Biomedical subjects

R A Olsson

Publications and source records attributed to R A Olsson.

At least 19 recordsLinked to original sources

PubMed1996

Functional characterization of adenosine A2 receptors in Jurkat cells and PC12 cells using adenosine receptor agonists.

The effect of several adenosine analogues on cyclic AMP accumulation was examined in the rat phaeochromocytoma cell PC12 and in the human T-cell leukaemia cell Jurkat, selected as prototypes of cells predominantly expressing adenosine A2A or A2B receptors. Using the reverse transcription-polymerase chain reaction it was, however, demonstrated that the Jurkat cell and the PC12 cell express both A2A and A2B receptor mRNA, albeit in different relative proportions. In PC12 cells the concentration required for half-maximal response (EC50) for the full agonist 5'-N-ethyl-carboxamidoadenosine (NECA) was 30 times lower than in Jurkat cells. There was no significant difference in the pA2 for the antagonist 5-amino-9-chloro-2-(2-furanyl)- 1,2,4-triazolo(1,5-C)quinazolinemonomethanesulphonate (CGS 15943) between the two cell types. In the presence of forskolin (1 microM in PC12 cells; 10 microM in Jurkat cells) the EC50 value for NECA was reduced two-to sixfold. Forskolin also increased the maximal cAMP accumulation twofold in PC12 cells and sevenfold in Jurkat cells. A series of 2-substituted adenosine analogues CV 1808 (2-phenylamino adenosine), CV 1674 [2-(4-methoxyphenyl)adenosine], CGS 21680 ¿2-[p-(2-carbonylethyl)phenylethylamino]-5'-N-ethyl- carboxamido adenosine¿, and four 2-substituted isoguanosines, SHA 40 [2-(2-phenylethoxy)adenosine; PEA], SHA 91 [2-(2-cyclohexylethoxy)adenosine; CEA], SHA 118 ¿2-[2-(p-methylphenyl)ethoxy]adenosine; MPEA¿, and SHA 125 (2-hexyloxyadenosine; HOA), all raised cAMP accumulation in PC12 cells, but had minimal or no effect in Jurkat cells. In the PC12 cells the addition of forskolin (1 microM) reduced the EC50 by a factor of 2(CV 1808) to 12 (SHA 125). In Jurkat cells all the analogues gave a significant, but submaximal, cAMP response in the presence of forskolin (10 microM), but they were essentially inactive in its absence. The results show that a series of 2-substituted adenosine analogues can be used to discriminate between A2A and A2B receptors. The two receptor subtypes appear to coexist, even in clonal cells selected for typical pharmacology. A2 receptor pharmacology can therefore be complex.

Adenosine↗

PubMed1996

Upregulated renal adenosine A1 receptors augment PKC and glucose transport but inhibit proliferation.

Adenosine A1 receptor densities were increased in cultured LLC-PK1 and OK cells by chronic treatment with the adenosine receptor antagonists 1,3,7-trimethylxanthine (caffeine, 1 mM) and 1,3-dimethyl-8-cyclopentylxanthine [cyclopentyltheophylline (CPT), < or = 0.4 mM], respectively. The A1 receptor number per cell was increased twofold by 10-day treatments with 1 mM caffeine or 0.1 mM CPT, and the sodium-coupled glucose uptake was augmented twofold by 1 mM caffeine and sevenfold by 0.1 microM CPT (higher doses of CPT were progressively less stimulatory). Glucose uptake was blocked by acute (2-h) treatment with CPT, adenosine deaminase, or calphostin C. Caffeine (1 mM) or CPT (> or = 0.1 mM) inhibited cell proliferation for the first 10 days, then cell growth assumed a normal proliferative rate despite continued presence of antagonist. Cytosolic protein kinase C (PKC) beta-isoform immunoactivity and PKC-beta II mRNA were elevated at least twofold during 10 days of 0.1 mM CPT or 1 mM caffeine treatment. The sustained elevation in sodium-glucose symport and PKC activity observed with adenosine receptor antagonists was similar to acute (2-h) effects of the adenosine A1 agonist R(-)-N6-phenylisopropyladenosine (R-PIA, 0.1-1 microM). Moreover, cell proliferation was increased by adenosine (0.1 microM R-PIA), whereas Na-K-adenosinetriphosphatase activity was unaltered with chronic antagonist or acute adenosine treatments. Caffeine treatment may have some non-adenosine A1 receptor-mediated actions, because it slightly (30%) augmented protein kinase A activity. It is concluded that chronic exposure of proximal tubule cells to caffeine or CPT augments PKC and sodium-glucose transport but retards cell proliferation mainly via adenosine A1 receptor-mediated mechanisms.

Adenosine Deaminase↗

PubMed1995

Characterization of two affinity states of adenosine A2a receptors with a new radioligand, 2-[2-(4-amino-3-[125I]iodophenyl)ethylamino]adenosine.

Adenosine analogs substituted in the 2-position with arylamino groups have been found to have high affinity and selectivity for A2a adenosine receptors. Two such compounds, 2-[2-(4-aminophenyl)ethylamino]adenosine and 2-[2-4-amino-3-iodophenyl)ethylamino]adenosine (I-APE), were synthesized and found to be potent coronary vasodilators (ED50 < 3 nm). These compounds bind weakly to A1 adenosine receptors of rat cortex (Ki > 150 nM). 125I-APE was synthesized and the new radioligand was found to bind to two affinity states of rat striatal A2a adenosine receptors (Kd = 1.3 +/- 0.1 nM and 19 +/- 4.5 nM). The high affinity site represents a previously unrecognized small (15-20%) fraction of A2a adenosine receptors coupled to G proteins. Guanosine 5'-O-(3-thio)triphosphate (GTP gamma S) reduces specific binding of 125I-APE half-maximally at a concentration of 45 +/- 2 nM. [3H]CGS21680 also binds to two affinity states of A2a receptors on striatal membranes (Kd = 3.9 +/- 0.9 and 51 +/- 5.5 nM), although in previous studies single Kd values ranging from 5 to 15 nM have been reported. This high affinity site is substantiated by the finding that the IC50 of CGS21680 in competition with 125I-APE binding to striatal membranes is shifted leftward in membranes diluted for 4 min before filtration, to selectively dissociate radioligand from low affinity receptors. Assuming that agonist radioligands bind to both coupled and uncoupled forms of striatal A2a adenosine receptors, we could simulate with the computer the finding that the decrease in specific binding induced by GTP gamma S (100 microM) is variable and depends on radioligand concentration, ranging from 20 to 90%. Unlike 125I-APE, [3H]CGS21680 is charged at physiological pH, and treatment of membranes with the pore-forming antibiotic alamethicin uncovers cryptic [3H]CGS21680 but not 125I-APE binding sites. We conclude that the GTP gamma S-sensitive high affinity form of the A2a adenosine receptor can be preferentially labeled by 125I-APE, due to both its high specific activity and its physicochemical properties. Possible functional manifestations of poor coupling of A2a adenosine receptors to G proteins are discussed.

Adenosine↗

PubMed1994

Substituted 1,3-dipropylxanthines as irreversible antagonists of A1 adenosine receptors.

This report describes the synthesis of 29 xanthines containing a chemoreactive chloroaryl, beta-chloroethylamino, alpha,beta-unsaturated carbonyl, bromoacetyl, 3-(fluorosulfonyl)benzoyl, or 4-(fluorosulfonyl)benzoyl group as part of an exocyclic 1-, 3-, or 8-substituent. The xanthines inhibited the binding of [3H]-8-cyclopentyl-1,3-dipropylxanthine ([3H]CPX) to the A1 adenosine receptor (A1AR) of DDT1 MF2 cells at IC50s in the low-nanomolar to low-micromolar range. Seven of the 29 analogues irreversibly inhibited the binding of [3H]CPX without changing the KD of that ligand; five were 1,3-dipropylxanthines having the following reactive groups as 8-substituents: (bromoacetamido)methyl (24), (bromoacetamido)ethyl (25), (bromoacetamido)propyl (26), [4-(fluorosulfonyl)benzamido]methyl (33) or 3-[[4-(fluorosulfonyl)benzoyl]oxy]cyclopentyl (42). Both 8-cyclopentyl-3-[3-[[4- (fluorosulfonyl)benzoyl]oxy]propyl]-1-propylxanthine (53) and 8-cyclopentyl-1,3-bis[3-[[4- (fluorosulfonyl)benzoyl]oxy]propyl]xanthine (55) inhibited [3H]CPX binding irreversibly. Five of the ligands, including 26, 33 (IC50 = 49 microM), and 53 (IC50 = 9 microM), antagonized the binding of [3H]NECA to the A2aAR of PC12 cells, but unlike binding to the A1AR, binding to the A2aAR was completely reversible. The potency of 33 (IC50 = 2 microM, 72% loss of CPX binding at 1 microM) and 53 (IC50 = 0.01 microM, 74% loss of CPX binding at 0.05 microM) and their selectivity for the A1AR suggest that those two ligands may be useful in studies of the structure and function of that receptor.

Adenosine↗

PubMed1994

The anti-infarct effect of an adenosine A1-selective agonist is diminished after prolonged infusion as is the cardioprotective effect of ischaemic preconditioning in rabbit heart.

Our aim was to determine whether adenosine A1 receptor-mediated protection could be maintained for a prolonged period of time by a continuous infusion of an A1-selective agonist. To produce myocardial infarction a branch of the left coronary artery of rabbit hearts was occluded for 30 min and reperfused for 3 h. Infarct size was determined with tetrazolium staining. Prior to the 30 min ischaemia, rabbits were subjected to one of the following six protocols: (1) 6 h i.v. saline infusion; (2) 6 h i.v. CCPA (0.043 mg/kg/h) infusion; (3) 72 h saline infusion; (4) 72 h CCPA infusion; (5) 72 h CCPA infusion plus preconditioning with 5 min ischaemia followed by 10 min reperfusion; (6) 72 h saline infusion plus preconditioning. The 6 h CCPA infusion group had significantly smaller infarct sizes than the 6 h vehicle group. 16.2 +/- 2.9% infarction of the ischaemic region v 39.5 +/- 2.6%, P < 0.01. Infarction in the 72 h CCPA infusion group (37.7 +/- 2.7%) was the same as in the 72 h vehicle group (35.2 +/- 3.1%). Ischaemic preconditioning could not limit infarct size in 72 h CCPA animals (%infarction; 29.1 +/- 4.6%) but did protect animals given vehicle for 72 h (8.4 +/- 1.2%, P < 0.01). After 72 h infusion of CCPA, both the cardioprotective effect of adenosine A1-selective agonist and ischaemic preconditioning were attenuated. These findings indicate that: (1) the myocytes become desensitized to the protective effect of CCPA with prolonged exposure; and (2) ischaemic preconditioning is no longer protective when tachyphylaxis to CCPA occurs.

Acetylcholine↗

PubMed1994

Inhibition of platelet aggregation by adenosine receptor agonists.

2-(Ar)alkoxyadenosines, which are agonists selective for the A2AAR in PC 12 cell and rat striatum membranes, are also agonists at the A2AR coupled to adenylate cyclase (AC) that mediates the inhibition of platelet aggregation. A panel of twelve well-characterized adenosine analogues stimulated human platelet AC and inhibited ADP-induced platelet aggregation at sub- to low-micromolar concentrations with a potency ranking CGS 21680 > adenosine > R-PIA. There were significant correlations between the EC50 of anti-aggregatory activity and either the EC50 of stimulation of platelet and PC 12 cell AC (r2 = 0.66 and 0.67, respectively) or the Ki of inhibition of [3H]NECA binding to the rat striatum membranes (r2 = 0.75). Likewise, platelet AC stimulation correlated well with stimulation of PC 12 cell AC and with [3H]NECA binding (r2 = 0.94 and 0.91, respectively). Ten 2-(ar)alkoxyadenosines stimulated platelet AC at EC50s ranging between 0.16 and 2.3 microM and inhibited platelet aggregation at EC50s ranging between 2 and 30 microM. There were no correlations between the EC50s of anti-aggregatory activity and either the EC50s of the stimulation of platelet or PC 12 AC (r2 = 0.08 and 0.06, respectively) or with the Ki of the inhibition of [3H]NECA binding to the A2aAR in rat striatum (r2 = 0.02). The EC50s of the stimulation of platelet AC correlated with those of the stimulation of PC 12 AC (r2 = 0.48), and also with the Ki of [3H]NECA binding (r2 = 0.71). Each of the 23 adenosines completely inhibited platelet aggregation and thus, functionally, all behaved as full agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗

PubMed1994

Evidence that the adenosine A3 receptor may mediate the protection afforded by preconditioning in the isolated rabbit heart.

OBJECTIVE: Agonists selective for the A1 adenosine receptor mimic the protective effect of ischaemic preconditioning against infarction in the rabbit heart. Unselective adenosine antagonists block this protection but, paradoxically, the A1 adenosine receptor selective antagonist 8-cyclopentyl- 1,3-dipropylxanthine (DPCPX) does not. The aim of this study was to test the hypothesis that the newly described A3 adenosine receptor, which has an agonist profile similar to the A1 receptor but is insensitive to DPCPX, might mediate preconditioning. METHODS: Isolated rabbit hearts perfused with Krebs buffer experienced 30 min of regional ischaemia followed by 120 min of reperfusion. Infarct size was measured by tetrazolium staining. RESULTS: In control hearts infarction was 32.2(SEM 1.5)% of the risk zone. Preconditioning by 5 min ischaemia and 10 min reperfusion reduced infarct size to 8.8(2.3)%. Replacing the regional ischaemia with 5 min perfusion with 10 microM adenosine or 65 nM N6-[2-(4-aminophenyl)ethyl]adenosine (APNEA), an adenosine A3 receptor agonist, was equally protective. The unselective antagonist 8-p-sulphophenyl theophylline at 100 microM abolished protection by preconditioning, adenosine, and APNEA, but 200 nM DPCPX did not block protection by any of the interventions. Likewise the potent but unselective A3 receptor antagonist 8-(4-carboxyethenylphenyl)-1,3-dipropylxanthine (BW A1433) completely blocked protection from ischaemic preconditioning. CONCLUSIONS: Because protection against infarction afforded by ischaemic preconditioning, adenosine, or the A3 receptor agonist APNEA could not be blocked by DPCPX and because the potent A3 receptor antagonist BW A1433 blocked protection from ischaemic preconditioning, these data indicate that the protection of preconditioning is not exclusively mediated by the adenosine A1 receptor in rabbit heart and could involve the A3 receptor.

Adenosine↗

PubMed1994

Glibenclamide reduces the coronary vasoactivity of adenosine receptor agonists.

Experiments in guinea pig heart Langendorff preparations assessed the effect of KATP channel blockade on the coronary vasoactivity of adenosine and 17 analogs chosen to represent a variety of purine and ribose modifications. Although glibenclamide is a functional antagonist that acts at the level of an effector rather than at a receptor, it caused parallel rightward shifts of agonist dose-response curves. The size of the shift of EC50 differed according to the kind of analog: the ranking was, generally, N6-phenethyladenosines > 2-aryl-aminoadenosines = 2-(1-alkyn-1-yl)adenosines > N6-cycloalkyladenosines = adenosine-5' -uronamides. The coronary vasoactivity ranking of agonists in the presence of supramaximal concentrations of glibenclamide was 2-(1-alkyn-1-yl)adenosines = 2-aralkoxyadenosines > 2-aralkylaminoadenosines > 2-arylaminoadenosines > N6-substituted adenosines. Glibenclamide did not affect the vasoactivity of adenosine itself, perhaps because avid uptake by endothelial cells prevented penetration of the agonist to receptors deeper in the vascular wall. The results exclude a model consisting of one kind of receptor acting exclusively through a KATP channel, argue against one kind of receptor coupled to a KATP channel as well as to an additional effector but is consistent with two kinds of vasodilatory adenosine receptors, one of which activates a KATP channel. The identity of the adenosine receptor coupled to the KATP channel is uncertain; the other receptor has the pharmacological profile of an A2a-adenosine receptor.

Adenosine↗

PubMed1993

Structure-activity relationship of 2-(ar) alkoxyadenosines at the adenosine A2 receptor in coronary artery.

We examined the ability of four 2-(ar)alkoxyadenosines (2-(2-phenylethoxy)adenosine, PEA; 2-[2-(2-naphthyl)ethoxy]adenosine, NEA; 2-[2-(4-methylphenyl)ethoxy]adenosine, mPEA; 2-(1-hexyloxy)adenosine, HOA) to relax porcine coronary artery in vitro. All four compounds produced concentration-dependent relaxations in rings contracted with 30 mM KCl. The EC25 values are as follows (x 10(-9) mol/l): CGS21680, (2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosi ne) (32.7) approximately NECA, 5'-N-ethylcarboxamidoadenosine (51.4) approximately mPEA (74.3) approximately NEA (160.7) > HOA (855.1) approximately PEA (1259) approximately 2-chloroadenosine (1871) > adenosine (9705). However, EC75 values for all the compounds except adenosine and 2-chloroadenosine converged to a range of 8.16 to 22.86 microM, suggesting a biphasic response. Furthermore, the responses were found to be independent of endothelial integrity. The unselective adenosine receptor antagonist 8-p-sulphophenyltheophylline (100 microM) attenuated the relaxant response to NEA (EC25 = 1172 nM), suggesting that adenosine receptors mediated relaxation. Structure-activity correlations suggest that the adenosine A2 receptor in porcine coronary artery contains a region of limited bulk tolerance juxtaposed to the region occupied by adenine C-2 and distal to that a large hydrophobic region.

Adenosine↗

PubMed1993

Covalent binding of a selective agonist irreversibly activates guinea pig coronary artery A2 adenosine receptors.

Experiments employing guinea pig heart Langendorff preparations compared the coronary vasoactivity of a functionalized congener of adenosine, 2-[(2-aminoethyl-aminocarbonylethyl)phenylethylamino]-5'-N-e thyl- carboxamidoadenosine, APEC, with the vasoactivity of the product of the reaction of APEC with 1,4-phenylene-diisothiocyanate, 4-isothiocyanatophenylaminothiocarbonyl-APEC (DITC-APEC). Previous experiments showed that whereas APEC binds reversibly to the A2A adenosine receptor of brain striatum, DITC-APEC binds irreversibly. APEC caused concentration-dependent coronary vasodilation that persisted unchanged when agonist administration continued for up to 165 min, but promptly faded when the agent was withdrawn. The unselective adenosine receptor antagonist 8-(4-sulfophenyl)theophyline (8-SPT) antagonized the vasoactivity of APEC. By contrast, DITC-APEC (0.125-1.0 nM) caused progressive, concentration-independent vasodilation that persisted unchanged for as long as 120 min after the agent was stopped and that was insensitive to antagonism by subsequently applied 8-SPT. However, perfusion of the heart with buffer containing 0.1 mM 8-SPT strongly antagonized the coronary vasodilatory action of DITC-APEC given subsequently. Such observations indicate that the covalent binding of DITC-APEC causes irreversible activation of the guinea pig coronary artery A2A adenosine receptor. Neither APEC nor DITC-APEC appeared to desensitize the coronary adenosine receptor during two or more hours of exposure to either agonist.

Adenosine↗

PubMed1993

Structure-activity relationships for 2-substituted adenosines at A1 and A2 adenosine receptors.

A series of 55 2-alkyloxy-, 2-aryloxy- and 2-aralkyloxy-adenosines was screened as inhibitors of the binding of [3H]R-phenyl-isopropyladenosine to A1 adenosine receptors in rat cerebral cortical membranes, and of the binding of [3]N-ethylcarboxamidoadenosine to A2 adenosine receptors in rat striatal membranes and as agonists at A2 adenosine receptors coupled to adenylate cyclase in rat pheochromocytoma PC12 cell membranes. The activities are consonant with a hydrophobic binding site in the A2 receptors at a distance from the 2-position of the adenine ring corresponding to a spacer chain of -O-CH2-CH2-. These is little lateral steric tolerance in the region occupied by the spacer chain. Interaction with the hydrophobic binding site is greatest in the 2-alkyloxy series for 2-cyclohexylethoxy-, 2-cyclohexylpropoxy- and 2-cyclohexylbutoxyadenosines and in the 2-aralkoxy series for 2-phenylethoxy-, 2-(4-methylphenyl)ethoxy-, 2-(4-chlorophenyl)ethoxy-, and 2-naphthylethoxy-adenosine. The affinities of the 2-substituted adenosines for the rat cerebral cortical A1 receptors are not as markedly altered by structural changes and are in almost all cases two- to hundredfold less than the affinity of the 2-substituted adenosine for the rat striatal A2 receptor. There is excellent correspondence of the present data on rat A2 receptors with reported potencies of these 2-substituted adenosines as coronary vasodilators in guinea pig heart preparations.

Adenosine↗

PubMed1993

Selective A2-adenosine receptor agonists do not alter action potential duration, twitch shortening, or cAMP accumulation in guinea pig, rat, or rabbit isolated ventricular myocytes.

In this study, the hypothesis that mammalian ventricular myocytes possess A2-adenosine receptors was tested. Electrophysiological, contractile, and cAMP responses to the selective A2-adenosine receptor agonists 2-[2-(4-methylphenyl)ethoxy]adenosine (WRC-0090) and 2-(2-cyclohexylethoxy)adenosine (WRC-0013) and the nonselective adenosine receptor agonist 5'-(N-ethylcarboxamido)adenosine (NECA) were measured using ventricular myocytes isolated from guinea pig, rabbit, and rat hearts. Pertussis toxin pretreatment and/or the selective A1-adenosine receptor antagonists 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and (+/-)N6-endonorbornan-2-yl-9-methyladenine (N-0861) were used to prevent activation of A1-adenosine receptors in these cells. Action potential duration at 50% repolarization was not altered by WRC-0090, NECA, or WRC-0013 with or without 0.1 microM DPCPX or pertussis toxin pretreatment, and WRC-0090 and NECA failed to prolong the action potential duration of myocytes exposed to 0.1 or 1 microM forskolin. WRC-0090 alone or with 0.1 microM DPCPX did not increase the amplitude of shortening of pertussis toxin-treated or untreated myocytes, and WRC-0090 or NECA did not significantly increase cAMP accumulation. In contrast to these results with myocytes, in the smooth muscle cell line DDT1MF-2 the effect of both selective A2-agonists on cAMP accumulation was biphasic: low concentrations (< or = 0.3 microM) increased but higher concentrations decreased accumulation of cAMP. The decreased cAMP accumulation seen at higher agonist concentrations was completely abolished by either 0.1 microM DPCPX or pretreatment of cells with pertussis toxin. In summary, the results of the present study do not provide evidence for A2-adenosine receptors on mammalian ventricular cardiomyocytes but confirm reports of the coexistence of both A1 and A2 subtypes of adenosine receptors on DDT1MF-2 cells.

Action Potentials↗

PubMed1993

2-Phenylethoxy-9-methyladenine: an adenosine receptor antagonist that discriminates between A2 adenosine receptors in the aorta and the coronary vessels from the guinea pig.

Substituting a methyl group for the ribose moiety of N6-substituted adenosines that are selective agonists at the adenosine A1 receptor creates antagonists that are A1-selective. Inasmuch as 2-phenylethoxyadenosine is a selective agonist for the adenosine A2 receptor, 2-phenylethoxy-9-methyl-adenine (PEMA) was synthesized and tested as a potential adenosine A2 receptor antagonist. In guinea pig hearts, PEMA antagonized with the same potency (pKB approximately 6.1) the A1-mediated negative dromotropic and inotropic actions and the A2-mediated coronary vasoactivity of the nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA). PEMA at concentrations up to 30 microM did not antagonize the NECA-induced relaxations in guinea pig aortic rings. At concentrations exceeding 10 microM, PEMA caused xanthine-insensitive relaxations of both the aorta and the coronary vessels. Pharmacological resultant analysis revealed A2 receptor antagonism by PEMA in the guinea pig aorta (pKB = 5.2). The nonselective adenosine receptor antagonist 8-p-sulfophenyl-theophylline antagonized NECA responses in all four assays with equal potency (pKB approximately 5.7). Thus, PEMA does not discriminate between A2 receptors in the coronary vessels and A1 receptors in the atria of the guinea pig, but it is 10-fold more potent at antagonizing the A2 receptor in coronaries than the A2 receptors in the aorta. The data suggest that the A2 receptors in the coronary vasculature may be of the A2a subtype, whereas those in the aorta may be of the A2b subtype.

Adenine↗

PubMed1992

2-(N'-alkylidenehydrazino)adenosines: potent and selective coronary vasodilators.

The reaction of aliphatic aldehydes and ketones with 2-hydrazinoadenosine under relatively mild conditions (at room temperature or in refluxing methanol) formed 2-(N'-alkylidenehydrazino)-adenosines, 5-22, in good yields. Two kinds of adenosine receptors regulate cardiac and coronary physiology. In supraventricular tissues an A1AR coupled to muscarinic K channels mediates the negative chronotropic, dromotropic, and inotropic actions of adenosine, and an inhibitory A1AR coupled to adenylate cyclase mediates the "antiadrenergic" action of adenosine. One or more kinds of A2 receptors mediate coronary vasodilation. Bioassays employing a guinea pig heart Langendorff preparation showed that 5-22 weakly retard impulse conduction through the AV node (negative dromotropic effect), but several analogues were very active coronary vasodilators. The coronary vasoactivity of the (n-alkylidene- and of the (isoalkylidenehydrazino)adenosines paralleled the length of the alkyl chain, the EC50s of the of the most active n-pentylidene (8) and isopentylidene (18) congeners being 1 nM. The EC50s of the cyclohexylmethylene (9), cyclohexylethylidene (10), and cyclohex-3-enylmethylene (12), analogues were likewise < 1 nM, but the cyclohex-1-enylmethylene congener 12 was 10 times less active than 9. The unselective adenosine receptor antagonist 8-(p-sulfophenyl)theophylline (0.1 mM) raised the EC50s of the negative dromotropic effects of 8, 9, and 18 by 5-28-fold and the EC50s of coronary vasodilation of 22-90-fold. Catalytic reduction of 9 increased the hydrophobicity and changed the UV spectrum, suggesting reduction of the --CH = N-- bond. The product darkened on exposure to air and so was not characterized further. A new method for preparing 2',3',5'-tri-O-acetyl-2,6-dichloropurine riboside, a precursor in the synthesis of 2-hydrazinoadenosine, consists of the addition of tert-butyl nitrite to a mixture of 2',3',5'-tri-O-acetyl-6-chloroguanosine and CuCl in CHCl3 saturated with Cl2.

Adenosine↗

PubMed1992

2-(N'-aralkylidenehydrazino)adenosines: potent and selective coronary vasodilators.

This study aimed at the development of 2-(N'-aralkylidenehydrazino)adenosines as coronary vasodilators. The reaction of aromatic aldehydes or ketones with 2-hydrazinoadenosine in refluxing methanol formed the target compounds 2-27 as crystalline products in good yields. Two kinds of receptors mediate the actions of adenosine on the heart. Retardation of impulse conduction through the atrioventricular node, the negative dromotropic action, is an example of adenosine's action at an A1 receptor (A1AR) and coronary vasodilation reflects adenosine's action at an A2 receptor (A2AR). Accordingly, bioassays employing guinea pig heart Langendorff preparations assessed the selectivity of 2-27 as coronary vasodilators. Analogues 2-27 were weak negative dromotropic agents; the EC50 of the most active analogue, 2-[N'-(1-naphthylmethylene)hydrazino]-adenosine, 23, was 0.8 microM, several orders of magnitude less than many A1AR agonists. Some of the analogues were quite active coronary vasodilators; 2-(N'-benzylidenehydrazino)adenosine, 2, and several of its para-substituted derivatives, namely, the fluoro (7), methyl (13), methoxy (16), and tert-butylcarbonylethyl, 31, had EC50s for coronary vasodilation in the range 1.7-3.2 nM. The selectivity ratios, EC50 (negative dromotropic)/EC50 (coronary vasodilatory), of these five analogues ranged between 5100 (analogue 31) and 43,000 (analogue 2). Phenyl ring substitutions of other kinds or at other positions, replacement of the phenyl ring by other aryl or heteroaryl groups, or the replacement of the benzylic H by a methyl group lowered coronary vasoactivity significantly. The unselective adenosine receptor antagonist 8-(p-sulfophenyl)theophylline raised the EC50 of the negative dromotropic activities of 2, 16, and 2-[N'-(2-naphthylmethylene)hydrazino]adenosine, 24, by 3-, 18-, and 7-fold, and raised the EC50s of coronary vasoactivity by 11-, 3-, and 30-fold, respectively evidence that vasoactivity was receptor-mediated.

Adenosine↗

PubMed1992

Intravenous pretreatment with A1-selective adenosine analogues protects the heart against infarction.

BACKGROUND: Recent data from this laboratory indicate that pretreatment with adenosine can protect the heart against infarction via A1-receptors, but because of systemic hypotension, adenosine had to be given into the coronary circulation. METHODS AND RESULTS: In this study, we tested whether the protection could be achieved by intravenous administration of the A1-selective adenosine agonists N6-(phenyl-2R-isopropyl)-adenosine (PIA) and 2-chloro-N6-cyclopentyladenosine (CCPA). Nine groups of open-chest anesthetized rabbits were subjected to 30 minutes of regional coronary ischemia and 3 hours of reperfusion. Infarct size was determined by tetrazolium staining. Control hearts receiving no treatment had 38 +/- 4% of the risk zone infarcted. Preconditioning with 5 minutes of ischemia and 10 minutes of reperfusion before ischemia limited the infarct to 8 +/- 4%. Intravenous PIA 15 minutes before 30-minute ischemia also limited infarct size to 6 +/- 2% at the highest dose. CCPA offered similar protection. When the PIA was given at reperfusion, infarct size was 46 +/- 6%, indicating that receptor activation must precede ischemia to protect. Pretreatment with CGS 21680, a selective A2-receptor agonist, caused identical hypotension but failed to limit infarct size (43 +/- 3%), indicating again that the A1-receptor is involved. When rabbits pretreated with PIA were paced at 220 beats per minutes, PIA still limited infarct size (16 +/- 4%), indicating that protection was not the result of bradycardia. CONCLUSIONS: These results indicate that stimulation of adenosine A1-receptors causes the heart to become resistant to ischemia and that this protection can be achieved with intravenous administration of A1-selective agents.

Adenosine↗

PubMed1992

Nitric oxide modulates coronary autoregulation in the guinea pig.

A guinea pig heart Langendorff preparation was used in the present study to test the hypothesis that the coronary endothelium modulates coronary autoregulation through the production of nitric oxide (NO). Pacing at 250 beats per minute and venting the left ventricle to ensure that the hearts did no external work were performed in an attempt to reduce the metabolic stimulus to coronary vasomotion and keep it constant. We measured the responses of coronary flow and oxygen metabolism to stepwise changes of the perfusion pressure over the range between 18 and 85 mm Hg. The hearts exhibited autoregulation between 25 and 55 mm Hg and active vasodilation at perfusion pressures above that range. Perfusion with 100 microM NG-nitro-L-arginine (NNLA), an inhibitor of NO synthase, decreased coronary flow over the entire range of perfusion pressures and abolished active vasodilation over 65 mm Hg, thus widening the autoregulatory range. The administration of 200 microM L-arginine, but not D-arginine, reversed the action of NNLA. Inhibition of the cyclooxygenase pathway by 10 microM indomethacin did not affect autoregulation. Perfusion with 1 nM arginine vasopressin, a direct smooth muscle constrictor, lowered coronary flow rate to the same extent as NNLA at 55 mm Hg but did not prevent the pressure-dependent increase in flow above that pressure. These observations suggest that 1) the coronary endothelium actively modulates coronary autoregulation through the production of NO but not prostanoids, 2) mechanical stress (shear stress and/or stretching secondary to vasodilation) may be the stimulus to NO production, especially above the autoregulatory range, and 3) autoregulatory tone is likely to be myogenic in origin rather than mediated by extrinsic vasoconstrictors.

Amino Acid Oxidoreductases↗

PubMed1991

Cardiovascular actions of adenosines, but not adenosine receptors, differ in rat and guinea pig.

This study compared the structure-activity relationships of 16 analogues at the A1 and A2 adenosine receptors (A1AR, A2AR) of rat and guinea pig. Radioligand binding studies revealed no marked differences in the affinities of each analogue at the A1AR of brain cortex or the A2AR of brain striatum. Bioassay employing Langendorff heart preparations showed that the guinea pig is more sensitive than the rat to A1AR-mediated slowing of conduction through the atrioventricular node and, in some instances, to A2AR-mediated coronary vasodilation. That difference could reflect factors such as receptor density or efficacy of coupling to effector systems.

Adenosine↗