sr-59230a and cyanopindolol

This study examines the action of the beta(3)-adrenoceptor antagonist SR59230A [3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanoloxalate] at cloned mouse beta(3)-adrenoceptors expressed in Chinese hamster ovary cells (CHO-K1-beta(3)) or endogenously expressed in 3T3-F442A adipocytes or ileum. SR59230A displayed partial agonist properties compared with the beta(3)-adrenoceptor agonist CL316243 [(R,R)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]-propyl]1,3-benzodioxole-2,2-dicarboxylate] in CHO-K1-beta(3) with the intrinsic activity increasing with the level of receptor expression. Functional affinity values for SR59230A at each level of receptor expression were in agreement with pK(I) values determined by binding. In cytosensor microphysiometer studies, SR59230A was a full agonist for increases in extracellular acidification rates (ECARs) at all levels of receptor expression, and antagonist actions were measurable only in medium- or low-expressing cells. In 3T3-F442A adipocytes, SR59230A antagonized CL316243-mediated increases of cAMP and had no agonist actions. However, in the cytosensor micro-physiometer, SR59230A (acting via beta(3)-adrenoceptors) was an agonist with an intrinsic activity greater than CL316243. In mouse ileum, SR59230A relaxed smooth muscle, although concentration-response curves were biphasic. Relaxant effects were produced by concentrations that did not affect cAMP levels. Differences in tissue responses to SR59230A were not caused by major differences in expression of Galphas. ECAR responses were not affected by pretreatment of cells with pertussis toxin, indicating that signaling did not involve Gi. Therefore, SR59230A displays agonist and antagonist actions at the mouse beta(3)-adrenoceptor. Because SR59230A only antagonized accumulation of cAMP in 3T3-F442A adipocytes yet in the same cells was an agonist for ECAR, cAMP-independent signaling pathways must mediate part of the agonist actions in the microphysiometer.

Topics: 3T3 Cells; Adipocytes; Adrenergic beta-3 Receptor Agonists; Adrenergic beta-3 Receptor Antagonists; Adrenergic beta-Antagonists; Animals; CHO Cells; Cricetinae; Cyclic AMP; Dioxoles; GTP-Binding Protein alpha Subunits, Gi-Go; GTP-Binding Protein alpha Subunits, Gs; Ileum; Mice; Pindolol; Propanolamines

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 (

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adrenergic alpha-1 Receptor Antagonists; Adrenergic beta-Antagonists; Alprenolol; Animals; Aorta, Thoracic; Binding Sites; Bupranolol; Cell Membrane; Cerebral Cortex; Dose-Response Relationship, Drug; Ethanolamines; Imidazoles; Male; Muscle, Smooth, Vascular; Phenylephrine; Pindolol; Prazosin; Propanolamines; Propranolol; Radioligand Assay; Rats; Rats, Wistar; Receptors, Adrenergic, alpha-1; Receptors, Adrenergic, beta-3; Tritium; United Kingdom; Vasoconstriction

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 (

Topics: Acetylcholine; Adrenergic alpha-Agonists; Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Aorta, Thoracic; Bupranolol; Dose-Response Relationship, Drug; Imidazoles; In Vitro Techniques; Isoproterenol; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Norepinephrine; Pindolol; Propanolamines; Propranolol; Rats; Rats, Wistar; Receptors, Adrenergic, beta; Receptors, Adrenergic, beta-1; Receptors, Adrenergic, beta-2; Substrate Specificity; Vasodilator Agents

The present study was carried out to further investigate the nature of the beta-adrenoceptor in rabbit jejunum using BRL 37344, a selective beta3-adrenoceptor agonist, cyanopindolol, a beta-adrenoceptor antagonist with blocking activity at beta3-adrenoceptors and SR 59230A, a new selective beta3-adrenoceptor antagonist. Isoprenaline produced a concentration-dependent inhibition of the spontaneous contractions of rabbit jejunum with a pD2 of 7.14. Propranolol (1 microM) shifted the isoprenaline concentration-response curve (CRC) to the right with a concentration-ratio of 5.85, considerably less than would be expected for an action at classical beta-adrenoceptors (estimated pA2 6.66). BRL 37344 also produced a concentration-dependent inhibition of spontaneous contractions with a pD2 of 7.41. The BRL 37344 CRC was unaffected by propranolol (1 microM). In the presence of propranolol (1 microM), cyanopindolol (1 microM) shifted the isoprenaline CRC to the right (concentration-ratio of 21). Cyanopindolol also shifted the BRL 37344 CRC to the right (concentration-ratio of 38). These shifts are consistent with the affinity of cyanopindolol for beta3-adrenoceptors (estimated pA2 values of 7.27 and 7.38 against isoprenaline and BRL 37344, respectively). In the presence of propranolol (1 microM), SR 59230A produced a concentration-dependent rightward shift of the isoprenaline CRC. The Schild plot gave a pA2 value of 7.16, although the slope of the regression line was significantly different from unity (0.65). SR 59230A also produced a concentration-dependent shift of the BRL 37344 CRC. The Schild plot gave a pA2 of 7.58 with the slope of the regression line not significantly different from unity (0.81). The presence of beta3-adrenoceptors mediating relaxation of spontaneous contractions in rabbit jejunum is supported by the relatively poor antagonism of isoprenaline by propranolol, the relaxant effect of BRL 37344 and the antagonism of isoprenaline and BRL 37344 by cyanopindolol and SR 59230A. The lack of simple competitive antagonism of isoprenaline, but not BRL 37344, by SR 59230A may suggest more than one population of atypical beta-adrenoceptor.

Topics: Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Dose-Response Relationship, Drug; Drug Interactions; Ethanolamines; Female; In Vitro Techniques; Isoproterenol; Jejunum; Male; Pindolol; Propanolamines; Propranolol; Rabbits; Receptors, Adrenergic, beta