Bradykinin inhibits ceramide production and activates phospholipase D in rabbit cortical collecting duct cells.
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Recent reports suggest that inflammatory cytokines, growth factors, and vasoconstrictor peptides induce sphingomyelinase (SMase) activity. This results in the hydrolysis of sphingomyelin (SM) into ceramide, which is implicated in various cellular functions. Although ceramide regulates phospholipase D (PLD) activity, there is controversy about this relationship. Thus we investigated whether the effect of bradykinin (BK), a proinflammatory factor and vasodilator, was mediated by ceramide signal transduction and by PLD. In rabbit cortical collecting duct (RCCD) cells, BK increased SM levels and decreased ceramide levels in a time-dependent manner. Thus SMase activity was inhibited by BK. Also, the production of ceramide was regulated in a concentration-dependent manner. The BK-B1 antagonist [Lys-des-Arg9,Leu8]BK did not affect ceramide signal transduction but the BK-B2 antagonist (Hoe-140) blocked the effect of BK on SMase, suggesting that the BK-B2 receptor mediates BK-induced inhibition of ceramide generation. Our results show that exogenous SMase significantly hydrolyzed endogenous SM to form ceramide and weakly activated PLD. In contrast, BK induced a significant activation of PLD. However, additive effects of BK and ceramide on PLD activity were not observed. We concluded that in RCCD cells, the BK-induced second messengers ceramide and phosphatidic acid were generated by distinct signal transduction mechanisms, namely the SMase and PLD pathways. (+info)
TGF-alpha reduces bradykinin-stimulated ion transport and prostaglandin release in human colonic epithelial cells.
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The effect of chronic exposure to transforming growth factor-alpha (TGF-alpha) on bradykinin-stimulated acute prostanoid production and ion secretion in monolayers of HCA-7 colony 29 colonic epithelial cells has been studied. Monolayers synthesized prostaglandin E2 (PGE2) at a basal rate of 2.10 +/- 0.31 pg. monolayer-1. min-1 over 24 h. Bradykinin (10(-8)-10(-5) M) dose dependently increased acute PGE2 release by three orders of magnitude. This was associated with a rise in cAMP from 1.60 +/- 0.14 to 2.90 +/- 0.1 pmol/monolayer (P < 0.02) and a dose-dependent increase in short-circuit current (SCC). When monolayers were primed by a 24-h exposure to TGF-alpha, basal PGE2 release rose to 6.31 +/- 0.38 pg. monolayer-1. min-1 (TGF-alpha concn 10 ng/ml; P = 0.001). However, the stimulation of acute prostaglandin release, intracellular cAMP, and increased SCC by bradykinin was significantly reduced by preincubation with TGF-alpha. Priming with PGE2 (10(-8)-10(-6) M) over 24 h mimicked the effect of TGF-alpha on bradykinin-induced changes in cAMP and SCC. These data suggest that enhanced chronic release of prostaglandins in response to stimulation with TGF-alpha may downregulate acute responses to bradykinin. In vivo, TGF-alpha could have an important modulatory function in regulating secretion under inflammatory conditions. (+info)
Bradykinin-stimulated protein synthesis by myocytes is dependent on the MAP kinase pathway and p70(S6K).
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Bradykinin (BK) has a direct hypertrophic effect on rat ventricular cardiomyocytes (VCM) as defined by an increase in protein synthesis and an increase in atrial natriuretic peptide mRNA and secretion. In the current study, we have examined the dependence of BK-induced protein synthesis on activation of 90-kDa ribosomal S6 kinase (p90(rsk)) and 70-kDa S6 kinase (p70(S6K)). Both of these kinases possess the ability to phosphorylate the ribosomal protein S6, which plays an important role in initiating mRNA translation. Stimulation of adult VCM with 10 microM BK increased p90(rsk) activity by 2.5 +/- 0.3-fold and increased p70(S6K) activity by 2.0 +/- 0.3-fold. p90(rsk) is a terminal kinase in the mitogen-activated protein (MAP) kinase pathway. Inhibition of MAP kinase kinase activation by Raf in the MAP kinase pathway with PD-098059 (25 microM) blocked BK-stimulated activation of p90(rsk) by 70% and unexpectedly blocked p70(S6K) by 72%. Rapamycin inhibited BK-stimulated p70(S6K) activity by 93% but had no effect on p90(rsk) activation by BK. Inhibition of the MAP kinase pathway and p70(S6K) with PD-098059 was paralleled by changes in protein synthesis. BK (10 microM) increased [3H]phenylalanine incorporation by 27 +/- 3 and 39 +/- 6% in cultured adult and neonatal VCM, respectively. Treatment with PD-098059 or rapamycin abolished the increase in protein synthesis stimulated by BK. These results suggest that 1) BK activates p70(S6K) and p90(rsk); 2) although both p70(S6K) and p90(rsk) have the potential to phosphorylate the ribosomal S6 protein, p70(S6K) and not p90(rsk) is the predominant kinase involved in increasing protein synthesis by BK; and 3) p70(S6K) activation is dependent on stimulation of the MAP kinase pathway at a point distal to Raf. (+info)
BACKGROUND: Proximal tubule epithelial cells are in close contact with the renal microvasculature, but the effect of endothelial cells (ECs) on proximal tubule epithelial cell (PTEC) function is not known. METHODS: To determine if ECs regulate PTECs, we coincubated ECs with PTECs in a system that permitted cross-talk between the two cell types and the vectorial transport of sodium. RESULTS: In the presence (but not absence) of ECs, adding bradykinin or acetylcholine increased cGMP and decreased sodium transport, as well as Na,K-ATPase in PTECs. Interleukin (IL)1B preconditioning of ECs also increased cGMP and decreased sodium transport and Na,K-ATPase in PTECs. Bradykinin, acetylcholine, and IL1B EC-dependent effects were reversed with the nitric oxide (NO) synthase inhibitor L-NNA. In the absence of ECs, the addition of NO donors to PTECs increased cGMP and decreased sodium transport and Na,K-ATPase. 8Br-cGMP also decreased PTEC sodium transport and Na,K-ATPase. CONCLUSION: Endothelial cells regulate PTEC function. This effect is mediated by NO synthase-dependent up-regulation of cGMP in PTECs. (+info)
Tranexamic acid increases peritoneal ultrafiltration volume in patients on CAPD.
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OBJECTIVE: The preservation of ultrafiltration (UF) capacity is crucial to maintaining long-term continuous ambulatory peritoneal dialysis (CAPD).The aim of the present study was to investigate whether the antiplasmin agent tranexamic acid (TNA) increases UF volume in CAPD patients. PATIENTS AND METHODS: Fifteen patients on CAPD, 5 with UF loss and 10 without UF loss, were recruited for the study. The effect of TNA was evaluated with respect to changes in UF volume, peritoneal permeability, peritoneal clearance, bradykinin (BK), and tissue plasminogen activator (tPA) concentration. SETTING: Dialysis unit of the Saiseikai Central Hospital. RESULTS: In patients with UF loss, 2 weeks of treatment with oral TNA produced a significant increase in UF volume in all subjects (5/5).TNA also produced a significant increase in peritoneal clearances of urea and creatinine (Cr). However, the peritoneal equilibration test (PET) revealed that TNA had no effect on dialysate/plasma (D/P) Cr, Kt/V, or the protein catabolic rate (PCR).TNA also had no effect on net glucose reabsorption. In contrast, significant decreases in BK and blood tPA concentrations in response to TNA treatment were noted. BK concentration in drainage fluid was also reduced. In the case of patients without UF loss,TNA produced an increase in UF volume in 70% (7/10). However, no differences were found in blood and drainage BK and tPA concentrations between theTNA treatment and nontreatment periods in these patients. A comparison of basal BK and tPA concentration showed that there were no differences in these parameters between patients with UF loss and those without loss of UF. Furthermore,TNA given intraperitoneally to a patient also produced a marked increase in UF volume. CONCLUSION: The present study suggests thatTNA enhances UF volume in patients both with and without UF loss. SinceTNA did not affect peritoneal permeability and glucose reabsorption, the mechanism by which TNA exerts an enhancing action on UF is largely unknown. We speculate that it may be associated with suppression of the BK and/or tPA system, at least in patients with UF loss. (+info)
Pharmacological characterization of the bradykinin B2 receptor: inter-species variability and dissociation between binding and functional responses.
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1. The present study addresses the differences in binding profiles and functional properties of the human and rat bradykinin (BK) B2 receptor using various kinin receptor peptide derivatives as well as the non-peptide receptor antagonists WIN 64338 (phosphonium, [[4-[[2-[[bis(cyclohexylamino)methylene]amino]-3-(2-naphtalenyl)1- oxopropyl]amino]-phenyl]-methyl]tributyl, chloride, monohydro-chloride), and FR173657 (E)-3-(6-acetamido-3-pyridyl)-N-[-N-[2,4-dichloro-3-[(2-methyl-8-quinoli nyl)oxymethyl]-phenyl]N-methylamino carbonyl methyl] acrylamide. 2. [3H]-BK bound with a similar affinity to membranes of Chinese hamster ovary cells (CHO-K1) expressing the cloned human (hB2-CHO) or rat (rB2-CHO) B2 receptor, human embryonic intestine cells (INT407) expressing the native B2 receptor, human umbilical vein (HUV) and rat uterus (RU). WIN 64338 and FR173657 bound with a 3.8-6.6 fold and 7.0-16.3 fold higher affinity the rat than the human B2 receptor, respectively. The affinity values of BK derivatives as well as non-peptide antagonists were reduced by 6-23 fold in physiological HBSS compared to low ionic strength TES binding buffer. 3. BK (0.01-3000 nM) increased inositol triphosphates (IP3) levels in hB2-CHO, rB2-CHO and INT407 cells. The B2 receptor antagonist, Hoe 140 (D-Arg0-[ Hyp3, Thi5, D-Tic7, Oic8]-BK) at 10(-7) M, significantly shifted to the right the IP3 response curves to BK giving apparent pKB values of 8.56, 9.79 and 8.84 for hB2-CHO, rB2-CHO and INT407 cells, respectively. 4. In human isolated umbilical vein, Hoe 140, D-Arg0-[Hyp3, D-Phe7, Leu8]-BK and NPC 567 had a lower potency in functional assays (pKB 8.18, 5.77 and 5.60, respectively) than expected from their affinity in binding studies (pKi 10.52, 8.64 and 8.27, respectively). 5. FR173657 behaved as a high affinity ligand with pKi values of 8.59 and 9.81 and potent competitive antagonist with pKB values of 7.80 and 8.17 in HUV and RU, respectively. FR173657 bound with a similar affinity the cloned and native bradykinin B2 receptor in human (pKi of 8.66 and 8.59, respectively) and in rat (pKi 9.67 and 9.81, respectively). 6. In conclusion, we suggest that the binding buffer composition has to be taken into account when screening new compounds and that inter-species differences should be considered when setting up animal models with the aim of developing bradykinin B2 receptor antagonists as therapeutic agents. (+info)
Endogenous endothelial nitric oxide synthase-derived nitric oxide is a physiological regulator of myocardial oxygen consumption.
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Our objective was to determine the precise role of endothelial nitric oxide synthase (eNOS) as a modulator of cardiac O2 consumption and to further examine the role of nitric oxide (NO) in the control of mitochondrial respiration. Left ventricle O2 consumption in mice with defects in the expression of eNOS [eNOS (-/-)] and inducible NOS [iNOS (-/-)] was measured with a Clark-type O2 electrode. The rate of decreases in O2 concentration was expressed as a percentage of the baseline. Baseline O2 consumption was not significantly different between groups of mice. Bradykinin (10(-4) mol/L) induced significant decreases in O2 consumption in tissues taken from iNOS (-/-) (-28+/-4%), wild-type eNOS (+/+) (-22+/-4%), and heterozygous eNOS(+/-) (-22+/-5%) but not homozygous eNOS (-/-) (-3+/-4%) mice. Responses to bradykinin in iNOS (-/-) and both wild-type and heterozygous eNOS mice were attenuated after NOS blockade with N-nitro-L-arginine methyl ester (L-NAME) (-2+/-5%, -3+/-2%, and -6+/-5%, respectively, P<0.05). In contrast, S-nitroso-N-acetyl-penicillamine (SNAP, 10(-4) mol/L), which releases NO spontaneously, induced decreases in myocardial O2 consumption in all groups of mice, and such responses were not affected by L-NAME. In addition, pretreatment with bacterial endotoxin elicited a reduction in basal O2 consumption in tissues taken from normal but not iNOS (-/-)-deficient mice. Our results indicate that the pivotal role of eNOS in the control of myocardial O2 consumption and modulation of mitochondrial respiration by NO may have an important role in pathological conditions such as endotoxemia in which the production of NO is altered. (+info)
Kallidin- and bradykinin-degrading pathways in human heart: degradation of kallidin by aminopeptidase M-like activity and bradykinin by neutral endopeptidase.
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BACKGROUND: Since kinins kallidin (KD) and bradykinin (BK) appear to have cardioprotective effects ranging from improved hemodynamics to antiproliferative effects, inhibition of kinin-degrading enzymes should potentiate such effects. Indeed, it is believed that this mechanism is partly responsible for the beneficial effects of angiotensin-converting enzyme (ACE) inhibitors. In the heart, enzymes other than ACE may contribute to local degradation of kinins. The purpose of this study was to investigate which enzymes are responsible for the degradation of KD and BK in human heart tissue. METHODS AND RESULTS: Cardiac membranes were prepared from the left ventricles of normal (n=5) and failing (n=10) hearts. The patients had end-stage congestive heart failure as the result of coronary heart disease or idiopathic dilated cardiomyopathy. Heart tissue was incubated with KD or BK in the presence or absence of enzyme inhibitors. We found no difference in the enzymes responsible for kinin metabolism or their activities between normal and failing hearts. Thus KD was mostly converted into BK by the aminopeptidase M-like activity. When BK was used as substrate, it was converted into an inactive metabolite BK-(1-7) mostly (80% to 90%) by the neutral endopeptidase (NEP) activity, with ACE unexpectedly playing only a minor role. The low enzymatic activity of ACE in the cardiac membranes, compared with that of NEP, was not due to chronic ACE inhibitor therapy, because the cardiac ACE activities of patients, whether receiving ACE inhibitors or not, and of normal subjects were all equal. CONCLUSIONS: The present in vitro study shows that in human cardiac membranes, the most critical step in kinin metabolism, that is, inactivation of BK, appears to be mediated mostly by NEP. This observation suggests a role for NEP in the local control of BK concentration in heart tissue. Thus inhibition of cardiac NEP activity could be cardioprotective by elevating the local concentration of BK in the heart. (+info)