Atypical beta-adrenoceptors mediating relaxation in the human colon: functional evidence for beta3-rather than beta4-adrenoceptors.

The aim of the present functional study was to assess the role of beta3-adrenoceptors in the light of recent findings suggesting the existence of a putative fourth beta-adrenoceptor in adipose and heart tissue. The effect of the non-conventional beta3-adrenoceptor partial agonist CGP12177A is resistant to the effect of the beta3-adrenoceptor antagonist SR59230A. Under isotonic conditions in circular muscle strips of human distal colon, the concentration-effect relationship of CGP12177A and SR59104A (beta3-adrenoceptor agonists), alone and in the presence of CGP20712A (beta1-adrenoceptor antagonist) ICI118551 (beta2-adrenoceptor antagonist) and SR59230A, all 0.1 microm was studied. CGP12177A concentration-dependently relaxed circular muscle strips (pEC50=6.16+/-0.05). This effect was left unchanged by beta1-/beta2-adrenoceptor blockade, but antagonised by SR59230A (pA2=8.12+/-0.02). SR59104A concentration-dependently relaxed circular muscle strips (pEC50=5.43+/-0.01), an effect that was not significantly affected by pretreatment with CGP20712A and ICI118551, but competitively antagonised by SR59230A (p KB=7.89). Isoprenaline-induced relaxations were antagonised by propranolol with a low pA2value (7.76+/-0.16). These results provide further evidence for the presence of functional beta3-adrenoceptors in the human colon, but do not support a role for an atypical beta-adrenoceptor distinct from the beta3-subtype.     

Evidence against beta 3-adrenoceptors or low affinity state of beta 1-adrenoceptors mediating relaxation in rat isolated aorta

1 The presence of beta(3)-adrenoceptors and the low affinity state of the beta(1)-adrenoceptor (formerly "putative beta(4)-adrenoceptor") was investigated in ring preparations of rat isolated aorta preconstricted with phenylephrine or prostaglandin F(2alpha) (PGF(2alpha)). Relaxant responses to isoprenaline, selective beta(3)-adrenoceptor agonists (BRL 37344, SR 58611A, CL 316243) and non-conventional partial agonists (CGP 12177A, cyanopindolol, pindolol) were obtained. 2 In phenylephrine-constricted, but not PGF(2alpha)-constricted rings, relaxations to isoprenaline showed a propranolol-resistant component. 3 In phenylephrine-constricted rings, relaxations to BRL 37344 (pEC(50), 4.64) and SR 58611A (pEC(50), 4.94) were not antagonized by the selective beta(3)-adrenoceptor antagonist SR 59230A (< or =1 microM). CL 316243 (< or =100 microM) failed to produce relaxation. In PGF(2alpha)-constricted rings only SR 58611A produced relaxation, which was not affected by SR 59230A (< or =3 microM). 4 Non-conventional partial agonists produced relaxation in phenylephrine-constricted but not PGF(2alpha)-constricted rings. The relaxation to CGP 12177A was unaffected by SR 59230A (< or =1 microM) or by CGP 20712A (10 microM), reported to block the low affinity state of the beta(1)-adrenoceptor. 5 beta-adrenoceptor antagonists also produced relaxation in phenylephrine-constricted rings with an order of potency of (pEC(50) values): bupranolol (5.5) approximately 38;SR 59230A (5.47) approximately 38;cyanopindolol (5.47)>pindolol (5.30)>alprenolol (5.10)>propranolol (4.83)>ICI 118551 (4.60)>CGP 12177A (4.38) approximately 38;CGP 20712A (4.35). Bupranolol (100 microM), alprenolol (30 microM), propranolol (100 microM) and SR 59230A (10 microM) produced no relaxation in PGF(2alpha)-constricted rings. 6 These results provide no evidence for the presence of functional beta(3)-adrenoceptors or the low affinity state of the beta(1)-adrenoceptor in rat aorta.     

Functional evidence of atypical beta 3-adrenoceptors in the human colon using the beta 3-selective adrenoceptor antagonist, SR 59230A.

The role of beta 3-adrenoceptors in human colonic circular smooth muscle was assessed in vitro by use of the beta 3-selective antagonist SR 59230A. Isoprenaline, in the presence of the selective beta-adrenoceptor antagonists CGP 20712A (beta 1) and ICI 118551 (beta 2), both at 0.1 microM, concentration-dependently relaxed the preparation (pEC50 = 5.22). This effect was potently and competitively antagonized by SR 59230A with a pA2 of 8.31, while its R,R enantiomer SR 59483A gave an apparent pKB of 6.21. Relaxation was likewise produced by CGP 12177A (pEC50 = 6.05), but not by BRL 37344. Although only one of these beta 3-selective agonists was effective, the remarkably high potency of SR 59230A as a stereospecific antagonist of non-beta 1 non-beta 2 relaxation of human colonic muscle by isoprenaline provides strong functional evidence of beta 3-adrenoceptors in that tissue.     

Beta 1-, beta 2- and atypical beta-adrenoceptor-mediated relaxation in rat isolated aorta

beta-adrenoceptor-mediated relaxation was investigated in ring preparations of rat isolated thoracic aorta. Rings were pre-constricted with a sub-maximal concentration of noradrenaline (1 microM) and relaxant responses to cumulative concentrations of beta-adrenoceptor agonists obtained. The concentration-response curve (CRC) to isoprenaline was shifted to the right by propranolol (0.3 microM) with a steepening of the slope. Estimation of the magnitude of the shift from EC(50) values gave a pA(2) of 7.6. Selective beta(1)- and beta(2)-adrenoceptor antagonists, CGP 20712A (0.1 microM) and ICI 118551 (0.1 microM), respectively, produced 4 and 14 fold shifts of the isoprenaline CRC. Atypical beta-adrenoceptor agonists also produced concentration-dependent relaxation of aortic rings. The order of potency of the beta-adrenoceptor agonists was (-log EC(50)): isoprenaline (6. 25)>cyanopindolol (5.59)>isoprenaline+propranolol (5.11)>CGP 12177A (4.40)>ZD 2079 (4.24)>ZM 215001 (4.07)>BRL 37344 (3.89). Relaxation to CGP 12177A and ZM 215001 was unaffected by propranolol (0.3 microM). SR 59230A (相似文献   

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.     

ALpha1-adrenoceptor antagonist properties of CGP 12177A and other beta-adrenoceptor ligands: evidence against beta(3)- or atypical beta-adrenoceptors in rat aorta

1. The alpha(1)-adrenoceptor antagonist properties of the beta-adrenoceptor nonconventional partial agonist, CGP 12177A, was investigated in functional assays in rat aorta and in radioligand binding assays in rat cerebral cortical membranes. In addition, binding affinities of other beta-adrenoceptor ligands were measured to investigate any correlation between alpha(1)-adrenoceptor affinity and relaxant potency in phenylephrine-constricted rings. 2. In functional studies, CGP 12177A produced parallel rightward shifts of the phenylephrine CRC with no reduction in the maximum responses. Schild regression analysis gave a straight line with a slope of 0.95 (95% CL: 0.87-1.04), suggesting reversible competitive antagonism, and gave a pK(B) value of 5.26. In contrast, CGP 12177A (相似文献   

Inhibitory effects of SR 58611A on canine colonic motility: evidence for a role of beta 3-adrenoceptors.

1. In order to clarify whether atypical or beta 3-adrenoceptors can modulate canine colonic motility in vivo, we studied the effects of SR 58611A (a selective agonist for atypical beta-adrenoceptors) alone and after pretreatment with beta-adrenoceptor antagonists on colonic motility in the conscious dog. The gastrocolonic response (postprandial increase in motility) was monitored by means of electrodes and strain-gauge force transducers chronically implanted along the distal colon. In some experiments, heart rate was also measured. The possible role of beta 3-adrenoceptors in mediating the effects of SR 58611A was also tested in vitro in circular muscle strips taken from the canine distal colon. 2. Intravenous infusion of SR 58611A, ritodrine or isoprenaline at doses inducing the same degree of tachycardia inhibited the gastrocolonic response to a different extent, with SR 58611A and ritodrine being more effective than isoprenaline. 3. In a dose-response study, SR 58611A was more potent in inhibiting colonic motility than in inducing tachycardia: the ED35 values for inhibition of colonic motility and induction of tachycardia were 23 and 156 micrograms kg-1, i.v., respectively. 4. The inhibitory effect of SR 58611A 100 micrograms kg-1, i.v., on the gastrocolonic response was reversed by alprenolol (non-selective beta-adrenoceptor antagonist), but resistant to CGP 20712A (beta 1-adrenoceptor antagonist) or ICI 118551 (beta 2-adrenoceptor antagonist). 5. In vitro, SR 58611A concentration-dependently relaxed circular muscle strips, an effect that was competitively antagonized by alprenolol with a pA2 value of 7.1, but resistant to CGP 20712A (100 nM), ICI 118551 (100 nM) or tetrodotoxin (1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional investigation of β-adrenoceptors in human isolated detrusor focusing on the novel selective β3-adrenoceptor agonist KUC-7322

This study aimed to characterize the β-adrenoceptor (β-AR) subtype mediating relaxation of isolated human bladder strips and to explore relaxation by the novel β3-AR-selective agonist KUC-7322 for its relaxant effect on the human isolated detrusor and for its effect on the carbachol (CCh)-induced contractile response. In two parallel studies, relaxation of isolated human bladder strips was tested for the β-AR agonists isoproterenol, clenbuterol, BRL 37344, and KUC-7322. For the isoproterenol and KUC-7322 responses, antagonism by CGP 20712A, ICI 118551, and SR59230A was determined. The potency and efficacy of the reference agonists for detrusor relaxation was in line with their known β3-AR activity. KUC-7322 relative to isoproterenol was a full agonist with a pEC(50) of 5.95 ± 0.09 and 5.92 ± 0.11 in the two studies. SR59230A exhibited antagonism of the expected potency against isoproterenol (apparent pK (B) 7.2) but not against KUC-7322. Neither isoproterenol nor KUC-7322 nor forskolin significantly attenuated CCh-induced contraction. These results suggest that KUC-7322 displays full agonistic activity in relaxing the human detrusor without inhibiting the contraction induced by cholinergic stimulation. These characteristics, if proven in vivo, may be beneficial for the treatment of overactive bladder, as increased bladder capacity with a negligible effect on voiding contractions may be anticipated.     

Atypical beta-adrenoceptors,different from beta 3-adrenoceptors and probably from the low-affinity state of beta 1-adrenoceptors,relax the rat isolated mesenteric artery

(1) We examined whether beta3- and/or atypical beta-adrenoceptors relax the rat isolated mesenteric artery. (2) Mesenteric arteries precontracted with phenylephrine were relaxed by beta-agonists with the following potencies (pD2): nonselective agonist isoprenaline (6.00)>nonconventional partial agonist cyanopindolol (5.45)>beta2-agonist fenoterol (4.98)>nonconventional partial agonist CGP 12177 (4.19)>beta3-agonist ZD 2079 (3.72). The beta3-agonist CL 316243 1 mm relaxed the vessel only marginally. (3) The concentration-response curves (CRCs) for cyanopindolol, CGP 12177 and ZD 2079 were not affected by the nonselective beta-antagonist propranolol 0.3 microm, the beta2-antagonist ICI 118551 1 microm and by CL 316243 60 microm, but shifted to the right by bupranolol (pA2 5.3-5.7), CGP 20712 (5.4) and SR 59230A (6.5-6.7) (the latter three drugs block atypical and/or beta3-adrenoceptors at high concentrations). (4) The CRC for isoprenaline was shifted to the right by propranolol (pA2 7.0) but, in the presence of propranolol 0.3 microm, not affected by SR 59230A 1 microm. The CRC for fenoterol was shifted to the right by propranolol (pA2 6.9) and ICI 118551 (6.8). (5) Removal of endothelium diminished the vasorelaxant effects of cyanopindolol, CGP 12177 and ZD 2079. (6) Fenoterol and cyanopindolol also relaxed (endothelium-intact) mesenteric arteries precontracted with serotonin. The relaxant effect of cyanopindolol was antagonized by bupranolol to about the same degree as in phenylephrine-contracted vessels. (7) In conclusion, beta2- and atypical beta-adrenoceptors (but not beta3-adrenoceptors) relax the rat mesenteric artery. The atypical beta-adrenoceptor, which is partially located endothelially, may differ from the low-affinity state of the beta1-adrenoceptor.     

Differences between the third cardiac beta-adrenoceptor and the colonic beta 3-adrenoceptor in the rat.

1. The heart of several species including man contains atypical beta-adrenoceptors, in addition to coexisting beta 1- and beta 2-adrenoceptors. We now asked the question whether or not the third cardiac beta-adrenoceptor is identical to the putative beta 3-adrenoceptor. We compared the properties of the third cardiac beta-adrenoceptor with those of beta 3-adrenoceptors in isolated tissues of the rat. To study the third cardiac beta-adrenoceptor we used spontaneously beating right atria, paced left atria and paced left ventricular papillary muscles. As a likely model for putative beta 3-adrenoceptors we studied atypical beta-adrenoceptors of the colonic longitudinal muscle precontracted with 30 mM KCl. We used beta 3-adrenoceptor-selective agonists, antagonists and non-conventional partial agonists (ie high-affinity blockers of both beta 1- and beta 2-adrenoceptors know to exert also stimulant effects through beta 3-adrenoceptors). 2. The non-conventional partial agonist (-)-CGP 12177 caused positive chronotropic effects in right atria (pD2 = 7.3) and positive inotropic effects in left atria (pD2 = 7.5). The stimulant effects of (-)-CGP 12177 were resistant to blockade by 200 nM-2 microM (-)-propranolol and 3 microM ICI 118551 (a beta 2-selective antagonist) but antagonized by 1 microM (-)-bupranolol (pKB = 6.4-6.8), 3 microM CGP 20712A (a beta 1-selective antagonist) (pKB = 6.3-6.4) and 6.6 microM SR 59230A (a beta 3-selective antagonist, pKB = 5.1-5.4). 3. The non-conventional partial agonist cyanopindolol caused positive chronotropic effects in right atria (pD2 = 7.7) and positive inotropic effects in left atria (pD2 = 7.1). The stimulant effects of cyanopindolol were resistant to blockade by 200 nM (-)-propranolol but antagonized by 1 microM (-)-bupranolol (pKB = 6.8-7.1). 4. Neither (-)-CGP 12177 nor cyanopindolol caused stimulant effects in papillary muscles at concentrations between 0.2 nM and 20 microM. 5. In the presence of 200 nM (-)-propranolol the beta 3-adrenoceptor-selective agonists BRL 37344 (6 microM), SR 58611A (6 microM), ZD 2079 (60 microM) and CL 316243 (60 microM) did not cause stimulant effects or modify the potency and efficacy of the effects of (-)-CGP 12177 in right and left atria. The combination of 2 microM (-)-propranolol and 2 microM (-)-noradrenaline did not modify the chronotropic potency and efficacy of (-)-CGP 12177 compared to the potency and efficacy in the presence of 2 microM (-)-propranolol alone. 6. (-)-CGP 12177 relaxed the colon with a pD2 of 6.9 and a maximum effect of 55% compared to (-)-isoprenaline. The relaxant effects of (-)-CGP 12177 were resistant to blockade by 200 nM (-)-propranolol, 3 microM CGP 20712A, 3 microM ICI 118551 but blocked by 2 microM (-)-propranolol (pKB = 6.0), 1 microM (-)-bupranolol (pKB = 6.4) and 3 microM SR 59230A (pKB = 6.3). In the presence of 200 nM (-)-propranolol, (-)-CGP 12177 (20 microM) antagonized surmountably the relaxant effects of BRL 37344 (pKP = 7.3) (-)-noradrenaline (pKP = 7.0); and CL 316243 (pKP = 7.0). 7. Cyanopindolol in the presence of 200 nM (-)-propranolol relaxed the colon with a pD2 of 7.0 and a maximum effect of 40% compared to (-)-isoprenaline. As expected from a partial agonist, cyanopindolol antagonized the relaxant effects of both BRL 37344 and CL 316243 with a pKP = 7.6 and (-)-noradrenaline with a pKP = 7.4. 8. The following beta 3-adrenoceptor-selective agonists were potent colonic relaxants (pD2 values between parentheses): BRL 37344 (9.1), ZD 2079 (7.0), CL 316243 (9.0) and SR 58611A (8.2). The relaxant effects of these agonists were only marginally affected by 200 nM (-)-propranolol, not blocked by 3 microM CGP 20712A or 3 microM ICI 118551, and blocked by SR 59230A 3 microM (pKB = 6.9-7.5), 1 microM (-)-bupranolol (pKB = 6.2-6.4) and 2 microM (-)-propranolol (pKB = 6.3-6.5). 9...     

Evidence for a functional beta 3-adrenoceptor in man.

1. The existence of a functional beta 3-adrenoceptor in man was investigated by studying the lipolytic action of selective beta-adrenoceptor agents in isolated white omental and subcutaneous fat cells. 2. The non-selective beta 1/beta 2-adrenoceptor antagonist, CGP 12177 was lipolytic in both omental and subcutaneous fat cells. The intrinsic activity relative to isoprenaline was greater in omental than in subcutaneous cells. 3. Addition of the beta 2-adrenoceptor antagonist, ICI 118,551 and the beta 1-adrenoceptor antagonist CGP 20712A in combination or the non-selective beta-adrenoceptor antagonist propranolol alone (all 10(-7) M), induced a rightward shift of the dose-response curves for isoprenaline- and BRL37344-stimulated lipolysis of about 4 and 2 log-units, respectively. However, the antagonists did not alter lipolysis induced by CGP12177. 4. Several concentrations of beta-adrenoceptor antagonists were used to determine the pA2 values by Schild analysis. The values for CGP 20712A and ICI 118,551 (6.63 +/- 0.20 and 6.25 +/- 0.12) as antagonists of the lipolytic effects of CGP 12177 were over 2 units lower than the pA2 value for CGP 20712A against the response to the selective beta 1-agonist dobutamine (8.58 +/- 0.23) and the pA2 value for ICI 118,551 against the response to the selective beta 2-agonist terbutaline (9.15 +/- 0.26). 5. beta 3-Adrenoceptor mRNA expression, investigated with a polymerase chain reaction assay, was demonstrated in both types of adipocytes in the same cell preparations that had a lipolytic response to CGP 12177. 6. In conclusion, human white fat cells express an atypical beta-adrenoceptor in addition to beta 1- and beta 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Classical and atypical binding sites for beta-adrenoceptor ligands and activation of adenylyl cyclase in bovine skeletal muscle and adipose tissue membranes.

1. The radioligand [125I]-iodocyanopindolol ([125I]-ICYP) was used under standard ligand binding conditions, to detect beta 1- and beta 2-adrenoceptors in membrane preparations from bovine skeletal muscle and adipose tissue. High concentrations of [125I]-ICYP were also used, to identify an 'atypical' binding site in skeletal muscle. Finally, adenosine 3':5'-cyclic monophosphate (cyclic AMP) production was measured in the same membrane preparations, to determine the relationship between the beta-adrenoceptor sub-types present and the production of this second-messenger. 2. According to the results of radioligand binding studies, both skeletal muscle and adipose tissue membranes have beta 2-adrenoceptors, characterized by a high affinity for the beta 2-selective antagonist, ICI 118551 (pK 8.3 and 8.6 respectively); and a low affinity for the beta 1-selective antagonist CGP 20712A (pK 5.2 in both tissues). Antagonism of (-)-isoprenaline-stimulated cyclic AMP production by low concentrations of ICI 118551, yielded pseudo pA2 values in muscle and adipose tissue of 7.6 and 8.7 respectively, confirming that beta 2-adrenoceptors in these tissues are linked to the production of the second-messenger. 3. Although beta 1-adrenoceptors could not be detected in either skeletal muscle or adipose tissue membranes by use of ligand binding techniques, high pseudo pA2 values were obtained (8.0 and 8.2 respectively), when CGP 20712A was used to block the stimulation of cyclic AMP production by (-)-isoprenaline. This finding is consistent with the presence in both tissues of a population of beta 1-adrenoceptors which is small, but efficiently coupled to the second-messenger.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mediation of the positive chronotropic effect of CGP 12177 and cyanopindolol in the pithed rat by atypical beta-adrenoceptors, different from beta 3-adrenoceptors.

1. The influence of beta 1-, beta 2-, and beta 3-adrenoceptor agonists and of CGP 12177 and cyanopindolol on heart rate and diastolic blood pressure was studied in the pithed rat. 2. The beta 1-adrenoceptor agonist, prenalterol, increased heart rate and the beta 2-adrenoceptor agonist, fenoterol, caused a fall in blood pressure. The effect of prenalterol was antagonized by the beta 1-adrenoceptor antagonist, CGP 20712 0.1 mumol kg-1 and the action of fenoterol was attenuated by the beta 2-adrenoceptor antagonist, ICI 118551 0.1 mumol kg-1. Both effects were markedly diminished by the non-selective beta-adrenoceptor antagonist, bupranolol 0.1 mumol kg-1. 3. The non-selective beta-adrenoceptor agonist, isoprenaline, three beta 3-agonists as well as CGP 12177 and cyanopindolol elicited a positive chronotropic effect, exhibiting the following pED delta 60 values (negative log values of the doses increasing heart rate by 60 beats min-1): isoprenaline 10.4, CGP 12177 8.3, cyanopindolol 7.2, BRL 37344 6.9, ZD 2079 5.2 and CL 316243 < 5. 4. CGP 20712 0.1 mumol kg-1, given together with ICI 118551 0.1 mumol kg-1, markedly attenuated the positive chronotropic effect of isoprenaline, BRL 37344, ZD 2079 and CL 316243 without affecting the increase in heart rate produced by CGP 12177 and cyanopindolol. 5. The positive chronotropic effect of CGP 12177 and cyanopindolol was attenuated by CGP 20712, 1 and 10 mumol kg-1 and bupranolol, 10 mumol kg-1 but was not affected by ICI 118551, 10 mumol kg-1. The effect of CGP 12177 was also not changed by BRL 37344 1 mumol kg-1, ZD 2079 10 mumol kg-1, CL 316243 10 mumol kg-1, the alpha 1-adrenoceptor antagonist, prazosin 1 mumol kg-1 and the 5-hydroxytryptamine 5-HT2A receptor antagonist, ketanserin 3 mumol kg-1. 6. CGP 12177 0.002 mumol kg-1 and cyanopindolol 0.003 mumol kg-1 shifted to the right the dose-response curve of prenalterol for its positive chronotropic effect. The -log values of the doses causing a twofold shift to the right were 9.6 and 9.5, respectively. 7. Isoprenaline 0.00001-0.001 mumol kg-1, BRL 37344 0.01-1 mumol kg-1 and CGP 12177 0.1 mumol kg-1 caused a fall in diastolic blood pressure which was markedly attenuated by combined administration of CGP 20712 and ICI 118551, 0.1 mumol kg-1 each. 8. CGP 12177 0.01 and 0.1 mumol kg-1 and cyanopindolol 1 mumol kg-1 elicited an increase in diastolic blood pressure. CGP 20712, ICI 118551, bupranolol and, in the case of CGP 12177, also BRL 37344, ZD 2079, CL 316243, prazosin and ketanserin did not influence this effect. 9. In conclusion, the positive chronotropic effect of CGP 12177 and cyanopindolol is not mediated via beta 1-, beta 2-, beta 3-, alpha 1-adrenoceptors or 5-HT2A receptors. This effect may involve atypical beta-adrenoceptors, similar or identical to those described by Kaumann (1989) in isolated heart preparations.     

The effects and selectivity of beta-adrenoceptor agonists in rat myometrium and urinary bladder

Recent evidence supports a role for beta(3)-adrenoceptors in human non-pregnant and pregnant myometrium. The present study was designed to characterize the pharmacology of beta-adrenoceptors involved in the function of non-pregnant rat myometrium by comparison of the activity of several beta-adrenoceptor agonists and antagonists in isolated rat uterus and urinary bladder. Contractions of myometrial and detrusor strips were induced by adding 1 nM oxytocin and 15 mM KCl respectively. Cumulative concentration-response curves to the selective beta(3)-adrenoceptor agonists, CL 316243 and BRL 37344 and the selective beta(2)-adrenoceptor agonist ritodrine were obtained in the presence and absence of the selective beta(2)-adrenoceptor antagonist ICI 118551 and the non-selective beta-adrenoceptor antagonist bupranolol. Both BRL 37344 (pD(2)=6.79+/-0.09) and ritodrine (pD(2)=6.89+/-0.19) produced potent inhibition of oxytocin-induced contractions in myometrial strips; CL 316243 was inactive at concentrations up to 10 microM. Concentration effect curves to both BRL 37344 and ritodrine were shifted (10 to 30-fold) to the right in the presence of ICI 118551 (10 nM). BRL 37344 (pD(2)=8.51+/-0.21) and CL 316243 (pD(2)=8.61+/-0.24) produced potent inhibition of detrusor strips, while ritodrine was almost 100-fold less potent (pD(2)=5.83+/-0.17). The response to all agonists was significantly attenuated by pretreatment with bupranolol (10 microM), but only ritodrine was affected by ICI 118551 (1 microM). These results demonstrate that relaxation of rat myometrium is mediated by beta(2)-adrenoceptors while, consistent with previous reports, the beta(3)-subtype is primarily responsible for relaxation of rat detrusor.     

Characterization of beta-adrenoceptor subtype in bladder smooth muscle in cynomolgus monkey

We first investigated the relaxations of the urinary bladder induced by beta-adrenoceptor agonists in anesthetized cynomolgus monkeys and then employed a variety of beta-adrenoceptor agonists and antagonists in vitro to identify the beta-adrenoceptor subtype responsible for the relaxation (using isolated monkey detrusors). Isoprenaline reduced bladder pressure in a dose-dependent manner. Isoprenaline, noradrenaline and adrenaline each produced a concentration-dependent relaxation of isolated detrusor strips, the rank order of relaxing potencies being isoprenaline > noradrenaline > adrenaline. Subtype-selective beta-adrenoceptor agonists also relaxed isolated detrusor strips, the rank order of potencies being CGP-12177 > BRL 37344 > dobutamine, salbutamol, procaterol > xamoterol. In the antagonist experiment, bupranolol (beta-antagonist, 10(-6) to 10(-5) M) and SR 58894A (beta3-antagonist, 10(-7) to 10(-5) M) caused a rightward shift of the concentration-relaxation curve for isoprenaline, but CGP-20712A (beta1-antagonist, 10(-9) to 10(-7) M) and ICI-118551 (beta2-antagonist, 10(-9) to 10(-7) M) did not. The present functional study provides the first evidence that relaxation of the monkey detrusor by beta-adrenoceptor activation is mediated via the beta3-subtype.     

Uptake of radioligands by rat heart and lung in vivo: CGP 12177 does and CGP 26505 does not reflect binding to beta-adrenoceptors.

The biodistribution of (-)-4-(3-t-butylamino-2-hydroxypropoxy)-[5,7-3H-benzimidazol-2-one (CGP12177, a non-selective beta-adrenoceptor antagonist) and 1-[2-(3-carbamoyl-4-hydroxy)-(5-3H-phenoxy)]-2-propanol methanesulfonate, (CGP26505, a beta 1-adrenoceptor antagonist) was studied in rats pretreated with various alpha- and beta-adrenoceptor blocking drugs (5 min before 3H injection, in dosages at which the drugs demonstrated the expected selectivity). Cardiac and pulmonary radioactivity were measured after 10 min, when specific binding was maximal. Uptake of [3H]CGP12177 was linked to binding to beta-adrenoceptors since it was not affected by prazosin or yohimbine, and was equally well inhibited by propranolol, unlabelled CGP12177 and isoprenaline. Moreover, atenolol and CGP20712A inhibited [3H]CGP12177 uptake in heart (predominantly beta 1-adrenoceptors) more potently than ICI 118,551, while in lungs (predominantly beta 2-adrenoceptors) ICI 118,551 was more potent than atenolol or CGP20712A. In contrast, [3H]CGP26505 uptake in the target organs was equally effectively inhibited by propranolol and ICI 118,551, and significantly lowered by alpha-adrenoceptor antagonists. We conclude that [11C]CGP12177, but not [11C]CGP2605 will be suitable for positron emission tomography imaging of beta-adrenoceptors in animals.     

Beta-adrenoceptor subtypes and the opening of plasmalemmal K(+)-channels in trachealis muscle: electrophysiological and mechanical studies in guinea-pig tissue.

1. Mechanical and electrophysiological studies of guinea-pig isolated trachealis have been made 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-adrenoceptor agonist, salmeterol and (c) clarifying the role of K(+)-channel opening in mediating the relaxant actions of agonists at beta-adrenoceptors. 2. Noradrenaline (10 nM-100 microM) caused a concentration-dependent increase in the rate of beating of guinea-pig isolated atria. The selective beta 1-adrenoceptor blocking drug, CGP 20712A (100 nM-10 microM) caused concentration-dependent antagonism of noradrenaline. The selective beta 2-adrenoceptor blocking drug, ICI 118551, also produced concentration-dependent antagonism of noradrenaline, but only when used in concentrations greater than 300 nM. 3. Cromakalim (100 nM-10 microM), isoprenaline (1-100 nM), procaterol (0.1-30 nM), salbutamol (1 nM-1 microM), salmeterol (1-100 nM) and theophylline (1 microM-1 mM) each caused concentration-dependent suppression of the spontaneous tone of guinea-pig isolated trachealis. 4. ICI 118551 (10 nM-1 microM) antagonized isoprenaline, procaterol and salmeterol in suppressing the spontaneous tone of the isolated trachea. The antagonism was concentration-dependent. In contrast, ICI 118551 (1 microM) antagonized neither cromakalim nor theophylline. CGP 20712A (up to 1 microM) failed to antagonize cromakalim, isoprenaline, procaterol, salmeterol or theophylline. In trachea treated with indomethacin (2.8 microM) and carbachol (10 microM), salmeterol (1 microM) antagonized the effects of isoprenaline but not aminophylline.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ligand binding properties of putative beta 3-adrenoceptors compared in brown adipose tissue and in skeletal muscle membranes.

1. The beta-adrenoceptor population was characterized in membrane preparations from rat brown adipose tissue (BAT) and from soleus muscle by use of the radioligand [125I]-iodocyanopindolol ([125I]-ICYP). In addition, atypical binding sites for [125I]-ICYP found in both tissues were examined, and the relationship between these sites and the putative rat beta 3-adrenoceptor is discussed. 2. It was established that BAT membranes host a mixed population of beta 1- and beta 2-adrenoceptors. Of these two sites, 55% showed a high affinity for the beta 1-selective ligand CGP 20712A (pK 8.5), and 45% showed a high affinity for the beta 2-selective antagonist ICI 118551 (pK 8.6). Soleus muscle membranes were found to host a population of beta 2-adrenoceptors, characterized by a high affinity for ICI 118551 (pK 9.1), but beta 1-adrenoceptors could not be detected in this preparation. 5-Hydroxytryptamine receptors were not detected in either preparation. 3. In addition to beta 1- and beta 2-adrenoceptors, atypical binding sites were identified in both tissues using high concentrations of radioligand (0.5-0.6 nM) and in the presence of 1 microM (-)-propranolol. The atypical sites were abundant, representing 80 and 81% of the total [125I]-ICYP binding sites in BAT and soleus muscle respectively. When the pK values for 11 ligands were compared, the correlation coefficient for atypical sites in BAT and soleus muscle was 0.94.(ABSTRACT TRUNCATED AT 250 WORDS)     

Beta 3-adrenoceptor stimulation induces vasorelaxation mediated essentially by endothelium-derived nitric oxide in rat thoracic aorta.

1. The relaxant effects of isoprenaline may result from activation of another beta-adrenoceptor subtype in addition to beta1 and beta2. This study evaluated the role of a third beta-adrenoceptor subtype, beta3, in beta-adrenoceptor-induced relaxation of rat thoracic aorta by isoprenaline. 2. Isoprenaline produced a concentration-dependent relaxation of phenylephrine pre-contracted rings of the thoracic aorta (pD2=7.46+/-0.15; Emax=85.9+/-3.4%), which was partially attenuated by endothelium removal (Emax=66.5+/-6.3%) and administration of the nitric oxide (NO) synthase inhibitor, L-NG-monomethyl arginine (L-NMMA) (Emax=61.3+/-7.9%). 3. In the presence of nadolol, a beta1- and beta2-adrenoceptor antagonist, isoprenaline-induced relaxation persisted (Emax=55.6+/-5.3%), but occurred at higher concentrations (pD2=6.71+/-0.10) than in the absence of nadolol and lasted longer. 4. Similar relaxant effects were obtained with two beta3-adrenoceptor agonists: SR 58611 (a preferential beta3-adrenoceptor agonist), and CGP 12177 (a partial beta3-adrenoceptor with beta1- and beta2-adrenoceptor antagonistic properties). SR 58611 caused concentration-dependent relaxation (pD2=5.24+/-0.07; Emax=59.5+/-3.7%), which was not modified by pre-treatment with nadolol but antagonized by SR 59230A, a beta3-adrenoceptor antagonist. The relaxation induced by SR 58611 was associated with a 1.7 fold increase in tissue cyclic GMP content. 5 Both relaxation and the cyclic GMP increase induced by SR 58611 were greatly reduced by endothelium removal and in the presence of L-NMMA. 6 We conclude that in the rat thoracic aorta, beta3-adrenoceptors are mainly located on endothelial cells, and act in conjuction with beta1- and beta2-adrenoceptors to mediate relaxation through activation of an NO synthase pathway and subsequent increase in cyclic GMP levels.