Cyclic adenosine monophosphate-dependent vascular responses to purinergic agonists adenosine triphosphate and uridine triphosphate in the anesthetized mouse

The effect of purinergic signaling via the P2Y11 receptor on vascular function in a rat model of acute inflammation

There is a growing body of evidence pointing to the role of purinergic signaling in the development and progression of various conditions that have inflammation as a common pathogenetic denominator. The aim of the present study was to assess the involvement of P₂Y₁₁ purinergic receptors in the regulation of vascular function in aortic segments obtained using an experimental model of acute inflammation, the lipopolysaccharide (LPS, 8 mg/kg, i.p)-treated rats. Twelve hours after LPS administration, thoracic aortas were isolated and used for studies of vascular reactivity in the organ bath and for the measurement of reactive oxygen species (ROS) generation, respectively. LPS treatment significantly increased contractility to phenylephrine and attenuated the endothelium-dependent relaxation of the vascular segments in response to acetylcholine; an increased production of hydrogen peroxide (H₂O₂) was also recorded. The P₂Y₁₁ activator, NF_546, decreased the LPS-induced aortic H₂O₂ release and partially normalized the vasomotor function, namely reduced contractility and improved relaxation. The effect was abolished by co-treatment with the P₂Y₁₁ inhibitor, NF_340, and also after endothelium denudation. Importantly, NF₅₄₆ did not elicit an antioxidant effect by acting as a H₂O₂ scavenger, suggesting that the beneficial outcome of this treatment on the vasculature is the consequence of P₂Y₁₁ stimulation. In conclusion, purinergic P₂Y₁₁ receptors stimulation improves vascular function and mitigates oxidative stress in the setting of acute systemic inflammation, revealing salutary effects and therapeutic potential in pathologies associated with endothelial dysfunction.

Renal Integrin-Linked Kinase Depletion Induces Kidney cGMP-Axis Upregulation: Consequences on Basal and Acutely Damaged Renal Function

Soluble guanylyl cyclase (sGC) is activated by nitric oxide (NO) and produces cGMP, which activates cGMP-dependent protein kinases (PKG) and is hydrolyzed by specific phosphodiesterases (PDE). The vasodilatory and cytoprotective capacity of cGMP-axis activation results in a therapeutic strategy for several pathologies. Integrin-linked kinase (ILK), a major scaffold protein between the extracellular matrix and intracellular signaling pathways, may modulate the expression and functionality of the cGMP-axis-related proteins. We introduce ILK as a novel modulator in renal homeostasis as well as a potential target for cisplatin (CIS)-induced acute kidney injury (AKI) improvement. We used an adult mice model of depletion of ILK (cKD-ILK), which showed basal increase of sGC and PKG expressions and activities in renal cortex when compared with wildtype (WT) littermates. Twenty-four h activation of sGC activation with NO enhanced the filtration rate in cKD-ILK. During AKI, cKD-ILK maintained the cGMP-axis upregulation with consequent filtration rates enhancement and ameliorated CIS-dependent tubular epithelial-to-mesenchymal transition and inflammation and markers. To emphasize the role of cGMP-axis upregulation due to ILK depletion, we modulated the cGMP axis under AKI in vivo and in renal cultured cells. A suboptimal dose of the PDE inhibitor ZAP enhanced the beneficial effects of the ILK depletion in AKI mice. On the other hand, CIS increased contractility-related events in cultured glomerular mesangial cells and necrosis rates in cultured tubular cells; ILK depletion protected the cells while sGC blockade with ODQ fully recovered the damage.

P2Y₂ receptor activation decreases blood pressure via intermediate conductance potassium channels and connexin 37

AIMS

Nucleotides are important paracrine regulators of vascular tone. We previously demonstrated that activation of P2Y₂ receptors causes an acute, NO-independent decrease in blood pressure, indicating this signalling pathway requires an endothelial-derived hyperpolarization (EDH) response. To define the mechanisms by which activation of P2Y₂ receptors initiates EDH and vasodilation, we studied intermediate-conductance (KCa3.1, expressed in endothelial cells) and big-conductance potassium channels (KCa1.1, expressed in smooth muscle cells) as well as components of the myoendothelial gap junction, connexins 37 and 40 (Cx37, Cx40), all hypothesized to be part of the EDH response.

METHODS

We compared the effects of a P2Y₂/₄ receptor agonist in wild-type (WT) mice and in mice lacking KCa3.1, KCa1.1, Cx37 or Cx40 under anaesthesia, while monitoring intra-arterial blood pressure and heart rate.

RESULTS

Acute activation of P2Y₂/₄ receptors (0.01-3 mg kg(-1) body weight i.v.) caused a biphasic blood pressure response characterized by a dose-dependent and rapid decrease in blood pressure in WT (maximal response % of baseline at 3 mg kg(-1) : -38 ± 1%) followed by a consecutive increase in blood pressure (+44 ± 11%). The maximal responses in KCa3.1(-/-) and Cx37(-/-) were impaired (-13 ± 5, +17 ± 7 and -27 ± 1, +13 ± 3% respectively), whereas the maximal blood pressure decrease in response to acetylcholine at 3 μg kg(-1) was not significantly different (WT: -53 ± 3%; KCa3.1(-/-) : -52 ± 3; Cx37(-/-) : -53 ± 3%). KCa1.1(-/-) and Cx40(-/-) showed an identical biphasic response to P2Y2/4 receptor activation compared to WT.

CONCLUSIONS

The data suggest that the P2Y2/4 receptor activation elicits blood pressure responses via distinct mechanisms involving KCa3.1 and Cx37.

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.

Effects of early rolipram treatment on histopathological outcome after controlled cortical impact injury in mice

Traumatic brain injury (TBI) pathology includes contusions, cavitation, cell death, all of which can be exacerbated by inflammation. We hypothesized that an anti-inflammatory drug, rolipram, may reduce pathology after TBI, since in several CNS injury models rolipram reduces inflammation and improves cell survival and functional recovery. Adult male C57BL/6 mice received a craniotomy over the right parietotemporal cortex. Vertically directed controlled cortical impact (CCI) injury was delivered. Naïve controls were used for comparison. At 30 min post-surgery, animals were treated with vehicle or rolipram (1 mg/kg), and then once per day for 3 days. On day 3, the brains were systematically sectioned and stained to visualize the resulting pathology using hematoxylin and eosin (H&E) staining and NeuN immunocytochemistry. Total parietotemporal cortical contusion and cavity volume were significantly increased in rolipram-treated as compared to vehicle-treated CCI animals. Contusion areas at specific bregma levels indicated a significant effect of drug across bregma levels. Neuronal cell loss in the dentate hilus and area CA3 of the hippocampus were similar between vehicle and rolipram-treated animals. Although rolipram is well known to reduce pathology and inflammation in several other CNS injury models, the pathology resulting from CCI was worsened with rolipram at this particular dose and administration schedule. These studies suggest that consideration of the unique characteristics of TBI pathology is important in the extrapolation of promising therapeutic interventions from other CNS injury models.

P2Y₂ receptor activation decreases blood pressure and increases renal Na⁺ excretion

ATP and UTP are endogenous agonists of P2Y(2/4) receptors. To define the in vivo effects of P2Y(2) receptor activation on blood pressure and urinary excretion, we compared the response to INS45973, a P2Y(2/4) receptor agonist and UTP analog, in wild-type (WT) and P2Y(2) receptor knockout (P2Y(2)-/-) mice. INS45973 was administered intravenously as a bolus injection or continuous infusion to determine effects on blood pressure and renal function, respectively. Within seconds, bolus application of INS45973 (0.1 to 3 mg/kg body wt) dose-dependently decreased blood pressure in WT (maximum response -35 ± 2 mmHg) and to a similar extent in endothelial nitric oxide synthase knockout mice. By contrast, blood pressure increased in P2Y(2)-/- (maximum response +18 ± 1 mmHg) but returned to basal levels within 60 s. Continuous infusion of INS45973 (25 to 750 μg·min(-1)·kg(-1) body wt) dose-dependently increased urinary excretion of Na(+) in WT (maximum response +46 ± 15%) but reduced Na(+) excretion in P2Y(2)-/- (maximum responses of -45 ± 15%) mice. In renal clearance experiments, INS45973 did not affect glomerular filtration rate but lowered blood pressure and increased fractional excretion of fluid, Na(+), and K(+) in WT relative to P2Y(2)-/- mice. The blood pressure responses to INS45973 are consistent with P2Y(2) receptor-mediated NO-independent vasodilation and implicate responses to endothelium-derived hyperpolarizing factor, and P2Y(2) receptor-independent vasoconstriction, probably via activation of P2Y(4) receptors on smooth muscle. Systemic activation of P2Y(2) receptors thus lowers blood pressure and inhibits renal Na(+) reabsorption, effects suggesting the potential utility of P2Y(2) agonism in the treatment of hypertension.

The ecto-nucleotidase NTPDase1 differentially regulates P2Y1 and P2Y2 receptor-dependent vasorelaxation

BACKGROUND AND PURPOSE

Extracellular nucleotides produce vasodilatation through endothelial P2 receptor activation. As these autacoids are actively metabolized by the ecto-nucleotidase nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), we studied the effects of this cell surface enzyme on nucleotide-dependent vasodilatation.

EXPERIMENTAL APPROACH

Vascular NTPDase expression and activity were evaluated by immunohistochemistry and histochemistry. The vascular effects of nucleotides were tested in vivo by monitoring mean arterial pressure, and in vitro comparing reactivity of aortic rings using wild-type and Entpd1(-/-) (lacking NTPDase1) mice.

KEY RESULTS

The absence of NTPDase1 in Entpd1(-/-) mice led to a dramatic drop in endothelial nucleotidase activity. This deficit was associated with an exacerbated decrease in blood pressure after nucleotide injection. Following ATP injection, mean arterial pressure was decreased in Entpd1(+/+) and Entpd1(-/-) mice by 5.0 and 17%, respectively, and by 0.1 and 19% after UTP injection (10 nmole.kg(-1) both). In vitro, the concentration-response curves of relaxation to ADP and ATP were shifted to the left, revealing a facilitation of endothelial P2Y1 and P2Y2 receptor activation in Entpd1(-/-) mice. EC(50) values in Entpd1(+/+) versus Entpd1(-/-) aortic rings were 14 microM versus 0.35 microM for ADP, and 29 microM versus 1 microM for ATP. In Entpd1(-/-) aortas, P2Y1 receptors were more extensively desensitized than P2Y2 receptors. Relaxations to the non-hydrolysable analogues ADPbetaS (P2Y1) and ATPgammaS (P2Y2) were equivalent in both genotypes confirming the normal functionality of these P2Y receptors in mutant mice.

CONCLUSIONS AND IMPLICATIONS

NTPDase1 controls endothelial P2Y receptor-dependent relaxation, regulating both agonist level and P2 receptor reactivity.

Pilot intervention: aerosolized adrenomedullin reduces pulmonary hypertension

In pulmonary hypertension, systemic infusion of adrenomedullin (ADM), a potent vasodilator peptide, leads to pulmonary vasodilatation. However, systemic blood pressure declines alike. The present study investigated the effect of aerosolized ADM on pulmonary arterial pressure in surfactant-depleted newborn piglets with pulmonary hypertension. Animals randomly received aerosolized ADM (ADM, n = 6), aerosolized ADM combined with intravenous application of NG-nitro-l-arginine methylester to inhibit nitric-oxide (NO) synthases (ADM + l-NAME, n = 5), or aerosolized normal saline solution (control, n = 6). Aerosol therapy was performed in 30-min intervals for 5 h. After a total experimental period of 8 h, mRNA expression of endothelial and inducible NO synthase and endothelin-1 (ET-1) in lung tissue was quantified using TaqMan real-time polymerase chain reaction. Aerosolized ADM reduced mean pulmonary artery pressure (MPAP) compared with control (p < 0.001; at the end of the study, Delta-MPAP -13.5 +/- 1.4 versus -6.2 +/- 2.4 mm Hg). PaO2 significantly increased in the ADM (DeltaPaO2 243.3 mm Hg) and the ADM + l-NAME group (DeltaPaO2 217.4 mm Hg) compared with the control group (DeltaPaO2 82.9 mm Hg; p < 0.001). Aerosolized ADM did not influence mean systemic arterial pressure (baseline 63.2 +/- 2.7 versus end of the study 66.3 +/- 6.5 mm Hg; not significant). NO synthases gene expressions were 20 to 30% lower with ADM compared with control. ET-1 gene expression was significantly reduced (>50%) after ADM aerosol therapy (p < 0.001). Aerosolized adrenomedullin significantly reduced MPAP without lowering the systemic arterial pressure and improved profoundly the arterial oxygen tension. This effect seems to be mediated at least in part by the reduction of ET-1.