isoalloxazine and 1-3-dipropyl-8-cyclopentylxanthine

Adenosine mediates vascular responses through four receptor subtypes: A(1), A(2A), A(2B), and A(3). The role of A(2A) receptors in aortic vascular tone was investigated using A(2A) adenosine receptor (AR) knockout (A(2A)KO) and corresponding wild-type (A(2A)WT) mice. Isolated aortic rings from A(2A)WT and A(2A)KO mice were precontracted with phenylephrine (10(-7) M), and concentration responses for adenosine analogs and selective agonists/antagonists were obtained. Nonselective adenosine analog (NECA; EC(50) = 6.78 microM) and CGS-21680 (A(2A)AR selective agonist; EC(50) = 0.013 microM) produced concentration-dependent relaxation (maximum of 25% and 28% relaxation at 10(-5) M NECA and CGS-21680, respectively) in A(2A)WT aorta. In A(2A)KO aorta, NECA (EC(50) = 0.075 microM) induced concentration-dependent contraction (maximum contraction of 47% at 10(-6) M; P < 0.05 compared with A(2A)WT), whereas CGS-21680 produced no response. SCH-58261 (10(-6) M; A(2A)AR selective antagonist) abolished both NECA- and CGS-21680-mediated vasorelaxation in A(2A)WT (P < 0.05), whereas no change was observed in A(2A)KO. When DPCPX (10(-5) M; A(1) selective antagonist) was used in NECA concentration response, greater vasorelaxation was observed in A(2A)WT (50% vs. 25% in controls at 10(-5) M; P < 0.05), whereas lower contraction was seen in A(2A)KO tissues (5% vs. 47% in controls at 10(-6) M; P < 0.05). Aortic endothelial function, determined by response to acetylcholine, was significantly higher in WT compared with KO (66% vs. 51%; P < 0.05). BAY 60-6583 (A(2B) selective agonist) produced similar relaxation in both KO and WT tissues. In conclusion, A(2A)AR KO mice had significantly lower aortic relaxation and endothelial function, suggesting that the A(2A)AR plays an important role in vasorelaxation, probably through an endothelium-dependent mechanism.

Topics: Acetylcholine; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Aminopyridines; Animals; Aorta; Dose-Response Relationship, Drug; Endothelium, Vascular; Female; Flavins; Gene Expression Regulation; In Vitro Techniques; Male; Mice; Mice, Knockout; Phenethylamines; Pyrimidines; Receptor, Adenosine A1; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Triazoles; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents; Xanthines

LPS stimulates CD14/Toll-like receptor (TLR) 4, leading to induce TNF-alpha production. Cell-to-cell interaction through the engagement between intercellular adhesion molecule (ICAM) 1 on monocytes and its ligand on T cells has been suggested to play a role in the TNF-alpha production by LPS-treated human peripheral blood mononuclear cells (PBMCs). Adenosine is reported to inhibit LPS-induced TNF-alpha production. However, little is known about the mechanism of the inhibitory effects induced by adenosine on the LPS-induced immune responses. We found that adenosine inhibited the expression of ICAM-1 and the production of TNF-alpha by human PBMC via adenosine A2A receptor in the presence of LPS. However, the stimulation of A1R or A3R enhanced the actions of adenosine. Adenosine had no effect on the expression of CD14 and TLR-4, suggesting that the inhibitory effects of adenosine on the LPS actions might be independent of the expression of CD14 and TLR-4. Thus, adenosine differentially regulates the expression of ICAM-1 and the production of TNF-alpha through plural subtypes of receptors.

Topics: Adenosine; Adenosine A1 Receptor Agonists; Adenosine A1 Receptor Antagonists; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Adenosine A3 Receptor Agonists; Adenosine A3 Receptor Antagonists; CD40 Antigens; Cells, Cultured; Cyclic AMP; Enzyme-Linked Immunosorbent Assay; Flavins; Flow Cytometry; Humans; Intercellular Adhesion Molecule-1; Leukocytes, Mononuclear; Lipopolysaccharide Receptors; Lipopolysaccharides; Receptor, Adenosine A2A; Triazines; Triazoles; Tumor Necrosis Factor-alpha; Xanthines

Chronic respiratory disorders such as asthma are believed to be associated with adverse cardiovascular events. We hypothesize that asthmatic inflammation translates into systemic inflammation and alters vascular responses where adenosine (AD) plays an important role. Therefore, this study investigated the effects of aerosolized AD, used to elevate lung AD levels, on vascular reactivity and inflammation in our allergic mouse model of asthma. Balb/c mice were divided into four groups: control (Con), Con + aerosolized AD (Con + AD), allergen sensitized and challenged (Sen), and Sen + aerosolized AD (Sen + AD). The animals were sensitized with ragweed (200 mug ip) on days 1 and 6, followed by 1% ragweed aerosol challenges from days 11 to 13. On day 14, the Con + AD and Sen + AD groups received a single AD aerosol challenge (6 mg/ml) for 2 min, followed by the collection of the aorta and plasma on day 15. Organ bath experiments showed concentration-dependent aortic relaxations to AD in the Con and Con + AD groups, which were impaired in the Sen and Sen + AD groups. Real-time PCR data showed changes in aortic AD receptors (ARs), with the expression of A(1)ARs upregulated, whereas the expression of A(2)ARs and endothelial nitric oxide synthase genes were downregulated, resulting in an impairment of vasorelaxation in the Sen and Sen + AD groups. The A(1)AR antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) reversed the impairment in vasorelaxation observed in the Sen and Sen + AD groups, whereas the A(2B)AR antagonist alloxazine inhibited vasorelaxation in all groups. Allergen challenge caused systemic inflammation in allergic mice, with AD aerosol further enhancing it as determined by the inflammatory cytokines profile in plasma. In conclusion, asthmatic mice showed altered vascular reactivity and systemic inflammation, with AD aerosol further exacerbating these effects.

Topics: Acetylcholine; Adenosine; Administration, Inhalation; Allergens; Ambrosia; Animals; Aorta; Asthma; Disease Models, Animal; Dose-Response Relationship, Drug; Flavins; Inflammation; Inflammation Mediators; Lung; Male; Mice; Mice, Inbred BALB C; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Plant Proteins; Receptor, Adenosine A1; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Vasodilation; Vasodilator Agents; Xanthines

Previously, we reported that a relatively selective adenosine A(2A) receptor agonist 2-(6-cyano-1-hexyn-1-yl)adenosine (2-CN-Ado) elicited ocular hypotension in rabbits (Journal of Pharmacological Sciences 2005;97:501-509). In the present study, we investigated the effect of 2-CN-Ado on ocular blood flow in rabbit eyes. An intravitreal injection of 2-CN-Ado increased ocular blood flow, measured by a non-contact laser flowmeter. 2-CN-Ado-induced increase in ocular blood flow was accompanied with the retinal vasodilation. The increase in ocular blood flow was inhibited by an adenosine A(2A) receptor antagonist 1,3,7-trimethyl-8-(3-chlorostyryl)xanthine, but not by an adenosine A(2B) receptor antagonist alloxazine or an adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. The repetitive applications of topical 2-CN-Ado twice a day for 7 days produced a persistent increase in ocular blood flow with ocular hypotension. These results suggest that 2-CN-Ado increases the ocular blood flow mainly via adenosine A(2A) receptor, and that the topical application of 2-CN-Ado for several days not only increases the ocular blood flow but also prolong ocular hypotension, indicating that 2-CN-Ado may be a useful lead compound for the treatment of ischemic retinal diseases such as glaucoma.

Topics: Adenosine; Adenosine A1 Receptor Antagonists; Adenosine A2 Receptor Antagonists; Animals; Caffeine; Eye; Flavins; Intraocular Pressure; Male; Rabbits; Regional Blood Flow; Retinal Vessels; Vasodilator Agents; Xanthines

Adenosine is known to act as a neuromodulator by suppressing synaptic transmission in the central and peripheral nervous system. Both the release of adenosine within the small intestine and the presence of adenosine receptors on enteric neurons have been demonstrated. The aim of the present study was to characterize a possible involvement of adenosine receptors in the modulation of the myenteric reflex. The experiments were carried out on ileum segments 10 cm in length incubated in an single chambered organ bath, and the reflex response was initiated by electrical stimulation (ES).. ES caused an ascending contraction and a descending relaxation followed by a contraction. All motility responses to ES were completely blocked by tetrodotoxin, indicating that they are mediated by neural mechanisms. Atropine blocked the contractile effects, whereas the descending relaxation was significantly increased. The A1 receptor agonist N6-cyclopentyladenosine increased the ascending contraction, whereas the ascending contraction was reduced by the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. Activation of the A1 receptor further reduced the descending relaxation and the latency of the peristaltic reflex. The A2B receptor antagonist alloxazine increased ascending contraction, whereas descending relaxation remained unchanged. For A2A and A3 receptors, we found contradictory effects of the agonists and antagonists, thus there is no clear physiological role for these receptors at this time.. This study suggests that the myenteric ascending and descending reflex response of the rat small intestine is modulated by release of endogenous adenosine via A1 receptors.

Topics: Adenosine; Animals; Dose-Response Relationship, Drug; Electric Stimulation; Flavins; Gastrointestinal Motility; Ileum; In Vitro Techniques; Male; Muscarinic Antagonists; Muscle Contraction; Neural Inhibition; Neurons; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Wistar; Receptors, Purinergic P1; Reflex; Tetrodotoxin; Xanthines

Adenosine causes voltage- and non-voltage-dependent inhibition of high voltage-activated (HVA) Ca2+ currents in Xenopus laevis embryo spinal neurons. As this inhibition can be blocked by 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX) and mimicked by N6-cyclopentyladenosine (CPA) it appears to be mediated by A1 receptors. Agents active at A2 receptors either were without effect or could be blocked by DPCPX. AMP had no agonist action on these receptors. By using omega-conotoxin GVIA we found that adenosine inhibited an N-type Ca2+ current as well as a further unidentified HVA current that was insensitive to dihydropyridines, omega-agatoxin TK and omega-conotoxin MVIIC. Both types of current were subject to voltage- and non-voltage-dependent inhibition. We used CPA and DPCPX to test whether A1 receptors regulated spinal motor pattern generation in spinalized Xenopus embryos. DPCPX caused a near doubling of, while CPA greatly shortened, the length of swimming episodes. In addition, DPCPX slowed, while CPA greatly speeded up, the rate of run-down of motor activity. Our results demonstrate a novel action of A1 receptors in modulating spinal motor activity. Furthermore they confirm that adenosine is produced continually throughout swimming episodes and acts to cause the eventual termination of activity.

Topics: Adenosine; Adenosine Monophosphate; Animals; Calcium; Calcium Channel Blockers; Calcium Channels, N-Type; Dinucleoside Phosphates; Dose-Response Relationship, Drug; Electric Stimulation; Embryo, Nonmammalian; Enzyme Inhibitors; Flavins; In Vitro Techniques; Ion Channel Gating; Membrane Potentials; Motor Neurons; omega-Conotoxin GVIA; Patch-Clamp Techniques; Receptors, Purinergic P1; Spinal Nerve Roots; Swimming; Xanthines; Xenopus