n(6)-cyclohexyladenosine and 1-3-dipropyl-8-(2-amino-4-chlorophenyl)xanthine

The present study had employed in vitro receptor autoradiography with [3H]DPCPX to visualise the presence of adenosine A1 receptors on the rat nodose ganglion, which contains the perikarya of vagal afferent neurons projecting the the nucleus tractus solitarius (NTS). In addition, unilateral vagal ligation resulted in an accumulation of [3H]DPCPX binding adjacent to the ligatures, indication that adenosine A1 receptors are subject to axoplasmic flow along the rat vagus nerve. Radioligand binding assays were utilised to characterise the properties of adenosine A1 receptors in the dorsal vagal complex (NTS, area postrema and dorsal motor nucleus of the vagus) of pup and adult normotensive (Wistar Kyoto, WKY) and hypertensive (spontaneously hypertensive, SHR) rats. Saturation binding indicated that the affinity (KD) of [3H]DPCPX, and the binding site density (Bmax) were not different between the adult WKY and SHR, although the pup SHR had a lower KD value than the pup WKY rat. Competition binding assays revealed complex differences between the two rat strains; however, with respect to hypertension, the affinity of the selective adenosine A1 agonist, cyclohexyladenosine (CHA), was markedly reduced in the membranes from SHR (Ki approximately 93 nM) compared to WKY (approximately 6 nM). Such an observation is consistent with the attenuated responses of SHRs to intra-NTS injections of adenosine.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Autoradiography; Axonal Transport; Binding, Competitive; Hypertension; Male; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Purinergic P1; Reference Values; Solitary Nucleus; Vagus Nerve; Xanthines

The present study has employed in vitro electrophysiology, utilising the isolated rat nodose ganglion preparation, to determine whether nitric oxide (NO) and adenosine interact with each other in vagal afferent neurons. The nucleophile NO donor, diethylamine-NO, caused reproducible, concentration-related depolarisations of the isolated rat nodose ganglia. Pre-incubation of the isolated rat nodose ganglia with the adenosine A2A receptor agonists CGS 21680 (2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride) and DPMA (N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)-ethyl]adenosine) (both 1 microM) resulted in a functional antagonism of the ability of diethylamine-NO to depolarise the preparation. A similar effect was observed with adenosine (10 microM) only in the presence of the adenosine A1 receptor antagonist PACPX (1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine, 100 nM). Conversely, the adenosine A1 receptor agonists ENBA (N6-[2-endo-norbomyl]adenosine, 1 microM) and cyclohexyladenosine (100 nM) potentiated the effect of diethylamine-NO on isolated rat nodose ganglia. Inclusion of either adenosine A3 agonists or ATP had no effect on the diethylamine-NO concentration-response curve. These data suggest an ability of NO to interact, in opposing manner, with adenosine A2A and A1 receptors in rat vagal afferent neurons. On the other hand, neither A3 receptors nor ATP appear capable of interacting with NO.

Topics: Adenosine; Animals; Antineoplastic Agents; Diethylamines; Dose-Response Relationship, Drug; Drug Interactions; Electrophysiology; In Vitro Techniques; Male; Neurons, Afferent; Nitric Oxide; Nodose Ganglion; Norbornanes; Phenethylamines; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P1; Vagus Nerve; Xanthines

CGS 15943A, a triazoloquinazoline, is a potent and selective adenosine receptor antagonist as assessed by its effects on radioligand binding and adenosine-stimulated adenylate cyclase activity in guinea pig synaptoneurosomes. At the adenosine A-1 receptor labeled with [3H]cyclohexyladenosine, CGS 15943A had an IC50 value of 20 nM. At the striatal A-2 receptor labeled with [3H]5'-N-ethylcarboxamidoadenosine in the presence of a low concentration of cyclopentyladenosine to block A-1 receptors labeled by this nonselective adenosine agonist, CGS 15943A had an IC50 value of 3 nM, indicating that the compound had some degree of selectivity for the A-2 receptor. Analysis of the effect of the compound on the saturation isotherms for each of the receptors indicated that it was a competitive antagonist at the brain A-1 receptor but that it was noncompetitive at the striatal A-2 receptor. CGS 15943A was a potent adenosine antagonist in the adenosine-stimulated adenylate cyclase system in guinea pig synaptoneurosomes, where the compound was found to have an IC50 value of 30 to 70 nM against the increase in cyclic AMP evoked by 5 microM adenosine. CGS 15943A had no effect on the binding of [3H]nitrobenzylthioinosine, a ligand thought to bind to adenosine uptake sites, and, at a concentration of 10 microM, had no effect on beef heart type III phosphodiesterase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Binding, Competitive; Brain; Guinea Pigs; Kinetics; Neurotransmitter Agents; Pyrazoles; Quinazolines; Rats; Receptors, Purinergic; Triazoles; Xanthines

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Brain; In Vitro Techniques; Kinetics; Rats; Receptors, Purinergic; Theophylline; Xanthines

The binding of [3H]-Cyclopentyladenosine (CPA), an N6-substituted analog of adenosine, was examined in vitro. CPA bound with high affinity (Kd = 0.48 nmol/l) to rat brain membranes. Specific binding, which represented 90-97% of the total counts bound at a ligand concentration of 1 nmol/l, was saturable, reversible and sensitive to protein denaturation. The pharmacology of binding was consistent with the labeling of an A-1 receptor, the R- and S-diasteromers of N6-phenylisopropyladenosine (PIA) showing a sixteenfold difference in their ability to displace CPA. The prototypic A-1 selective adenosine agonist, N6-cyclohexyladenosine (CHA) was twofold less active than CPA in displacing radiolabeled CPA. Comparison of the ability of cold CHA and CPA to displace [3H]-CPA gave rate dissociation constants of 1.88 and 1.80 X 10(4) s-1, respectively suggesting that both CHA and CPA bound to the same recognition site. In contrast however, comparison of the binding of [3H]-CPA with that of [3H]-CHA showed distinct differences. The Kd for CHA was approximately twice that of CPA while the apparent Bmax was 60% greater. In comparing the pharmacology of CPA binding with that of CHA, it was found that CHA, S-PIA and the antagonist, PACPX were more active in displacing CHA than CPA. In general however, CPA has a binding profile very similar to that observed with CHA.

Topics: Adenosine; Animals; Brain; Kinetics; Membranes; Phenylisopropyladenosine; Purine Nucleotides; Pyrazoles; Rats; Xanthines