118.551 was alinear indicating a possible heterogeneity of the beta-adrenoceptors in ferret trachea. The concentration-response curve for procaterol showed the biphasic form typical for organs with a mixed beta 1 and beta 2 population. However, the lower part of the curve, reflecting stimulation of beta 2-adrenoceptors reached only 17.5% (SE 1.4) of the maximally achieved inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Pre- and post-junctional actions of procaterol, a beta 2-adrenoceptor stimulant, on dog tracheal tissue

1. The effects of procaterol, a beta 2-adrenoceptor agonist, on excitatory neuro-effector transmission in the dog trachea were investigated and the findings were compared to those seen with isoprenaline, with microelectrode, double sucrose gap and tension recording methods. 2. Procaterol (10(-10)-10(-9) M) and isoprenaline (10(-9) M) had no effect on the resting membrane potential or on the input resistance of the smooth muscle cells of dog trachea. However with increased concentrations (greater than 10(-8) M), these agents hyperpolarized the membrane and decreased the input resistance of the membrane. 3. Procaterol (10(-10)-10(-7) M) and isoprenaline (10(-9)-10(-7) M) dose-dependently reduced the amplitude of the twitch contractions evoked by field stimulation in the combined presence of indomethacin (10(-5) M) and guanethidine (10(-6) M). In parallel with actions on twitch contractions, procaterol (10(-10)-10(-7) M) and isoprenaline (10(-9)-10(-7) M) reduced the amplitude of the excitatory junction potentials (e.j.ps), evoked by single pulse field stimulation in the dog trachea. 4. Procaterol (10(-8) M) had no effect on the post-junctional response of smooth muscle cells to exogenous acetylcholine (ACh) (10(-7)-10(-6) M). 5. Pretreatment with ICI-118551, a beta 2-adrenoceptor blocking agent, reduced the inhibitory action of procaterol on the amplitude of twitch contractions evoked by field stimulations in the dog trachea. 6. These results indicate that procaterol in low concentrations has a prejunctional action inhibiting the excitatory neuro-effector transmission in addition to a postsynaptic action, presumably by suppressing transmitter release from the vagus nerve terminals through beta 2-adrenoceptors in the dog tracheal tissue. The pre- and post-junctional actions of procaterol explain its potent bronchodilator effects in clinical use.

Presynaptic beta 2-adrenoceptors on the sympathetic nerve fibres of the human saphenous vein: no evidence for involvement in adrenaline-mediated positive feedback loop regulating noradrenergic transmission

Spirally cut strips of human saphenous veins preincubated with 3H-noradrenaline were superfused in the presence of corticosterone and, unless stated otherwise, of cocaine or desipramine. Tritium overflow was stimulated electrically (2 Hz). Adrenaline (in the presence of rauwolscine), isoprenaline and the preferential beta 2-adrenoceptor agonist procaterol concentration-dependently increased the electrically evoked tritium overflow. Prenalterol, a beta-adrenoceptor agonist with moderate preference for beta 1-adrenoceptors, was ineffective. The concentration-response curve of isoprenaline was shifted to the right by the nonselective beta-adrenoceptor antagonist propranolol and by the preferential beta 2-adrenoceptor antagonist ICI 118,551, but was not affected by the beta 1-selective antagonist atenolol. In experiments on strips preexposed to adrenaline 10 nmol/l (i.e. a concentration higher than that which normally occurs in vivo) for 32 min in the absence of cocaine or desipramine, the electrically evoked 3H overflow was not affected 12 and 44 min after withdrawal of adrenaline, irrespective of whether propranolol was absent or present in the superfusion fluid. In veins incubated with 3H-adrenaline, a considerable amount of the radioactivity was accumulated. During subsequent superfusion with 3H-adrenaline-free solution, electrical stimulation induced tritium overflow in a tetrodotoxin-sensitive manner. Propranolol failed to modify the evoked tritium overflow. It is concluded that the sympathetic nerve fibres of the human saphenous vein are endowed with facilitatory presynaptic beta 2-adrenoceptors. These receptors do not seem to play a substantial role in a local adrenaline (previously taken up)-mediated positive feedback loop regulating noradrenergic transmission, at least under the present in vitro conditions.

Comparison between oral procaterol and salbutamol in patients with bronchial asthma

The efficacy of procaterol, a new beta 2-selective sympathomimetic drug, was compared with that of salbutamol and placebo in a double-dummy crossover study in 20 asthmatic patients. Procaterol (0.1 mg orally) was given twice daily and salbutamol (4 mg orally) 3-times a day. The study was made up of four consecutive 4-day treatment periods including two periods of plain placebo. A significant direct bronchodilating effect of both procaterol and salbutamol could be seen in PEF values, measured 4-times a day, compared with the effect of placebo (p less than 0.01 for both). Procaterol was slightly superior to salbutamol. The afternoon and evening PEF values during the procaterol period did not differ from the values during the placebo period. In symptom scores, there was significantly more tremor during the procaterol period than during the placebo period (p less than 0.01). Both procaterol and salbutamol produced more palpitation than placebo (p less than 0.05). The study shows that oral procaterol is a potent bronchodilator. The doses of procaterol and salbutamol were not equivalent. Procaterol with the dose used in the study was more potent. Despite this, the duration of the bronchodilator effect of procaterol on a twice daily dosage did not seem to be long enough in all patients.

Characterization and autoradiographic localization of beta-adrenoceptor subtypes in human cardiac tissues

1 Receptor autoradiography using (-)-[125I]-cyanopindolol (CYP) was used to study the distribution of beta-adrenoceptor subtypes in human right atrial appendage, left atrial free wall, left ventricular papillary muscle and pericardium. 2 The binding of (-)-[125I]-CYP to slide-mounted tissue sections of human right atrial appendage was time-dependent (K1 = 4.11 +/- 1.01 X 10(8) M-1 min-1, K-1 = 1.47 +/- 0.25 X 10(-3) min-1, n = 3), saturable (42.02 +/- 2.96 pM, n = 4) and stereoselective with respect to the optical isomers of propranolol (pKD (-):8.97 +/- 0.02, (+):6.88 +/- 0.06, n = 3). 3 The proportions of beta-adrenoceptor subtypes were determined in slide-mounted tissue sections using the antagonists CGP 20712A (beta 1-selective) and ICI 118,551 (beta 2-selective). In right atrial appendage and left ventricular papillary muscle 40% (34-45%) of the beta-adrenoceptors were of the beta 2-subtype. 4 Images from X-ray film and nuclear emulsion coated coverslips exposed to (-)-[125I]-CYP-labelled sections showed an even distribution of beta-adrenoceptor subtypes over the myocardium of the right atrial appendage, left ventricular papillary muscle and left atrial free wall. Sections of pericardium exhibited predominantly beta 2-adrenoceptors. beta 2-Adrenoceptors were localized to the intimal surface of coronary arteries. 5 The selective beta 1-adrenoceptor agonist RO363 and beta 2-selective agonist procaterol produced concentration-dependent inotropic responses in right atrial appendage strips. Responses to RO363 were antagonized by CGP 20712A (pKB = 9.29) suggesting an interaction with beta 1-adrenoceptors. Responses to procaterol were antagonized by ICI 118,551 (pKB = 9.06) suggesting an interaction at beta 2-adrenoceptors. 6 The finding that a significant proportion of human myocardial adrenoceptors are of the beta 2-subtype has important clinical implications for the involvement of these receptors in the control of heart rate and force, and the autoradiographic evidence suggests other roles in the coronary vasculature and pericardium.

The role of cyclic AMP in the positive inotropic effect mediated by beta 1- and beta 2-adrenoceptors in isolated human right atrium

The time course of the effects of isoprenaline (3 X 10(-7) mol/l) on contractile force and on the cyclic AMP level was studied in the electrically driven isolated muscle strip of the human right atrium. Isoprenaline produced a rise in cyclic AMP content (maximum increase after 60 s) preceding the increase in contractile force. The effects of isoprenaline on contractile force and on the intracellular level of cyclic AMP were enhanced in the presence of the phosphodiesterase inhibitor papaverine (10(-5) mol/l). On the other hand, the beta-adrenoceptor antagonist propranolol (10(-7) mol/l) suppressed isoprenaline-induced cyclic AMP increases, but reduced the increase in force of contraction by only 35%. In addition, both the beta 1-selective antagonist bisoprolol (3 X 10(-9)-3 X 10(-8) mol/l) and the beta 2-selective antagonist ICI 118,551 (3 X 10(-9)-3 X 10(-8) mol/l) inhibited the isoprenaline-induced cyclic AMP increase concentration-dependently; ICI 118,551 produced more pronounced inhibition than bisoprolol. It is concluded that cyclic AMP is involved in the positive inotropic action of isoprenaline evoked by beta 1- and beta 2-adrenoceptor stimulation in isolated human right atrium; however, an additional cyclic AMP independent mechanism cannot be ruled out.

Involvement of the locus coeruleus in the potentiation of the quipazine-induced head-twitch response by diazepam and beta-adrenoceptor agonists

Head-twitching in rats induced by quipazine was reduced by bilateral lesions of the locus coeruleus (LC) produced by 6-hydroxydopamine. Both beta 1-and beta 2-adrenoceptor agonists potentiated the head-twitch induced by quipazine in sham-operated controls. Lesions of the locus coeruleus increased the responses to the beta 1-adrenoceptor agonists, prenalterol and dobutamine, but reduced the response to the beta 2-adrenoceptor agonists, salbutamol and procaterol. Diazepam (0.25 mg/kg) also potentiated the response to quipazine and this was reversed to inhibition by lesions of the locus coeruleus. These results suggest that the beta 1-adrenoceptors involved are postsynaptic and the beta 2-adrenoceptors are presynaptic to neurones of the locus coeruleus and indicate a dual action of diazepam on the head-twitch induced by quipazine. Possible mechanisms for these effects are discussed.

Partial agonism and functional selectivity: a study on beta-adrenoceptor mediated effects in tracheal, cardiac and skeletal muscle

Colterol, procaterol, sulfonterol, terbutaline and three monophenolic derivatives of terbutaline were examined with respect to their ability to react in vitro on beta-adrenoceptors in tissues isolated from guinea-pig. The effects measured were a) relaxation of the tracheal smooth muscle (mostly beta 2), b) depression of subtetanic contractions of the soleus muscle (beta 2), and c) increase in the force of the papillary muscle of the left ventricle (beta 1). Antagonistic effects were measured against isoprenaline as an agonist. The compounds studied showed a wide variation in selectivity, potency and intrinsic activity. All agonists showed a pronounced beta 2-selectivity, in general characterized by a higher intrinsic activity at beta 2- than at beta 1-adrenoceptors, while differences in affinity, as judged from the pA2-values were small. Partial agonists, such as sulfonterol, which did not cause a complete relaxation of a moderately contracted tracheal muscle, produced identical concentration-response curves from the trachea and soleus muscle. It is concluded that partial agonism at beta 1-adrenoceptors is an important factor for functional selectivity of beta 2-adrenoceptor agonists. On the other hand there seems to be no useful differences between the maximum effect elicited by a partial beta 2-adrenoceptor agonist on the skeletal muscle as compared with airway smooth muscle.

Human myocardial beta-adrenoceptors: demonstration of both beta 1- and beta 2-adrenoceptors mediating contractile responses to beta-agonists on the isolated right atrium

On the isolated electrically driven muscle strip of human right atrial appendages the beta-adrenoceptor subtypes mediating the positive inotropic effects of isoprenaline, dobutamine and procaterol were characterized using the beta 1-selective antagonist bisoprolol and the beta 2-selective antagonist ICI 118,551. The three agonists induced concentration-dependent increases in force of contraction with an order of potency: procaterol (pD2-value: 8.03) greater than isoprenaline (pD2-value: 7.73) greater than dobutamine (pD2-value: 5.44). In saturating concentrations all three agonists produced the same maximum of developed tension. ICI 118,551 (10(-9)--10(-7) mol/l) and bisoprolol (10(-9)--10(-7) mol/l) were nearly equipotent in antagonizing the positive inotropic effects of isoprenaline and dobutamine. However, the slopes of the Schild-plots for both antagonists against both agonists were significantly less than 1.0 indicating interaction with beta 1- and beta 2-adrenoceptors. On the other hand, ICI 118,551 (10(-10)--10(-8) mol/l) was approximately 100 times more potent than bisoprolol (10(-8)--10(-6) mol/l) in antagonizing the positive inotropic effect of the highly selective beta 2-agonist procaterol. In addition, the slopes of the Schild-plots for antagonism of ICI 118,551 and bisoprolol against procaterol were not significantly different from unity indicating interaction with a homogeneous class of beta-adrenoceptors. The pA2-value for ICI 118,551 was 9.49, for bisoprolol it amounted to 6.99.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on the cardiomegaly induced by beta-adrenoceptor agonists

Rats received continuous infusions of beta-adrenoceptor agonists by means of Alzet osmotic minipumps implanted subcutaneously. After 7 days of isoprenaline infusion (2 mg/kg per day) the heart/body weight ratio increased about 40 per cent compared with placebo treatment. The difference persisted after freeze-drying indicating a true hypertrophy and not merely an oedema. When terbutaline (20 mg/kg per day) was substituted for isoprenaline, the increase in wet weight ratio reached only about 5 per cent. Procaterol (2 mg/kg per day) and pirbuterol (20 mg/kg per day) had no effect on the heart weight. It is concluded that in doses expected to cause comparable stimulation of beta 2-adrenoceptors the unselective agonist isoprenaline is able, more than the beta 2-selective agonists terbutaline, procaterol and pirbuterol to cause cardiac hypertrophy thus indicating the involvement of beta 1-adrenoceptors.

The modulation of head-twitch behaviour by drugs acting on beta-adrenoceptors: evidence for the involvement of both beta 1- and beta 2-adrenoceptors

Drugs selective for either the beta 1- or beta 2-adrenoceptor have been investigated for their effects on the head-twitch behaviour induced by L-5-hydroxytryptophan (L-5-HTP) in mice. All four agonists, dobutamine and prenalterol (beta 1-), and salbutamol and procaterol (beta 2-), potentiated the effect of L-5-HTP although they were ineffective in inducing the head-twitch when administered alone. The corresponding antagonists, practolol and metoprolol (beta 1-) and butoxamine and ICI 118,551 (beta 2-), were without effect on the L-5-HTP head-twitch. The antagonists each significantly reduced the effect of the corresponding agonists but, while butoxamine and ICI 118,551 were inactive against dobutamine and prenalterol potentiation, both practolol and metoprolol reduced the effect of salbutamol and procaterol. Thus it is argued that dobutamine and prenalterol potentiation is due to an action at beta 1-adrenoceptors, while at least a component of the potentiating effect of salbutamol and procaterol is exerted through beta 2-adrenoceptors. The lack of effect of the antagonists alone is discussed.

A comparative study of a new selective beta 2-adrenoceptor agonist, procaterol and salbutamol in asthma

The effects of single oral doses of a new selective beta 2-adrenoceptor agonist procaterol (0.05 mg and 0.1 mg) and salbutamol (4 mg) on ventilatory function, were compared in 24 asthmatic patients. A bronchodilator effect of similar duration and magnitude followed all three treatments with no evidence of a dose-related response in the case of procaterol. There was no significant difference in blood pressure or heart rate responses or pattern of unwanted effects. We conclude that procaterol and salbutamol are clinically similar with oral dosing and that the maximum effective dose of procaterol is not greater than 0.05 mg.

Beta 1-adrenoceptor-mediated amylase release and cyclic AMP accumulation in rat parotid gland tissue

The present study was carried out to determine the relationship of beta 1- and Beta 2-subtype to amylase release and cyclic AMP (cAMP) accumulation in rat parotid tissue. In in vitro experiments, beta-adrenergic agents (isoproterenol and dobutamine)-induced amylase release and cAMP accumulation were all completely inhibited by the beta 1-antagonist metoprolol, but incompletely inhibited by the beta 2-antagonist butoxamine. The beta 2-agonist procaterol caused little or no amylase release or cAMP accumulation. Our results suggest that both amylase release and cAMP accumulation in rat parotid tissue may be selectively induced by beta 1-adrenergic stimulation.

Responses to the beta 2-selective agonist procaterol of vascular and atrial preparations with different functional beta-adrenoceptor populations

Relaxant responses to the beta-adrenoceptor agonist, procaterol, have been examined on preparations of guinea-pig pulmonary artery (beta 2-adrenoceptors only), rat and rabbit pulmonary artery and rat aorta (beta 2 greater than beta 1), and these responses have been compared with responses of dog left circumflex coronary artery (beta 1 only). Low concentrations of procaterol (3 nM to 100 nM) relaxed KC1-contracted preparations of rat aorta and pulmonary artery from rat, rabbit and guinea-pig whereas high concentrations (greater than 1 microM) were required to relax preparations of the dog left circumflex coronary artery. The dissociation constant (KP value) for procaterol on beta 1-adrenoceptors was 4.9 microM (determined on dog coronary artery) and on beta 2-adrenoceptors was 0.008 microM (rabbit pulmonary artery). Procaterol therefore had a beta 2:beta 1 selectivity value of 612. KP values obtained on guinea-pig atria for procaterol, on which the concentration-response curve was biphasic, confirmed that both beta 2- and beta 1-adrenoceptors mediate responses of this tissue. The KP values were 0.009 microM (data from the first phase of the control concentration-response curve) and 3.5 microM (data from the concentration-response curve in the presence of the beta 2-selective antagonist, ICI 118,551, 10 nM). Data obtained on rat atria indicated that chronotropic responses of preparations from some rats, but not others, involved a minor population of beta 2-adrenoceptors, but the beta 2-adrenoceptors, when present, were less important than in guinea-pig atria. 6 Procaterol appears to be a particularly useful drug for detecting a functional population of beta 2-adrenoceptors in tissues, whether they are the minor or the predominant receptor sub-type present.

Is there any evidence of beta 1-adrenoceptors mediating relaxation of guinea-pig lung parenchyma?

We tried to find functional evidence for the existence of beta 1- and beta 2-adrenoceptors in the isolated guinea-pig lung parenchymal strip preparation, using potent and selective beta 1- and beta 2-adrenoceptor stimulation. To obtain potent beta 1-adrenoceptor stimulation the nonselective beta-adrenoceptor agonist isoprenaline was combined with a highly selective beta 2-adrenoceptor antagonist--ICI 118,551. Potent beta 2-adrenoceptor stimulation was obtained by procaterol. Practolol (beta 1-adrenoceptor antagonist) and ICI 118,551 were used as antagonists. ICI 118,551, 10(-7) mol/l, shifted the concentration response (C/R) curve of isoprenaline to a higher concentration range. The C/R curve of procaterol was shifted in the same way and to the same degree by this concentration of ICI 118,551. The C/R curve of isoprenaline was not further shifted after blockade with a combination of ICI 118,551, 10(-7) mol/l, and practolol, 10(-6). However, in the trachea preparation, a tissue containing both beta 1- and beta 2-adrenoceptors, there was a further shift of the C/R curve of isoprenaline to a higher concentration range after blockade with a combination of ICI 118,551 and practolol in the concentrations given above. In this preparation the shift of the C/R curve of procaterol was ten times greater than that of isoprenaline after blockade with ICI 118,551, 10(-7) mol/l. We conclude that it is possible to characterize small fractions of beta 1-adrenoceptors coexisting with beta 2-adrenoceptors with the technique used. Furthermore there is still no functional evidence of the existence of beta 1-adrenoceptors in the lung parenchyma.

Beta 2-adrenoceptors in guinea-pig atria

The occurrence of beta 2-adrenoceptors in the isolated, spontaneously beating right atrium and the electrically driven left atrium of the guinea-pig was studied. Isoprenaline was used as reference compound and procaterol as selective beta 2-agonist. Cumulative concentration response (C/R) curves were obtained with the agonists. The C/R curve of procaterol was biphasic in both preparations. Compared with isoprenaline, procaterol was a partial agonist, with a mean maximum response of 0.78 +/- 0.04 in the right atrium and 0.29 +/- 0.05 in the left atrium. The beta 2-selective antagonist ICI 118,551, 10(-7) mol litre-1, caused a small but significant shift of the C/R curve of isoprenaline to a higher concentration range in both preparations. The same concentration of the beta 2-blocker changed the shape of the C/R curve of procaterol from biphasic to monophasic by blocking the responses to low concentrations of procaterol. Practolol, a beta 1-selective antagonist, 10(-6) mol litre-1, gave a highly significant shift of the C/R curve of isoprenaline to a higher concentration range in both preparations but had no effect on the responses to low concentrations of procaterol. The effect of practolol on the responses to high concentrations of procaterol is discussed. We conclude that the guinea-pig atria may contain beta 2-adrenoceptors mediating positive chronotropic and inotropic effects.

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.