Uridine adenosine tetraphosphate affects contractility of mouse aorta and decreases blood pressure in conscious rats and mice

Biphasic effects of single-dose intravenous injection of uridine adenosine tetraphosphate on blood pressure in mice

PURPOSE

To explore the effects of a single dose of uridine adenosine tetraphosphate (Up4A) administered through the tail vein, on the blood pressure of mice.

METHODS

The mice were separated into three groups: the Up4A group, the norepinephrine (NA) group, and the α, β-methylene adenosine triphosphate (α, β-meATP) group. Each group of mice were injected drugs through the tail vein at 1, 3, 10, and 30 nmol/kg doses in an ascending order. Additionally, six mice were injected Up4A through the tail vein at 20, 40, 60, and 80 nmol/kg doses in an ascending order. The administration intervals for each dose were 20 min.

RESULTS

Mice in these groups experienced a rapid increase in blood pressure, reaching its peak within 10 s after drug administration. It took approximately 120 s for the blood pressure to return to baseline levels after the administration of the drugs in both the NA and α, β-meATP groups. After higher doses of Up4A were administered to the mice, their blood pressure exhibited biphasic changes. Initially, blood pressure of the mice rapidly dropped to a minimum within 10 s, then rose rapidly to a peak within 30 s. Subsequently, it gradually declined, taking around 10 min to return to the levels before the drug administration.

CONCLUSION

Compared to NA and α, β-meATP, Up4A, which contains purine and pyrimidine components, displayed a weaker blood pressure-elevating potency. Through its corresponding structure, Up4A exerted vasodilatory and vasoconstrictive effects throughout the entire experiment resulting in biphasic changes in blood pressure.

Histamine H2-receptor antagonism improves conduit artery endothelial function and reduces plasma aldosterone level without lowering arterial blood pressure in angiotensin II-hypertensive mice

Aldosterone through the mineralocorticoid receptor MR has detrimental effects on cardiovascular disease. It reduces the bioavailability of nitric oxide and impairs endothelium-dependent vasodilatation. In resistance arteries, aldosterone impairs the sensitivity of vascular smooth muscle cells to nitric oxide by promoting the local secretion of histamine which activates H2 receptors. The present experiments tested in vivo and ex vivo the hypothesis that systemic H2-receptor antagonism reduces arterial blood pressure and improves vasodilatation in angiotensin II-induced chronic hypertension. Hypertension was induced by intravenous infusion of angiotensin II (60 ng kg-1 min-1) in conscious, unrestrained mice infused concomitantly with the H2-receptor antagonist ranitidine (27.8 µg kg-1 min-1) or vehicle for 24 days. Heart rate and arterial blood pressure were recorded by indwelling arterial catheter. Resistance (mesenteric) and conductance (aortae) arteries were harvested for perfusion myography and isometric tension recordings by wire myography, respectively. Plasma was analyzed for aldosterone concentration. ANGII infusion resulted in elevated arterial blood pressure and while in vivo treatment with ranitidine reduced plasma aldosterone concentration, it did not reduce blood pressure. Ranitidine improved ex vivo endothelial function (acetylcholine 10-9 to 10-6 mol L-1) in mesenteric resistance arteries. This was abolished by ex vivo treatment with aldosterone (10-9 mol L-1, 1 h). In aortic segments, in vivo ranitidine treatment impaired relaxation. Activation of histamine H2 receptors promotes aldosterone secretion, does not affect arterial blood pressure, and protects endothelial function in conduit arteries but promotes endothelial dysfunction in resistance arteries during angiotensin II-mediated hypertension. Aldosterone contributes little to angiotensin II-induced hypertension in mice.

Purinoceptor: a novel target for hypertension

Hypertension is the leading cause of morbidity and mortality globally among all cardiovascular diseases. Purinergic signalling plays a crucial role in hypertension through the sympathetic nerve system, neurons in the brain stem, carotid body, endothelium, immune system, renin-angiotensin system, sodium excretion, epithelial sodium channel activity (ENaC), and renal autoregulation. Under hypertension, adenosine triphosphate (ATP) is released as a cotransmitter from the sympathetic nerve. It mediates vascular tone mainly through P2X1R activation on smooth muscle cells and activation of P2X4R and P2YR on endothelial cells and also via interaction with other purinoceptors, showing dual effects. P2Y1R is linked to neurogenic hypertension. P2X7R and P2Y11R are potential targets for immune-related hypertension. P2X3R located on the carotid body is the most promising novel therapeutic target for hypertension. A₁R, A_2AR, A_2BR, and P2X7R are all related to renal autoregulation, which contribute to both renal damage and hypertension. The main focus is on the evidence addressing the involvement of purinoceptors in hypertension and therapeutic interventions.

Airway Exposure to Modified Multi-walled Carbon Nanotubes Perturbs Cardiovascular Adenosinergic Signaling in Mice

The broad list of commercial applications for multi-walled carbon nanotubes (MWCNT) can be further expanded with the addition of various surface chemistry modifications. For example, standard commercial grade MWCNT (C-grade) can be carboxylated (COOH) or nitrogen-doped (N-doped) to suite specific utilities. We previously reported dose-dependent expansions of cardiac ischemia/reperfusion (I/R) injury, 24 h after intratracheal instillation of C-grade, COOH, or N-doped MWCNT in mice. Here, we have tested the hypothesis that airway exposure to MWCNT perturbs cardiovascular adenosinergic signaling, which could contribute to exacerbation of cardiac I/R injury. 100 µL of Vehicle or identical suspension volumes containing 100 µg of C-grade, COOH, or N-doped MWCNT were instilled into the trachea of CD-1 ICR mice. 1 day later, we measured cyclic adenosine monophosphate (cAMP) concentrations in cardiac tissue and evaluated arterial adenosinergic smooth muscle signaling mechanisms related to nitric oxide synthase (NOS) and cyclooxygenase (COX) in isolated aortic tissue. We also verified cardiac I/R injury expansion and examined both lung histology and bronchoalveolar lavage fluid cellularity in MWCNT exposed mice. Myocardial cAMP concentrations were reduced (p < 0.05) in the C-grade group by 17.4% and N-doped group by 13.7% compared to the Vehicle group. Curve fits to aortic ring 2-Cl-Adenosine concentration responses were significantly greater in the MWCNT groups vs. the Vehicle group. Aortic constrictor responses were more pronounced with NOS inhibition and were abolished with COX inhibition. These findings indicate that addition of functional chemical moieties on the surface of MWCNT may alter the biological responses to exposure by influencing cardiovascular adenosinergic signaling and promoting cardiac injury.

Uridine adenosine tetraphosphate and purinergic signaling in cardiovascular system: An update

Uridine adenosine tetraphosphate (Up4A), biosynthesized by activation of vascular endothelial growth factor receptor (VEGFR) 2, was initially identified as a potent endothelium-derived vasoconstrictor in perfused rat kidney. Subsequently, the effect of Up4A on vascular tone regulation was intensively investigated in arteries isolated from different vascular beds in rodents including rat pulmonary arteries, aortas, mesenteric and renal arteries as well as mouse aortas, in which Up4A produces vascular contraction. In contrast, Up4A produces vascular relaxation in porcine coronary small arteries and rat aortas. Intravenous infusion of Up4A into conscious rats or mice decreases blood pressure, and intravenous bolus injection of Up4A into anesthetized mice increases coronary blood flow, indicating an overall vasodilator influence in vivo. Although Up4A is the first dinucleotide described that contains both purine and pyrimidine moieties, its cardiovascular effects are exerted mainly through activation of purinergic receptors. These effects not only encompass regulation of vascular tone, but also endothelial angiogenesis, smooth muscle cell proliferation and migration, and vascular calcification. Furthermore, this review discusses a potential role for Up4A in cardiovascular pathophysiology, as plasma levels of Up4A are elevated in juvenile hypertensive patients and Up4A-mediated vascular purinergic signaling changes in cardiovascular disease such as hypertension, diabetes, atherosclerosis and myocardial infarction. Better understanding the vascular effect of the novel dinucleotide Up4A and the purinergic signaling mechanisms mediating its effects will enhance its potential as target for treatment of cardiovascular disease.

Endothelial mineralocorticoid receptor ablation does not alter blood pressure, kidney function or renal vessel contractility

Aldosterone blockade confers substantial cardiovascular and renal protection. The effects of aldosterone on mineralocorticoid receptors (MR) expressed in endothelial cells (EC) within the renal vasculature have not been delineated. We hypothesized that lack of MR in EC may be protective in renal vasculature and examined this by ablating the Nr3c2 gene in endothelial cells (EC-MR) in mice. Blood pressure, heart rate and PAH clearance were measured using indwelling catheters in conscious mice. The role of the MR in EC on contraction and relaxation was investigated in the renal artery and in perfused afferent arterioles. Urinary sodium excretion was determined by use of metabolic cages. EC-MR transgenics had markedly decreased MR expression in isolated aortic endothelial cells as compared to littermates (WT). Blood pressure and effective renal plasma flow at baseline and following AngII infusion was similar between groups. No differences in contraction and relaxation were observed between WT and EC-MR KO in isolated renal arteries during baseline or following 2 or 4 weeks of AngII infusion. The constriction or dilatations of afferent arterioles between genotypes were not different. No changes were found between the groups with respect to urinary excretion of sodium after 4 weeks of AngII infusion, or in urinary albumin excretion and kidney morphology. In conclusion, deletion of the EC-MR does not confer protection towards the development of hypertension, endothelial dysfunction of renal arteries or renal function following prolonged AngII-infusion.

Divergent coronary flow responses to uridine adenosine tetraphosphate in atherosclerotic ApoE knockout mice

Uridine adenosine tetraphosphate (Up4A) exerts potent relaxation in porcine coronary arteries that is reduced following myocardial infarction, suggesting a crucial role for Up4A in the regulation of coronary flow (CF) in cardiovascular disorders. We evaluated the vasoactive effects of Up4A on CF in atherosclerosis using ApoE knockout (KO) mice ex vivo and in vivo. Functional studies were conducted in isolated mouse hearts using the Langendorff technique. Immunofluorescence was performed to assess purinergic P2X1 receptor (P2X1R) expression in isolated mouse coronary arteries. In vivo effects of Up4A on coronary blood flow (CBF) were assessed using ultrasound. Infusion of Up4A (10-9-10-5 M) into isolated mouse hearts resulted in a concentration-dependent reduction in CF in WT and ApoE KO mice to a similar extent; this effect was exacerbated in ApoE KO mice fed a high-fat diet (HFD). The P2X1R antagonist MRS2159 restored Up4A-mediated decreases in CF more so in ApoE KO + HFD than ApoE KO mice. The smooth muscle to endothelial cell ratio of coronary P2X1R expression was greater in ApoE KO + HFD than ApoE KO or WT mice, suggesting a net vasoconstrictor potential of P2X1R in ApoE KO + HFD mice. In contrast, Up4A (1.6 mg/kg) increased CBF to a similar extent among the three groups. In conclusion, Up4A decreases CF more in ApoE KO + HFD mice, likely through a net upregulation of vasoconstrictor P2X1R. In contrast, Up4A increases CBF in vivo regardless of the atherosclerotic model.

Alteration of Vascular Responsiveness to Uridine Adenosine Tetraphosphate in Aortas Isolated from Male Diabetic Otsuka Long-Evans Tokushima Fatty Rats: The Involvement of Prostanoids

We investigated whether responsiveness to dinucleotide uridine adenosine tetraphosphate (Up₄A) was altered in aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats compared with those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats at the chronic stage of disease. In OLETF aortas, we observed the following: (1) Up₄A-induced contractions were lower than those in the LETO aortas under basal conditions, (2) slight relaxation occurred due to Up₄A, but this was not observed in phenylephrine-precontracted LETO aortas, (3) acetylcholine-induced relaxation was reduced (vs. LETO), and (4) prostanoid release (prostaglandin (PG)F_2α, thromboxane (Tx)A₂ metabolite, and PGE₂) due to Up₄A was decreased (vs. LETO). Endothelial denudation suppressed Up₄A-induced contractions in the LETO group, but increased the contractions in the OLETF group. Under nitric oxide synthase (NOS) inhibition, Up₄A induced contractions in phenylephrine-precontracted aortas; this effect was greater in the LETO group (vs. the OLETF group). The relaxation response induced by Up₄A was unmasked by cyclooxygenase inhibitors, especially in the LETO group, but this effect was abolished by NOS inhibition. These results suggest that the relaxant component of the Up₄A-mediated response was masked by prostanoids in the LETO aortas and that the LETO and OLETF rats presented different contributions of the endothelium to the response.

Altered purinergic signaling in uridine adenosine tetraphosphate-induced coronary relaxation in swine with metabolic derangement

We previously demonstrated that uridine adenosine tetraphosphate (Up4A) induces potent and partially endothelium-dependent relaxation in the healthy porcine coronary microvasculature. We subsequently showed that Up4A-induced porcine coronary relaxation was impaired via downregulation of P1 receptors after myocardial infarction. In view of the deleterious effect of metabolic derangement on vascular function, we hypothesized that the coronary vasodilator response to Up4A is impaired in metabolic derangement, and that the involvement of purinergic receptor subtypes and endothelium-derived vasoactive factors (EDVFs) is altered. Coronary small arteries, dissected from the apex of healthy swine and swine 6 months after induction of diabetes with streptozotocin and fed a high-fat diet, were mounted on wire myographs. Up4A (10-9-10-5 M)-induced coronary relaxation was maintained in swine with metabolic derangement compared to normal swine, despite impaired endothelium-dependent relaxation to bradykinin and despite blunted P2X7 receptor and NO-mediated vasodilator influences of Up4A. Moreover, a thromboxane-mediated vasoconstrictor influence was unmasked. In contrast, an increased Up4A-mediated vasodilator influence via P2Y1 receptors was observed, while, in response to Up4A, cytochrome P450 2C9 switched from producing vasoconstrictor to vasodilator metabolites in swine with metabolic derangement. Coronary vascular expression of A2A and P2X7 receptors as well as eNOS, as assessed with real-time PCR, was reduced in swine with metabolic derangement. In conclusion, although the overall coronary vasodilator response to Up4A was maintained in swine with metabolic derangement, the involvement of purinergic receptor subtypes and EDVF was markedly altered, revealing compensatory mechanisms among signaling pathways in Up4A-mediated coronary vasomotor influence in the early phase of metabolic derangement. Future studies are warranted to investigate the effects of severe metabolic derangement on coronary responses to Up4A.

Impaired Aortic Contractility to Uridine Adenosine Tetraphosphate in Angiotensin II-Induced Hypertensive Mice: Receptor Desensitization?

OBJECTIVE

We previously showed that uridine adenosine tetraphosphate (Up4A)-mediated aortic contraction is partly mediated through purinergic P2X1 receptors (P2X1R). It has been reported that the plasma level of Up4A is elevated in hypertensive patients, implying a potential role for Up4A-P2X1R signaling in hypertension. This study investigated the vasoactive effect of Up4A in aortas isolated from angiotensin (Ang) II-infused (21 days) hypertensive mice.

METHODS

Blood pressure was measured by tail cuff plethysmography. Aortas were isolated for isometric tension measurements, and protein expression was analyzed by western blot.

RESULTS

Mean and systolic arterial pressures were elevated by ~50% in Ang II-infused mice. Protein levels of both AT1R and P2X1R were upregulated in Ang II-infused aortas. Surprisingly, Up4A (10-9-10-5 M)-induced concentration-dependent contraction was significantly impaired in Ang II-infused mice. Studies in control mice revealed that both P2X1R (MRS2159) and AT1R (losartan) antagonists significantly attenuated Up4A-induced aortic contraction. In addition, desensitization of AT1R by prior Ang II (100 nM) exposure had no effect on Up4A-induced aortic contraction. However, subsequent serial exposure responses to Up4A-induced aortic contraction were markedly reduced, suggesting a desensitization of purinergic receptors. This desensitization was further confirmed in control mice by prior exposure of aortas to the P2X1R desensitizer α, β-methylene ATP (10 μM).

CONCLUSION

Despite upregulation of AT1R and P2X1R in hypertension, Up4A-mediated aortic contraction was impaired in Ang II-infused mice, likely through the desensitization of P2X1R but not AT1R. This implies that vascular P2X1R activity, rather than plasma Up4A level, may determine the role of Up4A in hypertension.

The role of dinucleoside polyphosphates on the ocular surface and other eye structures

Dinucleoside polyphosphates comprises a group of dinucleotides formed by two nucleosides linked by a variable number of phosphates, abbreviated NpnN (where n represents the number of phosphates). These compounds are naturally occurring substances present in tears, aqueous humour and in the retina. As the consequence of their presence, these dinucleotides contribute to many ocular physiological processes. On the ocular surface, dinucleoside polyphosphates can stimulate tear secretion, mucin release from goblet cells and they help epithelial wound healing by accelerating cell migration rate. These dinucleotides can also stimulate the presence of proteins known to protect the ocular surface against microorganisms, such as lysozyme and lactoferrin. One of the latest discoveries is the ability of some dinucleotides to facilitate the paracellular way on the cornea, therefore allowing the delivery of compounds, such as antiglaucomatous ones, more easily within the eye. The compound Ap₄A has been described being abnormally elevated in patient's tears suffering of dry eye, Sjogren syndrome, congenital aniridia, or after refractive surgery, suggesting this molecule as biomarker for dry eye condition. At the intraocular level, some diadenosine polyphosphates are abnormally elevated in glaucoma patients, and this can be related to the stimulation of a P2Y₂ receptor that increases the chloride efflux and water movement in the ciliary epithelium. In the retina, the dinucleotide dCp₄U, has been proven to be useful to help in the recovery of retinal detachments. Altogether, dinucleoside polyphosphates are a group of compounds which present relevant physiological actions but which also can perform promising therapeutic benefits.

Constrictor prostanoids and uridine adenosine tetraphosphate: vascular mediators and therapeutic targets in hypertension and diabetes

Vascular dysfunction plays a pivotal role in the development of systemic complications associated with arterial hypertension and diabetes. The endothelium, or more specifically, various factors derived from endothelial cells tightly regulate vascular function, including vascular tone. In physiological conditions, there is a balance between endothelium-derived factors, that is, relaxing factors (endothelium-derived relaxing factors; EDRFs) and contracting factors (endothelium-derived contracting factors; EDCFs), which mediate vascular homeostasis. However, in disease states, such as diabetes and arterial hypertension, there is an imbalance between EDRF and EDCF, with a reduction of EDRF signalling and an increase of EDCF signalling. Among EDCFs, COX-derived vasoconstrictor prostanoids play an important role in the development of vascular dysfunction associated with hypertension and diabetes. Moreover, uridine adenosine tetraphosphate (Up4 A), identified as an EDCF in 2005, also modulates vascular function. However, the role of Up4 A in hypertension- and diabetes-associated vascular dysfunction is unclear. In the present review, we focused on experimental and clinical evidence that implicate these two EDCFs (vasoconstrictor prostanoids and Up4 A) in vascular dysfunction associated with hypertension and diabetes.

Mechanisms underlying uridine adenosine tetraphosphate-induced vascular contraction in mouse aorta: Role of thromboxane and purinergic receptors

Uridine adenosine tetraphosphate (Up4A), a novel endothelium-derived vasoactive agent, is proposed to play a role in cardiovascular disorders and induces aortic contraction through activation of cyclooxygenases (COXs). We and others demonstrated that activation of A1 or A3 adenosine receptors (ARs) results in vascular contraction via thromboxane (TX) A2 production. However, the mechanisms of Up4A-induced vascular contraction in mouse aorta are not understood. We hypothesize that Up4A-induced aortic contraction is through COX-derived TXA2 production, which requires activation of A1 and/or A3AR. Concentration responses to Up4A were conducted in isolated aorta. The TXB2 production, a metabolite of TXA2, was also measured. Up4A (10(-9)-10(-5)M) produced a concentration-dependent contraction >70%, which was markedly attenuated by COX and COX1 but not by COX2 inhibition. Notably, Up4A-induced aortic contraction was blunted by both TX synthase inhibitor ozagrel and TXA2 receptor (TP) antagonist SQ29548. Surprisingly, A3AR deletion had no effect on Up4A-induced contraction. Moreover, A1AR deletion or antagonism as well as A1/A3AR deletion potentiated Up4A-induced aortic contraction, suggesting a vasodilator influence of A1AR. In contrast, non-selective purinergic P2 receptor antagonist PPADS significantly blunted Up4A-induced aortic contraction to a similar extent as selective P2X1R antagonist MRS2159, the latter of which was further reduced by addition of ozagrel. Endothelial denudation almost fully attenuated Up4A-induced contraction. Furthermore, Up4A (3μM) increased TXB2 formation, which was inhibited by either MRS2159 or ozagrel. In conclusion, Up4A-induced aortic contraction depends on activation of TX synthase and TP, which partially requires the activation of P2X1R but not A1 or A3AR through an endothelium-dependent mechanism.

Differential effect of T-type voltage-gated Ca2+ channel disruption on renal plasma flow and glomerular filtration rate in vivo

Voltage-gated Ca(2+) (Cav) channels play an essential role in the regulation of renal blood flow and glomerular filtration rate (GFR). Because T-type Cav channels are differentially expressed in pre- and postglomerular vessels, it was hypothesized that they impact renal blood flow and GFR differentially. The question was addressed with the use of two T-type Cav knockout (Cav3.1(-/-) and Cav3.2(-/-)) mouse strains. Continuous recordings of blood pressure and heart rate, para-aminohippurate clearance (renal plasma flow), and inulin clearance (GFR) were performed in conscious, chronically catheterized, wild-type (WT) and Cav3.1(-/-) and Cav3.2(-/-) mice. The contractility of afferent and efferent arterioles was determined in isolated perfused blood vessels. Efferent arterioles from Cav3.2(-/-) mice constricted significantly more in response to a depolarization compared with WT mice. GFR was increased in Cav3.2(-/-) mice with no significant changes in renal plasma flow, heart rate, and blood pressure. Cav3.1(-/-) mice had a higher renal plasma flow compared with WT mice, whereas GFR was indistinguishable from WT mice. No difference in the concentration response to K(+) was observed in isolated afferent and efferent arterioles from Cav3.1(-/-) mice compared with WT mice. Heart rate was significantly lower in Cav3.1(-/-) mice compared with WT mice with no difference in blood pressure. T-type antagonists significantly inhibited the constriction of human intrarenal arteries in response to a small depolarization. In conclusion, Cav3.2 channels support dilatation of efferent arterioles and affect GFR, whereas Cav3.1 channels in vivo contribute to renal vascular resistance. It is suggested that endothelial and nerve localization of Cav3.2 and Cav3.1, respectively, may account for the observed effects.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Enhanced uridine adenosine tetraphosphate-induced contraction in renal artery from type 2 diabetic Goto-Kakizaki rats due to activated cyclooxygenase/thromboxane receptor axis

The dinucleotide uridine adenosine tetraphosphate (Up4A), which has both purine and pyrimidine moieties, was reported as a novel endothelium-derived contracting factor. Recently, growing evidence has suggested that Up4A plays an important role in regulation of the cardiovascular function. We previously demonstrated that Up4A-induced vasoconstrictions are altered in arteries from DOCA-salt hypertensive rats. We have assessed responses to Up4A shown by renal arteries from type 2 diabetic Goto-Kakizaki (GK) rats (42-46 weeks old) and identified the molecular mechanisms involved. Concentration-dependent contractions to Up4A were greater in renal arterial rings from the GK than age-matched control Wistar group. In both groups, the inhibition of nitric oxide synthase (with N (G)-nitro-L-arginine) increased the response to Up4A, whereas the inhibition of cyclooxygenase (COX) (with indomethacin) decreased the response. Specific inhibitors of COX-1 (valeroyl salicylate) and COX-2 (NS398), a thromboxane (TX) receptor (TP) antagonist (SQ29548), and P2 receptor antagonist (suramin) also decreased the response to Up4A. Protein expressions of COXs in renal arteries were greater in the GK than Wistar group. The production of TXB2 (a metabolite of TXA2) by Up4A did not differ between these groups. Concentration-dependent contractions to U46619, an agonist of the TP receptor, were greater in renal arteries from the GK than Wistar group. The expression of P2X1 and P2Y2 receptors did not differ between these groups. These results suggest that enhancement of the Up4A-induced contraction in renal arteries from GK rats may be attributable to the increased activation of COXs/TP receptor signaling.

Uridine adenosine tetraphosphate induces contraction of circular and longitudinal gastric smooth muscle by distinct signaling pathways

Extracellular nucleotides uridine-5'-triphosphate (UTP) and adenosine-5'-triphosphate (ATP) induce contraction of gastric smooth muscle (SM). The dinucleotide uridine adenosine tetraphosphate (Up4 A), an endothelium-derived contraction factor, induces vascular SM contraction. Its effect on gastric SM contractions, however, is unknown. We addressed the hypothesis that Up4 A induces gastric SM contraction via a mechanism that may differ between circular and longitudinal muscle (CM and LM, respectively). CM and LM were isolated from rat gastric fundus for the measurement of isometric tension. Up4 A induced transient contractile responses in both CM and LM, which were similar to those induced by ATP and UTP. Up4 A failed to induce contraction of either LM or CM in the absence of extracellular Ca(2+) or in the presence of nimodipine, an inhibitor of voltage-gated Ca(2+) channels. P2X1, 2, 4, 5 and 7 and P2Y1, 2, 4 and 6 receptor expression was detected in gastric SM by reverse transcription-polymerase chain reaction. IP5 I (a P2X receptor antagonist) and α,β-methylene-ATP (a P2X receptor agonist) had no effect on Up4 A-induced contractions of either LM or CM, and α,β-methylene-ATP alone failed to induce a contractile response in either tissue. Suramin (a P2Y receptor antagonist), on the other hand, significantly inhibited Up4 A-induced contraction of CM, but not LM. Up4 A-induced contraction of CM, but not LM, was also inhibited by pretreatment with Y-27632, an inhibitor of Rho-associated kinase. We conclude that Up4 A induces extracellular Ca(2+) -dependent contractions of rat gastric LM and CM, and Up4 A-induced contraction of CM is mediated by suramin-sensitive P2Y receptors and subsequent activation of the Rho-associated kinase pathway.

The mineralocorticoid receptor antagonist eplerenone reduces renal interstitial fibrosis after long-term cyclosporine treatment in rat: antagonizing cyclosporine nephrotoxicity

Background

Chronic cyclosporine-(CsA)-mediated loss of kidney function is a major clinical problem in organ transplantation. We hypothesized that the mineralocorticoid receptor antagonist eplerenone (EPL) prevents chronic CsA-induced renal interstitial volume increase, tubule loss, and functional impairment in a rat model.

Methods

Sprague–Dawley rats received CsA alone (15 mg/kg/d p.o.), CsA and EPL (approximately 100 mg/kg/day p.o.) or vehicle (control) for 12 weeks. At 11 weeks, chronic indwelling arterial and venous catheters were implanted for continuous measurements of arterial blood pressure (BP) and GFR (inulin clearance) in conscious, freely moving animals. Plasma was sampled for analysis and kidney tissue was fixed for quantitative stereological analyses.

Results

Compared to controls, CsA-treatment reduced relative tubular volume (0.73±0.03 vs. 0.85±0.01, p<0.05) and increased relative interstitial volume (0.080±0.004 vs. 0.045±0.003, p<0.05); EPL attenuated these changes (0.82±0.02, p<0.05, and 0.060±0.006, p<0.05, respectively). CsA-treated rats had more sclerotic glomeruli and a higher degree of vascular depositions in arterioles; both were significantly reduced in CsA+EPL-treated animals. CsA increased BP and reduced body weight gain and GFR. In CsA+EPL rats, weight gain, GFR and BP at rest (daytime) were normalized; however, BP during activity (night) remained elevated. Plasma sodium and potassium concentrations, kidney-to-body weight ratios and CsA whole blood concentration were similar in CsA and CsA+EPL rats.

Conclusions

It is concluded that in the chronic cyclosporine rat nephropathy model, EPL reduces renal tissue injury, hypofiltration, hypertension, and growth impairment. MR antagonists should be tested for their renoprotective potential in patients treated with calcineurin inhibitors.

Uridine adenosine tetraphosphate is a novel vasodilator in the coronary microcirculation which acts through purinergic P1 but not P2 receptors

Uridine adenosine tetraphosphate (Up4A) has been identified as an endothelium-derived contracting factor, which acts through purinergic P2X and P2Y receptors. Since the coronary vascular actions of Up4A are unknown, we investigated the vasoactive profile of Up4A in coronary microvessels, and studied the involvement of purinergic receptor subtypes. Studies were performed in isolated porcine coronary small arteries (diameter∼250 μm), with and without endothelial denudation, mounted on a Mulvany wire myograph. Purinergic receptor expression was assessed by real-time PCR. Up4A (10(-9)-10(-5) M) failed to induce contraction at basal tone, but produced concentration-dependent vasorelaxation in precontracted microvessels. Up4A was slightly less potent than adenosine, ATP, and ADP in producing vasorelaxation, but significantly more potent than UTP and UDP. mRNA expression of P2X(4), P2Y(1), P2Y(2), P2Y(4), P2Y(6) and A(2A), but not P2X(1), receptors was observed. Up4A-induced vasodilation was unaffected by non-selective P2 receptor antagonist PPADS, P2X(1) antagonist MRS2159, P2Y(1) antagonist MRS2179 and P2Y(6) antagonist MRS2578, but was markedly attenuated by non-selective P1 receptor antagonist 8PT and A(2A) antagonist SCH58261. Up4A-induced vasodilation was not affected by ectonucleotidase inhibitor ARL67156, suggesting that A(2A) stimulation was not the result of Up4A breakdown to adenosine. Up4A-induced vasodilation was blunted in denuded vessels; additional A(2A) receptor blockade further attenuated Up4A-induced vasodilation, suggesting that A(2A) receptor-mediated vasodilation is only partly endothelium-dependent. In conclusion, Up4A exerts a vasodilator rather than a vasoconstrictor influence in coronary microvessels, which is mediated via A(2A) receptors and is partly endothelium-dependent.

The role of uridine adenosine tetraphosphate in the vascular system

The endothelium plays a pivotal role in vascular homeostasis, and endothelial dysfunction is a major feature of cardiovascular diseases, such as arterial hypertension, atherosclerosis, and diabetes. Recently, uridine adenosine tetraphosphate (Up(4)A) has been identified as a novel and potent endothelium-derived contracting factor (EDCF). Up(4)A structurally contains both purine and pyrimidine moieties, which activate purinergic receptors. There is an accumulating body of evidence to show that Up(4)A modulates vascular function by actions on endothelial and smooth muscle cells. In this paper, we discuss the effects of Up(4)A on vascular function and a potential role for Up(4)A in cardiovascular diseases.

Alterations in vasoconstrictor responses to the endothelium-derived contracting factor uridine adenosine tetraphosphate are region specific in DOCA-salt hypertensive rats

Uridine adenosine tetraphosphate (Up(4)A) has been recently identified as a novel and potent endothelium-derived contracting factor and contains both purine and pyrimidine moieties, which activate purinergic P2X and P2Y receptors. The present study was designed to compare contractile responses to Up(4)A and other nucleotides such as ATP (P2X/P2Y agonist), UTP (P2Y(2)/P2Y(4) agonist), UDP (P2Y(6) agonist), and α,β-methylene ATP (P2X(1) agonist) in different vascular regions [thoracic aorta, basilar, small mesenteric, and femoral arteries] from deoxycorticosterone acetate-salt (DOCA-salt) and control rats. In DOCA-salt rats [vs. control uninephrectomized (Uni) rats]: (1) in thoracic aorta, Up(4)A-, ATP-, and UTP-induced contractions were unchanged; (2) in basilar artery, Up(4)A-, ATP-, UTP- and UDP-induced contractions were increased, and expression for P2X(1), but not P2Y(2) or P2Y(6) was decreased; (3) in small mesenteric artery, Up(4)A-induced contraction was decreased and UDP-induced contraction was increased; expression of P2Y(2) and P2X(1) was decreased whereas P2Y(6) expression was increased; (4) in femoral artery, Up(4)A-, UTP-, and UDP-induced contractions were increased, but expression of P2Y(2), P2Y(6) and P2X(1) was unchanged. The α,β-methylene ATP-induced contraction was bell-shaped and the maximal contraction was reached at a lower concentration in basilar and mesenteric arteries from Uni rats, compared to arteries from DOCA-salt rats. These results suggest that Up(4)A-induced contraction is heterogenously affected among various vascular beds in arterial hypertension. P2Y receptor activation may contribute to enhancement of Up(4)A-induced contraction in basilar and femoral arteries. These changes in vascular reactivity to Up(4)A may be adaptive to the vascular alterations produced by hypertension.

Uridine adenosine tetraphosphate-induced contraction is increased in renal but not pulmonary arteries from DOCA-salt hypertensive rats

Uridine adenosine tetraphosphate (Up(4)A) was reported as a novel endothelium-derived contracting factor. Up(4)A contains both purine and pyrimidine moieties, which activate purinergic (P2)X and P2Y receptors. However, alterations in the vasoconstrictor responses to Up(4)A in hypertensive states remain unclear. The present study examined the effects of Up(4)A on contraction of isolated renal arteries (RA) and pulmonary arteries (PA) from DOCA-salt rats using isometric tension recording. RA from DOCA-salt rats exhibited increased contraction to Up(4)A versus arteries from control uninephrectomized rats in the absence and presence of N(G)-nitro-l-arginine (nitric oxide synthase inhibitor). On the other hand, the Up(4)A-induced contraction in PA was similar between the two groups. Up(4)A-induced contraction was inhibited by suramin (nonselective P2 antagonist) but not by diinosine pentaphosphate pentasodium salt hydrate (Ip(5)I; P2X(1) antagonist) in RA from both groups. Furthermore, 2-thiouridine 5'-triphosphate tetrasodium salt (2-ThioUTP; P2Y(2) agonist)-, uridine-5'-(γ-thio)-triphosphate trisodium salt (UTPγS; P2Y(2)/P2Y(4) agonist)-, and 5-iodouridine-5'-O-diphosphate trisodium salt (MRS 2693; P2Y(6) agonist)-induced contractions were all increased in RA from DOCA-salt rats. Protein expression of P2Y(2)-, P2Y(4)-, and P2Y(6) receptors in RA was similar between the two groups. In DOCA-salt RA, the enhanced Up(4)A-induced contraction was reduced by PD98059, an ERK pathway inhibitor, and Up(4)A-stimulated ERK activation was increased. These data are the first to indicate that Up(4)A-induced contraction is enhanced in RA from DOCA-salt rats. Enhanced P2Y receptor signaling and activation of the ERK pathway together represent a likely mechanism mediating the enhanced Up(4)A-induced contraction. Up(4)A might be of relevance in the pathophysiology of vascular tone regulation and renal dysfunction in arterial hypertension.