adenosine-5--(n-ethylcarboxamide) 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 behavioral effect of the adenosine antagonists CPT, PACPX, DPCPX and PD 115,199 on spontaneous locomotor activity was investigated in mice after parenteral administration. CPT, PACPX and PD 115,199 affected locomotor activity in a biphasic way. Doses in the nanomolar/kg range significantly reduced locomotion (PACPX> or =PD 115,199>>CPT). Higher doses were progressively less active until they became ineffective or slightly stimulated locomotion. NECA, a mixed A1/A2 agonist, and CCPA, a highly selective A1 agonist, also induced a biphasic behavior, with low doses stimulating and high doses inhibiting locomotion. The stimulant effect of 1 nmol/kg NECA was antagonized by depressant doses of antagonists, whereas antagonists-induced hypomotility was potentiated by a depressant dose of NECA (20 nmol/kg). It is suggested that the blockade of A1 receptors by antagonists is probably responsible for reducing locomotor activity, whereas the activation of A2 receptors by agonists is likely responsible for reducing locomotion in mice.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Antineoplastic Agents; Male; Mice; Motor Activity; Purinergic P1 Receptor Agonists; Purines; Sulfonamides; Theophylline; Xanthines

1. Radioligand binding and functional studies were undertaken to investigate the P1-purinoceptors present in the separated myometrial layers and the endometrium of the guinea-pig uterus. 2. In preparations of endometrium-denuded circular myometrium, the A2-selective agonists (2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido-adeno sin e (CGS 21680, 100 mumol/L) and N-ethylcarboxamido adenosine (NECA, 1-10 mumol/L) inhibited contractile responses to phenylephrine. In preparations of endometrium-intact circular myometrium, NECA (10 mumol/L) enhanced responses to phenylephrine. NECA did not modulate the spontaneous contractions of longitudinal myometrium. 3. Homogenate binding studies with circular myometrium, longitudinal myometrium and endometrium revealed saturable high affinity [3H]-NECA binding sites. The mean maximal densities of binding sites (Bmax) were 2.08, 14.7 and 15.5 fmol/mg protein, and pKD (neg. log dissociation constant) values were 9.82, 9.19 and 7.44, respectively. 4. (R-) and (S-)-N6-(2-phenylisopropyl)adenosine (R- and S-PIA) both competed for two [3H]-NECA binding sites in preparations of circular myometrium. CGS 21680 competed for two [3H]-NECA binding sites in preparations of endometrium and longitudinal myometrium. All other agonist competition was for one site only. The rank orders of potency of high affinity binding were S-PIA > or =R-PIA > or = CGS 21680 (circular myometrium), R-PIA > CGS 21680 > or = S-PIA (longitudinal myometrium) and CGS 21680 > > S-PIA > or = R-PIA (endometrium). 5. In preparations of circular myometrium, longitudinal myometrium and endometrium the selective A1-purinoceptor antagonist, 1,3-dipropyl-8-(2-amino-4-chloro)-phenylxanthine (PACPX), competed for two [3H]-NECA binding sites, the non-selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX), competed for one site only.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Binding, Competitive; Cyclic AMP; Dose-Response Relationship, Drug; Endometrium; Female; Guinea Pigs; In Vitro Techniques; Myometrium; Phenethylamines; Phenylephrine; Phenylisopropyladenosine; Radioligand Assay; Receptors, Purinergic; Theobromine; Uterine Contraction; Xanthines

To determine which subtype of adenosine receptor mediates the potentiating effect of 2-chloroadenosine on the noradrenaline-induced inositol-phosphate formation, we used the monoclonal anti-idiotypic antibody AA1 that acts as an 'internal image' of adenosine and specifically recognizes the A1 adenosine receptor. In cultured mouse striatal astrocytes, AA1 increased the noradrenaline-evoked inositol phosphate (IP) accumulation, thus demonstrating a biological activity of an anti-idiotypic antibody. This effect was inhibited by PACPX, a selective A1 antagonist. Inhibitors of phospholipase A2 activity prevented the potentiation. These results establish the involvement of A1 adenosine receptors in the modulation of phospholipase C activity.

Topics: 2-Chloroadenosine; 5,8,11,14-Eicosatetraynoic Acid; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Antibodies, Anti-Idiotypic; Antibodies, Monoclonal; Astrocytes; Cells, Cultured; Corpus Striatum; Enzyme Activation; Female; Mice; Norepinephrine; Pregnancy; Quinacrine; Receptors, Adrenergic, alpha; Receptors, Purinergic; Type C Phospholipases; 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