15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and alpha-beta-methyleneadenosine-5--triphosphate

Noradrenaline and ATP are sympathetic co-transmitters. In rat isolated mesenteric small arteries, activation of sympathetic nerves can produce a vasoconstrictor response mediated by ATP. In contrast, the rat perfused mesenteric bed displays vasoconstrictor responses that are blocked solely by alpha1-adrenoceptor antagonists. This study assessed the effect of raising tone with a vasoconstrictor on purinergic and noradrenergic responses to sympathetic nerve stimulation in the rat perfused mesentery. Rat mesenteric vascular beds were perfused with physiological salt solution and responses to nerve stimulation, or P2X-receptor agonists, were determined under basal conditions and after raising tone with endothelin-1. The contribution of noradrenaline and ATP to sympathetic nerve-mediated responses was assessed using the alpha1-adrenoceptor antagonist, prazosin and the P2X-receptor desensitizing agent, alpha,beta-methyleneATP. The effect of endothelin-1 on excitatory junction potentials generated in response to nerve stimulation in isolated mesenteric arteries was also assessed. Under baseline conditions, responses to nerve stimulation were mediated solely by activation of alpha1-adrenoceptors. After raising perfusion pressure with endothelin-1 or the thromboxane mimetic 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F2alpha (U44619), sympathetic nerve-mediated responses were larger than under basal conditions and the response was partly sensitive to P2X-receptor desensitization. Responses to exogenous P2X-receptor agonists were enhanced after treatment with endothelin-1, while endothelin-1 decreased the amplitude of excitatory junction potentials. These results indicate that ATP acts as an important, functional, sympathetic neurotransmitter in the perfused mesentery under raised tone conditions, where the perfusion pressure is closer to that found in vivo. This effect is due to a postjunctional enhancement of purinergic function.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Adrenergic alpha-Antagonists; Animals; Dose-Response Relationship, Drug; Electric Stimulation; Endothelin-1; In Vitro Techniques; Male; Mesenteric Arteries; Norepinephrine; Prazosin; Rats; Rats, Wistar; Receptors, Adrenergic, alpha-1; Receptors, Purinergic P2; Receptors, Purinergic P2X; Splanchnic Circulation; Sympathetic Nervous System; Vascular Resistance; Vasoconstriction; Vasoconstrictor Agents

Noradrenaline and ATP are sympathetic co-transmitters. In the rat perfused mesenteric bed cannabinoids have been shown to modify the overall response to sympathetic nerve stimulation. This study has assessed whether cannabinoid receptor activation modulates differentially the noradrenergic and purinergic components of sympathetic vasoconstriction.. Rat mesenteric beds were perfused with physiological salt solution and the effects of cannabinoids on responses to nerve stimulation, or exogenous noradrenaline or alpha,beta-methylene ATP (alpha,beta-meATP; P2X receptor agonist) were determined after raising tone with U46619. The effects of cannabinoids on the noradrenaline and ATP components of sympathetic neurotransmission were assessed using the alpha 1-adrenoceptor antagonist, prazosin, or after P2X receptor desensitization with alpha,beta-meATP.. Anandamide, WIN 55,212-2 and CP55,940 attenuated sympathetic neurogenic vasoconstrictor responses. The inhibitory actions of anandamide and WIN 55,212-2 were blocked by LY320135, a CB1 receptor antagonist, but not by SR144528, a CB2 receptor antagonist. The inhibitory actions of CP55,940 were unaffected by LY320135 and SR144528. WIN 55,212-3, the inactive S(-) enantiomer of WIN 55,212-2, had no effect on sympathetic neurogenic responses. None of the cannabinoids affected contractile responses to exogenous noradrenaline or alpha,beta-meATP. Anandamide and WIN 55,212-2 inhibited both the noradrenaline and ATP components of the sympathetic neurogenic contractile responses, with effects on the ATP component being most marked.. These results indicate that prejunctional CB1-like receptors mediate the sympathoinhibitory action of anandamide and WIN 55,212-2, but not CP55,940, in the rat mesenteric bed. Cannabinoids inhibit both the noradrenergic and purinergic components of sympathetic neurotransmission.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Adrenergic Fibers; Animals; Arachidonic Acids; Benzofurans; Benzoxazines; Camphanes; Cannabinoids; Cyclohexanols; Dose-Response Relationship, Drug; Electric Stimulation; Endocannabinoids; In Vitro Techniques; Male; Mesenteric Arteries; Morpholines; Muscle Tonus; Muscle, Smooth, Vascular; Naphthalenes; Norepinephrine; Perfusion; Polyunsaturated Alkamides; Prazosin; Pyrazoles; Rats; Rats, Wistar; Receptor, Cannabinoid, CB1; Receptor, Cannabinoid, CB2; Receptors, Purinergic P2

The contracting and relaxing effects of purines and UTP were investigated on rings of mouse thoracic aorta in vitro. UTP, ATP gamma S, and alpha-beta-Methyleneadenosine 5'triphosphate contracted rings with and without endothelium. On the contrary, adenosine, AMP, ADP, ATP, and 2-(methylthio)adenosine 5'-diphosphate had no effect on relaxed rings. When rings were tonically contracted by U46619 a thromboxane A2 analogue, ATP, ADP, ATP gamma S, 2-(methylthio)adenosine 5'-diphosphate, and UTP caused endothelium-dependent but not independent relaxations.I conclude that ATP acts on P2Y2 and P2Y1 receptors on the endothelial cells to cause endothelium-dependent relaxation. In this tissue, the relaxing effect of ATP dominates by endothelium-dependent ways when aorta rings are contracted by a stable thromboxane A2 analog. However receptors mediating contraction in response to purines and pyrimidines are present on smooth muscle cells. Indeed, the stimulation of P2Y receptors by UTP as well as the activation of P2X family receptors by ATP gamma S causes a contraction. The potential contractile effect of ATP seems masked by its hydrolysis by ectonucleotidases.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Adenosine; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Aorta, Thoracic; Biological Factors; Calcimycin; Dose-Response Relationship, Drug; Endothelium, Vascular; Male; Mice; Mice, Inbred ICR; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroglycerin; Phenylephrine; Receptors, Purinergic P2; Uridine Triphosphate

Responses to the P2X-purinoceptor agonist alpha,beta-methylene-ATP (alpha,beta-MeATP) were investigated in the pulmonary, hindquarter, and mesenteric vascular beds in the cat. Under constant-flow conditions, injections of alpha,beta-MeATP caused dose-related increases in perfusion pressure in the pulmonary and hindquarter beds and a biphasic response in the mesenteric circulation. In the pulmonary vascular bed, the order of potency was alpha,beta-MeATP > U-46619 > angiotensin II, whereas, in the hindquarters, the order of potency was angiotensin II > U-46619 > alpha,beta-MeATP. The order of potency was similar in the hindquarter and mesenteric beds when the pressor component of the response to alpha,beta-MeATP was compared with responses to angiotensin II and U-46619. The P2X-receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid attenuated the pressor response to alpha,beta-MeATP in the hindquarter circulation and the pressor component in the mesenteric vascular bed. Pressor responses to alpha,beta-MeATP were not altered by cyclooxygenase, alpha-adrenergic, or angiotensin AT(1) antagonists. These data show that alpha,beta-MeATP has potent pressor activity in the pulmonary circulation, where it was 100-fold more potent than angiotensin II. In contrast, alpha,beta-MeATP had modest pressor activity in the systemic bed, where it was 1,000-fold less potent than angiotensin II. These data suggest that responses to alpha,beta-MeATP are dependent on the vascular bed studied and may be dependent on the density of P2X receptors in the vascular bed.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Angiotensin II; Animals; Blood Vessels; Cats; Dose-Response Relationship, Drug; Female; Hindlimb; Male; Mesenteric Arteries; Perfusion; Pressure; Prostaglandin-Endoperoxide Synthases; Pulmonary Circulation; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Receptor, Angiotensin, Type 1; Receptors, Adrenergic, alpha; Receptors, Angiotensin; Vasoconstrictor Agents

Changes in bronchial vascular tone, in part due to cooling during ventilation, may contribute to altered control of airflow during airway inflammation, asthma, and exercise-induced bronchoconstriction. We investigated the responses of canine bronchial vasculature to excitatory stimuli and cooling. Electrical stimulation evoked contractions in only some (8 of 88) tissues; these were phentolamine sensitive and augmented by N(omega)-nitro-L-arginine. However, sustained contractions were evoked in all tissues by phenylephrine [concentration evoking a half-maximal response (EC(50)) approximately 2 microM] or the thromboxane A(2) mimetic U-46619 (EC(50) approximately 5 nM) and less so by beta,gamma-methylene-ATP or histamine. Cooling to room temperature markedly suppressed ( approximately 75%) adrenergic responses but had no significant effect against U-46619 responses. Adrenergic responses, but not those to U-46619, were accompanied by an increase in intracellular Ca(2+) concentration. Chelerythrine (protein kinase C antagonist) markedly antagonized adrenergic responses (mean maxima reduced 39% in artery and 86% in vein) but had no significant effect against U-46619, whereas genistein (a nonspecific tyrosine kinase inhibitor) essentially abolished responses to both agonists. We conclude that cooling of the airway wall dramatically interferes with adrenergic control of bronchial perfusion but has little effect on thromboxane-mediated vasoconstriction.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Animals; Anti-Inflammatory Agents, Non-Steroidal; Bronchi; Bronchial Arteries; Calcium; Cold Temperature; Dogs; Dose-Response Relationship, Drug; Electric Stimulation; Enzyme Inhibitors; Genistein; In Vitro Techniques; Nitroarginine; Phentolamine; Protein Kinase C; Protein-Tyrosine Kinases; Trachea; Vasoconstriction; Vasoconstrictor Agents; Veins

Evidence that secreted dense granule adenine nucleotides mediate part of the agonist-induced cytosolic calcium ([Ca2+]i) responses in human platelets was obtained from comparisons of fura-2-loaded platelets from normal subjects and from patients with a form of platelet storage pool deficiency (SPD) in which the secretory dense granules and their contents are virtually absent. SPD platelets had normal initial [Ca2+]i increases induced by thrombin and the endoperoxide analog U46619, but a significantly enhanced decay of elevated [Ca2+]i levels following the initial increases. With thrombin, this enhanced [Ca2+]i decay was associated with decreased Ca2+ influx, as measured by Mn2+ quench of fura-2 fluorescence. Addition of micromolar concentrations of ADP, alone or together with ATP, after stimulation reversed the enhanced [Ca2+]i decay and increased Mn2+ quench in SPD platelets, but had no effect on these responses in normal platelets, while addition of 100-fold higher concentrations of ATP or apyrase before stimulation increased [Ca2+]i decay and decreased Mn2+ quench in normal platelets, but had little effect in SPD platelets. ATP and alpha,beta-methylene ATP, a specific agonist for P2X1 receptors, at micromolar concentrations also increased Mn2+ quench, but to lesser extents than did ADP, in SPD platelets isolated and loaded with fura-2 in the presence of apyrase. Similar effects of ADP and excess ATP were seen in U46619-stimulated platelets, but decreased Ca2+ influx could not be measured directly in SPD platelets, presumably due to the very transient influx response seen with U46619. These results suggest that secreted dense granule ADP and ATP contribute to the maintenance of elevated [Ca2+]i levels, but not to the initial [Ca2+]i increases, in stimulated human platelets, most likely via a nucleotide-specific component of Ca2+ influx which may be mediated by interactions with both P2X1 and P2Y1 purinoceptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenine Nucleotides; Adenosine Diphosphate; Adenosine Triphosphate; Apyrase; Blood Platelets; Calcium; Cytoplasmic Granules; Cytosol; Drug Interactions; Fura-2; Humans; Ion Transport; Platelet Activation; Platelet Storage Pool Deficiency; Purinergic P2 Receptor Agonists; Receptors, Purinergic P2X; Thrombin

ATP and ADP are simultaneously released from activated platelets in equimolar concentrations. Micromolar concentrations of ATP inhibit platelet aggregation by both competitive and non-competitive mechanisms. The current studies addressed the question of how platelets respond to agonists in the presence of nanomolar and micromolar concentrations of ATP and ADP alone or in combination. This is a significant issue since the concentration of ATP +/- ADP may vary widely within a microenvironment depending upon the source and cause for the release of the nucleotides. ATP (1-10 nM) was found to significantly enhance the thromboxane A2 analog, U44619-, collagen- and thrombin-induced platelet aggregations. Conversely, ATP at 1-100 microM inhibited these same reactions. ADP, in general, behaved exactly opposite to ATP. When equal amounts of ATP and ADP were added together the ADP response appeared to predominate. The observed ATP-induced response was not due to a hydrolytic product as evidenced by an unaltered response to ATP in the presence of adenosine deaminase or the ATP generating system, creatine phosphate plus creatine phosphokinase. Adenosine (1-10 nM), like ADP, inhibited agonist-induced platelet aggregation. The stimulation of agonist-induced platelet aggregation by 1-10 nM extracellular ATP appears to depend upon the phosphorylation of platelet membrane ecto proteins. The ATP analog, beta gamma-methylene ATP, that is incapable of serving as a phosphate donor for protein kinases, inhibited rather than stimulated agonist-induced platelet aggregation. The dual response of platelets to low and high concentrations of extracellular ATP +/- ADP may play a physiological role in hemostasis and thrombosis under normal and pathological conditions.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Adenosine Triphosphate; Chromatography, High Pressure Liquid; Collagen; Dose-Response Relationship, Drug; Humans; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Thrombin; Thromboxane A2

1. The potentiating effect of NG-nitro-L-arginine methyl ester, (L-NAME) a nitric oxide synthesis inhibitor, on responses of the rat pulmonary vascular pressure (PVP) to purinoceptor agonists was examined. 2. At a constant flow of 23 ml min-1 the PVP was 22.4 +/- 2.5 mmHg (n = 15), and treatment with 100 microM L-NAME for 15 min was without effect on the PVP. After the tone was raised with 28 nmol 9,11-dideoxy-11 alpha, 9 alpha-epoxymethano-prostaglandin F2 alpha (U-46619), the PVP was 29.4 +/- 3.3 mmHg and treatment with 100 microM L-NAME was still without effect on the PVP. It appears that there is a graded release of nitric oxide in response to different levels of steady shear stress and in our experimental model the threshold for detection was not reached under basal conditions. 3. In contrast, when the circulation was challenged with 30 s step, additive increases in flow between 11 and 50 ml min-1 (n = 8), treatment with 100 microM L-NAME produced a significant (P < 0.05) increase in PVP suggesting that changes in flow-derived forces evoke the release of nitric oxide. This was evident for flow rates above 30 ml min-1. 4. In preparations in which tone was raised with U-46619, a dose of 1 x 10(-8) mol ATP or 2-meSATP evoked a drop in PVP while alpha,beta-meATP produced an increase in PVP under constant flow of 23 ml min-1. After treatment with 100 microM L-NAME, all three purinoceptor agonists evoked an increase in PVP. The increase in Pvp evoked by alpha, beta-meATP was not affected by L-NAME. These results suggest that P2Y-purinoceptor stimulation evokes the release of nitric oxide to produce vasodilatation.5. Under conditions of constant flow and basal pressure, 100 microM L-NAME significantly (P<0.05)potentiated the increase in Pvp evoked by 1 x 10-6 mol ATP, although the increase evoked by 1 x 10-8 mol (alpha,beta-meATP, which was of similar magnitude, was not affected. These results indicate that a blockade of evoked nitric oxide release is responsible for the potentiation of the increase in Pvp evoked by ATP.6. This study shows that, while nitric oxide does not appear to be released in the pulmonary circulation of the rat under constant flow conditions, nitric oxide release evoked by purinoceptor agonists attenuates increases in pulmonary vascular pressure.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Animals; Arginine; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Pulmonary Wedge Pressure; Rats; Rats, Wistar; Regression Analysis; Thromboxane A2; Vascular Resistance; Vasoconstrictor Agents