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Ennio Ongini - One of the best experts on this subject based on the ideXlab platform.
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binding of the radioligand 3h sch 58261 a new non xanthine a2a Adenosine receptor antagonist to rat striatal membranes
British Journal of Pharmacology, 1996Co-Authors: C Zocchi, Ennio Ongini, Silvia Ferrara, Silvio DionisottiAbstract:1. The present study describes the binding to rat striatal A2A Adenosine receptors of the new potent and selective antagonist radioligand, [3H]-5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazol o [1,5-c] pyrimidine, [3H]-SCH 58261. 2. [3H]-SCH 58261 specific binding to rat striatal membranes ( > 90%) was saturable, reversible and dependent upon protein concentration. Saturation experiments revealed that [3H]-SCH 58261 labelled a single class of recognition sites with high affinity (Kd = 0.70 nM) and limited capacity (apparent Bmax = 971 fmol mg-1 of protein). The presence of 100 microM GTP in the incubation mixture did not modify [3H]-SCH 58261 binding parameters. 3. Competition experiments showed that [3H]-SCH 58261 binding is consistent with the labelling of A2A striatal receptors. Adenosine receptor agonists competed with the binding of 0.2 nM [3H]-SCH 58261 with the following order of potency: 2-hexynyl-5'-N-ethyl carboxamidoAdenosine (2HE-NECA) > 5'-N-ethylcarboxamidoAdenosine (NECA) > 2-[4-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoadenosi ne (CGS 21680) > 2-phenylaminoAdenosine (CV 1808) > R-N6-phenylisopropylAdenosine (R-PIA) > N6-cyclohexylAdenosine (CHA) = 2-chloro-N6-cyclopentylAdenosine (CCPA) > S-N6-phenylisopropylAdenosine (S-PIA). 4. Adenosine Antagonists inhibited [3H]-SCH 58261 binding with the following order: 5-amino-9-chloro-2-(2-furyl)-[1,2,4]-triazolo[1,5-c] quinazoline (CGS 15943) > 5-amino-8-(4-fluorobenzyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4-triazolo [1,5-c] pyrimidine (8FB-PTP) = SCH 58261 > xanthine amine congener (XAC) = (E,18%-Z,82%)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropylxanthine (KF 17837S) > 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) > or = 8-phenyltheophylline (8-PT). 5. The Ki values for Adenosine Antagonists were similar to those labelled with the A2A agonist [3H]-CGS 21680. Affinities of agonists were generally lower. The A1-selective agonist, R-PIA, was found to be about 9 fold more potent than its stereoisomer, S-PIA, thus showing the stereoselectivity of [3H]-SCH 58261 binding. Except for 8-PT, the Adenosine agonists and Antagonists examined inhibited [3H]-SCH 58261 binding with Hill coefficients not significantly different from unity. 6. The present results indicate that [3H]-SCH 58261 is the first non-xanthine Adenosine antagonist radioligand which directly labels A2A striatal receptors. High receptor affinity, good selectivity and very low non-specific binding make [3H]-SCH 58261 an excellent probe for studying the A2A Adenosine receptor subtype in mammalian brain.
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pyrazolo 4 3 e 1 2 4 triazolo 1 5 c pyrimidine derivatives potent and selective a2a Adenosine Antagonists
Journal of Medicinal Chemistry, 1996Co-Authors: Pier Giovanni Baraldi, C Zocchi, Silvio Dionisotti, Barbara Cacciari, Giampiero Spalluto, Pineda De Las Infantas Y Villatoro Mj, Ennio OnginiAbstract:A series of pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine derivatives (10a−o,q,r), bearing alkyl and aralkyl chains on positions 7 and 8, were synthesized in the attempt to obtain potent and selective Antagonists for the A2A Adenosine receptor subtype. The compounds were tested in binding and functional assays to evaluate their potency for the A2A compared with the A1 Adenosine receptor subtype. In binding studies in rat brain membranes, most of the compounds showed affinity for A2A receptors in the low nanomolar range with a different degree of A2A versus A1 selectivity. Comparison of N7 (10a−d,h−o)- and N8 (10e−g)-substituted pyrazolo derivatives indicates that N7 substitution decreases the A1 affinity with the concomitant increase of A2A selectivity. Specifically, the introduction of a 3-phenylpropyl group at pyrazolo nitrogen in position 7 (10l) increased significantly the A2A selectivity, being 210-fold, while the A2A receptor affinity remained high (Ki = 2.4 nM). With regards to the affinity for A...
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effects of the new a2 Adenosine receptor antagonist 8fb ptp an 8 substituted pyrazolo triazolo pyrimidine on in vitro functional models
British Journal of Pharmacology, 1994Co-Authors: Silvio Dionisotti, C Zocchi, A Conti, Daniele Sandoli, Franco Gatta, Ennio OnginiAbstract:1. We have characterized the in vitro pharmacological profile of putative A2 Adenosine Antagonists, two non-xanthine compounds, 5-amino-8-(4-fluorobenzyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine (8FB-PTP) and 5-amino-9-chloro-2-(2-furyl 1,2,4-triazolo [1,5-c] quinazoline (CGS 15943), and the xanthine derivative (E)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropyl- xanthine (KF 17837). 2. In binding studies on bovine brain, 8FB-PTP was the most potent (Ki = 0.074 nM) and selective (28 fold) drug on A2 receptors, whereas CGS 15943 and KF 17837 exhibited affinity in the low and high nanomolar range, respectively, and showed little selectivity. 3. In functional studies, 8FB-PTP antagonized 5'-N-ethyl-carboxamidoAdenosine (NECA)-induced vasorelaxation of bovine coronary artery (pA2 = 7.98) and NECA-induced inhibition of rabbit platelet aggregation (pA2 = 8.20). CGS 15943 showed weak activity in the platelet aggregation model (pA2 = 7.43) and failed to antagonize NECA-induced vasodilatation. KF 17837 was ineffective in both models up to micromolar concentrations. 4. Antagonism of A1-mediated responses was tested versus 2-chloro-N6-cyclopentylAdenosine (CCPA) in rat atria. 8FB-PTP and CGS 15943 also antagonized competitively the negative chronotropic response induced by CCPA. Conversely, KF 17837 was unable to reverse A1-mediated responses. 5. 8FB-PTP is a potent and competitive antagonist of responses mediated by A2 Adenosine receptors. The data provided a basis to reduce, by further chemical modifications, the affinity at A1 receptor and therefore enhance A2 receptor selectivity.
Silvio Dionisotti - One of the best experts on this subject based on the ideXlab platform.
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binding of the radioligand 3h sch 58261 a new non xanthine a2a Adenosine receptor antagonist to rat striatal membranes
British Journal of Pharmacology, 1996Co-Authors: C Zocchi, Ennio Ongini, Silvia Ferrara, Silvio DionisottiAbstract:1. The present study describes the binding to rat striatal A2A Adenosine receptors of the new potent and selective antagonist radioligand, [3H]-5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazol o [1,5-c] pyrimidine, [3H]-SCH 58261. 2. [3H]-SCH 58261 specific binding to rat striatal membranes ( > 90%) was saturable, reversible and dependent upon protein concentration. Saturation experiments revealed that [3H]-SCH 58261 labelled a single class of recognition sites with high affinity (Kd = 0.70 nM) and limited capacity (apparent Bmax = 971 fmol mg-1 of protein). The presence of 100 microM GTP in the incubation mixture did not modify [3H]-SCH 58261 binding parameters. 3. Competition experiments showed that [3H]-SCH 58261 binding is consistent with the labelling of A2A striatal receptors. Adenosine receptor agonists competed with the binding of 0.2 nM [3H]-SCH 58261 with the following order of potency: 2-hexynyl-5'-N-ethyl carboxamidoAdenosine (2HE-NECA) > 5'-N-ethylcarboxamidoAdenosine (NECA) > 2-[4-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoadenosi ne (CGS 21680) > 2-phenylaminoAdenosine (CV 1808) > R-N6-phenylisopropylAdenosine (R-PIA) > N6-cyclohexylAdenosine (CHA) = 2-chloro-N6-cyclopentylAdenosine (CCPA) > S-N6-phenylisopropylAdenosine (S-PIA). 4. Adenosine Antagonists inhibited [3H]-SCH 58261 binding with the following order: 5-amino-9-chloro-2-(2-furyl)-[1,2,4]-triazolo[1,5-c] quinazoline (CGS 15943) > 5-amino-8-(4-fluorobenzyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4-triazolo [1,5-c] pyrimidine (8FB-PTP) = SCH 58261 > xanthine amine congener (XAC) = (E,18%-Z,82%)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropylxanthine (KF 17837S) > 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) > or = 8-phenyltheophylline (8-PT). 5. The Ki values for Adenosine Antagonists were similar to those labelled with the A2A agonist [3H]-CGS 21680. Affinities of agonists were generally lower. The A1-selective agonist, R-PIA, was found to be about 9 fold more potent than its stereoisomer, S-PIA, thus showing the stereoselectivity of [3H]-SCH 58261 binding. Except for 8-PT, the Adenosine agonists and Antagonists examined inhibited [3H]-SCH 58261 binding with Hill coefficients not significantly different from unity. 6. The present results indicate that [3H]-SCH 58261 is the first non-xanthine Adenosine antagonist radioligand which directly labels A2A striatal receptors. High receptor affinity, good selectivity and very low non-specific binding make [3H]-SCH 58261 an excellent probe for studying the A2A Adenosine receptor subtype in mammalian brain.
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pyrazolo 4 3 e 1 2 4 triazolo 1 5 c pyrimidine derivatives potent and selective a2a Adenosine Antagonists
Journal of Medicinal Chemistry, 1996Co-Authors: Pier Giovanni Baraldi, C Zocchi, Silvio Dionisotti, Barbara Cacciari, Giampiero Spalluto, Pineda De Las Infantas Y Villatoro Mj, Ennio OnginiAbstract:A series of pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine derivatives (10a−o,q,r), bearing alkyl and aralkyl chains on positions 7 and 8, were synthesized in the attempt to obtain potent and selective Antagonists for the A2A Adenosine receptor subtype. The compounds were tested in binding and functional assays to evaluate their potency for the A2A compared with the A1 Adenosine receptor subtype. In binding studies in rat brain membranes, most of the compounds showed affinity for A2A receptors in the low nanomolar range with a different degree of A2A versus A1 selectivity. Comparison of N7 (10a−d,h−o)- and N8 (10e−g)-substituted pyrazolo derivatives indicates that N7 substitution decreases the A1 affinity with the concomitant increase of A2A selectivity. Specifically, the introduction of a 3-phenylpropyl group at pyrazolo nitrogen in position 7 (10l) increased significantly the A2A selectivity, being 210-fold, while the A2A receptor affinity remained high (Ki = 2.4 nM). With regards to the affinity for A...
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effects of the new a2 Adenosine receptor antagonist 8fb ptp an 8 substituted pyrazolo triazolo pyrimidine on in vitro functional models
British Journal of Pharmacology, 1994Co-Authors: Silvio Dionisotti, C Zocchi, A Conti, Daniele Sandoli, Franco Gatta, Ennio OnginiAbstract:1. We have characterized the in vitro pharmacological profile of putative A2 Adenosine Antagonists, two non-xanthine compounds, 5-amino-8-(4-fluorobenzyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine (8FB-PTP) and 5-amino-9-chloro-2-(2-furyl 1,2,4-triazolo [1,5-c] quinazoline (CGS 15943), and the xanthine derivative (E)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropyl- xanthine (KF 17837). 2. In binding studies on bovine brain, 8FB-PTP was the most potent (Ki = 0.074 nM) and selective (28 fold) drug on A2 receptors, whereas CGS 15943 and KF 17837 exhibited affinity in the low and high nanomolar range, respectively, and showed little selectivity. 3. In functional studies, 8FB-PTP antagonized 5'-N-ethyl-carboxamidoAdenosine (NECA)-induced vasorelaxation of bovine coronary artery (pA2 = 7.98) and NECA-induced inhibition of rabbit platelet aggregation (pA2 = 8.20). CGS 15943 showed weak activity in the platelet aggregation model (pA2 = 7.43) and failed to antagonize NECA-induced vasodilatation. KF 17837 was ineffective in both models up to micromolar concentrations. 4. Antagonism of A1-mediated responses was tested versus 2-chloro-N6-cyclopentylAdenosine (CCPA) in rat atria. 8FB-PTP and CGS 15943 also antagonized competitively the negative chronotropic response induced by CCPA. Conversely, KF 17837 was unable to reverse A1-mediated responses. 5. 8FB-PTP is a potent and competitive antagonist of responses mediated by A2 Adenosine receptors. The data provided a basis to reduce, by further chemical modifications, the affinity at A1 receptor and therefore enhance A2 receptor selectivity.
C Zocchi - One of the best experts on this subject based on the ideXlab platform.
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binding of the radioligand 3h sch 58261 a new non xanthine a2a Adenosine receptor antagonist to rat striatal membranes
British Journal of Pharmacology, 1996Co-Authors: C Zocchi, Ennio Ongini, Silvia Ferrara, Silvio DionisottiAbstract:1. The present study describes the binding to rat striatal A2A Adenosine receptors of the new potent and selective antagonist radioligand, [3H]-5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazol o [1,5-c] pyrimidine, [3H]-SCH 58261. 2. [3H]-SCH 58261 specific binding to rat striatal membranes ( > 90%) was saturable, reversible and dependent upon protein concentration. Saturation experiments revealed that [3H]-SCH 58261 labelled a single class of recognition sites with high affinity (Kd = 0.70 nM) and limited capacity (apparent Bmax = 971 fmol mg-1 of protein). The presence of 100 microM GTP in the incubation mixture did not modify [3H]-SCH 58261 binding parameters. 3. Competition experiments showed that [3H]-SCH 58261 binding is consistent with the labelling of A2A striatal receptors. Adenosine receptor agonists competed with the binding of 0.2 nM [3H]-SCH 58261 with the following order of potency: 2-hexynyl-5'-N-ethyl carboxamidoAdenosine (2HE-NECA) > 5'-N-ethylcarboxamidoAdenosine (NECA) > 2-[4-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoadenosi ne (CGS 21680) > 2-phenylaminoAdenosine (CV 1808) > R-N6-phenylisopropylAdenosine (R-PIA) > N6-cyclohexylAdenosine (CHA) = 2-chloro-N6-cyclopentylAdenosine (CCPA) > S-N6-phenylisopropylAdenosine (S-PIA). 4. Adenosine Antagonists inhibited [3H]-SCH 58261 binding with the following order: 5-amino-9-chloro-2-(2-furyl)-[1,2,4]-triazolo[1,5-c] quinazoline (CGS 15943) > 5-amino-8-(4-fluorobenzyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4-triazolo [1,5-c] pyrimidine (8FB-PTP) = SCH 58261 > xanthine amine congener (XAC) = (E,18%-Z,82%)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropylxanthine (KF 17837S) > 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) > or = 8-phenyltheophylline (8-PT). 5. The Ki values for Adenosine Antagonists were similar to those labelled with the A2A agonist [3H]-CGS 21680. Affinities of agonists were generally lower. The A1-selective agonist, R-PIA, was found to be about 9 fold more potent than its stereoisomer, S-PIA, thus showing the stereoselectivity of [3H]-SCH 58261 binding. Except for 8-PT, the Adenosine agonists and Antagonists examined inhibited [3H]-SCH 58261 binding with Hill coefficients not significantly different from unity. 6. The present results indicate that [3H]-SCH 58261 is the first non-xanthine Adenosine antagonist radioligand which directly labels A2A striatal receptors. High receptor affinity, good selectivity and very low non-specific binding make [3H]-SCH 58261 an excellent probe for studying the A2A Adenosine receptor subtype in mammalian brain.
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pyrazolo 4 3 e 1 2 4 triazolo 1 5 c pyrimidine derivatives potent and selective a2a Adenosine Antagonists
Journal of Medicinal Chemistry, 1996Co-Authors: Pier Giovanni Baraldi, C Zocchi, Silvio Dionisotti, Barbara Cacciari, Giampiero Spalluto, Pineda De Las Infantas Y Villatoro Mj, Ennio OnginiAbstract:A series of pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine derivatives (10a−o,q,r), bearing alkyl and aralkyl chains on positions 7 and 8, were synthesized in the attempt to obtain potent and selective Antagonists for the A2A Adenosine receptor subtype. The compounds were tested in binding and functional assays to evaluate their potency for the A2A compared with the A1 Adenosine receptor subtype. In binding studies in rat brain membranes, most of the compounds showed affinity for A2A receptors in the low nanomolar range with a different degree of A2A versus A1 selectivity. Comparison of N7 (10a−d,h−o)- and N8 (10e−g)-substituted pyrazolo derivatives indicates that N7 substitution decreases the A1 affinity with the concomitant increase of A2A selectivity. Specifically, the introduction of a 3-phenylpropyl group at pyrazolo nitrogen in position 7 (10l) increased significantly the A2A selectivity, being 210-fold, while the A2A receptor affinity remained high (Ki = 2.4 nM). With regards to the affinity for A...
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effects of the new a2 Adenosine receptor antagonist 8fb ptp an 8 substituted pyrazolo triazolo pyrimidine on in vitro functional models
British Journal of Pharmacology, 1994Co-Authors: Silvio Dionisotti, C Zocchi, A Conti, Daniele Sandoli, Franco Gatta, Ennio OnginiAbstract:1. We have characterized the in vitro pharmacological profile of putative A2 Adenosine Antagonists, two non-xanthine compounds, 5-amino-8-(4-fluorobenzyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine (8FB-PTP) and 5-amino-9-chloro-2-(2-furyl 1,2,4-triazolo [1,5-c] quinazoline (CGS 15943), and the xanthine derivative (E)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropyl- xanthine (KF 17837). 2. In binding studies on bovine brain, 8FB-PTP was the most potent (Ki = 0.074 nM) and selective (28 fold) drug on A2 receptors, whereas CGS 15943 and KF 17837 exhibited affinity in the low and high nanomolar range, respectively, and showed little selectivity. 3. In functional studies, 8FB-PTP antagonized 5'-N-ethyl-carboxamidoAdenosine (NECA)-induced vasorelaxation of bovine coronary artery (pA2 = 7.98) and NECA-induced inhibition of rabbit platelet aggregation (pA2 = 8.20). CGS 15943 showed weak activity in the platelet aggregation model (pA2 = 7.43) and failed to antagonize NECA-induced vasodilatation. KF 17837 was ineffective in both models up to micromolar concentrations. 4. Antagonism of A1-mediated responses was tested versus 2-chloro-N6-cyclopentylAdenosine (CCPA) in rat atria. 8FB-PTP and CGS 15943 also antagonized competitively the negative chronotropic response induced by CCPA. Conversely, KF 17837 was unable to reverse A1-mediated responses. 5. 8FB-PTP is a potent and competitive antagonist of responses mediated by A2 Adenosine receptors. The data provided a basis to reduce, by further chemical modifications, the affinity at A1 receptor and therefore enhance A2 receptor selectivity.
Margaret M Redfield - One of the best experts on this subject based on the ideXlab platform.
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acute decompensated heart failure and the cardiorenal syndrome
Critical Care Medicine, 2008Co-Authors: Kelly V Liang, Amy W Williams, Eddie L Greene, Margaret M RedfieldAbstract:Heart failure is one of the leading causes of hospitalizations in the United States. Concomitant and significant renal dysfunction is common in patients with heart failure. Increasingly, the syndrome of heart failure is one of cardiorenal failure, in which concomitant cardiac and renal dysfunctions exist, with each accelerating the progression of the other. One fourth of patients hospitalized for the treatment of acute decompensated heart failure will experience significant worsening of renal function, which is associated with worse outcomes. It remains unclear whether worsening renal function specifically contributes to poor outcomes or whether it is merely a marker of advanced cardiac and renal dysfunction. Diuretic resistance, with or without worsening renal function, is also common in acute decompensated heart failure, although the definition of diuretic resistance, its prevalence, and prognostic implications are less well defined. The term cardiorenal syndrome has been variably associated with cardiorenal failure, worsening renal function, and diuretic resistance but is more comprehensively defined as a state of advanced cardiorenal dysregulation manifest by one or all of these specific features. The pathophysiology of the cardiorenal syndrome is poorly understood and likely involves interrelated hemodynamic and neurohormonal mechanisms. When conventional therapy for acute decompensated heart failure fails, mechanical fluid removal via ultrafiltration, hemofiltration, or hemodialysis may be needed for refractory volume overload. While ultrafiltration can address diuretic resistance, whether ultrafiltration prevents worsening renal function or improves outcomes in patients with cardiorenal syndrome remains unclear. Evidence regarding the potential renal-preserving effects of nesiritide is mixed, and further studies on the efficacy and safety of different doses of nesiritide in heart failure therapy are warranted. Newer therapeutic agents, including vasopressin Antagonists and Adenosine Antagonists, hold promise for the future, and clinical trials of these agents are underway.
Bertil B Fredholm - One of the best experts on this subject based on the ideXlab platform.
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the effect of alkylxanthines and other phosphodiesterase inhibitors on Adenosine receptor mediated decrease in lipolysis and cyclic amp accumulation in rat fat cells
Pharmacology & Toxicology, 2009Co-Authors: Bertil B Fredholm, Eva LindgrenAbstract:Cyclic AMP accumulation and glycerol release were studied in isolated rat fat cells. Both processes were inhibited by R-site specific Adenosine analogues (L-PIA greater than NECA greater than 2-chloro-Adenosine greater than D-PIA), but poorly or not at all by the P-site selective analogue SQ 22,536. The effect of a series of xanthine derivatives and of some structurally unrelated phosphodiesterase inhibitors as inhibitors of 2-chloro-Adenosine induced inhibition of NA stimulated cyclic AMP accumulation and lipolysis was subsequently examined. The 2-chloroAdenosine effect on cyclic AMP accumulation was antagonized by the xanthines with the following order of potency: DPX greater than 8-phenyl-theophylline greater than 8-p-sulpho-phenyl-theophylline greater than verrophylline greater than IBMX greater than theophylline greater than HWA 285 greater than pentoxiphylline greater than caffeine greater than 7-benzyl IBMX greater than theobromine greater than enprofylline greater greater than ZK 62,711. The rank order potency of xanthines against the antilipolytic effect of 2-chloro-Adenosine was the same with two notable exceptions: the two potent phosphodiesterase inhibitors 7-benzyl-IBMX and ZK 62,711 were more than 20 times more potent as inhibitors of the antilipolytic effect of 2-chloro-Adenosine. The results show that antagonism of Adenosine analogue-induced antilipolytic effects is a convenient assay for Adenosine antagonistic potency of drugs, except for drugs with a high potency as phosphodiesterase inhibitors. The lipolytic potency of the xanthine derivatives was also studied. The ability of the xanthines to stimulate basal and noradrenaline stimulated lipolysis was generally in agreement with their potency as Adenosine Antagonists. Adenosine deaminase induced lipolysis was stimulated by potent phosphodiesterase inhibitors.
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evidence for high affinity binding sites for the Adenosine a2a receptor agonist 3h cgs 21680 in the rat hippocampus and cerebral cortex that are different from striatal a2a receptors
Naunyn-schmiedebergs Archives of Pharmacology, 1996Co-Authors: Rodrigo A Cunha, M D Constantino, Ana M Sebastiao, Bjorn Johansson, Bertil B FredholmAbstract:The binding of the Adenosine A2A receptor selective agonist 2-[4-(2-p-carboxyethyl) phenylamino]-5′-N-ethylcarboxamidoAdenosine (CGS 21680) to the rat hippocampal and cerebral cortical membranes was studied and compared with that to striatal membranes. [3H] CGS 21680, in the concentration range tested (0.2–200 nM), bound to a single site with a Kd of 58 nM and a Bmax of 353 fmol/mg protein in the hippocampus, and with a Kd of 58 nM and a Bmax of 264 fmol/mg protein in the cortex; in the striatum, the single high-affinity [3H] CGS 21680 binding site had a Kd of 17 nM and a Bmax of 419 fmol/mg protein. Both guanylylimidodiphosphate (100 μM) and Na+ (100 mM) reduced the affinity of [3H] CGS 21680 binding in the striatum by half and virtually abolished [3H] CGS 21680 binding in the hippocampus and cortex. The displacement curves of [3H] CGS 21680 binding with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), N6-cyclohexylAdenosine (CHA), 5′-N-ethyl-carboxamidoAdenosine (NECA) and 2-chloroAdenosine (CADO) were biphasic in the hippocampus and cortex as well as in the striatum. The predominant [3H]CGS 21680 binding site in the striatum (80%) had a pharmacological profile compatible with A2A receptors and was also present in the hippocampus and cortex, representing 10–25% of [3H]CGS 21680 binding. The predominant [3H]CGS 21680 binding site in the hippocampus and cortex had a pharmacological profile distinct from A2A receptors: the relative potency order of Adenosine Antagonists DPCPX, 1,3-dipropyl8-{4-[(2-aminoethyl)amino]carbonylmethyloxyphenyl} xanthine (XAC), 8-(3-chlorostyryl) caffeine (CSC), and (E)-1,3-dipropyl-8-(3,4-dimethoxystyryl)-methylxanthine (KF 17,837) as displacers of [3H] CGS 21680 (5 nM) binding in the hippocampus and cerebral cortex was DPCPX > XAC ≫ CSC ≈ KF 17,837, and the relative potency order of Adenosine agonists CHA, NECA, CADO, 2-[(2-aminoethylamino)carbonylethylphenylethylamino]-5′-N-ethylcar-boxamidoAdenosine (APEC), and 2-phenylaminoAdenosine (CV 1808) was CHA ≈ NECA ⩾ CADO > APEC ≈ CV1808 > CGS 21680. In the presence of DPCPX (20 nM), [3H] CGS 21680 (0.2-200 nM) bound to a site (A2A-like) with a Kd of 20 nM and a Bmax of 56 fmol/mg protein in the hippocampus and with a Kd of 22 nM and a Bmax of 63 fmol/mg protein in the cortex. In the presence of CSC (200 nM), [3H]CGS 21680 (0.2–200 nM) bound to a second high-affinity site with a Kd of 97 nM and a Bmax of 255 fmol/mg protein in the hippocampus and with a Kd of 112 nM and a Bmax of 221 fmol/mg protein in the cortex. Two pharmacologically distinct [3H]CGS 21680 binding sites were found in synaptosomal membranes of the hippocampus and cortex and in the striatum, one corresponding to A2A receptors and the other to the second high-affinity [3H]CGS 21680 binding site. In contrast, the pharmacology of [3H]CHA binding was similar in synaptosomal membranes of the three brain areas. The present results establish the existence of at least two high-affinity [3H]CGS 21680 binding sites in the CNS and demonstrate that the [3H]CGS 21680 binding site predominant in the hippocampus and cerebral cortex has different binding characteristics from the classic A2A Adenosine receptor, which predominates in the striatum.