adenosine-5--(n-ethylcarboxamide) and isoalloxazine

Previous reports have suggested that the posterior hypothalamic adenosine A2 receptors may play a role in central cardiovascular regulation. In this study, we examined the influence of posterior hypothalamic adenosine A2B receptors on the regulation of blood pressure and heart rate. Drugs were injected into the posterior hypothalamus of anesthetized, artificially ventilated, male Sprague-Dawley rats. Four nanomoles of 5'-N-ethylcarboxamidoadenosine (NECA), an adenosine A 2A receptor agonist, decreased arterial blood pressure and heart rate, whereas 5 nmol of alloxazine, an adenosine A2B receptor antagonist, blocked the depressor and bradycardiac effects of 4 nmol NECA. We examined the role of nitric oxide (NO) and K+ channels on cardiovascular regulation by adenosine A2B receptors in the posterior hypothalamus. Pretreatment with 40 nmol of NG-nitro-L-arginine methyl ester, a NO synthase inhibitor, significantly attenuated the effects of NECA, and 10 nmol of sodium nitroprusside, a NO releaser, strengthened the action of drug. In addition, posterior hypothalamic administration of 20 nmol of glipizide, an K ATP blocker, blocked the cardiovascular depression elicited by NECA. These results suggest that NO mediates cardiovascular regulation by activation of A2B receptors in the posterior hypothalamus. Additionally, ATP-sensitive K+ channels modulate the action of adenosine A2B receptors.

Topics: Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Adenosine-5'-(N-ethylcarboxamide); Aminoquinolines; Animals; Blood Pressure; Enzyme Inhibitors; Flavins; Glipizide; Heart Rate; Hypothalamus, Posterior; Imines; KATP Channels; Male; Microinjections; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitroprusside; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2B; Vasodilator Agents

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

Cardiovascular inhibitory effects induced by the posterior hypothalamic adenosine A(2) receptors were suggested by our previous reports. In this experiment, we examined the influence of the posterior hypothalamic adenosine A(2B) receptors on central cardiovascular regulation of blood pressure (BP) and heart rate (HR). Posterior hypothalamic injection of drugs was performed in anesthetized, artificially ventilated male Sprague-Dawley rats. Injection of 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA; 2 nmol), an adenosine A(2) receptor agonist, showed the decrease of arterial blood pressure and heart rate, and the alloxazine, an adenosine A(2B) receptor antagonist, partially blocked the depressor and bradycardiac effects of CPCA (2 nmol). To examine the role of adenosine A(2B) receptors among the adenosine A(2) subtypes, we applied the 5'-N-Ethylcarboxamidoadenosine (NECA), an adenosine A(2B) receptor agonist, to the posterior hypothalamus. Injection of NECA (1, 4 and 8 nmol) produced a dose-dependent decrease of arterial blood pressure and HR. Pretreatment with alloxazine (5 nmol) partially blocked the depressor and bradycardiac effects of NECA (4 nmol). Also, pretreatment with LY-83,583 (5 nmol), a soluble guanylate cyclase inhibitor, attenuated the depressor and bradycardiac effects of NECA (4 nmol). However, pretreatment with MDL-12,330 (10 nmol), an adenylate cyclase inhibitor, did not affect these effects of NECA (4 nmol). These results suggest that adenosine A(2B) receptor in the posterior hypothalamus plays an inhibitory role in central cardiovascular regulation, and that guanylate cyclase mediates the depressor and bradycardiac actions of adenosine A(2B) receptors.

Topics: Adenosine; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Adenosine-5'-(N-ethylcarboxamide); Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Aminoquinolines; Anesthesia; Animals; Blood Pressure; Bradycardia; Enzyme Inhibitors; Flavins; Guanylate Cyclase; Heart Rate; Hypothalamus, Posterior; Imines; Male; Microinjections; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A2B; Receptors, Adenosine A2; Vasodilator Agents

To clarify the relative roles of A(2) adenosine receptor subtypes in the regulation of coronary flow and myocardial contractility, coronary vascular and functional responses to adenosine and its analogs were examined in isolated wild-type (WT) and A(2A) receptor knockout (A(2A)KO) mouse hearts. Nonselective agonists adenosine and 5'-N-ethyl-carboxamido-adenosine (NECA) increased coronary flow in A(2A)KO hearts, albeit with a rightward shift of concentration-response curves and decreased maximal vasodilation compared with WT hearts. 2-p-(2-Carboxy-ethyl)phenethylamino-5'-N-ethyl-carboxamidoadenosine (CGS-21680, a selective A(2A) receptor agonist) increased coronary flow in WT hearts but did not affect A(2A)KO hearts. Adenosine and NECA each elicited equal maximal increases in developed pressure in WT and A(2A)KO hearts, whereas CGS-21680 did not affect developed pressure in A(2A)KO hearts. Alloxazine, a selective A(2B) receptor antagonist, attenuated NECA-induced coronary vasodilation (from 202 +/- 14% to 128 +/- 9% of baseline, P < 0.05) and NECA-induced increases in developed pressure (from 133 +/- 8% to 112 +/- 7% of baseline, P < 0.05) in A(2A)KO hearts. Together, these findings support the conclusion that A(2B) adenosine receptor activation increases coronary flow and developed pressure in isolated murine hearts.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Antihypertensive Agents; Coronary Circulation; Flavins; Mice; Mice, Knockout; Phenethylamines; Purinergic P1 Receptor Antagonists; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Receptors, Purinergic P1; Vasodilation; Vasodilator Agents; Ventricular Pressure

The characteristics of adenosine receptors found in glial fibrillary acid protein (GFAP)-positive astrocytes acutely isolated from the cerebral cortices of 4- to 12-day old rats were examined by evaluating the effects of adenosine and its analogues on intracellular calcium levels. First, these effects were compared with those seen in primary astrocytic cultures, and it was found that acutely isolated astrocytes showed much greater sensitivity to adenosine than their cultured counterparts. Then, the adenosine evoked calcium responses in acutely isolated cells were evaluated under various conditions. The responses to adenosine were not inhibited by papaverine, an uptake blocker, or by removal of extracellular calcium. U73122, a phospholipase C inhibitor, was able to completely inhibit the adenosine response. The receptor inhibitor 3-isobutyl-1-methylxanthine inhibited the calcium response to adenosine, providing evidence that the response is not coupled to the xanthine-insensitive A3 receptor. The stimulatory action of NECA, a non-selective analogue, was blocked neither by the A2A-selective receptor antagonist 8-(3-chlorostyryl) caffeine nor by the A1-selective receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. The A2B receptor antagonist alloxazine, however, was able to completely inhibit the increase in intracellular calcium produced by NECA. Taken together, these data suggest that the adenosine-evoked calcium response in acutely isolated astrocytes is coupled to the A2B receptor.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Astrocytes; Calcium; Cell Separation; Cells, Cultured; Estrenes; Flavins; Intracellular Membranes; Pyrrolidinones; Rats; Receptors, Purinergic P1; Type C Phospholipases