Biomedical subjects

R A Olsson

Publications and source records attributed to R A Olsson.

At least 19 recordsLinked to original sources

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↗

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↗

PubMed1991

2-Alkoxyadenosines: potent and selective agonists at the coronary artery A2 adenosine receptor.

A Langendorff guinea pig heart preparation served for the assay of agonist activity of a series of 24 2-alkoxyadenosines at the A1 and A2 adenosine receptors of, respectively, the atrioventricular node (conduction block) and coronary arteries (vasodilation). Activities are low at the A1 receptor and do not show a clear relationship to the size or hydrophobicity of the C-2 substituent. All the analogues are more potent at the A2 receptor, activity varying directly with the size and hydrophobicity of the alkyl group. The most potent analogue in this series, 2-(2-cyclohexylethoxy)adenosine has an EC50 of 1 nM for coronary vasodilation and is 8700-fold selective for the A2 receptor.

Adenosine↗

PubMed1991

2-aralkoxyadenosines: potent and selective agonists at the coronary artery A2 adenosine receptor.

A Langendorff guinea pig heart preparation served for the assay of agonist potency of a series of 26 2-aralkoxyadenosines at the A1 and A2 receptors of, respectively, the atrioventricular node (conduction block) and coronary arteries (vasodilation). All of the analogues are weak agonists at the A1 receptor, requiring concentrations greater than 9 microM to cause second degree heart block. At the A2 receptor 2-phenethoxyadenosine is the most potent of the 2-phenylalkyladenosines. The activity of ring-substituted (F, Cl, CH3, and OCH3) 2-phenethoxyadenosines increases ortho less than meta less than para. The EC50s of coronary vasoactivity of several para-substituted analogues are in the subnanomolar range. The most potent analogue, 2-[2-(4-methylphenyl)ethoxy]adenosine 19, has an EC50 for coronary vasodilation of 190 pM and an A1/A2 selectivity ratio of 44,000. Aryl groups such as thienyl, indoloyl, or naphthyl also support A2 agonist activity. Although 2-oxoadenosine is 3 times more vasoactive than 2-aminoadenosine, the activities of the phenyl derivatives are markedly different; 2-phenoxyadenosine is 23 times weaker than 2-(phenylamino)adenosine (CV-1808).

Adenosine↗

PubMed1991

N6,9-disubstituted adenines: potent, selective antagonists at the A1 adenosine receptor.

N6-Substituted 9-methyladenines are potent antagonists of the activation of A1 adenosine receptors. The present study assessed the effect of N6 and N-9 substituents on the binding of adenines to the A1 and A2 receptors, respectively, of rat brain cortex and striatum and also on the antagonism of the A2 receptor mediated stimulation of the adenylate cyclase of PC12 cells by N-ethyladenosine-5'-uronamide. The potency ranking of 9-substituted adenines varied directly with the hydrophobicity of the substituent: cyclopentyl greater than phenyl greater than tetrahydrofuryl greater than ethyl greater than methyl greater than 2-hydroxyethyl. The 9-substituted adenines showed little selectivity for either receptor and the R enantiomer of N6-(1-phenyl-2-propyl)-9-methyladenine was only 4-fold more potent than the S enantiomer at the A1 receptor. An N6-cyclopentyl substituent increased potency at the A1 receptor and decreased potency at the A2 receptor, resulting in selectivity for the A1 receptor of up to 39-fold. The N6-cyclopentyl group completely overshadowed the effect of the hydrophobicity of the 9-substituent. A 2-chloro substituent did not alter the potency of an N6-substituted 9-methyladenine.

Adenine↗

PubMed1991

Activity of N6-substituted 2-chloroadenosines at A1 and A2 adenosine receptors.

Radioligand binding studies of N6-substituted adenosines at the A1 and A2 adenosine receptors of rat brain cortex and rat brain striatum, respectively, show that a 2-chloro substituent does not consistently change the affinity or the selectivity of these analogues for the A1 receptor. A 2-chloro substituent lowers the characteristic stereoselectivity of the A1 receptor toward the R diastereomer of N6-(1-phenyl-2-propyl)adenosine. A 2-chloro substituent consistently increases potency of N6-substituted adenosines as agonists at an adenosine A2 receptor stimulatory to adenylate cyclase in PC12 cell membranes.

2-Chloroadenosine↗

PubMed1991

Potency of N6 secondary and tertiary alkyladenosine analogues at presynaptic A1 adenosine receptors in guinea-pig ileum.

1. The potencies of a series of N6-substituted secondary and tertiary alkyladenosine analogues as inhibitors of the twitch responses of isolated guinea-pig ileum stimulated at 0.2 Hz have been determined. 2. All the analogues tested were full agonists. 3. Since their inhibitory effects were antagonized by theophylline and they had no significant effect on responses of ileum to carbachol, it was concluded that they acted predominantly by causing presynaptic inhibition of transmitter release. 4. Their structure-activity relationships indicated that the S4 subregion of the adenosine receptor in this tissue is capacious enough to accommodate a methyl group while the nature of the secondary alkyl moiety appears to determine the degree to which the tertiary methyl group reduces activity.

Adenosine↗

PubMed1991

Adenosine stimulates phosphate and glucose transport in opossum kidney epithelial cells.

We have examined the effects of adenosine on sodium-coupled phosphate and glucose transport in cultured opossum kidney (OK) cells, a continuous cell line that resembles proximal tubule. Adenosine analogues R-(-)-N6-phenylisopropyladenosine (PIA) and 2',5'-dideoxy-adenosine (DDA) were employed as adenosine A1 receptor and P site-selective agonists, respectively. Sodium-dependent phosphate uptake activity (Na-Pi symport) increased by approximately 25% above both basal and parathyroid hormone (PTH)-inhibited levels in cells treated with PIA (0.1, 1 microM) but not in cells treated with DDA (100 microM). Adenosine (PIA) also stimulated sodium-coupled 3-O-methylglucose transport by approximately 40%. Intracellular adenosine 3',5'-cyclic monophosphate (cAMP) content was inversely related to Na-Pi symport activity in cells treated with PIA and PTH. However, changes in Na-Pi symport activity did not consistently relate to changes in intracellular cAMP. Protein kinase C was activated 15 s after treatment of OK cells with 1 microM PIA. Preincubation of cells with 3 microM staurosporine attenuated the effect of 1 microM PIA on phosphate uptake. These data suggest that Na-Pi and Na-glucose symport activities are stimulated by adenosine acting at a receptor coupled to more than one intracellular signal. It is likely that both protein kinases A and C are involved in these actions of adenosine.

Adenosine↗

PubMed1991

Protection against infarction afforded by preconditioning is mediated by A1 adenosine receptors in rabbit heart.

BACKGROUND: Preconditioning (5 minutes of ischemia followed by 10 minutes of recovery) renders the heart very resistant to infarction from subsequent ischemia. This study tests whether adenosine receptors might mediate preconditioning protection. METHODS AND RESULTS: We examined the effect on infarct size of pretreatment with either of two adenosine receptor antagonists in both control and preconditioned in situ rabbit hearts. Hearts underwent 30 minutes of regional ischemia plus 3 hours of reperfusion, and infarct size was measured with tetrazolium. Infarct size averaged 39% of the zone at risk in controls but only 8% in preconditioned hearts. Preconditioned and nonpreconditioned hearts receiving either blocker had infarcts not different in size from the controls. A 5-minute intracoronary infusion of adenosine was as effective as 5 minutes of ischemia in protecting parabiotically perfused isolated hearts against infarction from a 45-minute ischemic insult. Similarly, intracoronary infusion of N6-1-(phenyl-2R-isopropyl)adenosine, an A1-selective adenosine receptor agonist, at a dose that delayed conduction but did not dilate the coronary vessels, also limited infarct size. The protection disappeared when we reduced the coronary concentration of drug by intravenous infusion of adenosine, indicating that cardiac rather than peripheral receptors were involved in the protection. CONCLUSIONS: We conclude that adenosine released during the preconditioning occlusion stimulates cardiac A1 receptors, which leaves the heart protected against infarction even after the adenosine has been withdrawn.

Adenosine↗