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TRPV4 channel activation leads to endothelium-dependent relaxation mediated by nitric oxide and endothelium-derived hyperpolarizing factor in rat pulmonary artery

The purpose of the present study was to characterize TRPV4 channels in the rat pulmonary artery and examine their role in endothelium-dependent relaxation. Tension, Real-Time polymerase chain reaction (Real-Time PCR) and Western blot experiments were conducted on left and right branches of the main pulmonary artery from male Wistar rats. TRPV4 channel agonist GSK1016790A (GSK) caused concentration-related robust relaxation (Emax 88.6±5.5%; pD2 8.7±0.2) of the endothelium-intact pulmonary artery. Endothelium-denudation nearly abolished the relaxation (Emax 5.6±1.3%) to GSK. TRPV4 channel selective antagonist HC067047 significantly attenuated GSK-induced relaxation (Emax 56.2±6.6% vs. control Emax 87.9±3.3%) in endothelium-intact vessels, but had no effect on either ACh-induced endothelium-dependent or SNP-induced endothelium-independent relaxations. GSK-induced relaxations were markedly inhibited either in the presence of NO synthase inhibitor L-NAME (Emax 8.5±2.7%) or sGC inhibitor ODQ (Emax 28.1±5.9%). A significant portion (Emax 30.2±4.4%) of endothelium-dependent relaxation still persisted in the combined presence of L-NAME and cyclooxygenase inhibitor indomethacin. This EDHF-mediated relaxation was sensitive to inhibition by 60mM K(+) depolarizing solution or K(+) channel blockers apamin (SKCa; KCa2.3) and TRAM-34 (IKCa; KCa3.1). GSK (10(-10)-10(-7)M) caused either modest decrease or increase in the basal tone of endothelium-intact or denuded rings, respectively. We found a greater abundance (>1.5 fold) of TRPV4 mRNA and protein expressions in endothelium-intact vs. denuded vessels, suggesting the presence of this channel in pulmonary endothelial and smooth muscle cells as well. The present study demonstrated that NO and EDHF significantly contributed to TRPV4 channel-mediated endothelium-dependent relaxation of the rat pulmonary artery.

Atorvastatin prevents vascular hyporeactivity to norepinephrine in sepsis: Role of nitric oxide and α1-adrenoceptor mRNA Expression

Hyporeactivity to vasoconstrictors is one of the clinical manifestations of sepsis in man and experimental animals. The objective of the investigation was to examine whether atorvastatin can prevent hyporeactivity to norepinephrine (NE) in mouse aorta in sepsis, and if so, what are the mechanisms involved. Sepsis in mice was induced by cecal ligation and puncture. The aorta was harvested for tension experiment, nitric oxide (NO) and cyclic guanosine monophosphate measurements, and inducible NO synthase (iNOS) and &agr;1D-adrenoceptor mRNA expression studies. In comparison with sham-operated controls, sepsis significantly decreased the contractile response to NE in the mouse aorta. Pretreatment with atorvastatin of septic animals completely restored NE-induced contractions to levels similar to those of sham-operated controls and significantly increased survival time and mean arterial pressure. Atorvastatin also attenuated iNOS-induced overproduction of NO, as well as iNOS mRNA expression. Accordingly, hyporeactivity to NE was not evident in tissues pretreated with selective iNOS inhibitor 1400W in sepsis. Although basal cyclic guanosine monophosphate accumulation in the aorta was reduced in sepsis, pretreatment of the tissues with soluble guanylyl cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ) partially restored the reactivity to NE. Interestingly, hyporeactivity to NE in sepsis was associated with a decreased &agr;1D-adrenoceptor mRNA expression in the mouse aorta. Atorvastatin pretreatment, however, prevented the decrease in &agr;1D-adrenoceptor mRNA expression in septic animals. In conclusion, atorvastatin seems to prevent hyporeactivity to vasoconstrictor NE in the aorta from septic mice through attenuation of overproduction of NO as well as improved &agr;1D-adrenoceptor mRNA expression. The findings of the present study may explain the beneficial effects of atorvastatin on improved hemodynamic functions in sepsis.

Atorvastatin prevents sepsis-induced downregulation of myocardial β1-adrenoceptors and decreased cAMP response in mice.

ABSTRACT Impaired cardiac &bgr;-adrenoceptor signaling is an important cause of sepsis-induced myocardial depression in man and experimental animals. We examined the effect of atorvastatin (ATR) pretreatment on myocardial &bgr;1-adrenoceptor (&bgr;1-AR) expressions and post–receptor signaling in a mouse model of sepsis (cecal ligation and puncture [CLP]). After 20 ± 2 h of surgery, hearts were isolated for the measurement of left ventricular functions (left ventricular developed pressure, dp/dtmax and dp/dtmin) using Langendorff setup. Western blot was used to determine &bgr;1-AR and G protein–coupled receptor kinase 2 protein expressions. Real-time polymerase chain reaction was done to determine &bgr;1-AR mRNA expression. Atorvastatin prevented sepsis-induced decrease in left ventricular functions, such as left ventricular developed pressure (CLP 75.90 ± 0.53 vs. ATR 100.24 ± 1.64 mmHg), dp/dtmax (CLP 3,742 ± 71 vs. ATR 4,291 ± 88 mmHg/s), and dp/dtmin (CLP −1,010 ± 24 vs. ATR −1,346 ± 84 mmHg/s). Associated with functional impairments, sepsis decreased both myocardial &bgr;1-AR protein and mRNA expressions by 52% ± 9% and 62% ± 7%, respectively. However, ATR treatment of CLP mice (ATR) preserved &bgr;1-AR protein (96% ± 11%) and mRNA (88% ± 14%) expressions comparable to sham-operated level. Furthermore, it not only attenuated sepsis-induced decrease in basal cardiac adenosine 3′,5′-cyclic monophosphate content (CLP 1.30 ± 0.27 vs. ATR 6.30 ± 0.67 pmol/mg protein), but also prevented its refractoriness to dobutamine stimulation (CLP 1.72 ± 0.27 vs. ATR 10.83 ± 1.37 pmol/mg protein). Atorvastatin also inhibited sepsis-induced increase in cardiac G protein–coupled receptor kinase 2 protein expression (CLP 1.73 ± 0.18-fold vs. ATR 1.10 ± 0.18-fold), protein kinase A activity (CLP 1.12 ± 0.14 vs. ATR 0.66 ± 0.08 U/mg protein) and plasma catecholamines (CLP 138 ± 22 vs. ATR 59 ± 2 pg/mL). In conclusion, ATR seems to improve left ventricular functions in vitro through the preservation of &bgr;1-AR signaling in sepsis.

Role of voltage-dependent potassium channels and myo-endothelial gap junctions in 4-aminopyridine-induced inhibition of acetylcholine relaxation in rat carotid artery

The present study examined the role of voltage-gated potassium (K(v)) channels and myo-endothelial gap junctions in 4-aminopyridine-induced inhibition of acetylcholine-evoked endothelium-dependent relaxation and NO release in the rat carotid artery. The acetylcholine-induced relaxation was drastically inhibited by 94% and 82%, respectively in the presence of either 100 microM N(G)-nitro-l-arginine methyl ester (L-NAME) or 10 microM 1H-[1,2,4]oxadiazolo[4,3,a]quinoxalin-1-one (ODQ), while it was abolished following endothelium removal. 4-aminopyridine (1 mM), a preferential blocker of the K(v) channels significantly decreased the vasodilator potency, as well as efficacy of acetylcholine (pD(2) 5.7+/-0.09, R(max) 86.1+/-3.5% versus control 6.7+/-0.10 R(max) 106+/-3.5%, n=6), but had no effect on the relaxations elicited by either sodium nitroprusside (SNP) or 8-bromo-cyclic guanosine monophosphate (8-Br-cGMP). 4-AP (1 mM) also inhibited acetylcholine (3 microM)-stimulated nitrite release in the carotid artery segments (99.4+/-4.93 pmol/mg tissue weight wt; n=6 versus control 123.8+/-7.43 pmol/mg tissue weight wt, n=6). 18alpha-glycyrrhetinic acid (18alpha-GA, 5 microM), a gap junction blocker, completely prevented the inhibition of acetylcholine-induced relaxation, as well as nitrite release by 4-AP. In the pulmonary artery, however antagonism of acetylcholine-evoked relaxation by 4-AP was not reversed by 18alpha-GA. These results suggest that 4-AP-induced inhibition of endothelium-dependent relaxation and NO release involves electrical coupling between vascular smooth muscle and endothelial cells via myo-endothelial gap junctions in the rat carotid artery, but not in the pulmonary artery. Further, direct activation of 4-AP-sensitive vascular K(v) channels by endothelium-derived NO is not evident in the carotid blood vessel, while this appears to be an important mechanism of acetylcholine-induced relaxation in the pulmonary artery.

Molecular and functional characteristics of β3-adrenoceptors in late pregnant mouse uterus: A comparison with β2-adrenoceptors

β(3)-adrenoceptor is a potential target for uterine relaxant drugs for the treatment of preterm labor. Mouse is an ideal experimental model for preterm labor. However, there is limited information on the molecular and functional characteristics of β(3)-adrenoceptors in mouse uterus. Therefore, the current study was undertaken to characterize the β(3)-adrenoceptors in late pregnant mouse uterus by molecular and functional experiments and to compare their expression and function with the β(2)-adrenoceptors. Using RT-PCR, we demonstrated the presence of β(3)-adrenoceptor mRNA in the mouse uterus. Accordingly, selective β(3)-adrenoceptor agonist SAR150640 (ethyl-4-{trans-4-[((2S)-2-hydroxy-3-{4-hydroxy-3[(methylsulfonyl)amino]-phenoxy}propyl)amino]cyclohexyl}benzoate hydrochloride) caused concentration-dependent relaxation of the isolated tissue. SR59230A (1 μM), a selective antagonist of β(3)-adrenoceptors, antagonized the relaxant response to SAR150640. Using real-time PCR we found that in comparison to β(3)-adrenoceptor mRNA, β(2)-adrenoceptor mRNA is predominantly expressed in the late pregnant mouse uterus. We then assessed the comparative efficiency of different β-adrenoceptor agonists, such as SAR150640, salbutamol and isoprenaline to relax the tissue. SAR150640 (pD(2) 6.64±0.21, E(max) 104.9±7.95), salbutamol (pD(2) 8.57±0.062, E(max) 103.1±3.22) and isoprenaline (pD(2) 9.48±0.084, E(max) 102.9±5.18) caused concentration-dependent inhibition of uterine rhythmic contractions. While the maximal relaxation to these agonists was comparable, the order of potency was isoprenaline>salbutamol>SAR. These results suggest that β(3)-adrenoceptor mRNA is present in the pregnant mouse uterus and is functionally active. The predominance of β(2)- over β(3)-adrenoceptor expression may explain variable potency amongst the β-adrenoceptor agonists.

Combined treatment with atorvastatin and imipenem improves survival and vascular functions in mouse model of sepsis

We have recently reported that pre-treatment, but not the post-treatment with atorvastatin showed survival benefit and improved hemodynamic functions in cecal ligation and puncture (CLP) model of sepsis in mice. Here we examined whether combined treatment with atorvastatin and imipenem after onset of sepsis can prolong survival and improve vascular functions. At 6 and 18h after sepsis induction, treatment with atorvastatin plus imipenem, atorvastatin or imipenem alone or placebo was initiated. Ex vivo experiments were done on mouse aorta to examine the vascular reactivity to nor-adrenaline and acetylcholine and mRNA expressions of α1D AR, GRK2 and eNOS. Atorvastatin plus imipenem extended the survival time to 56.00±4.62h from 20.00±1.66h observed in CLP mice. The survival time with atorvastatin or imipenem alone was 20.50±1.89h and 27.00±4.09h, respectively. The combined treatment reversed the hyporeactivity to nor-adrenaline through preservation of α1D AR mRNA/protein expression and reversal of α1D AR desensitization mediated by GRK2/Gβγ pathway. The treatment also restored endothelium-dependent relaxation to ACh through restoration of aortic eNOS mRNA expression and NO availability. In conclusion, combined treatment with atorvastatin and imipenem exhibited survival benefit and improved vascular functions in septic mice.

Molecular and functional characterization of TRPV4 channels in pregnant and nonpregnant mouse uterus.

AIMS The aim of the present study was to characterize TRPV4 channels in pregnant and nonpregnant mouse uterus and examine their functional role in spontaneous and agonist-induced contractions. MAIN METHODS We used RT-PCR, Western blot and immunohistochemistry experiments to demonstrate the presence of TRPV4 mRNA and protein, respectively in both pregnant and nonpregnant mouse uterus. Tension experiments were conducted for functional characterization of the TRPV4 channels. KEY FINDINGS TRPV4 mRNA and protein were detected in both pregnant and nonpregnant mouse uterus with distribution in both endometrium and myometrium. The TRPV4 channel agonist GSK1016790A (GSK) increased myometrial contraction in pregnant (Emax 336.8±21.35%; pD2 7.79±0.29) and nonpregnant (Emax 238±28.13%; pD2 7.61±0.57) animals. HC067047 (1μM), a selective blocker of the TRPV4 channel, antagonized the contractions to GSK in pregnant (Emax 171±18.26%; pD2 6.58±0.37) and nonpregnant (Emax 78.12±9.32%; pD2 7.54±0.9) uteri. Further, HC067047 (1μM) inhibited contractions induced by PGF2α in the pregnant (Emax 183.2±13.94%; pD2 7.01±0.30 versus control Emax 495.7±42.49%; pD2 7.12±0.24) and nonpregnant (Emax 105.3±7.10%; pD2 7.24±0.34 versus control Emax 232.5±12.27%; pD2 7.83±0.29) uteri. SIGNIFICANCE TRPV4 channels are present in the pregnant and nonpregnant mouse uteri, and their activation by endogenous ligands like prostaglandin increases myometrial contractility. Thus, the TRPV4 channel can be an important target in reducing myometrial contractility in preterm labor.

Arachidonic acid inhibits Na+–K+–ATPase via cytochrome P-450, lipoxygenase and protein kinase C-dependent pathways in sheep pulmonary artery

The purpose of the study was to examine whether arachidonic acid inhibits vascular Na(+)-K(+)-ATPase in pulmonary vasculature and if so, what are the mechanisms involved. Functional Na(+)-K(+)-ATPase activity was studied in terms of K(+)-induced relaxation in sheep pulmonary arterial rings contracted with K(+)-free solution and 5-HT. Arachidonic acid (10-100 μM) caused concentration-dependent inhibition of KCl-induced relaxations and also increased basal arterial tone. Cytochrome P-450 inhibitor, 17-octadecynoic acid (17-ODYA) completely reversed the arachidonic acid (30 μM)-induced inhibition of KCl relaxation. Further, in the presence of HET0016, a selective blocker of 20-hydroxyeicosatetraenoic acid (20-HETE), arachidonic acid-induced inhibition of KCl relaxation was not evident. Accordingly, 20-HETE, a cytochrome P-450 metabolite of arachidonic acid, also significantly attenuated KCl-induced relaxations. Norhydihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, however, partially restored the relaxation to K(+), impaired in the presence of arachidonic acid (30 μM). On the other hand, cyclooxygenase inhibitor indomethacin failed to reverse the inhibitory effect of arachidonic acid on KCl-induced relaxation. Staurosporin, a protein kinase C inhibitor, completely reversed the inhibitory effect of arachidonic acid and 20-HETE on K(+)-induced relaxation. In conclusion, the results suggest that 20-HETE, a cytochrome P-450 metabolite of arachidonic acid has a predominant role in the inhibition of functional Na(+)-K(+)-ATPase activity in the sheep pulmonary artery, while the lipooxygenase pathway has a secondary role. It is also evident that protein kinase C is involved in the inhibition of Na(+)-K(+)-ATPase by arachidonic acid/20-HETE in sheep pulmonary artery.

NO synthase inhibition attenuates EDHF-mediated relaxation induced by TRPV4 channel agonist GSK1016790A in the rat pulmonary artery: Role of TxA2

BACKGROUND The aim of the present study was to observe the concomitant activation of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) pathways by TRPV4 channel agonist GSK1016790A in the rat pulmonary artery and explore the mechanism by which NO synthase inhibition attenuates EDHF-mediated relaxation in endothelium-intact rat pulmonary artery. METHODS Tension experiments were conducted on the pulmonary artery from male Wistar rats. RESULTS TRPV4 channel agonist GSK1016790A (GSK) caused concentration-dependent relaxation (Emax 86.9±4.6%; pD2 8.7±0.24) of the endothelium-intact rat pulmonary artery. Combined presence of apamin and TRAM-34 significantly attenuated the relaxation (Emax 61.1±6.0%) to GSK. l-NAME (100μM) significantly attenuated (8.2±2.9%) the relaxation response to GSK that was resistant to apamin plus TRAM-34. However, presence of ICI192605 or furegrelate alongwith l-NAME revealed the GSK-mediated EDHF-response (Emax of 28.5±5.2%; Emax 24.5±4.3%) in this vessel, respectively. Further, these two TxA2 modulators (ICI/furegrelate) alongwith l-NAME had no effect on SNP-induced endothelium-independent relaxation in comparison to l-NAME alone. This EDHF-mediated relaxation was sensitive to inhibition by K(+) channel blockers apamin and TRAM-34 or 60mMK(+) depolarizing solution. Further, combined presence of apamin and TRAM-34 in U46619 pre-contracted pulmonary arterial rings significantly reduced the maximal relaxation (Emax 71.6±6.9%) elicited by GSK, but had no effect on the pD2 (8.1±0.03) of the TRPV4 channel agonist in comparison to controls (Emax, 92.4±4.3% and pD2, 8.3±0.06). CONCLUSION The present study suggests that NO and EDHF are released concomitantly and NO synthase inhibition attenuates GSK-induced EDHF response through thromboxane pathway in the rat pulmonary artery.

Atorvastatin along with imipenem attenuates acute lung injury in sepsis through decrease in inflammatory mediators and bacterial load

Lung is one of the vital organs which is affected during the sequential development of multi-organ dysfunction in sepsis. The purpose of the present study was to examine whether combined treatment with atorvastatin and imipenem could attenuate sepsis-induced lung injury in mice. Sepsis was induced by caecal ligation and puncture. Lung injury was assessed by the presence of lung edema, increased vascular permeability, increased inflammatory cell infiltration and cytokine levels in broncho-alveolar lavage fluid (BALF). Treatment with atorvastatin along with imipenem reduced the lung bacterial load and pro-inflammatory cytokines (IL-1β and TNFα) level in BALF. The markers of pulmonary edema such as microvascular leakage and wet-dry weight ratio were also attenuated. This was further confirmed by the reduced activity of MPO and ICAM-1 mRNA expression, indicating the lesser infiltration and adhesion of inflammatory cells to the lungs. Again, expression of mRNA and protein level of iNOS in lungs was also reduced in the combined treatment group. Based on the above findings it can be concluded that, combined treatment with atorvastatin and imipenem dampened the inflammatory response and reduced the bacterial load, thus seems to have promising therapeutic potential in sepsis-induced lung injury in mice.