Stimulation of cyclic GMP production in cultured endothelial cells of the pig by bradykinin, adenosine diphosphate, calcium ionophore A23187 and nitric oxide

A novel murine in vivo model for acute hereditary angioedema attacks

Hereditary Angioedema (HAE) is a rare genetic disease generally caused by deficiency or mutations in the C1-inhibitor gene, SERPING1, a member of the Serpin family. HAE results in acute attacks of edema, vasodilation, GI pain and hypotension. C1INH is a key inhibitor of enzymes controlling complement activation, fibrinolysis and the contact system. In HAE patients, contact system activation leads to uncontrolled production of bradykinin, the vasodilator responsible for the characteristic symptoms of HAE. In this study, we present the first physiological in vivo model to mimic acute HAE attacks. We evaluate hypotension, one of the many hallmark symptoms of acute HAE attacks using Serping1 deficient mice (serping1−/−) and implanted telemetry. Attacks were induced by IV injection of a silica nanoparticle (SiNP) suspension. Blood pressure was measured in real time, in conscious and untethered mice using implanted telemetry. SiNP injection induced a rapid, reversible decrease in blood pressure, in the presence of angiotensin converting enzyme (ACE) inhibition. We also demonstrate that an HAE therapeutic, ecallantide, can prevent HAE attacks in this model. The in vivo murine model described here can facilitate the understanding of acute HAE attacks, support drug development and ultimately contribute to improved patient care.

Increased Reactive Oxygen Species Generation Contributes to the Atherogenic Activity of the B2 Bradykinin Receptor

Atherosclerosis and ensuing cardiovascular disease are major causes of death with insufficient treatment options. In search for pathomechanisms of atherosclerosis, we investigated the impact of the B2 bradykinin receptor, Bdkrb2, on atherosclerotic lesion formation, because to date it is not clear whether the B2 bradykinin receptor is atheroprotective or atherogenic. As a model of atherosclerosis, we used hypercholesterolemic ApoE-deficient (apolipoprotein E-deficient) mice, which develop atherosclerotic lesions in the aorta with increasing age. The role of Bdkrb2 in atherosclerosis was studied in ApoE-deficient mice, which were either Bdkrb2-deficient, or had moderately increased aortic B2 bradykinin receptor protein levels induced by transgenic BDKRB2 expression under control of the ubiquitous CMV promoter. We found that Bdkrb2 deficiency led to a significantly decreased atherosclerotic plaque area whereas transgenic BDKRB2 expression enhanced atherosclerotic lesion formation in the aorta of ApoE-deficient mice at an age of 8 months. Concomitantly, the aortic content of reactive oxygen species (ROS) was higher in BDKRB2-expressing mice whereas Bdkrb2 deficiency decreased aortic ROS levels of ApoE-deficient mice. In addition, aortic nitrate as a marker of nitric oxide activity and the endothelial nitric oxide synthase (eNOS) co-factor, tetrahydrobiopterin (BH4) were reduced in BDKRB2-expressing ApoE-deficient mice. The decreased aortic BH4 content could be a consequence of increased ROS generation and down-regulated aortic expression of the BH4-synthesizing enzyme, Gch1 (GTP cyclohydrolase 1). In agreement with a causal involvement of decreased BH4 levels in the atherogenic function of BDKRB2, we found that treatment with the BH4 analog, sapropterin, significantly retarded atherosclerotic plaque formation in BDKRB2-expressing ApoE-deficient mice. Together our data show that the B2 bradykinin receptor is atherogenic, and the atherosclerosis-promoting function of BDKRB2 is partially caused by decreased aortic BH4 levels, which could account for eNOS uncoupling and further enhancement of ROS generation.

[Vasoreactivity changes during extracorporeal circulation: effects of halogenated agents]

During cardiopulmonary bypass (CPB), endothelium is exposed to multiple disturbances leading to significant vasomotor tone and vascular systemic resistances (VSR) level modifications. Properties of endothelial function on vascular tone were summarized herein. According bibliographic findings, physiological and clinical impacts of respectively halogenated agents and CPB concerning vasomotor tone were reported. Main effects of halogenated agents administered through oxygenator during CPB were also identified. Usually when administered above one MAC, halogenated agents decreased VSR during hypothermic bypass. Once those mechanisms summarized, increase of halogenated agent's effects on VSR during normothermic CPB was postulated. Assuming that decrease of VSR could be deleterious favoring severe vasoplegia event, clinical experience of administration of isoflurane during CPB among more 4000 patients was retrospectively reported. Incidence of severe vasoplegia was established to 9.5 % in the studied population and this result was similar as others. More over predicting factors of severe vasoplegia were the same as previously reported : severity of preoperative clinical status according Euroscore, hemodynamical instability before induction of anesthesia, surgical procedure complexity and CPB duration. Absence of deleterious effects in SVR decrease when administering isoflurane during normothermic CPB was assumed but prospective comparative studies comparing effects of halogenated agents and other anesthetic agents are needed in order to confirm these findings.

Attenuation of Doxorubicin-induced cardiomyopathy by endothelin-converting enzyme-1 ablation through prevention of mitochondrial biogenesis impairment

Doxorubicin is an effective antineoplastic drug; however, its clinical benefit is limited by its cardiotoxicity. The inhibition of mitochondrial biogenesis is responsible for the pathogenesis of doxorubicin-induced cardiomyopathy. Endothelin-1 is a vasoconstrictive peptide produced from big endothelin-1 by endothelin-converting enzyme-1 (ECE-1) and a multifunctional peptide. Although plasma endothelin-1 levels are elevated in patients treated with doxorubicin, the effect of ECE-1 inhibition on doxorubicin-induced cardiomyopathy is not understood. Cardiomyopathy was induced by a single IP injection of doxorubicin (15 mg/kg). Five days after treatment, cardiac function, histological change, and mitochondrial biogenesis were assessed. Echocardiography revealed that cardiac systolic function was significantly deteriorated in doxorubicin-treated wild-type (ECE-1(+/+)) mice compared with ECE-1 heterozygous knockout (ECE-1(+/-)) mice. In histological analysis, cardiomyocyte size in ECE-1(+/-) mice was larger, and cardiomyocyte damage was less. In ECE-1(+/+) mice, tissue adenosine triphosphate content and mitochondrial superoxide dismutase were decreased, and reactive oxygen species generation was increased compared with ECE-1(+/-) mice. Cardiac mitochondrial deoxyribonucleic acid copy number and expressions of key regulators for mitochondrial biogenesis were decreased in ECE-1(+/+) mice. Cardiac cGMP content and serum atrial natriuretic peptide concentration were increased in ECE-1(+/-) mice. In conclusion, the inhibition of ECE-1 attenuated doxorubicin-induced cardiomyopathy by inhibiting the impairment of cardiac mitochondrial biogenesis. This was mainly induced by decreased endothelin-1 levels and an enhanced atrial natriuretic peptide-cGMP pathway. Thus, the inhibition of ECE-1 may be a new therapeutic strategy for doxorubicin-induced cardiomyopathy.

Nitric oxide ventilation of rat lungs from non-heart-beating donors improves posttransplant function

Lungs from non-heart-beating donors (NHBDs) would enhance the donor pool. Ex vivo perfusion and ventilation of NHBD lungs allows functional assessment and treatment. Ventilation of rat NHBD lungs with nitric oxide (NO) during ischemia, ex vivo perfusion and after transplant reduced ischemia-reperfusion injury (IRI) and improved lung function posttransplant. One hour after death, Sprague-Dawley rats were ventilated for another hour with either 60% O2 or 60% O2/40 ppm NO. Lungs were then flushed with 20-mL cold Perfadex, stored cold for 1 h, perfused in an ex vivo circuit with Steen solution and warmed to 37 degrees C, ventilated 15 min, perfusion-cooled to 20 degrees C, then flushed with cold Perfadex and stored cold. The left lung was transplanted and ventilated separately. Recipients were sacrificed after 1 h. NO-ventilation was associated with significantly reduced wet:dry weight ratio in the ex vivo circuit, better oxygenation, reduced pulmonary vascular resistance, increased lung tissue levels of cGMP, maintained endothelial NOS eNOS, and reduced increases in tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS). NO-ventilation had no effect on MAP kinases or NF-kappaB activation. NO administration to NHBDs before and after lung retrieval may improve function of lungs from NHBDs.

Heparin reverses anaphylactoid shock in a porcine model

STUDY OBJECTIVE

Heparin binds histamine and has been advocated as a therapy for anaphylactic and anaphylactoid shock. The efficacy of heparin in treating anaphylactoid shock is compared with therapy with diphenhydramine and epinephrine, as well as sham treatment with saline.

METHODS

This controlled study of 9 anesthetized, intubated pigs induced shock with intravenous calcium ionophore A23187 (5 mg/kg), which is known to degranulate mast cells in vitro. Serum histamine levels were measured using an enzyme-linked immunosorbent assay. Shock, defined as a greater than 20% decrease in mean arterial blood pressure, was treated with intravenous saline, epinephrine with diphenhydramine, or heparin. Data were analyzed using Wilcoxon rank sum and analysis of variance, as appropriate.

RESULTS

All pigs developed anaphylactoid shock after injection with A23187, as evidenced by hypotension, flushing, and an increase in plasma histamine. Mean arterial blood pressure fell from a mean of 73 (SD 10) mm Hg to 28 (SD 16) mm Hg after injection (P<.001; 95% confidence interval [CI] of the difference in pressures 34 to 57 mm Hg). Mean serum histamine levels increased from 712 micromol/dL (SD 731) to 1,154 micromol/dL (SD 799) after injection (Z value -2.201; P=.0277; 95% CI of the difference -610 to -99). Both epinephrine with diphenhydramine and heparin but not saline reversed shock.

CONCLUSION

A23187 induced anaphylactoid shock in all subjects. Therapy with intravenous epinephrine combined with diphenhydramine reversed shock. Heparin also rapidly reversed shock.

Nitric Oxide Synthase in Spontaneously Hypertensive Rats

Since its discovery by Furchgott and Zawadzki in 1980 [18], endothelium-derived relaxing factor (EDRF) has been shown to play a central role in the cardiovascular system [10]. The endothelial product is chemically equivalent to nitric oxide (NO) [23, 40] or a biochemical congener thereof [48]. Fifteen years ago, this small, simple and highly toxic molecule was known as a lengthy list of environmental pollutants found in unsavory haunts such as smoke and smog, and even as destroyer of ozone, suspected carcinogen, and precursor of acid rain. In addition, NO seems an unlikely biological jack of all trades for most of the body's functions are regulated by extraordinarily large and complex proteins and compounds. But over the past decade, diverse lines of evidence have converged to show that this sometime poison is a fundamental player in the everyday business of the human body.

Update on pulmonary edema: the role and regulation of endothelial barrier function

Discovery of the pathophysiologic mechanisms leading to pulmonary edema and identification of effective strategies for prevention remain significant clinical concerns. Endothelial barrier function is a key component for maintenance of the integrity of the vascular boundary in the lung, particularly since the gas exchange surface area of the alveolar-capillary membrane is large. This review is focused on new insights in the pulmonary endothelial response to injury and recovery, reversible activation by edemagenic agents, and the biochemical/structural basis for regulation of endothelial barrier function. This information is discussed in the context of fundamental concepts of lung fluid balance and pulmonary function.

Angiotensin II-stimulated nitric oxide release from porcine pulmonary endothelium is mediated by angiotensin IV

In this study, a nitric oxide (NO) sensor was used to examine the ability of angiotensin II (AngII), AngIV, and bradykinin (Bk) to stimulate NO release from porcine pulmonary artery (PPAE) and porcine aortic endothelial (PAE) cells and to explore the mechanism of the AngII-stimulated NO release. Physiologic concentrations of AngII, but not Bk, caused release of NO from PPAE cells. In contrast, Bk, but not AngII, stimulated NO release from PAE cells. AngIII-stimulated NO release from PPAE cells required extracellular L-arginine and was inhibited by L-nitro-arginine methyl ester. AT1 and AT2 receptor inhibition had no affect on AngII-mediated NO release or activation of NO synthase (NOS). AngIV, an AngII metabolite with binding sites that are pharmacologically distinct from the classic AngII receptors, stimulated considerably greater NO release and greater endothelial-type constitutive NOS activity than the same amount of AngII. The AngIV receptor antagonist, divalinal AngIV, blocked both AngII- and AngIV-mediated NO release as well as NOS activation. The results demonstrate that AngIV and the AngIV receptor are responsible, at least in part, for AngII-stimulated NO release and the associated endothelium-dependent vasorelaxation. Furthermore, these results suggest that differences exist in both AngII- and Bk-mediated NO release between PPAE and PAE cells, which may reflect important differences in response to these hormones between vascular beds.

Changes in plasma levels of cyclic nucleotides during low-density lipoprotein apheresis

The negative charges of dextran sulfate (DS) used for low-density lipoprotein (LDL) apheresis activate the intrinsic coagulation pathway, accompanied by the production of bradykinin. This study was undertaken to see whether cyclic nucleotide plasma levels are affected by DS LDL apheresis. Previously, we showed the rise in plasma levels of prostaglandins and nitric oxide derivatives accompanied by the rise in bradykinin levels. The physiologic effects of prostaglandins and nitric oxide become manifest through the intracellular signal of cyclic nucleotides. The plasma levels of the cyclic nucleotides (cyclic adenosine monophosphate [cAMP] and cyclic guanosine monophosphate [cGMP]) were examined when either of 2 anticoagulants, heparin or nafamostat mesilate (NM), was used during DS LDL apheresis. The plasma levels of cAMP during LDL apheresis using heparin were 9.2 +/- 0.3 (mean +/- SE) 12.4 +/- 0.6, 12.0 +/- 0.5, and 12.1 +/- 0.3 pmol/ml, respectively, at the 0, 1,000, 2,000, and 3,000 ml stages. The rise in cAMP levels was suppressed during apheresis using NM. There were no significant increases in cGMP during apheresis with heparin or with NM. There were significant negative correlations between changes in cAMP and those in the blood pressure. These findings suggest that bradykinin generated during apheresis exerts some physiologic effects via activation of the adenylate cyclase dependent pathway.

Cyclic AMP mediates endothelial protection by nitric oxide

Incubation with TNF-alpha (50 ng/ml) for 72 hours markedly reduced viability of endothelial cells. A 6-hour preincubation with S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 3-100 microM) protected cells in a concentration-dependent manner and decreased TNF-alpha-mediated toxicity by up to 70%. Cytoprotection by SNAP was completely abolished by the adenylyl cyclase inhibitor 2', 5'-dideoxyadenosine and mimicked by 8-bromo cyclic AMP or forskolin. SNAP produced significant increases in cyclic GMP and cyclic AMP, both being abrogated in the presence of the NO scavenger 2-phenyl-4, 4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). Moreover, no endothelial protection by SNAP was detected in the presence of the protein kinase A inhibitor KT5720, whereas the protein kinase G inhibitor KT5823 left cytoprotection virtually unaltered. Our results demonstrate a crucial role for cyclic AMP in mediating NO-induced endothelial protection against TNF-alpha, possibly through cyclic GMP-dependent inhibition of cyclic AMP breakdown. NO-dependent endothelial protection may ultimately result from cyclic AMP-induced up-regulation of antioxidant proteins or down-regulation of cytotoxic processes.

Identification of cytokeratin 1 as a binding protein and presentation receptor for kininogens on endothelial cells

A kininogen binding protein(s), a putative receptor, was identified on endothelial cells. A 54-kDa protein was isolated by a biotin-high molecular mass kininogen (HK) affinity column that, on aminoterminal sequencing of tryptic digests, was identified as cytokeratin 1. Multiple antibodies directed to cytokeratin 1 reacted with a 54-kDa band on immunoblot of lysates of endothelial cells. On laser scanning confocal microscopy, cytokeratin 1 antigen was found on the surface of endothelial cells. Cytokeratin 1 antigen also was detected on endothelial cell membranes by flow cytometry. Moreover, an antipeptide antibody to a sequence unique to cytokeratin 1 also specifically bound to nonpermeabilized endothelial cells. Biotin-HK specifically bound to cytokeratin only in the presence of Zn2+, and cytokeratin blocked biotin-HK binding to endothelial cells. Further, HK and low molecular mass kininogen, but not factor XII, blocked biotin-HK binding to cytokeratin, and peptides of each cell binding region of HK on domains 3,4, and 5 blocked biotin-HK binding to cytokeratin. gC1qR and soluble urokinase-like plasminogen activator receptor also inhibited biotin-HK binding to cytokeratin. These investigations identify a new function for cytokeratin 1 as a kininogen binding protein. Cytokeratins, members of the family of intermediate filament proteins, may represent a new class of receptors.

Characteristics of the in vitro vasoactivity of beta-amyloid peptides

The beta-amyloid (A beta 1-40) peptide has previously been shown to enhance phenylephrine contraction of aortic rings in vitro. We have employed a novel observation, that A beta peptides enhance endothelin-1 (ET-1) contraction, to examine the relationship between vasoactivity and potential amyloidogenicity of A beta peptides, the role played by free radicals and calcium in the vasoactive mechanism, and the requirement of an intact endothelial layer for enhancement of vasoactivity. Rings of rat aortae were constricted with ET-1 before and after addition of amyloid peptide and/or other compounds, and a comparison was made between post- and pre-treatment contractions. In this system, vessel constriction is consistently dramatically enhanced by A beta 1-40, is enhanced less so by A beta 1-42, and is not enhanced by A beta 25-35. The endothelium is not required for A beta vasoactivity, and calcium channel blockers have a greater effect than antioxidants in blocking enhancement of vasoconstriction by A beta peptides. In contrast to A beta-induced cytotoxicity, A beta-induced vasoactivity is immediate, occurs in response to low doses of freshly solubilized peptide, and appears to be inversely related to the amyloidogenic potential of the A beta peptides. We conclude that the mechanism of A beta vasoactivity is distinct from that of A beta cytotoxicity. Although free radicals appear to modulate the vasoactive effects, the lack of requirement for endothelium suggests that loss of the free radical balance (between NO and O2-) may be a secondary influence on A beta enhancement of vasoconstriction. These effects of A beta on isolated vessels, and reported effects of A beta in cells of the vasculature, suggest that A beta-induced disruption of vascular tone may be a factor in the pathogenesis of cerebral amyloid angiopathy and Alzheimer's disease. Although the mechanism of enhanced vasoconstriction is unknown, it is reasonable to propose that in vivo contact of A beta peptides with small cerebral vessels may increase their tendency to constrict and oppose their tendency to relax. The subclinical ischemia resulting from this would be expected to up-regulate beta APP production in and around the vasculature with further increase in A beta formation and deposition. The disruptive and degenerative effects of such a cycle would lead to the complete destruction of cerebral vessels and consequently neuronal degeneration in the affected areas.

B1 bradykinin receptors and carboxypeptidase M are both upregulated in the aorta of pigs after LPS infusion

Bradykinin receptor subtypes were characterized in aortic cryosections obtained from healthy normal pigs, animals that were given an LPS infusion, and animals that came with a pre-existing infection or inflammation to the laboratory by binding studies and in vitro autoradiography. In control aorta a single class of high affinity B2 binding sites, located within the endothelium, but with no significant binding of B1 ligand were identified. No major changes in the expression of B2 BK receptors were noted in inflammed tissues. In cryosections of inflammed vascular tissue a markedly increased endothelial carboxypeptidase M activity was verified that parallelled an upregulation of B1 receptors in the aortic smooth muscle layer. In crosstalk between endothelial cells and smooth muscle cells B1 receptor mediated functional responses may counteract some of the detrimental effects of inflammation.

Changes in plasma levels of nitric oxide derivative during low-density lipoprotein apheresis

The negative charges of dextran-sulfate (DS) used for low-density lipoprotein (LDL) apheresis activates the intrinsic coagulation pathway, in which plasma kallikrein acts on high-molecular-weight kininogen (HMWK) to produce large amounts of bradykinin. This study was undertaken to see whether bradykinin generated during DS LDL apheresis has some physiologic effects in vivo. The plasma levels of bradykinin and nitric oxide derivatives (NOx) were examined when either of 2 anticoagulants, heparin or nafamostat mesilate (NM), was used during DS LDL apheresis. Although anticoagulative action by NM depends on the inhibition of thrombin activity, this substance also inhibits the activity of plasma kallikrein. During apheresis using heparin, the marked increase in bradykinin levels (before apheresis, 18 +/- 3 (mean +/- SE, n = 5) pg/ml; after apheresis 470 +/- 140, p < 0.01) was associated with the increase in NOx (before apheresis 50 +/- 11 pg/ml; after apheresis 66 +/- 15). Interestingly, these changes in bradykinin and NOx levels were suppressed during apheresis using NM. The changes in plasma NOx levels were negatively correlated with those in blood pressures. These findings suggest that bradykinin generated during apheresis exerts some physiologic effects by means of activation of endothelium-derived relaxant factor (EDRF). Our results support the view that bradykinin produced during DS LDL apheresis has physiologic significance.

Pyridoxalated hemoglobin polyoxyethylene conjugate does not restore hypoxic pulmonary vasoconstriction in ovine sepsis

OBJECTIVES

Hypoxic pulmonary vasoconstriction, a protective mechanism, minimizes perfusion of underventilated lung areas to reduce ventilation-perfusion mismatching. We studied the effects of sepsis on hypoxic pulmonary vasoconstriction and attempted to determine whether hypoxic pulmonary vasoconstriction is influenced by pyridoxalated hemoglobin polyoxyethylene conjugate, a nitric oxide scavenger.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational intensive care unit at a university medical center.

SUBJECTS

Nineteen female merino sheep, divided into three groups: group 1, controls (n = 5); group 2, sheep with sepsis (n = 6); and group 3, septic sheep treated with pyridoxalated hemoglobin polyoxyethylene conjugate (n = 8).

INTERVENTIONS

All sheep were instrumented for chronic study. An ultrasonic flow probe was placed around the left pulmonary artery. After a 5-day recovery, a tracheostomy was performed and a double-lumen endotracheal tube was placed. Animals in groups 2 and 3 received a 48-hr infusion of live Pseudomonas aeruginosa (6 x 10(4) colony-forming units/kg/hr). After 24 hrs, sheep in group 3 received pyridoxalated hemoglobin polyoxyethylene conjugate (20 mg/kg/hr) for 16 hrs; sheep in groups 1 and 2 received only the vehicle. Hypoxic pulmonary vasoconstriction was repeatedly tested by unilateral hypoxia of the left lung with 100% nitrogen. Hypoxic pulmonary vasoconstriction was assessed as the change in left pulmonary blood flow.

MEASUREMENTS AND MAIN RESULTS

In the animals in group 1, left pulmonary blood flow decreased by 62 +/- 8 (SEM)% during left lung hypoxia and remained stable during repeated hypoxic challenges throughout the study period. After 24 hrs of sepsis, left pulmonary blood flow decreased from 56 +/- 10% to 26 +/- 2% (group 2) and from 50 +/- 8% to 23 +/- 6% (group 3). In the sheep in group 2, there was no adaptation over time. Pulmonary shunt fraction increased. Pyridoxalated hemoglobin polyoxyethylene conjugate had no effect on hypoxic pulmonary vasoconstriction or pulmonary shunt. The animals receiving the bacterial infusion developed a hyperdynamic circulatory state with hypotension, decreased systemic vascular resistance, and increased cardiac output. Pyridoxalated hemoglobin polyoxyethylene conjugate increased mean arterial pressure and systemic vascular resistance but did not influence cardiac index. Pulmonary arterial pressure was increased during sepsis and increased even further after pyridoxalated hemoglobin polyoxyethylene conjugate administration. Oxygenation and oxygen delivery and uptake were not affected by pyridoxalated hemoglobin polyoxyethylene conjugate.

CONCLUSIONS

Hypoxic pulmonary vasoconstriction is blunted during sepsis and there is no adaptation over time. It is not influenced by pyridoxalated hemoglobin polyoxyethylene conjugate. Pyridoxalated hemoglobin polyoxyethylene conjugate reversed hypotension and, with the exception of an increase in pulmonary arterial pressure, had no adverse effects on hemodynamics or oxygenation.

Nitric oxide and cGMP regulate endothelial permeability and F-actin distribution in hydrogen peroxide-treated endothelial cells

We have previously reported that hydrogen peroxide (H2O2) has a concentration-dependent effect on endothelial permeability and F-actin distribution. In the present study, we considered the involvement of endogenous production of nitric oxide (NO) in the indicated effect of H2O2. This was done by measuring endothelial permeability to sodium fluorescein (MW 376 Da, Na-F) and to different-sized fluorescein-isothiocynate-labeled dextrans (FITC-dextrans) and by staining F-actin with rhodamine-labeled phalloidin in cultured bovine aortic endothelial cells growing on filters. A low concentration of H2O2 (10(-5) M) had no effect on either dense peripheral bands of F-actin (DPBs) or permeability. When N-nitro-l-arginine methylester (l-NAME), an inhibitor of NO production, was coadministrated with 10(-5) M H2O2, DPBs were disrupted and the permeability to FITC-dextran 40 and FITC-dextran 70, but not to Na-F and FITC-dextran 20, was increased. Combining of 10(-5) M H2O2 with l-arginine, a substrate for nitric oxide synthase, caused an increase in DPBs and a decrease in permeability to FITC-dextran 40 and FITC-dextran 70. l-arginine or l-NAME alone had no effect on either F-actin structure or endothelial permeability. A 10-fold higher concentration of H2O2 caused a disruption of DPBs and an increase in permeability; this could be prevented by adding l-arginine. An analogue of cGMP, i.e., 8-Br-cGMP, maintained DPBs and abolished the increase in permeability induced by the treatment with either 10(-4) M H2O2 or a combination of H2O2 and l-NAME. These results suggest that the endogenous production of NO is involved in maintaining endothelial junctions in H2O2-treated cells and that this involvement occurs via a cGMP-dependent mechanism.

Induction of endothelial cell injury by cigarette smoke

Cigarette smoke contains different populations of free radicals which may be responsible for endothelial cell (EC) injury of smokers. The purpose of this study was to examine the effects of gas-phase cigarette smoke on EC endothelium-derived relaxing factor (EDRF)/NO-guanylate cyclase (GC)-cGMP pathway and on EC detachment-type injury after incubation with smoke. Furthermore, we examined whether different kind of antioxidants can prevent smoke-caused EC injury. We measured cGMP pathway using direct (sodium nitroprusside, SNP) and indirect (A23187, the calcium ionophore and bradykinin, BK) activators of GC. Directly and indirectly stimulated EC cGMP production dose-dependently decreased and EC detachment increased after incubation with smoke. Externally added thiols (glutathione, GSH; D-Penicillamine, DP; N-acetylcysteine, NAC) protected EC from damage of cGMP production and cell detachment. Other antioxidants (catalase, deferoxamine and superoxide dismutase) were ineffective. These results suggest that the thiol containing GC in EC is destroyed or inactivated or thiol like species responsible for activation of GC is incomplete in EC after incubation with smoke. It is also possible that externally added thiols bind an unknown component of smoke and this way, EC is protected. EC injury may contribute to vascular diseases associated with cigarette smoking.

The renin-angiotensin system and vascular hypertrophy

In addition to its vasoconstrictor and aldosterone-stimulating action, angiotensin II also drives cell growth and replication in the cardiovascular system, which may result in myocardial hypertrophy and hypertrophy or hyperplasia of conduit and resistance vessels in certain subjects. These actions are mediated through angiotensin II receptors (subtype AT1), which activate the G protein, phospholipase C, diacylglycerol and inositol trisphosphate pathway, to increase the expression of certain protooncogenes (c-fos, c-myc and c-jun) and growth factors (platelet-derived growth factor-A-chain, transforming growth factor-beta 1 and basic fibroblast growth factor). The cellular responses to angiotensin II in vascular smooth muscle have been shown in different hypertensive vessels to be either hypertrophy alone, hypertrophy and DNA synthesis without cell division (polyploidy) or DNA synthesis with cell division (hyperplasia). In genetic hypertension, the altered structure of small arteries is due to either cellular hyperplasia or remodeling, whereas in renovascular hypertension there is hypertrophy of vascular smooth muscle cells. Angiotensin II also increases synthesis of some matrix components, activates blood monocytes and is thrombogenic. Angiotensin-converting enzyme (ACE) inhibitors prevent or reverse vascular hypertrophy in animal models of hypertension; this seems to be a class effect, shared to some extent with calcium channel blocking agents. In human hypertension, ACE inhibitors reduce the increased media/lumen ratio of large and small arteries in hypertension and increase arterial compliance. These properties are also shared by losartan, the first of the new class of angiotensin II receptor (AT1) antagonists. The clinical implications of these findings need to be tested through rigorous and prospective clinical trials.

Contribution of sustained Ca2+ elevation for nitric oxide production in endothelial cells and subsequent modulation of Ca2+ transient in vascular smooth muscle cells in coculture

To elucidate the intracellular Ca2+ (Ca2+i ) transient responsible for nitric oxide (NO) production in endothelial cells (ECs) and the subsequent Ca2+i reduction in vascular smooth muscle cells (VSMCs), we administrated four agonists with different Ca2+i-mobilizing mechanisms for both cells in iso- or coculture. We monitored the Ca2+i of both cells by two-dimensional fura-2 imaging, simultaneously measuring NO production as NO2-. The order of potency of the agonists in terms of the peak Ca2+i in ECs was bradykinin (100 nM) > ATP (10 microM) > ionomycin (50 nM) > thapsigargin (1 microM). In contrast, the order in reference to both the extent of Ca2+i reduction in cocultured VSMCs and the elevation in NO production over the level of basal release in ECs completely matched and was ranked as thapsigargin > ionomycin > ATP > bradykinin. Treatment by NG-monomethyl-L-arginine monoacetate but not indomethacin or glybenclamide restored the Ca2+i response in cocultured VSMCs to the isoculture level. In ECs, when the Ca2+ influx was blocked by Ni2+ or by chelating extracellular Ca2+, all four agonists markedly decreased NO production, the half decay time of the Ca2+i degenerating phase, and the area under the Ca2+i curve. The amount of produced NO hyperbolically correlated to the half decay time and the area under the Ca2+i curve but not to the Ca2+i peak level. Thus, the sustained elevation of Ca2+i in ECs, mainly a result of Ca2+ influx, determines the active NO production and subsequent Ca2+i reduction in adjacent VSMCs. Furthermore, L-arginine but not D-arginine or L-lysine at high dose (5 mM) without agonist enhanced the NO production, weakly reduced the Ca2+i in ECs, and markedly decreased the Ca2+i in VSMCs, demonstrating the autocrine and paracrine effects of NO (Shin, W. S., Sasaki, T., Kato, M., Hara, K., Seko, A., Yang, W. D., Shimamoto, N., Sugimoto, T., and Toyo-oka, T. (1992) J. Biol. Chem. 267, 20377-20382).

The mechanisms of the renal effects of neutral endopeptidase inhibitor in rats

To further investigate the mechanisms of renal effects of neutral endopeptidase 24.11 (NEP) inhibition, we employed a specific NEP inhibitor, UK 73967 (UK), with or without a specific kinin receptor antagonist, Hoe 140 (Hoe), or nitric oxide (NO) synthase inhibitor, N-monomethyl-L-arginine (L-NMMA), in Sprague-Dawley rats, and evaluated the urinary NEP, kinins, cGMP and plasma atrial natriuretic peptide (ANP). None of the variables changed with vehicle injection. After injection of UK, NEP decreased significantly and urinary kinins, cGMP, urine volume (UV) and urinary sodium excretion (UNaV) increased significantly. Injected Hoe canceled the increase in UV and UNaV induced by UK. Plasma ANP did not show any difference between vehicle and UK groups. With a pretreatment of L-NMMA, injected UK decreased NEP and increased kinins, while urinary cGMP, UV and UNaV did not increase. In conclusion, augmented kinins may play an important role in the renal water-sodium metabolism by NEP inhibition, and NO may contribute to the kinins' action on this mechanism, while ANP may not contribute to it, at least in normotensive rats. Moreover, changes in urinary cGMP do not reflect the changes in plasma ANP, but rather, those in NO under this condition.

Rolipram increases cyclic GMP content in L-arginine-treated cultured bovine aortic endothelial cells

Cultured bovine aortic endothelial cells only contain two cyclic nucleotide phosphodiesterases isoforms: PDE II (cyclic GMP stimulated) and PDE IV (rolipram sensitive). The effects of cilostamide or rolipram alone or together, on cyclic AMP and cyclic GMP levels, were measured in indomethacin-treated endothelial cells alone or in the presence of nitric oxide (NO) modulators. In all conditions, cyclic AMP levels were potently increased (8-13-fold) only when PDE II and PDE IV inhibitors were given together. Cyclic GMP levels were not modified by these PDE inhibitors in control and NG-nitro-L-arginine-methyl ester-treated cells. But surprisingly, in L-arginine-treated cells, cyclic GMP content was increased by 42% by rolipram alone, and combination of rolipram with cilostamide resulted in a further increase in cyclic GMP content (to 153% compared to control cells). These results suggest that in presence of the NO synthase substrate (L-arginine), an increase in cyclic AMP level may upregulate the L-arginine/NO/cyclic GMP pathway.

cGMP and nitric oxide modulate thrombin-induced endothelial permeability. Regulation via different pathways in human aortic and umbilical vein endothelial cells

Previous studies have demonstrated that cGMP and cAMP reduce the endothelial permeability for fluids and macromolecules when the endothelial permeability is increased by thrombin. In this study, we have investigated the mechanism by which cGMP improves the endothelial barrier function and examined whether nitric oxide (NO) can serve as an endogenous modulator of endothelial barrier function. Thrombin increased the passage of macromolecules through human umbilical vein and human aortic endothelial cell monolayers and concomitantly increased [Ca]2+ in vitro. Inhibition of these increases by the intracellular Ca2+ chelator BAPTA indicated that cytoplasmic Ca2+ elevation contributes to the thrombin-induced increase in endothelial permeability. The cGMP-dependent protein kinase activators 8-bromo-cGMP (8-Br-cGMP) and 8-(4-chlorophenylthio)cGMP (8-PCPT-cGMP) decreased the thrombin-induced passage of macromolecules. Two pathways accounted for this observation. Activation of cGMP-dependent protein kinase by 8-PCPT-cGMP decreased the accumulation of cytoplasmic Ca2+ in aortic endothelial cells and hence reduced the thrombin-induced increase in permeability. On the other hand, in umbilical vein endothelial cells, cGMP-inhibited phosphodiesterase (PDE III) activity was mainly responsible for the cGMP-dependent reduction of endothelial permeability. The PDE III inhibitors Indolidan (LY195115) and SKF94120 decreased the thrombin-induced increase in permeability by 50% in these cells. Thrombin treatment increased cGMP formation in the majority of, but not all, cell cultures. Inhibition of NO production by NG-nitro-L-arginine methyl ester (L-NAME) enhanced the thrombin-induced increase in permeability, which was restricted to those cell cultures that displayed an increased cGMP formation after addition of thrombin. Simultaneous elevation of the endothelial cGMP concentration by atrial natriuretic factor, sodium nitroprusside, or 8-Br-cGMP prevented the additional increase in permeability induced by L-NAME. These data indicate that cGMP reduces thrombin-induced endothelial permeability by inhibition of the thrombin-induced Ca2+ accumulation and/or by inhibition of cAMP degradation by PDE III. The relative contribution of these mechanisms differs in aortic and umbilical vein endothelial cells. NO can act in vitro as an endogenous permeability-counteracting agent by raising cGMP in endothelial cells of large vessels.

Coronary vasoconstriction in the conscious rabbit following intravenous infusion of L-NG-nitro-arginine

Intravenous infusion of L-NG-nitro-arginine, an inhibitor of endothelial nitric oxide (NO) synthesis, produced vasoconstriction in the coronary, cerebral, renal and duodenal vascular beds of the conscious rabbit. In this study, using radiolabelled microspheres, we provide in vivo evidence for a basal NO-dependent vasodilator tone in the coronary vascular bed.

Escherichia coli endotoxin inhibits agonist-mediated cytosolic Ca2+ mobilization and nitric oxide biosynthesis in cultured endothelial cells

Altered release of endothelium-derived relaxing factor/nitric oxide (EDRF/NO) has been proposed as a final common pathway underlying the abnormal vasodilator responses to gram-negative lipopolysaccharide (endotoxin). However, mechanisms responsible for lipopolysaccharide-induced changes in EDRF/NO release from endothelial cells have not been clarified. We evaluated direct effects of Escherichia coli endotoxin on agonist-stimulated cytosolic Ca2+ mobilization and NO biosynthesis in cultured bovine and porcine aortic endothelial cells (ECs). Two methods were used to assay for NO: (1) analysis of NO-induced endothelial levels of cGMP as a biological indicator of NO generation and (2) direct quantitative measurement of NO release (chemiluminescence method). Cytosolic free Ca2+ ([Ca2+]i) was evaluated using fura 2 fluorescence methodology (340/380-nm ratio excitation and 500-nm emission). Incubation of ECs with endotoxin (0.5 microgram/mL, 1 hour plus 1-hour wash) significantly inhibited bradykinin (100 nmol/L)- and ADP (10 mumol/L)-mediated increases in endothelial cell cGMP to 37% and 22% of control responses, respectively. In contrast, endotoxin failed to inhibit the increase in cGMP produced by the non-receptor-dependent Ca2+ ionophore A23187 (1 mumol/L) or sodium nitroprusside (1 mmol/L). Similarly, incubation with endotoxin inhibited ADP-stimulated increases in NO release and EDRF bioactivity to 55% and 56% of control values, respectively, but did not affect A23187-stimulated increases in NO release or EDRF bioactivity. Endotoxin produced significant decreases in both transient and sustained [Ca2+]i responses of ECs to bradykinin and ADP. For example, the initial rapid increase in bovine EC [Ca2+]i in response to bradykinin was reduced to 31% of the initial increases in control cells, and the secondary plateau phase was reduced to only 3% of respective control responses. Concentration-response relation to endotoxin (10(-3)) to 10(0) micrograms/mL) indicated high correlation and similar IC50 values (0.025 and 0.021 micrograms/mL, respectively) for inhibitory effects on cGMP and [Ca2+]i. Endotoxin had no effect on inositol trisphosphate formation ([3H]myo-inositol incorporation) and intracellular Ca2+ release ([Ca2+]i responses in Ca(2+)-free medium) induced by bradykinin. However, agonist-stimulated Mn2+ quenching (index of Ca2+ influx) was significantly attenuated by endotoxin treatment. These studies demonstrate that endotoxin directly decreases agonist (bradykinin and ADP)-mediated biosynthesis and release of EDRF/NO from ECs. These effects can be explained by altered [Ca2+]i mobilization mechanisms, which in turn produce subsequent decreases in activity of the Ca(2+)-calmodulin-dependent constitutive isoform of NO synthase and, ultimately, impairment of agonist-mediated NO release and endothelium-dependent vasodilation.

Nitric oxide pathway-mediated relaxant effect of bradykinin in the guinea-pig isolated trachea

1. The effects of two nitric oxide (NO) biosynthesis-inhibitors NG-nitro-L-arginine (L-NOARG) and NG-monomethyl-L-arginine (L-NMMA) on the relaxation induced by bradykinin (BK, 100 nM), isoprenaline (Iso, 1 microM) and sodium nitroprusside (SNP, 1 microM) were investigated in epithelium-intact strips of guinea-pig isolated trachea. 2. Relaxations induced by BK (100 nM) in guinea-pig tracheal strips under spontaneous tone were inhibited in a concentration-related manner by L-NOARG and L-NMMA (1 to 100 microM), with IC50s (and 95% confidence limits) of 9.1 (6.9-11.6) microM and 7.0 (4.2-12.3) microM, respectively. However, at the maximal concentration (100 microM) used, neither of these drugs inhibited completely BK-induced relaxation (maximal inhibition of 74 +/- 7 and 67 +/- 7%, respectively). On the other hand, D-NMMA, the D-enantiomer of L-NMMA, up to 100 microM failed to inhibit BK-induced relaxation. The relaxation induced by Iso (1 microM) and SNP (1 microM) were not affected by either L-NOARG or L-NMMA (30 microM). 3. The inhibition of BK-induced relaxation caused by L-NOARG and L-NMMA was partially reversed by addition of excess of L-arginine but not D-arginine (1 mM). 4. Like L-NOARG and L-NMMA, methylene blue (10 microM), an agent that inhibits the activation of soluble guanylate cyclase by NO, also significantly inhibited BK-induced relaxation, leaving responses to Iso unaffected. 5. Indomethacin (0.3 nM to 10 nM), a cyclo-oxygenase inhibitor, concentration-dependently inhibited BK-mediated relaxation, with an IC50 of 2.6 (1.7-3.8) nM, without affecting Iso and SNP-mediated relaxant responses. 6. A combination of a very low concentration of indomethacin (1 nM) and either L-NOARG or L-NMMA (100 microM) changed the response of tracheal preparations to BK (100 nM) from a relaxation to a sustained contraction. 7. These findings indicate that BK-induced relaxation in guinea-pig trachea is mediated jointly by the release of NO or a NO-related substance and a prostanoid, probably prostaglandin E2.

S35b, a new phenylsulfonylfuroxan compound, inhibits thrombin-induced synthesis of platelet-activating factor and prostacyclin in human endothelial cells

Endothelial cells (EC) produce platelet activating factor (PAF) and prostacyclin (PGI2) in response to inflammatory agents such as thrombin. Upon cell stimulation a calcium-dependent phospholipase A2 (PLA2) is activated which hydrolyzes a membrane phospholipid to yield 1-0-alkyl-2-lyso-sn-glycero-3-phospho-choline (lyso-PAF) and free arachidonic acid. Lyso-PAF is in turn converted into PAF by a specific acetyltransferase and arachidonic acid is metabolized via cyclic endoperoxides to PGI2. In the present study we report that S35b (4-methyl-3-phenylsulfonylfuroxan), a new phenyl-sulfonylfuroxan compound with potent antiaggregatory effect, inhibits thrombin-induced PAF synthesis and acetyltransferase activation as well as PGI2 production in human umbilical vein endothelial cells (HUVEC) in a concentration-dependent way. Additionally, we show that S35b stimulates the production of cyclic GMP (cGMP) in HUVEC in a concentration- and time-dependent manner. At high concentration, S35b potentiates the cAMP increase induced by iloprost or forskolin without having a significant influence on cAMP level itself. Potentiation of cAMP increase during agonist-induced EC stimulation seems not to be important for the effect of S35b on cellular function as the compound is active in inhibiting PAF production when endothelial cells are pretreated with indomethacin to block PGI2 synthesis. The increase of cGMP evoked by S35b may account for the effect on endothelial cell function.

Effect of endothelium-derived relaxing factor on renin secretion from isolated mouse renal juxtaglomerular cells

This study aimed to examine the direct influence of native endothelium derived relaxing factor (EDRF) on renin secretion. To this end isolated mouse renal juxtaglomerular cells were cocultured with bovine aortic endothelial cells which produced and released significant amounts of EDRF as assayed by guanylate cyclase activities which were measured separately in endothelial and juxtaglomerular cells as well as in the cocultures of juxtaglomerular with endothelial cells. EDRF production was blunted in the absence of extracellular L-arginine and in the presence of N omega-nitro-L-arginine (L-NAG; 200 microM). Inhibition of endothelial EDRF production by removal of arginine or addition of L-NAG was associated with a significant decrease of renin secretion from the cocultures while the same regimen had no effect on renin secretion from JG cells alone. Exogenous generation of nitric oxide by the addition of sodium nitroprusside (100 microM) stimulated renin secretion in the cocultures both at normal and inhibited EDRF formation as well as from juxtaglomerular cells alone. These findings suggest that native EDRF released from vascular endothelial cells is a stimulatory signal for renin secretion from renal juxtaglomerular cells.

G proteins in aortic endothelial cells and bradykinin-induced formation of nitric oxide

In bovine aortic endothelial cells (BAEC), pertussis toxin (PTx) ADP-ribosylated two major substrates with apparent molecular masses of 40 and 41 kDa, whereas cholera toxin (CTx) ADP-ribosylated two other substrates of 44 and 50 kDa. [alpha-32P]GTP bound to three bands in the 22-27 kDa range. Immunoblot analysis revealed the simultaneous presence of G alpha i1, G alpha i2, G alpha i3, G alpha q or G alpha 11 and of different forms of G alpha s but did not detect significant levels of G alpha 0. Bradykinin caused a 9-fold increase in intracellular cyclic GMP level in BAEC (measured as an index of NO production). Preincubation of BAEC with CTx, but not with PTx, inhibited bradykinin-dependent production of cyclic GMP. These results show that G alpha s, G alpha q or alpha 11, Gi and small GTP-binding proteins are present in BAEC and suggest that a CTx-sensitive G-protein (possibly either small G-protein, G alpha q or G alpha 11) could be associated with the bradykinin-mediated NO formation.

Heparin regulates endothelin production through endothelium-derived nitric oxide in human endothelial cells

Heparin shows blood pressure lowering effect in hypertensive patients and animal models. The present study examined the effect of heparin on vasoconstrictor endothelin-1 (ET-1) production in cultured human umbilical vein endothelial cells (ECs) to elucidate the mechanism of antihypertensive effect of heparin. Heparin suppressed both basal and thrombin-stimulated ET-1 mRNA expression paralleled with a decrease in ET-1 peptide release in a dose-dependent manner. Heparin concomitantly enhanced nitric oxide (NO) formation measured by NO2/NO3 levels and cGMP production in ECs. These enhancements were more marked when ECs were stimulated by thrombin. However, these heparin's effects were blunted in the presence of endothelium-derived nitric oxide (EDNO) synthesizing inhibitor NG-monomethyl L-arginine. Therefore, these results suggest that suppression of ET-1 production by heparin is EDNO mediated.

Induction of nitric oxide synthase gene by interleukin in vascular smooth muscle cells

To elucidate whether cytokines induce nitric oxide synthase in vascular smooth muscle cells, we studied the effects of human recombinant interleukin-1 beta on the synthesis and release of nitric oxide in cultured rat vascular smooth muscle cells by measurement of NO2-/NO3- levels. Furthermore, we performed Northern blot analysis using subcloned polymerase chain reaction products as probes for constitutive and inducible nitric oxide synthase. Interleukin-1 beta dose dependently (1 to 20 ng/mL) stimulated NO2-/NO3- production as a function of time. Northern blotting demonstrated the interleukin-1 beta-induced expression of messenger RNA for an inducible but not for the constitutive nitric oxide synthase after 3 hours. NG-Monomethyl L-arginine completely blocked the interleukin-1 beta-induced NO2-/NO3- production, the effect of which was reversed by L-arginine but not by D-arginine. Dexamethasone inhibited the interleukin-1 beta-induced NO2-/NO3- production in a dose-dependent manner (10(-9) to 10(-7) M) and the interleukin-1 beta-inducible nitric oxide synthase messenger RNA levels. Neither a calmodulin inhibitor (W-7) nor a protein kinase C inhibitor (staurosporine) showed any effects on the induction of nitric oxide synthase transcripts or production of NO2-/NO3- stimulated by interleukin-1 beta, whereas cycloheximide and actinomycin D completely inhibited the basal and stimulated NO2-/NO3- production. These data demonstrate for the first time that interleukin-1 beta induces gene expression of inducible nitric oxide synthase and its de novo protein synthesis in rat vascular smooth muscle cells, thereby leading to generation of nitric oxide via Ca2+/calmodulin-independent and protein kinase C-independent mechanisms.

Role of cyclic AMP in promoting the thromboresistance of human endothelial cells by enhancing thrombomodulin and decreasing tissue factor activities

1. The effects of forskolin, prostaglandin E1 (PGE1), dibutyryl cyclic AMP (db cyclic AMP), dibutyryl cyclic GMP (db cyclic GMP) and 3-isobutyl-l-methyl-xanthine (IBMX) were investigated on the expression of tissue factor and thrombomodulin activities on the surface of human saphenous vein endothelial cells (HSVEC) in culture. 2. Forskolin (10(-6) to 10(-4) M), PGE1 (10(-7) to 10(-5) M) and db cyclic AMP (10(-4) to 10(-3) M) caused a concentration-dependent decrease of cytokine-induced tissue factor activity. 3. Similar concentrations of forskolin, PGE1 and db cyclic AMP enhanced significantly constitutive thrombomodulin activity and reversed the decrease of this activity caused by interleukin-1 (IL-1). 4. IBMX (10(-4) M) decreased tissue factor activity and enhanced the effect of forskolin on tissue factor and thrombomodulin activities. 5. Forskolin (10(-4) M) decreased the IL-1-induced tissue factor mRNA and increased the thrombomodulin mRNA level. IL-1 did not change the thrombomodulin mRNA level after 2 h of incubation with HSVEC in culture. 6. Dibutyryl cyclic GMP (10(-4) M to 10(-3) M) did not influence tissue factor or thrombomodulin activity. 7. Our data suggest that elevation of intracellular cyclic AMP levels may participate in the regulation of tissue factor and thrombomodulin expression, thus contributing to promote or restore antithrombotic properties of the endothelium.

Selective inhibition of endothelium-dependent vasodilator capacity by Escherichia coli endotoxemia

Increased release of endothelium-derived relaxing factor/nitric oxide has been proposed as the final common pathway for vasodilator responses to gram-negative lipopolysaccharide (endotoxin). To test this hypothesis, we examined endothelium-dependent and endothelium-independent vasodilator agents in vascular smooth muscle isolated from guinea pigs 16 hours after injection of saline (control group) or induction of Escherichia coli endotoxemia; aortic rings (approximately 1 mm in diameter) were studied with standard isometric tension techniques. Endotoxemia resulted in a significant loss of vasodilator responses to the endothelium-dependent receptor agonists acetylcholine (10(-10)-10(-5) M) and ADP (10(-8)-10(-5) M). In contrast, endotoxemia did not affect vasodilator responses to either the endothelium-dependent receptor agonist substance P (10(-11)-10(-7) M), the endothelium-dependent and receptor-independent agonist A23187 (10(-9)-10(-6) M), or the endothelium-independent agonist nitroprusside (10(-10)-10(-4) M). The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) inhibited the vasodilator response to acetylcholine more in vessels from lipopolysaccharide-injected than control guinea pigs. Unexpectedly, L-NAME converted the endothelium-dependent vasodilator action of ADP to an endothelium-dependent vasoconstrictor response that was blocked individually by the cyclooxygenase inhibitor indomethacin, the thromboxane synthase inhibitor dazoxiben, and the thromboxane A2 receptor antagonist SQ29548. We conclude that in vivo endotoxemia inhibits the constitutive isoform of nitric oxide synthase in endothelial cells by selectively disrupting receptor-coupled activation mechanisms shared by acetylcholine and ADP. Furthermore, since L-NAME unmasks a thromboxane A2-mediated vasoconstrictor action of the endogenous purinoceptor agonist ADP, drugs that inhibit nitric oxide synthase could exacerbate sepsis-induced vasoconstriction and ischemia by synergizing with lipopolysaccharide-induced inhibition of endothelial nitric oxide synthase.

Ginsenosides protect pulmonary vascular endothelium against free radical-induced injury

We studied the actions of saponin (ginsenosides) from Panax ginseng on free radical-induced pulmonary endothelial injury which is manifest as reversal of the normal vasodilator response to acetylcholine in perfused, vasoconstricted lungs. 50 or 200 micrograms/ml ginsenosides prevented this injury response and also reduced the pulmonary edema which follows free radical injury but did not alter the normal ACh-induced vasodilation in intact lungs. In control perfused lungs preconstricted with U46619, the ginsenoside mixture or purified ginsenosides Rb1 and Rg1 caused vasodilatation. This effect was eliminated by 100 microM nitro-L-arginine, an inhibitor of nitric oxide synthase. In cultured bovine aortic endothelial cells, ginsenosides (10 micrograms/ml) stimulated the conversion of [14C]-L-arginine to [14C]-L-citrulline. These data indicate that GS may cause vasorelaxation and prevent manifestations of oxygen free radical injury by promoting release of nitric oxide.

Increases in endothelial cyclic AMP levels amplify agonist-induced formation of endothelium-derived relaxing factor (EDRF)

The interaction between intracellular cyclic AMP and agonist-induced endothelium-derived relaxing factor (EDRF) (NO) formation was investigated in pig aortic endothelial cells. Three potent stimulators of adenylate cyclase, namely forskolin, adenosine and isoprenaline, amplified bradykinin- and ATP-induced biosynthesis and release of EDRF. None of the substances by itself affected basal EDRF formation. The effects of forskolin, adenosine and isoprenaline corresponded to an enhanced agonist-induced rise in intracellular free Ca2+ concentration ([Ca2+]i), were mimicked by the membrane-permeable cyclic AMP analogue dibutyryl cyclic AMP and were antagonized by the protein kinase inhibitor N-[2-(methylamino)ethyl]-5-isoquinolinesulphonamide dihydrochloride (H-8). Our data suggest that cyclic AMP-dependent phosphorylation modulates Ca(2+)-signalling and thus the function of endothelial cells. This mechanism may be of particular physiological importance, since it allows a joint regulation of endothelial functions by tissues factors such as bradykinin, which directly affects [Ca2+]i and agonists which affect intracellular cyclic AMP levels.

Bradykinin receptors: pharmacological properties and biological roles

Kinins contribute to the acute inflammatory response and are implicated in the pathophysiology of inflammatory disease. The development of therapeutically viable agents that counteract the effects of kinins is, therefore, potentially very rewarding. Since kinin actions are generally mediated via an interaction with cell-surface receptors, one approach is the development of site-specific receptor antagonists. The emphasis in this review is to outline our current understanding of the properties of bradykinin receptors and the potential therapeutic applications for drugs acting at these sites. As a result of the recent introduction of potent bradykinin receptor antagonists and the cloning of bradykinin receptor genes, considerable advances in kinin research can now be confidently anticipated.

Bradykinin inhibition of cyclic AMP accumulation in D384 astrocytoma cells. Evidence against a role of cyclic GMP

The present studies were performed in order to examine the possible role of cyclic GMP-stimulated phosphodiesterase (cGMP-PDE) activity in the inhibitory action of the inflammatory peptide bradykinin on cyclic AMP (cAMP) accumulation in D384 cells. Bradykinin decreased the forskolin-stimulated cAMP accumulation in the presence of the phosphodiesterase inhibitor rolipram, and caused a transient 50% rise in cellular cGMP in the presence of the nonselective PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX). Both basal and bradykinin-stimulated cGMP accumulation were about 8 times higher in the presence of IBMX than in the presence of rolipram. Sodium nitroprusside, which caused a 20-70-fold increase in cGMP levels reduced forskolin stimulated cAMP accumulation, whereas hydroxylamine, which maximally caused a 16-fold increase in cGMP, did not. 8-bromo-cGMP or dibutyryl cGMP had no effect on cAMP accumulation induced by forskolin. The inhibitory effect of nitroprusside was totally reversed by blocking the soluble guanylate cyclase activity by methylene blue treatment; however, the inhibitory action of bradykinin on cAMP accumulation was not changed by this treatment. Additionally, inhibition of nitric oxide synthesis, which is known to be regulated by Ca2+ and in turn stimulates cGMP production, by N omega-nitro-L-arginine (L-NAME) treatment did not alter the inhibitory effect of bradykinin on forskolin-induced cAMP accumulation. These results indicate that large increases in cGMP may regulate cAMP via cGMP-PDE whereas the small increase induced by bradykinin is insufficient and that cGMP is not involved in the inhibitory action of bradykinin on cAMP levels in D384 cells.

Identification of a B2-bradykinin receptor linked to phospholipase C and inhibition of dopamine stimulated cyclic AMP accumulation in the human astrocytoma cell line D384

We have examined the activation of a phospholipase C signal transduction pathway by a B2-bradykinin receptor in the human astrocytoma cell line D384 and how this influences D1-dopamine receptor stimulated cyclic AMP accumulation. Addition of bradykinin to D384 cells resulted in a concentration-dependent (10(-11)-10(-6) M) increase in the accumulation of [3H]inositol phosphates and a similar concentration-dependent transient increase in specific [3H]beta-phorbol-12,13-dibutyrate binding which is indicative of translocation of protein kinase C from the cytosol to the membrane. Changes in intracellular Ca2+ of single cells, measured using the fluorescent indicator dye fura-2, indicated that bradykinin produced a rapid, but transient, increase in intracellular calcium. The Ca2+ response was largely independent of extracellular Ca2+ supporting the idea that receptor activation leads to mobilization of Ca2+ from intracellular stores. However, extracellular Ca2+ was required for a response to a rechallenge with bradykinin. The bradykinin B2-receptor agonist kallidin increased cytosolic Ca2+ in a similar manner to bradykinin. The Ca2+ response to bradykinin could be partially reduced in the presence of the B2-receptor antagonist [D-Arg0-Hyp,D-Phe7,beta-(2-Thienyl)-Ala5,8]-bradykinin, whereas the B1-receptor agonists (Des-Arg9]-bradykinin and [Des-Arg10]-kallidin were ineffective. Bradykinin was also found to attenuate dopamine stimulated cyclic AMP accumulation in D384 cells, at similar concentrations previously observed to stimulate the phospholipase C signal transduction pathway, in the presence of the phosphodiesterase inhibitor, rolipram. In contrast, no attenuation was observed in the presence of the phosphodiesterase inhibitor 1-isobutyl 3-methylxanthine, although the level of dopamine stimulated cyclic AMP observed was lower than in the presence of rolipram.(ABSTRACT TRUNCATED AT 250 WORDS)

The quantitative contribution of nitric oxide and sensory nerves to bradykinin-induced inflammation in rat skin microvasculature

Using a blister model in the rat hind footpad, the present study undertook to examine the relative contribution of sensory nerves and nitric oxide (NO) to the inflammatory response induced by bradykinin (BK). Using this model, combined with laser Doppler flowmetry, we were able to simultaneously monitor two parameters of the inflammatory response, namely vasodilatation (VD) and plasma extravasation (PE). Perfusion of BK (1, 10 or 100 microM) over the blister base elicited both VD and PE responses which were dose-dependent. The VD response was of rapid onset, sustained at the lowest concentration (1 microM), and showed tachyphylaxis at the highest two concentrations (10 and 100 microM). The PE response, however, was delayed in onset at the lower concentration but the response was maintained at all concentrations. The endothelium-independent vasodilator, sodium nitroprusside. (SNP, 100 microM), was used as an internal control and elicited a rapid maintained VD response. In rats pretreated as neonates with capsaicin to destroy primary sensory afferents, the inflammatory response to 10 microM BK was significantly smaller (50% and 64% decrease in VD and PE, respectively). The selective inhibitor of NO synthase, NG-nitro-L-arginine (L-NORAG) at 100 microM significantly attenuated the inflammatory response to BK in control rats (76% and 60% decrease in VD and PE, respectively) with a further decrease in the response in capsaicin pretreated rats. The inactive stereoisomer NG-nitro-D-arginine (D-NORAG) (100 microM) did not affect the inflammatory response to BK. The vasodilator response to SNP was intact in capsaicin pretreated rats and was not affected by either L-NORAG or D-NORAG.(ABSTRACT TRUNCATED AT 250 WORDS)

SK&F 96365 inhibits histamine-induced formation of endothelium-derived relaxing factor in human endothelial cells

Formation of endothelium-derived relaxing factor (EDRF) strictly correlates with the intracellular free Ca2+ ([Ca2+]i) concentration. We now demonstrate that the histamine-induced rise in [Ca2+]i of human umbilical vein endothelial cells is mostly due to activation of a membrane current which allows Ca2+ entry. This membrane current is sensitive to the novel inhibitor of agonist-induced Ca2+ entry, SK&F 96365, which blocked the histamine-induced sustained rise in [Ca2+]i, as well as 45Ca2+ uptake and membrane currents. Inhibition of the above cellular responses to histamine was accompanied by a considerable reduction of EDRF formation and release. Thus biosynthesis and release of EDRF from human umbilical vein endothelial cells significantly depend on agonist-induced Ca2+ entry involving receptor-operated Ca(2+)-permeable channels which can be blocked by SK&F 96365.

Oxidized low density lipoproteins induce mRNA expression and release of endothelin from human and porcine endothelium

Experiments were designed to examine the effect of oxidized low density lipoproteins (Ox-LDLs) on the expression and the release of endothelin from cultured endothelial cells and intact blood vessels. Ox-LDLs (30-300 micrograms/ml), but not native low density lipoproteins (200 micrograms/ml), stimulated the expression of preproendothelin mRNA in porcine and human endothelial cells, leading to a time- and concentration-dependent release of the peptide into the culture medium. The Ox-LDL-stimulated release of endothelin was mimicked by acetylated low density lipoprotein and abolished by downregulation of protein kinase C by phorbol ester. In the intact porcine aorta, Ox-LDLs, but not native low density lipoproteins, also increased the release of peptide in an endothelium- and concentration-dependent manner. The maximal effect was observed at a concentration of 100 micrograms/ml. Incubation of the intact porcine aorta with the scavenger receptor antagonist dextran sulfate decreased the formation of endothelium evoked by Ox-LDLs. The Ox-LDL-stimulated production of the peptide was further augmented in the presence of thrombin (4 units/ml) and was unaffected by nitric oxide-generating compound 3-morpholinosydnonimine (10(-5) M). These results suggest that Ox-LDL may be an endogenous mediator of the augmented release of endothelin observed in hyperlipidemia and atherosclerosis. The increased production of the peptide could contribute to vasospastic events and may promote vascular smooth muscle proliferation and progression of atherosclerotic vascular disease.

Endothelium-dependent relaxation to acetylcholine in the rabbit basilar artery: importance of membrane hyperpolarization

1. Muscarinic stimulation of isolated, preconstricted segments of the basilar artery, with either acetylcholine or carbachol, was followed by endothelium-dependent smooth muscle relaxation and membrane hyperpolarization. 2. Smooth muscle relaxation to acetylcholine was stimulated in the presence of lower concentrations than the associated hyperpolarization (EC50 values 3.2 microM and 31.6 microM, respectively), and was sustained during agonist application, while the hyperpolarization was relatively transient. 3. Repeated exposure to acetylcholine was associated with loss of membrane hyperpolarization, while smooth muscle relaxation was unaltered. Following a second exposure to 100 microM acetylcholine, mean hyperpolarization was markedly depressed from 8.5 to 2 mV, and subsequent exposures failed to induce any hyperpolarization. Relaxations with a similar amplitude and rate of development, were recorded with each subsequent addition of acetylcholine. 4. The competitive substrate inhibitors for nitric oxide synthase, L-NG-monomethyl arginine (100 microM L-NMMA) or L-NG-nitro arginine methyl ester (100 microM L-NAME), modified the form and amplitude of both the relaxation and the hyperpolarization to acetylcholine. In the majority of experiments, both the hyperpolarization and the relaxation were almost totally abolished. 5. Neither nitric oxide, applied directly in physiological salt solution, nor sodium nitroprusside, produced smooth muscle hyperpolarization except in high concentrations. Reproducible, small amplitude (around 2 mV) hyperpolarization followed the application of either NO gas (15 microM) or sodium nitroprusside (100 microM), both of which induced almost maximal smooth muscle relaxation. 6. These data show that muscarinic stimulation of endothelial cells in the rabbit basilar artery is followed by both smooth muscle hyperpolarization and relaxation. They indicate that nitric oxide is involved in both of these responses, but that the smooth muscle hyperpolarization is not an essential component of the relaxation.

Involvement of the L-arginine-nitric oxide pathway in internal anal sphincter relaxation

The purpose of this study was to examine the role of the L-arginine-nitric oxide pathway in neurogenic relaxation of the internal anal sphincter. Muscle strips representing the internal anal sphincter were prepared from 17 adult opossums. The preparations were mounted in organ baths for recording of isometric tension. N omega-nitro-L-arginine, an agent known to inhibit the L-arginine-nitric oxide pathway, concentration-dependently reduced relaxations induced by transmural field stimulation. At the highest concentration of N omega-nitro-L-arginine (10(-4) mol/L), no relaxation was evoked at any frequency tested (0.5-40 Hz). The inhibitory response to exogenous vasoactive intestinal polypeptide was unaffected by N omega-nitro-L-arginine pretreatment, indicating that vasoactive intestinal polypeptide relaxation does not use the L-arginine-nitric oxide pathway. In addition, responses to forskolin and sodium nitroprusside were not influenced by N omega-nitro-L-arginine preincubation, suggesting that the effect observed was not caused by a direct influence on the adenylate or the guanylate cyclases. It is concluded that the nonadrenergic, noncholinergic innervation of the internal anal sphincter involves an inhibitory substance generated from the L-arginine-nitric oxide pathway. Whether this substance is nitric oxide or a related nitroso compound remains to be settled.