bw-a1433 and 1-3-dipropyl-8-cyclopentylxanthine

The A1 adenosine receptor (A1ar) antagonist 1,3-dipropyl-8-(p-acrylic)-phenylxanthine (BW-1433) was administered to lean and obese Zucker rats to probe the influence of endogenously activated A1ars on whole body energy metabolism. The drug induced a transient increase in lipolysis as indicated by a rise in serum glycerol in obese rats. The disappearance of the response by day 7 of chronic studies was accompanied by an increase in A1ar numbers. Glucose tolerance tests were administered to rats treated with BW-1433. Peak serum insulin levels and areas under glucose curves (AUGs) were 34 and 41% lower in treated obese animals than in controls, respectively, and 19 and 39% lower in lean animals. With chronic administration (6 wk), AUGs decreased 47 and 33% in obese and lean animals, respectively. There was no effect of BW-1433 in either lean or obese rats on weight gain or percent body fat. Thus the major sustained influence of whole body A1ar antagonism in both lean and obese animals was an increase in whole body glucose tolerance at lower levels of insulin.

Topics: Adipocytes; Adipose Tissue; Administration, Oral; Animals; Brain; Female; Glucose; Glucose Tolerance Test; Glycerol; Insulin Resistance; Lipolysis; Male; Muscle, Skeletal; Obesity; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Rats, Zucker; Xanthines

Ischemic preconditioning reduces post-ischemic myocardial injury by activating myocellular adenosine A1 receptors. Adenosine A3 receptors have also been implicated but there is no evidence for A3 receptors in cardiac myocytes. The aim of this study was to develop a model of preconditioning in isolated cardiac myocytes to evaluate the role of the adenosine A1 and A3 receptors in preconditioning-induced protection from ischemic injury. Reverse transcription polymerase chain reaction (PCR) was also employed to establish the presence of adenosine A3 receptors in these cells. In the preconditioning studies, ischemic injury was simulated by exposing isolated rabbit myocytes (placed in the cell chamber and paced at l Hz) to buffer containing (in mM) 2'-deoxyglucose (20), NaCN (1), Na (+)-lactate (20), KCl (10) at pH 6.6 (37 degrees C). Changes of diastolic and systolic cell length were monitored with an optical-video edge imaging system, and hypercontracture was assessed as an index of irreversible cell injury. Preconditioning (2 min brief ischemia and 15 min reperfusion) significantly reduced cell injury resulting from a subsequent prolonged ischemia (10 min) and reperfusion (15 min), as indicated by a reduction in the incidence of cell hypercontracture from 67 +/- 6% to 29 +/- 5% (P < 0.001). Preconditioning-induced cardioprotection was only partially blocked by a maximally effective concentration (100 nM) of the adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (cell hypercontracture = 43 +/- 3%, P < 0.05 vs. control) but completely blocked by either the combination of DPCPX (100 nM) with the adenosine A1/A3 receptor antagonist DPCPX +8-(4-carboxyethylphenyl)-1,3-dipropylxanthine (BWA1433; 1 microM) or the non-selective adenosine receptor antagonist, 8-(p-sulfophenyl)theophylline (8-SPT; 100 microM) (cell hypercontracture = 64 +/- 4%, 59 +/- 5%, respectively; P = NS vs. control). In non-hypercontractured myocytes, preconditioning also substantially enhanced the recovery of the contractile amplitude and, similarly, this effect was only partially blocked by DPCPX but completely blocked by either the combination of DPCPX with BWA1433, or 8-SPT. These studies suggest that preconditioning protects isolated cardiac myocytes from ischemic injury independent of other cell types, and that maximal preconditioning-induced cardioprotection requires activation of both adenosine A1 and A3 receptors. Reverse transcription-PCR using primers for the

Topics: Animals; Ischemic Preconditioning, Myocardial; Male; Myocardial Reperfusion Injury; Myocardium; Polymerase Chain Reaction; Purinergic P1 Receptor Antagonists; Rabbits; Receptors, Purinergic P1; Theophylline; Transcription, Genetic; Xanthines

Activation of the adenosine A3 receptor subtype by the agonist N6-2-(4-aminophenyl)ethyladenosine is shown here to induce bronchospasm (increased pulmonary resistance and decreased pulmonary compliance) in BDE strain rats. The effect is substantially reduced by pretreating the rats with compound 48/80, disodium cromoglycate (30 micrograms/kg) or epinastine (10 micrograms/kg), which is compatible with involvement of mast cells. It is also substantially reduced by combined vagotomy and atropinization or by pretreatment with the NK2 receptor antagonist L-659,877, suggesting involvement of neuropeptide-mediated neural pathways. The mechanism by which activation of the adenosine A3 receptor induces bronchospasm is distinct from the mechanism by which activation of the adenosine A1 receptor induces bronchospasm. In particular, the A1 agonist 2-chloro-N6-cyclopentyladenosine can increase pulmonary resistance independently of mast cell activation. These results are in accord with the concept that a pathway exists in vivo by which activation of mast-like cells can activate axon reflexes, that adenosine acting through its A3 receptor can potentially up-regulate this pathway and that antiallergic substances such as disodium cromoglycate and epinastine may interfere with this pathway.

Topics: Adenosine; Animals; Atropine; Blood Pressure; Bronchial Spasm; Female; Injections, Intravenous; Lung; Male; Mast Cells; Neuropeptides; Peptides, Cyclic; Purinergic P1 Receptor Agonists; Rats; Receptors, Neurokinin-2; Receptors, Purinergic P1; Vagotomy; Xanthines

Adenosine receptor (AR) agonists and antagonists are approximately 100-fold and 100,000-fold, respectively, more potent at the bovine A1AR as compared to the rat A3AR. To determine regions of ARs involved in ligand recognition, chimeric receptors composed of bovine A1AR and rat A3AR sequence were constructed and their ligand binding properties examined following expression in COS-7 cells. Substitutions of the second extracellular loop or a region encompassing transmembrane domains 6 and 7 of the A1AR into the A3AR resulted in enhanced affinities of both agonists and antagonists compared to wild-type A3AR. The region of the second extracellular loop of the A1AR responsible for this effect was identified as the distal eleven amino acids of the loop. Replacement of this segment of the A3AR with that of the A1AR in combination with the regions encompassing transmembrane domains 6 and 7 resulted in a 50,000-fold increase in the Kd for antagonist radioligand, [3H]1,3-dipropyl-8- cyclopentylxanthine. Agonist affinity at this chimeric was over 100-fold greater than that displayed by wild-type A3AR. Thus, multiple regions of ARs including a segment of the second extracellular loop are involved in ligand recognition, and considerable overlap exists in structural features required for agonist and antagonist binding.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Amino Acid Sequence; Animals; Binding Sites; Cattle; Cells, Cultured; Molecular Sequence Data; Rats; Receptors, Purinergic P1; Recombinant Fusion Proteins; Structure-Activity Relationship; Xanthines