Absence of mitochondrial beta-adrenoceptors in guinea pig myocardium: evidence for tissue disparity.

1. Binding sites in guinea pig myocardial tissue labelled by (-)-[125I] cyanopindolol (CYP) were investigated using differential centrifugation and autoradiographic techniques. Autoradiographs of myocardial sections (0.1 microns) indicated (-)-[125I]CYP binding to sarcolemmal membrane. A low density of binding sites was observed to mitochondria. 2. Binding studies were performed in subcellular fractions. The density of binding sites in the mitochondrial fraction (36.1 +/- 9.4 fmol/mg protein) was less than 10% that in the sarcolemmal membrane (371.7 +/- 38.2 fmol/mg protein). The beta 1/beta 2-adrenoceptor subtype ratio in the mitochondrial fraction (83.3/16.7) was similar to that in the sarcolemmal fraction (87.1/12.9). 3. Ouabain (100 microM), in the presence of sodium azide (0.4 mM), inhibited a Na+K+ stimulated ATPase activity (1.0 +/- 0.2 mumol Pi/mg protein/hr reduction), indicating a low but significant level of sarcolemmal contamination of the mitochondrial fraction. 4. The study showed beta-adrenoceptors in guinea pig heart are located primarily on the sarcolemmal membrane of myocardium. No evidence was obtained for beta-adrenoceptors over mitochondria, as has been suggested in other tissues and species, but that this binding was to sarcolemmal inclusions in the mitochondrial fraction.     

The distribution of beta-adrenoceptors in dog kidney: an autoradiographic analysis

The distribution of beta-adrenoceptors in slide-mounted dog kidney sections was determined using the radioligand (-)-[125I]cyanopindolol ((-)-[125I]CYP) and autoradiography. Using conditions designed to prevent (-)-[125I]CYP binding to non-beta-adrenoceptor sites, biochemical studies revealed that (-)-[125I]CYP binding equilibrated within 150 min (K1 = 3.2 X 10(8) M-1 min-1), was saturable (KD = 30.72 +/- 2.96 pM; Bmax = 0.57 +/- 0.03 fmol/section, n = 4) and stereoselective with respect to the stereoisomers of propranolol and pindolol. Delineation of beta-adrenoceptor subtypes with the selective beta 1-adrenoceptor antagonist betaxolol and beta 2-adrenoceptor antagonist ICI 118,551 demonstrated that the proportions of beta 1-: beta 2-adrenoceptors was between 1:6 and 1:11. Autoradiographic studies showed that beta 1-adrenoceptors were localized on the juxtaglomerular apparatus and glomeruli, while beta 2-adrenoceptors were localized on medullary rays. The distribution of beta-adrenoceptors with respect to renal function in the dog kidney is discussed.     

Characterization of atypical beta-adrenoceptors in the guinea pig duodenum.

The atypical beta-adrenoceptors mediating relaxation in the guinea pig duodenum were studied using catecholamines (isoprenaline, noradrenaline and adrenaline), a selective beta3-adrenoceptor agonist BRL37344 ((R*,R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phe noxyacetic acid sodium salt) and a non-conventional partial beta3-adrenoceptor agonist CGP12177A ((-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one)). Catecholamines and beta3-adrenoceptor agonists induced concentration-dependent relaxation in this preparation. Propranolol (1 microM) produced only small rightward shifts in the concentration-response curves of these agonists. In the presence of propranolol (1 microM), however, a non-selective beta1-, beta2- and beta3-adrenoceptor antagonist bupranolol caused a concentration-dependent rightward shift of the concentration-response curves for catecholamines and beta3-adrenoceptor agonists. Schild plot analyses of the effects of bupranolol against these agonists gave pA2 values of 6.02 (isoprenaline), 5.98 (noradrenaline), 5.93 (adrenaline), 6.51 (BRL37344) and 5.70 (CGP12177A), respectively, and all Schild slopes were not significantly different from unity. These results suggest that atypical beta-adrenoceptors are present in the guinea pig duodenum and involved in mediating the functional relaxant response.     

Characterization of mexiletine as an antagonist of beta-adrenoceptor in Chinese hamster ovary cells expressing cloned human beta-adrenoceptors

We characterized the beta-adrenoceptor-blocking property of mexiletine, a class Ib antiarrhythmic drug, on Chinese hamster ovary (CHO) cells stably expressing cloned human beta1-, beta2-, and beta3-adrenoceptors. In radioligand binding experiments, mexiletine (10 microM-1 mM) concentration-dependently displaced the specific binding of [125I]cyanopindolol to human beta1- and beta2-adrenoceptors in the membrane fraction of the cells. High concentration (100 microM-1 mM) of mexiletine partially displaced the specific binding of [125I]cyanopindolol to human beta3-adrenoceptor. On the other hand, high concentration (300 microM and 1 mM) of lidocaine, another class Ib antiarrhythmic drug, partially displaced the specific binding of [125I]cyanopindolol to human beta1-adrenoceptor, whereas it did not affect the specific binding of [125I]cyanopindolol to human beta2- and beta3-adrenoceptors. Mexiletine (5, 50, and 500 microM) reduces basal adenosine 3',5'-cyclic monophosphate (cAMP) level and isoprenaline-induced cAMP accumulation on CHO cells stably expressing cloned human beta1- and beta2-adrenoceptors. Lidocaine (10 and 100 microM and 1 mM) tend to reduce basal cAMP level on CHO cells stably expressing cloned human beta1-adrenoceptors, whereas the drug did not reduce the isoprenaline-induced cAMP accumulation on CHO cells stably expressing cloned human beta1-, beta2-, and beta3-adrenoceptors. Mexiletine and lidocaine have no effect on forskolin (0.1, 1, and 3 microM)-induced cAMP accumulation. These results demonstrate that mexiletine blocks the binding of agonists to beta1- and beta2-adrenoceptors, and thereby attenuates the agonist-induced cAMP accumulation, and that the action of mexiletine as an antagonist of beta1- and beta2-adrenoceptors is independent of its antiarrhythmic property.     

Beta-adrenoceptors and human skeletal muscle characterisation of receptor subtype and effect of age.

1. Rectus abdominis muscle biopsies were obtained from 28 patients undergoing abdominal surgery. In membranes prepared from these biopsies beta-adrenoceptor binding was examined. The apparent affinity (KD) and the density (Bmax) of the receptors for the radioligand (-)-[125I]cyanopindolol were 28.5 +/- 2.7 (pM) and 25.9 +/- 2.1 (fmol mg-1 protein) (mean +/- s.e. mean) respectively. In forceps biopsies from vastus lateralis muscle from four healthy volunteers the values for KD and Bmax were 22.5 +/- 4.4 (pM) and 16.4 +/- 2.2 (fmol mg-1 protein). The binding characteristics for the radioligand were similar in the biopsies from the two muscle sites. 2. Inhibition of the radioligand binding by the selective beta 2-adrenoceptor antagonist ICI 118551 (KI = 117 +/- 45 nM) and selective beta 1-adrenoceptor antagonist metoprolol (KI = 15229 +/- 5046 nM) suggests the dominance of beta 2-adrenoceptor subtype in human skeletal muscle. 3. There were no significant differences in the skeletal muscle beta-adrenoceptor densities or affinities between the young and older patients.     

Comparison of beta-adrenoceptor populations in cat and guinea-pig left atria

The subtypes of beta-adrenoceptor present in left atrial preparations from the guinea-pig and cat have been assessed using both responses obtained in organ bath experiments and radioligand binding studies. From the positive inotropic responses to procaterol, the pKB values for practolol using a variety of agonists, and from displacement of [125I]cyanopindolol from left atrial membrane homogenates by the selective beta 1- and beta 2-adrenoceptor antagonists L643,717-01J10 and ICI 118,551, it was concluded that guinea-pig left atria possess only beta 1-adrenoceptors, whilst cat left atria possess both beta 1- and beta 2-adrenoceptor subtypes.     

Effect of SR59230A on atypical beta-adrenoceptor mediating relaxation in the Guinea Pig gastric fundus

The purpose of the present study was to clarify whether atypical beta-adrenoceptors which presented in the guinea pig gastric fundus are beta(3)-adrenoceptors or putative beta(4)-adrenoceptors. In the presence of both the selective beta(1)-adrenoceptor antagonist atenolol (10(-4) mol/l) and the selective beta(2)-adrenoceptor antagonist butoxamine (10(-4) mol/l), the selective beta(3)-adrenoceptor antagonist SR59230A caused a concentration-dependent rightward shift of the concentration-response curve to catecholamines (isoprenaline, noradrenaline and adrenaline) and beta(3)-adrenoceptor agonists (BRL37344 and CGP12177A) in the guinea pig gastric fundus. Schild plot analyses of SR59230A against these agonists gave pA(2) values of 7.35 +/- 0.03 (isoprenaline), 7.26 +/- 0.04 (noradrenaline), 7.26 +/- 0.05 (adrenaline), 7.79 +/- 0.03 (BRL37344) and 6.74 +/- 0.03 (CGP12177A), respectively, and all Schild slopes were not significantly different from unity. These results suggest that atypical beta-adrenoceptors mediating relaxant responses of these agonists in the guinea pig gastric fundus are beta(3)-adrenoceptors rather than putative beta(4)-adrenoceptors.     

Characterization of beta 1- and beta 2-adrenoceptors in rat skeletal muscles.

Binding studies with (-)-[125I]cyanopindolol (ICYP) were conducted to characterize beta-adrenoceptors in plantaris and soleus muscles of rats (male, 250-300 g). The distribution of beta 1- and beta 2-adrenoceptors in different muscle fiber types, identified in serial sections by succinic dehydrogenase (SDH) staining, was studied by autoradiography. The densities of binding sites (Bmax, fmol/mg protein) were 5.4 +/- 0.9 (mean +/- SEM) in plantaris and 11.5 +/- 2.0 in soleus muscle. In plantaris muscle, monophasic competition curves were observed when binding experiments were performed using CGP20712A (50 pM to 0.5 mM), a beta 1-adrenoceptor selective antagonist, or ICI 118,551 (50 pM to 20 microM), a beta 2-adrenoceptor selective antagonist, to compete for ICYP binding. Analysis with LIGAND revealed a single binding site with a KD value of 2.41 +/- 0.56 nM (mean +/- SEM) for ICI 118,551 and 8.93 +/- 3.00 microM for CGP 20712A, indicating the presence of a homogeneous population of beta 2-adrenoceptors. In soleus muscle, competition curves were biphasic with 16-21% beta 1-adrenoceptors. Autoradiographic studies supported the findings from binding studies with membrane homogenates. The ICYP binding pattern was associated closely with the muscle fiber types identified by SDH staining. Propranolol-resistant binding sites were observed, and these sites were associated with muscle fibers positive to SDH staining.     

Influence of assay buffer on dissociation constants of drugs at beta-adrenoceptor subtypes

The present investigation has assessed the influence of assay buffer (Tris versus Krebs) on the abilities of several beta-adrenoceptor agonists and antagonists to displace the radioligand (-)-[125I]iodocyanopindolol [( 125I]CYP) from beta 1-(left atrial) and beta 2- (uterine) adrenoceptor sites. Saturation studies indicated that the dissociation constant (KD) for [125I]CYP at both beta-receptor sites was approximately 2-fold greater in Krebs as opposed to Tris buffer, and that the maximal density of binding sites (Bmax) in atria (but not uterus) was also reduced 2-fold. In general, the KD values for beta-adrenoceptor agonists were more influenced by the type of buffer used than were KD values for antagonists. Agonist KD values at beta 2-adrenoceptor sites were higher in Krebs than in Tris buffer, while at beta 1-adrenoceptor sites, variable changes resulted. The selective affinity of agonists at beta 1- and beta 2-adrenoceptor sites was therefore markedly influenced by the buffer used and could not be predicted from the established beta 1-/beta 2-adrenoceptor selectivity of the agonists as found in organ bath studies.     

Partial agonistic effects of carteolol on atypical beta-adrenoceptors in the guinea pig gastric fundus

The properties of the beta1-/beta2-adrenoceptor partial agonist carteolol were investigated in atypical beta-adrenoceptors on the guinea pig gastric fundus. Carteolol induced concentration-dependent relaxation in this tissue (pD2 = 5.55, intrinsic activity = 0.94). However, a combination of the selective beta1-adrenoceptor antagonist atenolol (100 microM) and the selective beta2-adrenoceptor antagonist butoxamine (100 microM) produced only small rightward shifts in the concentration-response curves of carteolol in the gastric fundus (pD2 = 4.91, intrinsic activity = 0.94). In the presence of both atenolol (100 microM) and butoxamine (100 microM), the non-selective beta1-, beta2- and beta3-adrenoceptor antagonist (+/-)-bupranolol (10-100 microM) caused a concentration-dependent right-ward shift of the concentration-response curves for carteolol in the guinea pig gastric fundus. Schild plot analyses of the effects of (+/-)-bupranolol against carteolol gave the pA2 value of 5.29 and the Schild slope was not significantly different from unity. Furthermore, carteolol (10 microM) weakly but significantly antagonized the relaxant responses to catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline), a selective beta3-adrenoceptor agonist BRL37344 ((R*,R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxy-acetic acid sodium salt) and a non-conventional partial beta3-adrenoceptor agonist (+/-)-CGP12177A ([4-[3-[(1,1dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one] hydrochloride) in the guinea pig gastric fundus. These results suggest that the partial agonistic effects of carteolol are mediated by atypical beta-adrenoceptors in the guinea pig gastric fundus.     

(+/-)-Pindolol acts as a partial agonist at atypical beta-adrenoceptors in the guinea pig duodenum

The agonistic and antagonistic effects of (+/-)-pindolol (1-(1H-indol-4-yloxy)-3-[(1-methylethyl)amino]-2-propanol) were estimated to clarify whether (+/-)-pindolol acts as a partial agonist on atypical beta-adrenoceptors in the guinea pig duodenum. (+/-)-Pindolol induced concentration-dependent relaxation with a pD2 value of 5.10 +/- 0.03 and an intrinsic activity of 0.83 +/- 0.03. However, the relaxations to (+/-)-pindolol were not antagonized by the non-selective beta1- and beta2-adrenoceptor antagonist (+/-)-propranolol (1 microM). In the presence of (+/-)-propranolol (1 microM), the non-selective beta1-, beta2- and beta3-adrenoceptor antagonist (+/-)-bupranolol (30 microM) induced a rightward shift of the concentration-response curves for (+/-)-pindolol (apparent pA2 = 5.41 +/- 0.06). In the presence of (+/-)-propranolol, (+/-)-pindolol (10 microM) weakly but significantly antagonized the relaxant effects to catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline), a selective beta3-adrenoceptor agonist BRL37344 ((R*,R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl) amino]propyl]phenoxyacetic acid sodium salt) and a non-conventional partial beta3-adrenoceptor agonist (+/-)-CGP12177A([4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one] hydrochloride). These results demonstrate that (+/-)-pindolol possesses both agonistic and antagonistic effects on atypical beta-adrenoceptors in the guinea pig duodenum.     

Involvement of the spleen in the endotoxin-induced deterioration of the respiratory airway and lymphocyte beta-adrenergic systems of the guinea pig

The beta-adrenergic binding sites on splenic lymphocyte membranes of the guinea pig were characterized with the radio-ligand [125I]cyanopindolol and showed a maximal number of binding sites (Bmax) of 125 fmol/mg protein and an affinity (Kd) of 170 pM. The potency of various beta-adrenoceptor antagonists to compete for [125I]cyanopindolol binding suggested that the receptor is of the beta 2 subtype. Endotoxin (1 mg/kg) induced a 35% decrease in the number of beta-adrenergic binding sites on lymphocytes, 4 days after i.p. administration. The reduction in the number of beta-adrenoceptors on the lymphocytes was accompanied by a 30% decrease in the relaxation of isolated guinea pig tracheal spirals to isoprenaline and a 20% reduction in the number of beta-adrenergic binding sites in peripheral lung tissue. The endotoxin-induced deterioration of the beta-adrenergic system in the respiratory airways was completely prevented by splenectomy. It is concluded that the spleen, and or cells or products derived from the spleen, are involved in the changes of the beta-adrenergic system in the respiratory airways and lymphocytes.     

Distribution of beta 1- and beta 2-adrenoceptors in mouse trachea and lung: a quantitative autoradiographic study.

1. Binding and quantitative autoradiography were used to detect [125I]-iodocyanopindolol (I-CYP) associated with beta 1- and beta 2-adrenoceptors in mouse tracheal epithelium and airway smooth muscle as well as in lung parenchymal tissue. 2. Specific I-CYP binding to slide-mounted tissue sections of both trachea and parenchyma was of high affinity (KD = 49.0 pM, n = 3, trachea; KD = 118.9 pM, n = 3, parenchyma) and saturable, involving single populations of non-interacting binding sites (Hill coefficient nH = 1.00 +/- 0.02, trachea; nH = 0.99 +/- 0.03, parenchyma). 3. Direct measurement of tissue radioactivity also showed that specific I-CYP binding was competitively inhibited in the presence of the beta-adrenoceptor antagonists (-)-propranolol (non-selective), CGP 20712A (beta 1-selective) and ICI 118,551 (beta 2-selective). Analysis of the competition binding curves for the two selective antagonists revealed mixed populations of beta 1- and beta 2-adrenoceptors in the approximate proportions 33% and 67% respectively in mouse trachea and 28% and 72% respectively in mouse lung parenchyma. 4. Densities of autoradiographic grains derived from specific I-CYP binding to alveolar wall tissue and to tracheal epithelium and airway smooth muscle were quantified by a computer-assisted image analysis system, which allowed the construction of competition binding curves in the presence of the selective beta-adrenoceptor antagonists CGP 20712A and ICI 118,551. Analysis of these data demonstrated that in alveolar wall, beta 1- and beta 2-adrenoceptors co-existed in the proportions 18% and 82%, respectively. 5. Quantitative autoradiographic analyses also showed that beta 1- and beta 2-adrenoceptors were differentially distributed in tracheal epithelium and airway smooth muscle. The beta 2-adrenoceptor subtype accounted for 71% of all beta-adrenoceptors in epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological analysis of atypical beta-adrenoceptors in the guinea pig gastrointestinal tissue systems

The purpose of the present study was to characterize the atypical beta-adrenoceptors involved in relaxant responses in guinea pig gastric fundus, duodenum and ileum in functional experiments with catecholamines (isoprenaline, noradrenaline and adrenaline), beta 3-adrenoceptor agonists (BRL37344 and CGP12177A) and a non-selective beta 1-, beta 2- and beta 3-adrenoceptor antagonist bupranolol, and to obtain further evidence to clarify whether there is a tissue difference in atypical beta-adrenoceptors in the guinea pig gastrointestinal tissue systems. The atypical beta-adrenoceptors are present in gastric fundus, duodenum and ileum of guinea pig. In the presence of propranolol (1 microM) or atenolol (100 microM) plus butoxamine (100 microM), bupranolol caused a concentration-dependent rightward shift of the concentration-response curves for catecholamines and beta 3-adrenoceptor agonists. There was not a significant difference of pA2 values for bupranolol against these agonists between gastric fundus, duodenum and ileum of guinea pig. These results suggest that guinea pig gastric fundus, duodenum and ileum relaxation are mediated predominantly by an atypical beta-adrenoceptor population whereas the classical beta 1- or/and beta 2-adrenoceptors play a subordinate function role and that the receptors of three tissues are pharmacological identified by functional approaches. There is not a tissue difference in atypical beta-adrenoceptors in the guinea pig gastrointestinal tissue systems between stomach and ileum.     

Partial agonist activity of carteolol on atypical beta-adrenoceptors in the guinea pig duodenum

The partial agonist activities of carteolol were investigated on atypical beta-adrenoceptors of duodenum on the guinea pig. Carteolol produced a concentration-dependent relaxation of the guinea pig duodenum (pD(2)=4.85), which was not significantly affected by propranolol (1 microM). In the presence of propranolol (1 microM), however, the non-selective beta(1)-, beta(2)- and beta(3)-adrenoceptor antagonist, bupranolol (30 microM), caused a rightward shift of the concentration-response curves for carteolol (apparent pA(2)=5.31). Moreover, carteolol (10 microM) weakly, but significantly, antagonized the relaxations in response to catecholamines (isoprenaline, noradrenaline and adrenaline), to a selective beta(3)-adrenoceptor agonist, (R*, R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]pheno xyacetic acid sodium salt (BRL37344), and to a non-conventional partial beta(3)-adrenoceptor agonist, [4-[3-[(1, 1-dimethylethyl)amino]-2-hydroxypropoxy]-1, 3-dihydro-2H-benzimidazol-2-one] hydrochloride (CGP12177A), also in the guinea pig duodenum (apparent pA(2)=5.77, 5.92, 6.05, 6.56 and 5. 58, respectively). These results suggest that the partial agonist effects of carteolol are mediated by atypical beta-adrenoceptors in the guinea pig duodenum.     

Regional distribution of beta-adrenoceptors in the human heart: coexistence of functional beta 1- and beta 2-adrenoceptors in both atria and ventricles in severe congestive cardiomyopathy

We evaluated the amount of beta 1- and beta 2-adrenoceptors in human right and left atrium as well as in right and left ventricular wall obtained from heart transplant recipients who suffered from end-stage congestive cardiomyopathy. The total number of myocardial beta-adrenoceptors was assessed with the nonsubtype selective beta-adrenoceptor radioligand (-)[125I]iodocyanopindolol (ICYP); concomitantly, the number of beta 1-adrenoceptors was determined with the selective beta 1-adrenoceptor radioligand (-)[3H]bisoprolol. The number of beta 2-adrenoceptors was calculated by subtracting (-)[3H]bisoprolol binding sites from ICYP binding sites. With this technique, a beta 1/beta 2-ratio of approximately 65/35% for both atria and of approximately 75/25% for both ventricles was found. Identical results were obtained when the beta 1/beta 2-ratio was calculated indirectly by nonlinear regression analysis of competition curves of the selective beta 1-adrenoceptor antagonist bisoprolol and the selective beta 2-adrenoceptor antagonist ICI 118,551 with ICYP binding. In addition, on atria and on ventricles, adenylate cyclase was activated by norepinephrine (presumably by beta 1- and beta 2-adrenoceptor stimulation) and by procaterol (by beta 2-adrenoceptor stimulation). It is concluded that in the human heart functional beta 1- and beta 2-adrenoceptors coexist on both atria and both ventricles. In end-stage congestive cardiomyopathy, there appears to be a selective down-regulation of cardiac beta 1-adrenoceptors, whereas beta 2-adrenoceptors are obviously not affected. This may explain the beneficial effects of beta 2-adrenoceptor agonists in severe heart failure.     

Selective labelling of beta 1-adrenoceptors in rabbit lung membranes by (-)[3H]bisoprolol

The binding properties of a newly developed, highly selective beta 1-adrenoceptor antagonist radioligand, (-)[3H]bisoprolol (EMD 33512) were investigated in rabbit lung membranes containing a mixture of 80% beta 1-and 20% beta 2-adrenoceptors. The binding of (-)[3H]bisoprolol at 25 degrees C was saturable, of high affinity (KD = 4.7 +/- 0.6 nM, N = 4), rapid and readily reversible. The maximal number of (-)[3H]bisoprolol binding sites (244 +/- 31 fmol bound/mg protein, N = 4), however, was only 80% of the number of sites labelled by the non-selective beta-adrenoceptor radioligand (-)[125I]iodocyanopindolol (299 +/- 36 fmol bound/mg protein, N = 4). beta-Adrenoceptor antagonists (non-selective: propranolol, alprenolol; beta 1-selective: metoprolol, practolol, bisoprolol; beta 2-selective: ICI 118,551) inhibited (-)[3H]bisoprolol binding with monophasic displacement curves and pseudo-Hill coefficients of 1.0 indicating that in rabbit lung membranes (-)[3H]bisoprolol labels a homogeneous class of beta-adrenoceptors. Agonists inhibited binding with an order of potency: (-)-isoprenaline greater than (-)-noradrenaline = (-)-adrenaline, which is a typical one for beta 1-adrenoceptors. It is concluded that in rabbit lung membranes (-)[3H]bisoprolol selectively labels beta 1-adrenoceptors. (-)[3H]Bisoprolol therefore seems to be a suitable ligand for direct determination of the properties of beta 1-adrenoceptors in those tissues where both beta-adrenoceptor subtypes coexist.     

FUNCTION, CHARACTERIZATION AND AUTORADIOGRAPHIC LOCALIZATION AND QUANTITATION OF β-ADRENOCEPTORS IN CARDIAC TISSUES

1. This paper demonstrates the use of organ bath, radioligand binding and autoradiography to detect beta 1- and beta 2-adrenoceptors in human and guinea-pig cardiac tissues. 2. In organ bath experiments, non-selective and beta 1- and beta 2-adrenoceptor selective agonists produced concentration-dependent inotropic responses in human right atrial appendage. Both subtypes mediate inotropic responses. In guinea-pig right atria chronotropic responses were mediated predominantly through beta 1-adrenoceptors. 3. Receptor binding studies using (-)[125I]-cyanopindolol (CYP) and beta 1- and beta 2-adrenoceptor selective antagonists showed that beta 2-adrenoceptors comprised 25% of the total population of beta-adrenoceptors in guinea-pig right atria. In human right atria the proportion is higher (40%). 4. Quantitative autoradiography was used to determine the location and densities of beta 1- and beta 2-adrenoceptors in guinea-pig heart. Both beta 1- and beta 2-adrenoceptors were distributed on myocardium. The atrioventricular conducting system had a higher density of beta 2-adrenoceptors compared with myocardium.     

Autoradiographic localization of beta-adrenoceptors in pig lung using [125I]-iodocyanopindolol.

The binding of the beta-adrenoceptor radioligand [125I]-iodocyanopindolol (I-CYP) has been studied in pig lung parenchyma and the distribution of binding sites visualised by light microscopic autoradiography. I-CYP binding was saturable (maximum binding capacity Bmax = 51 +/- 3 fmol mg-1 protein), involving sites with high affinity (dissociation constant KD = 73 +/- 10 pM). Specific I-CYP binding was displaceable both by beta-adrenoceptor agonists ((-)-isoprenaline greater than (-)-adrenaline greater than (+/-)-fenoterol greater than (-)-noradrenaline greater than (+)-isoprenaline greater than (+/-)-RO363) and antagonists ((+/-)-propranolol greater than ICI-118551 greater than atenolol), indicating a predominance of beta 2-adrenoceptors. Further analysis showed that displacement data for the beta 1-selective antagonist atenolol and the beta 2-selective antagonist ICI-118551 were fitted best to a 2 binding site model and that both beta 1- and beta 2-adrenoceptors were present in pig lung in the ratio 28:72 respectively. Autoradiographic grains were localized over tissue and were most dense over alveolar walls greater than vascular endothelium greater than vascular smooth muscle greater than bronchial smooth muscle = bronchial epithelium. Atenolol (10(-5) M) caused a 31% reduction in specific grain density over alveolar wall tissue, while a 10 fold lower concentration of ICI-118551 (10(-6) M) caused a 50% decrease. These results are consistent with binding data in pig lung parenchyma demonstrating a mixed population of beta-adrenoceptors with a predominance of the beta 2 subtype.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional properties of atypical beta-adrenoceptors on the guinea pig duodenum

In this study, we attempted to further characterize atypical beta-adrenoceptors on the guinea pig duodenum. (-)-Enantiomers of isoprenaline and noradrenaline were more potent than its (+)-enantiomers. The isomeric activity ratios ((+)/(-)) were less than those obtained in the guinea pig atria and trachea. The concentration-response curves to catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline), to the selective beta(3)-adrenoceptor agonist, BRL37344 ((R*, R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid sodium), and to the non-conventional partial beta(3)-adrenoceptor agonist, (+/-)-CGP12177A ((+/-)-[4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one] hydrochloride), were resistant to blockade by (+/-)-pindobind, the beta-adrenoceptor alkylating agent. (-)-Noradrenaline and (-)-adrenaline were more potent than dopamine and (-)-phenylephrine, respectively. Selective beta(2)-adrenoceptor agonists possess agonistic activities at atypical beta-adrenoceptors. (+/-)-Propranolol and (+/-)-bupranolol had no agonistic effect, whereas (+/-)-alprenolol, (+/-)-pindolol, (+/-)-nadolol, (+/-)-CGP12177A and (+/-)-carteolol exhibited agonistic activities at atypical beta-adrenoceptors. These results suggest that pharmacological properties of atypical beta-adrenoceptors differ from those of conventional beta(1)- and beta(2)-adrenoceptors on the guinea pig.