Shear stress-induced release of nitric oxide from endothelial cells grown on beads

Nitric oxide increases dramatically in air exhaled from lung regions with occluded vessels

BACKGROUND

We observed dramatic changes in exhaled nitric oxide concentration (DeltaNOE) during wedge measurements, and hypothesised that occlusion and redistribution of pulmonary blood flow affects NOE.

METHODS

We inflated the balloon of the pulmonary artery catheter and measured NOE and central hemodynamics in closed chest anesthetised pigs (n = 11) ventilated with hyperoxic gas (fraction of inspired oxygen [FIO2] = 0.5), before and during lung injury, and in open chest anesthetised pigs (n = 17) before and during left lower lobar (LLL) hypoxia (FIO2 0.05), and during hyperoxic (FIO2 0.8) ventilation of the other lung regions (HL).

RESULTS

In the closed chest pigs NOE increased from 2.0 (0.9) to 3.4 (2.0) p.p.b. (P < 0.001) during wedge, and returned to 2.0 (1.0) p.p.b. when the balloon was deflated. The increase in mean pulmonary artery pressure (MPaP) during wedge was small and insignificant (P > 0.07). When the balloon was inflated in the right pulmonary artery in the open chest pigs, the perfusion of the HL decreased from 2.57 (0.58) to 2.34 (0.55) l min(-1) (P < 0.001), and NOEHL increased from 2.5 (0.9) to 6.2 (3.2) p.p.b. (P < 0.001). The perfusion of the LLL increased from 0.33 (0.26) to 0.54 (0.34) l min(-1) (P < 0.001), and NOELLL decreased from 1.7 (0.6) to 1.5 (0.5) p.p.b. (P < 0.001). Neither lung injury nor LLL hypoxia had any influence on DeltaNOE (P > 0.07) during wedge. The correlation coefficient (R2) was 0.66 between changes in regional blood flow and DeltaNOE, and 0.37 between changes in MPaP and DeltaNOE.

CONCLUSIONS

Nitric oxide concentration increases dramatically from lung regions with occluded vessels, whereas changes in MPaP have minor effects on NOE. This is an important fact to consider when comparing NOE within or between studies, and indicates a possible marker of diseases with occluded lung vessels.

Beneficial effects of antioxidants and L-arginine on oxidation-sensitive gene expression and endothelial NO synthase activity at sites of disturbed shear stress

Atherogenesis is enhanced in arterial segments exposed to disturbed blood flow, indicating the active participation of the hemodynamic environment in lesion formation. Turbulent shear stress selectively regulates responsive genes in the endothelium and increases the damage induced by free radicals. The purpose of the present study was to evaluate the effects of intervention with antioxidants and l-arginine on endothelial NO synthase (eNOS) and oxidation-sensitive gene perturbation induced by disturbed flow in vitro and in vivo. Both human endothelial cells exposed to shear stress and high atherosclerosis-prone areas of hypercholesterolemic low-density lipoprotein receptor knockout (LDLR(-/-)) mice showed increased activities of redox-transcription factors (ELK-1, p-Jun, and p-CREB) and decreased expression of eNOS. Intervention with antioxidants and l-arginine reduced the activation of redox-transcription factors and increased eNOS expression in cells and in vivo. These results demonstrate that atherogenic effects induced by turbulent shear stress can be prevented by cotreatment with antioxidants and l-arginine. The therapeutic possibility to modulate shear stress-response genes may have important implications for the prevention of atherosclerosis and its clinical manifestations.

Folate Improves Endothelial Function in Patients with Coronary Heart Disease

Elevated plasma homocysteine is associated with increased cardiovascular risk but it remains unproven that the effect is directly causal. Folate and homocysteine metabolism are closely linked such that administration of folic acid in doses ranging from 0.2-10 mg/day lowers plasma total homocysteine (tHcy) by up to 25%. Folic acid has been widely advocated as a therapy which may reduce cardiovascular risk, but the clinical benefit remains as yet unproven and the choice of dose remains unclear. The effect of folic acid on endothelial function has been investigated in patients with proven coronary heart disease (CHD) by measuring flow-mediated dilatation (FMD) in the brachial artery. Oral folic acid (5 mg/day) markedly enhances endothelial function (FMD) and lowers homocysteine. Studies of the acute effects of folic acid have shown that this improvement occurs within the first 2-4 hours following the first dose, at which times there was no significant reduction in plasma tHcy. Administration of 5-methyltetrahydrofolate directly into the brachial artery markedly enhances FMD, an effect that is blocked by monomethyl arginine (LNMMA), suggesting that the effects of folate are mediated by nitric oxide. This Review summarises studies which show that pharmacological doses of folate markedly enhance endothelial function in patients with CHD. The discordance with changes in plasma homocysteine suggests that these effects may occur by mechanisms distinct from homocysteine lowering.

NOS inhibition increases bubble formation and reduces survival in sedentary but not exercised rats

Previously we have shown that chronic as well as a single bout of exercise 20 h prior to a simulated dive protects rats from severe decompression illness (DCI) and death. However, the mechanism behind this protection is still not known. The present study determines the effect of inhibiting nitric oxide synthase (NOS) on bubble formation in acutely exercised and sedentary rats exposed to hyperbaric pressure. A total of 45 adult female Sprague-Dawley rats (270-320 g) were randomly assigned into exercise or sedentary control groups, with and without NOS inhibition, using L-NAME (0.05 or 1 mg ml(-1)) (a nonselective NOS inhibitor). Exercising rats ran intervals on a treadmill for 1.5 h, 20 h prior to the simulated dive. Intervals alternated between 8 min at 85-90 % of maximal oxygen uptake, and 2 min at 50-60 %. Rats were compressed (simulated dive) in a pressure chamber, at a rate of 200 kPa min(-1) to a pressure of 700 kPa, and maintained for 45 min breathing air. At the end of the exposure period, rats were decompressed linearly to the "surface" (100 kPa) at a rate of 50 kPa min(-1). Immediately after reaching the surface the animals were anaesthetised and the right ventricle was insonated using ultrasound. The study demonstrated that sedentary rats weighing more than 300 g produced a large amount of bubbles, while those weighing less than 300 g produced few bubbles and most survived the protocol. Prior exercise reduced bubble formation and increased survival in rats weighing more than 300 g, confirming the results from the previous study. During NOS inhibition, the simulated dive induced significantly more bubbles in all sedentary rats weighing less than 300 g. However, this effect could be attenuated by a single bout of exercise 20 h before exposure. The present study demonstrates two previously unreported findings: that administration of L-NAME allows substantial bubble formation and decreased survival in sedentary rats, and that a single bout of exercise protects NOS-inhibited rats from severe bubble formation and death. This is the first report to indicate that biochemical processes are involved in bubble formation, and this information may be important in the search for preventive measures for and treatment of DCI.

Stretch activation of Ca2+ transients in pancreatic beta cells by mobilization of intracellular stores

INTRODUCTION

Nonadrenergic, noncholinergic neurons have been proposed to synchronize pulsatile insulin release from the islets in the pancreas by triggering transient increases of the cytoplasmic Ca2+ concentration ([Ca2+]i) in beta-cells via an inositol trisphoshate-dependent mechanism.

AIMS

To test whether pancreatic beta-cells respond to stretch activation with similar types of transients and whether these Ca signals propagate to other beta-cells in the presence and absence of cell contacts.

METHODOLOGY

Single cells and small aggregates were prepared from beta-cell-rich islets from mice. After 2-5 days of culture, [Ca2+]i was measured with digital imaging and the indicator fura-2 during superfusion with a medium containing 20 mmol/L glucose and 50 micromol/L methoxyverapamil. Membrane stretch was induced by osmotic swelling or focal touch stimulation.

RESULTS

Lowering the medium osmolarity with 100-102 mOSM/L by removal of sucrose or by dilution resulted in a 2-3-fold increase in the number of transients during an initial 5-minute period. Sucrose omission was stimulatory also after isosmolar replacement with readily penetrating urea. The intracellular Ca2+-ATPase inhibitor thapsigargin suppressed both the spontaneously occurring transients and those initiated by volume expansion. Touch stimuli induced [Ca2+]i transients, which rapidly propagated to cells within the same aggregate or lacking contact.

CONCLUSION

The observations support the idea that beta-cells both receive and regenerate extracellular signals triggering [Ca2+]i transients. Touch stimulation is a useful tool for investigating the propagation of [Ca2+]i signals between pancreatic beta-cells lacking physical contact.

Nitric oxide and portal hypertension

In liver cirrhosis, an increase in hepatic resistance is the initial phenomenon leading to portal hypertension. This is primarily due to the structural distortion of the intrahepatic microcirculation caused by cirrhosis. However, similar to other vascular conditions, architectural changes in the liver are associated with a deficient nitric oxide (NO) production, which results in an increased vascular tone with a further increase in hepatic resistance and portal pressure. New therapeutic strategies are being developed to selectively provide the liver with NO, overcoming the deleterious effects of systemic vasodilators. On the other hand, a strikingly opposite process occurs in splanchnic arterial circulation, where NO production is increased. This results in splanchnic vasodilatation and subsequent increase in portal inflow, which contributes to portal hypertension. Systemic blockade of NO in portal hypertension attenuates the hyperdynamic circulation, but its effects increasing hepatic resistance may offset the benefit of reducing portal inflow, thus preventing an effective reduction of portal pressure. Moreover, it cannot be ruled out that NO blockade may have a deleterious action on cirrhosis progression, which raises caution about their use in patients with cirrhosis.

Blood letting in high-ferritin type 2 diabetes: effects on vascular reactivity

OBJECTIVE

In a recent study, iron chelation with deferoxamine led to improvement of endothelial dysfunction in patients with coronary artery disease. We tested the hypothesis that decreasing circulating iron stores might improve vascular dysfunction in patients with type 2 diabetes and increased serum ferritin concentration.

RESEARCH DESIGN AND METHODS

A total of 28 type 2 diabetic male patients with serum ferritin levels >200 ng/ml ( approximately 18% of consecutive type 2 diabetic men attending our outpatient clinic) were randomized to iron depletion (three extractions of 500 ml blood at 2-week intervals; group 1A) or to observation (group 1B). C282Y mutation was absent in all patients. Vascular reactivity (high-resolution external ultrasound) was evaluated at baseline and at 4 and 12 months thereafter. The two groups of patients were matched for age, BMI, pharmacological treatment, and chronic diabetic complications.

RESULTS

Endothelium-dependent vasodilation remained essentially unchanged in both groups of patients. In contrast, the vasodilation induced by glyceryl trinitrate (GTN) improved significantly after iron depletion (P = 0.006). These changes occurred in parallel to decreases in transferrin saturation index and HbA(1c) levels (-0.6%, P < 0.05) only in group 1A patients. The best predictor of the modifications in endothelium-independent vasodilation was the change in HbA(1c) levels. Changes in endothelium-independent vasodilation also correlated with the change in serum ferritin (r = -0.45, P = 0.04). At 12 months, transferrin saturation index and GTN-induced vasodilation returned to values similar to those at baseline in both groups of subjects.

CONCLUSIONS

Iron depletion improves vascular dysfunction in type 2 diabetic patients with high ferritin concentrations. The mechanisms by which these changes occur should be further investigated.

The structural basis of pulmonary hypertension in chronic lung disease: remodelling, rarefaction or angiogenesis?

Chronic lung disease in humans is frequently complicated by the development of secondary pulmonary hypertension, which is associated with increased morbidity and mortality. Hypoxia, inflammation and increased shear stress are the primary stimuli although the exact pathways through which these initiating events lead to pulmonary hypertension remain to be completely elucidated. The increase in pulmonary vascular resistance is attributed, in part, to remodelling of the walls of resistance vessels. This consists of intimal, medial and adventitial hypertrophy, which can lead to encroachment into and reduction of the vascular lumen. In addition, it has been reported that there is a reduction in the number of blood vessels in the hypertensive lung, which could also contribute to increased vascular resistance. The pulmonary endothelium plays a key role in mediating and modulating these changes. These structural alterations in the pulmonary vasculature contrast sharply with the responses of the systemic vasculature to the same stimuli. In systemic organs, both hypoxia and inflammation cause angiogenesis. Furthermore, remodelling of the walls of resistance vessels is not observed in these conditions. Thus it has been generally stated that, in the adult pulmonary circulation, angiogenesis does not occur. Prompted by previous observations that chronic airway inflammation can lead to pulmonary vascular remodelling without hypertension, we have recently shown, using quantitative stereological techniques, that angiogenesis can occur in the adult pulmonary circulation. Pulmonary angiogenesis has also been reported in some other conditions including post-pneumonectomy lung growth, metastatic disease of the lung and in biliary cirrhosis. Such angiogenesis may serve to prevent or attenuate increased vascular resistance in lung disease. In view of these more recent data, the role of structural alterations in the pulmonary vasculature in the development of pulmonary hypertension should be carefully reconsidered.

Plasma Levels of Nitrites/Nitrates in Patients with Chronic Atrial Fibrillation are Increased after Electrical Restoration of Sinus Rhythm

INTRODUCTION

Patients with persistent atrial fibrillation (AF) have hemodynamic changes, which impair endothelial cell function resulting in decreased nitric oxide (NO) production. The aim of this work was to assess endothelial function in AF patients before and at various time points after cardioversion.

METHODS

Forty-two patients with AF and 21 normal and age-adjusted healthy controls were studied. Nitrites and nitrates (NO(x)) and von Willebrand factor (vWf) concentrations were measured on blood samples taken just before cardioversion and over a 30 day period after the procedure.

RESULTS

Plasma levels of NO(x) in AF were significantly lower compared to healthy controls (p < 0.001), but after cardioversion gradually increased to approach to those of the healthy controls by the end of the first month of sustained sinus rhythm (p = 0.004). Interestingly plasma levels of NO(x) were negatively correlated to left atrial volume measured by ultrasonography (r = -0.34, p < 0.05). Plasma levels of vWf in AF patients were significantly higher compared to the healthy controls (p < 0.01) but with sustained sinus rhythm decreased (p = 0.02).

CONCLUSION

The parallel normalization of the NO(x) titers and vWf levels suggests that vascular endothelial function improves after 30 days of normal sinus rhythm.

Maintenance of a functional endothelial cell monolayer on a fibroblast/polymer substrate under physiologically relevant shear stress conditions

The suitability of using a fibroblast-seeded polymer scaffold as a substrate for forming an endothelial monolayer which is responsive to flow has been investigated. The results indicate that a confluent monolayer of endothelial cells can be formed on the top surface of the fibroblast/polymer substrate. This monolayer has an elongated, oriented morphology and alignment even in static culture, and the application of shear stress perpendicular to the endothelium's static alignment causes a progressive reorganization of the cytoskeletal component, F-actin, with a corresponding change in endothelial cell shape from elongated in the direction of flow, to a more "cobble-stone" morphology, to finally elongation in the direction of flow. The production of nitric oxide by this co-culture increases not only in a time and shear stress dependent fashion, but also as a function of the direction of flow in relation to the static alignment of the endothelium. The data obtained also indicate that the coculture had higher levels of ICAM-1 production and monocyte adhesion than seen in ECs on tissue culture plastic, which may be a function of the endothelial cells being in direct contact with the fibroblast cell line. These results demonstrate that a fibroblast/polymer scaffold can serve as a suitable substrate for ECs and that such a monolayer demonstrates the normal EC responsiveness to flow.

Perioperative hemodilution

Acute normovolemic hemodilution (ANH) entails the removal of blood from a patient either immediately before or shortly after induction of anesthesia and the simultaneous replacement with cell-free fluid, preferably synthetic colloids with a predictable volume effect (6% dextran 60/70, 6% hydroxyethyl starch 200,000 and 130.000, respectively). Hemodilution is part of the concept for avoiding or limiting the use of allogeneic blood and should be considered for patients undergoing elective surgery free of contraindications and presenting with an initial hemoglobin concentration > or = 12 g/dl and an anticipated blood loss of > or = 1500 ml. The efficacy of ANH, judged by the necessity to transfuse homologous blood, depends on the preoperative (initial) hematocrit, the target hematocrit (to which hemodilution is performed), and the preset intra- and postoperative transfusion trigger. In the past data from clinical trials have shown that in healthy subjects a target hematocrit of 20-25% (7.0-8.0 g/dl hemoglobin concentration) is feasible and safe for the patient. The lower the target hemoglobin concentration, the more extensive monitoring is required: intraoperative target hemoglobin concentrations of 5.0 g/dl and less have been tolerated by young surgical patients without adverse effects. The safety as well as efficacy of acute normovolemic hemodilution in terms of reducing homologous blood transfusion requirements have been demonstrated in various clinical studies. ANH therefore is regarded an integral part of programs aimed at reducing the need for homologous blood, and can thus be successfully combined with preoperative autologous blood deposition, intraoperative blood salvage and carefully adjusted surgical techniques.

Wei Lun Visiting Professorial Lecture: Nitric oxide in the regulation of vascular function: an historical overview

The field of nitric oxide (NO) research has developed in explosive proportions since the discovery of endogenous NO in 1986. The biological importance of NO was first shown by the findings that nitroglycerin causes vasodilation by liberating NO in the smooth muscle, and activating guanylate cyclase to raise smooth muscle levels of cyclic GMP. NO also inhibits platelet aggregation by cyclic GMP mechanisms. NO activates guanylate cyclase by heme dependent mechanisms involving the formation of a nitrosyl-heme complex. The high pharmacological potency of NO was finally understood when NO was shown to be formed endogenously, and to be the same as EDRF. Based on these properties of NO, new drugs can be developed as vasodilators and antiplatelet agents for the treatment of a variety of vascular disorders including impotency. NO elicits many other actions in mammalian systems including inhibition of cell proliferation, airway bronchodilation, antimicrobial effects, other host defense effects, and also modulates learning and memory as well as other central functions. This allows for an extensive opportunity to develop novel drugs for the diagnosis, prevention, and treatment of a number of different diseases, many of which are vascular in origin.

Impaired exercise-induced vasodilatation in chronic atrial fibrillation--role of endothelium-derived nitric oxide

Exercise capacity is often reduced in patients with atrial fibrillation (AF), but very few studies have focused on changes in endothelial function as a potential mechanism for the exercise limitation. The present study used using venous occlusion plethysmography to investigate whether nitric oxide (NO)-mediated vasodilatation is attenuated during exercise in patients with AF by measuring forearm blood flow (FBF) in 10 patients at rest and immediately after 2 levels of rhythmic handgrip exercise, before and after inhibition of NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA, 100 micromol). The measurements were repeated 1 day after restoration of sinus rhythm by cardioversion. FBF responses to graded doses of acetylcholine (ACh) were also observed before and after cardioversion. Heart rate decreased after cardioversion, but blood pressure did not change. FBF at rest was not affected by cardioversion, but at the highest level of exercise it increased from 28.4+/-2.3 ml x min(-1) x dl(-1) before to 39.4+/-3.2 ml x min(-1) x dl(-1) after cardioversion (p<0.05). L-NMMA significantly decreased FBF at rest (p<0.01) and depressed the increase in FBF response to exercise after (p<0.01), but not before cardioversion. The FBF response to ACh was also accelerated significantly after cardioversion. The present results provide new evidence that NO bioavailability is depressed at rest and during exercise in patients with AF.

Endothelial nitric oxide synthase and its negative regulator caveolin-1 localize to distinct perinuclear organelles

Caveolin-1 is a member of a subset of intracellular proteins that regulate endothelial nitric oxide synthase (eNOS) activity. In caveolae, caveolin-1 inhibits eNOS activity via a direct interaction with the enzyme. Previous work has indicated that both eNOS and caveolin-1 are also localized at the perinuclear Golgi complex. Whether caveolin-1 is involved in eNOS regulation in this cell compartment is unknown. Here we studied the localization of eNOS and caveolin-1 in the perinuclear region of primary bovine aortic endothelial cells. By immunofluorescence microscopy we show that both eNOS and caveolin-1 co-localize with Golgi markers. On treatment of the cells with the microtubule-depolymerizing drug nocodazole, the Golgi complex is scattered and caveolin-1 is found in vesicles at the periphery of the cell, while eNOS is localized at large structures near the nucleus. The nocodazole-induced redistribution of eNOS is similar to that of cis-, medial-, and trans-Golgi markers, while the caveolin-1 redistribution resembles that of sec22, a marker for the intermediate compartment. The localization of eNOS and caveolin-1 at distinct perinuclear compartments that behave differently in the presence of nocodazole indicates that eNOS activity is not regulated by caveolin-1 in the Golgi complex.

Effects of shear stress on nitric oxide and matrix protein gene expression in human osteoarthritic chondrocytes in vitro

Mechanical loading alters articular cartilage metabolism. However, mechanisms underlying intracellular signaling and communication between cells in response to mechanical stresses remain enigmatic. This study tested the hypothesis that shear stress-induced nitric oxide (NO) production participates in the regulation of matrix protein gene expression. The data presented here demonstrate that exposure of human osteoarthritic chondrocytes to a continuously applied shear stress (1.64 Pa) upregulated NO synthase gene expression and increased NO release by 1.8-, 2.4-, and 3.5-fold at 2, 6, and 24 h, respectively. Exposure of chondrocytes to a short duration of shear stress for 2 h resulted in the release of accumulation of NO in the culture medium. Exposure of chondrocytes to shear stress for 2, 6, and 24 h inhibited type II collagen mRNA signal levels by 27%, 18% and 20% after a constant post-shear incubation period of 24 h. Aggrecan mRNA signal levels were inhibited by 30%, 32% and 41% under identical conditions. Addition of an NO antagonist increased type II collagen mRNA signal levels by an average of 1.8-fold (137% of the un-sheared control) and reestablished the aggrecan mRNA signal levels by an average of 1.4-fold after shear stress (92% of the un-sheared control) (ANOVA p < 0.05). These data support the hypothesis that shear stress-induced NO release may influence the development of degenerative joint diseases by inhibiting matrix macromolecule synthesis.

Endothelial responses to mechanical stress: where is the mechanosensor?

OBJECTIVE

The endothelium is normally subjected to mechanical deformation resulting from shear stress and from strain associated with stretch of the vessel wall. These stimuli are detected by a mechanosensor that initiates a variety of signaling systems responsible for triggering the functional responses. The identity of the mechanosensor has not been established. This article discusses the different mechanisms of mechanosensing that have been proposed and reviews the literature with respect to signaling systems that are activated in response to stress and strain in endothelium.

DATA SOURCES

Published literature related to mechanotransduction, signal transduction pathways initiated by strain in endothelium, and pathophysiologic effects of abnormal shear forces in diseases.

DATA EXTRACTION AND SYNTHESIS

Proposed mechanisms of mechanosensing include stretch-sensitive ion channels, protein kinases associated with the cytoskeleton, integrin-cytoskeletal interactions, cytoskeletal-nuclear interactions, and oxidase systems capable of generating reactive oxygen species. However, the molecular identity of the mechanosensor is not known, nor is it clear whether multiple sensing mechanisms exist.

CONCLUSIONS

Many responses are initiated in cells subjected to mechanical deformation, including alterations in ion channel conductance, activation of signal transduction pathways, and altered expression of specific genes. Future progress in this field will require a critical distinction between cell systems that become activated during mechanical strain and the identity of the cellular mechanosensor that triggers subsequent responses.

Control of coronary blood flow during exercise

Under normal physiological conditions, coronary blood flow is closely matched with the rate of myocardial oxygen consumption. This matching of flow and metabolism is physiologically important due to the limited oxygen extraction reserve of the heart. Thus, when myocardial oxygen consumption is increased, as during exercise, coronary vasodilation and increased oxygen delivery are critical to preventing myocardial underperfusion and ischemia. Exercise coronary vasodilation is thought to be mediated primarily by the production of local metabolic vasodilators released from cardiomyocytes secondary to an increase in myocardial oxygen consumption. However, despite various investigations into this mechanism, the mediator(s) of metabolic coronary vasodilation remain unknown. As will be seen in this review, the adenosine, K(+)(ATP) channel and nitric oxide hypotheses have been found to be inadequate, either alone or in combination as multiple redundant compensatory mechanisms. Prostaglandins and potassium are also not important in steady-state coronary flow regulation. Other factors such as ATP and endothelium-derived hyperpolarizing factors have been proposed as potential local metabolic factors, but have not been examined during exercise coronary vasodilation. In contrast, norepinephrine released from sympathetic nerve endings mediates a feed-forward betaadrenoceptor coronary vasodilation that accounts for approximately 25% of coronary vasodilation observed during exercise. There is also a feed-forward alpha-adrenoceptor-mediated vasoconstriction that helps maintain blood flow to the vulnerable subendocardium when heart rate, myocardial contractility, and oxygen consumption are elevated during exercise. Control of coronary blood flow during pathophysiological conditions such as hypertension, diabetes mellitus, and heart failure is also addressed.

Overproduction of platelet microparticles in cyanotic congenital heart disease with polycythemia

OBJECTIVES

We sought to clarify the role of platelets in the pathogenesis of abnormal coagulation in patients with cyanotic congenital heart disease (CCHD) with polycythemia; we evaluated the production of platelet microparticles (MPs), platelet degranulation and aggregation response, as well as the correlations of these variables with polycythemia.

BACKGROUND

A shortened life span and suppressed aggregability of platelets are well known in patients with CCHD. Although platelet MPs are overproduced and play an important role in the coagulation process in various hematologic and cardiovascular disorders, the production of MPs remains to be elucidated in CCHD. We studied 19 patients who had CCHD with polycythemia and 21 age-matched subjects with acyanotic congenital heart disease (ACHD). Flow cytometry, using monoclonal antibodies, showed the presence of MPs as particles positive for the surface antigen (glycoprotein IIb/IIIa) specific to platelets, and platelet alpha-degranulation was recognized as platelets positive for the surface antigen of P-selectin. Platelet aggregation was assessed as the response to adenosine diphosphate (ADP). Relationships between these indexes and hematocrit (Hct) values were also evaluated.

RESULTS

Production of MPs correlated positively with Hct and markedly increased at Hct values above 60% in patients with CCHD. Surface P-selectin and the mean platelet volume in patients with CCHD were comparable with those in patients with ACHD. The platelet aggregation response to ADP significantly and negatively correlated with Hct. In two subjects who showed hemoptysis and underwent phlebotomy, MPs were reduced 6 h after the procedure.

CONCLUSIONS

Platelet MPs are overproduced in patients who have CCHD with polycythemia, probably due to a high shear stress derived from blood hyperviscosity. Circulating incompetent platelets, which have already been activated, as well as MPs, might play an important role in the coagulation abnormalities identified in such patients.

Repeated sauna treatment improves vascular endothelial and cardiac function in patients with chronic heart failure

OBJECTIVES

The purpose of this study was to determine the mechanism by which 60 degrees C sauna treatment improves cardiac function in patients with chronic heart failure (CHF).

BACKGROUND

We have previously reported that repeated 60 degrees C sauna treatment improves hemodynamic data and clinical symptoms in patients with CHF. We hypothesized that the sauna restores endothelial function and then improves cardiac function.

METHODS

Twenty patients (62 plus minus 15 years) in New York Heart Association (NYHA) functional class II or III CHF were treated in a dry sauna at 60 degrees C for 15 min and then kept on bed rest with a blanket for 30 min, daily for two weeks. Ten patients with CHF, matched for age, gender and NYHA functional class, were placed on a bed in a temperature-controlled (24 degrees C) room for 45 min as the nontreated group. Using high-resolution ultrasound, we measured the diameter of the brachial artery at rest and during reactive hyperemia (percent flow-mediated dilation, %FMD: endothelium-dependent dilation), as well as after sublingual administration of nitroglycerin (%NTG: endothelium-independent dilation). Cardiac function was evaluated by measuring the concentrations of plasma brain natriuretic peptide (BNP).

RESULTS

Clinical symptoms were improved in 17 of 20 patients after two weeks of sauna therapy. The %FMD after two-week sauna treatment significantly increased from the baseline value, whereas the %NTG-induced dilation did not. Concentrations of BNP after the two-week sauna treatment decreased significantly. In addition, there was a significant correlation between the change in %FMD and the percent improvement in BNP concentrations in the sauna-treated group. In contrast, none of the variables changed at the two-week interval in the nontreated group.

CONCLUSIONS

Repeated sauna treatment improves vascular endothelial function, resulting in an improvement in cardiac function and clinical symptoms.

Lysophosphatidylcholine enhances superoxide anions production via endothelial NADH/NADPH oxidase

Reactive oxygen species (ROS) including superoxide anions (O2(-)) play a key role in atherogenesis, and endothelial cells have the ability to generate ROS. To investigate the enzymatic sources of ROS and the effects of lysophosphatidylcholine (LPC), an atherogenic lipid, we measured ROS production in cultured bovine aortic endothelial cells (BAECs) by the lucigenin-enhanced chemiluminescence (CL) method and electron spin resonance (ESR). BAEC homogenates had the enzymatic activity of NADH/NADPH oxidase. BAECs cultured on microcarrier beads generated O2(-) under basal conditions. The inhibition of NADH/ NADPH oxidase by diphenylene iodonium (DPI) significantly attenuated O2(-) production, whereas no inhibitors of other oxidases suppressed it. Although LPC enhanced O2(-) production approximately 3.1-fold, its action was suppressed by DPI. Tyrosine kinase inhibitors significantly attenuated LPC-induced O2(-) production. ESR with DMPO demonstrated that LPC increased the formation of the DMPO-hydroxyl adduct in dose- and time-dependent manners. These data suggest that the basal production of O2(-) in endothelial cells is mainly mediated by the NADH/NADPH oxidase system and that LPC activates this oxidase to enhance O2(-) production through a tyrosine kinase-dependent pathway. The enhancement of ROS production by LPC is probably involved in its atherogenic property.

Effect of L-canavanine, an Inhibitor of inducible nitric oxide synthase, on myocardial dysfunction during septic shock

Overproduction of nitric oxide (NO) by inducible NO synthase (iNOS) plays a role in the pathophysiology of septic shock. The depression of cardiac contractility in such situations is mediated by proinflammatory cytokines, including interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha). The effects of two NOS inhibitors with different isoform selectivity were compared in isolated working rat hearts. The depression of contractility by IL-1beta and TNF-alpha was prevented by administration of a nonselective nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) or an inhibitor of inducible nitric oxide synthase, L-canavanine. In contrast, when L-NAME was administered in the absence of IL-1beta and TNF-alpha, it depressed contractility over the 2h perfusion period by significantly reducing coronary flow. These results support current thinking that the depression of myocardial function by IL-1beta and TNF-alpha is mediated, at least in part, by an intracardiac increase in inducible nitric oxide synthase, and that in contrast to L-NAME, the decline in coronary conductance seen in cytokine-treated is not prevented by L-canavanine hearts. L-canavanine shows selective inhibition of inducible nitric oxide synthase unlike the vasopressor action of L-NAME in cytokine-treated hearts.

Variation at the Angiotensin-converting enzyme and endothelial nitric oxide synthase genes is associated with the risk of esophageal varices among patients with alcoholic cirrhosis

Esophageal varices are a frequent complication among patients with liver cirrhosis. Nitric oxide and other vasoactive molecules regulate the vascular tone in both the liver microcirculation and the systemic and splanchnic circulation. Several genes that encode proteins involved in the maintenance of vascular tone, such as the endothelial-constitutive nitric oxide synthase (ecNOS), the angiotensinogen (AGT), the angiotensin-converting enzyme (ACE), and the angiotensin II receptor type 1 (AT1R) are polymorphic, and these polymorphisms have been associated with several cardiovascular diseases. Our aim was to define a possible role for DNA polymorphisms at these genes in the risk of developing esophageal varices among patients with alcoholic cirrhosis. We analyzed 145 male patients with liver cirrhosis. Patients and 200 healthy controls were genotyped by polymerase chain reaction for the ACE-I/D, the AGT-M235T, the AT1R-A1166C, and the ecNOS-4/5 (intron 4) polymorphisms. Ninety-five patients had varices and 50 did not show this complication. Carriers of the ACE-I allele (ID + II genotypes) were at a significantly higher frequency among patients with varices (p = 0.013). Patients without varices had a higher frequency of the ecNOS-4 allele compared with patients with varices (p = 0.026). ACE-I carriers + ecNOS-55 were at a significantly higher frequency (p = 0.0012; odds ratio = 3.19; 95% CI = 1.55-6.55) among patients with varices (51 of 95, 54%) compared with patients without (18 of 50, 36%). Allele and genotype frequencies for the AGT and AT1R polymorphisms did not differ between the two groups. The genotypes associated with an increased risk for varices have been linked to higher plasma levels of nitric oxide and reduced levels of ACE. These genotypes could have a vasodilatory effect in the systemic and splanchnic circulation, thus favoring the development of portocollaterals.

Aerobic endurance training reduces bubble formation and increases survival in rats exposed to hyperbaric pressure

1. The formation of bubbles is the basis for injury to divers after decompression, a condition known as decompression illness. In the present study we investigated the effect of endurance training in the rat on decompression-induced bubble formation. 2. A total of 52 adult female Sprague-Dawley rats (300-370 g) were randomly assigned to one of two experimental groups: training or sedentary control. Trained rats exercised on a treadmill for 1.5 h per day for 1 day, or for 2 or 6 weeks (5 days per week) at exercise intervals that alternated between 8 min at 85-90% of maximal oxygen uptake (VO2,max) and 2 min at 50-60% of VO2,max. Rats were compressed (simulated dive) in a decompression chamber in pairs, one sedentary and one trained, at a rate of 200 kPa x min(-1) to a pressure of 700 kPa, and maintained for 45 min breathing air. At the end of the exposure period, rats were decompressed linearly to the 'surface' (100 kPa) at a rate of 50 kPa x min(-1). Immediately after reaching the 'surface' (100 kPa) the animals were anaesthetized and the right ventricle was insonated using Doppler ultrasound. 3. Intensity-controlled interval training significantly increased VO2,max by 12 and 60% after 2 and 6 weeks, respectively. At 6 weeks, left and right ventricular weights were 14 and 17 % higher, respectively, in trained compared to control rats. No effect of training was observed on skeletal muscle weight. Bubble formation was significantly reduced in trained rats after both 2 and 6 weeks. However, the same effect was seen after a single bout of aerobic exercise lasting 1.5 h on the day prior to decompression. All of the rats that exercised for 1.5 h and 2 weeks, and most of those that trained for 6 weeks, survived the protocol, whereas most sedentary rats died within 60 min post-decompression. 4. This study shows that aerobic exercise protects rats from severe decompression and death. This may be a result of less bubbling in the trained animals. The data showed that the increase in aerobic capacity per se was not the main mechanism, but rather an acute effect that was most notable 20 h after a single, or the last, exercise bout, with less effect after 48 h.

NO and prostaglandin interactions during hemodynamic stress in the fetal ovine pulmonary circulation

Nitric oxide (NO) and prostacyclin (PGI(2)) are potent fetal pulmonary vasodilators, but their relative roles and interactions in the regulation of the perinatal pulmonary circulation are poorly understood. We compared the separate and combined effects of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibition during acute hemodynamic stress caused by brief mechanical compression of the ductus arteriosus (DA) in chronically prepared fetal lambs. Nitro-L-arginine (L-NNA; NOS antagonist), meclofenamate (Mec; COX inhibitor), combined drugs (L-NNA-Mec), or saline (control) was infused into the left pulmonary artery (LPA) before DA compression. In controls, DA compression decreased pulmonary vascular resistance (PVR) by 43% (P < 0.01). L-NNA, but not Mec, treatment completely blocked vasodilation and caused a paradoxical increase in PVR (+31%; P < 0.05). The effects of L-NNA-Mec and L-NNA on PVR were similar. To determine if the vasodilator effect of PGI(2) is partly mediated by NO release, we studied PGI(2)-induced vasodilation before and after NOS inhibition. L-NNA treatment blocked the PGI(2)-induced rise in LPA blood flow by 73% (P < 0.001). We conclude that NO has a greater role than PGs in fetal pulmonary vasoregulation during acute hemodynamic stress and that PGI(2)-induced pulmonary vasodilation is largely mediated by NO release in the fetal lung.

Oxygen delivery and oxygen consumption in rat hindlimb during systemic hypoxia: role of adenosine

1. In anaesthetised rats, the increase in femoral vascular conductance (FVC) evoked by moderate systemic hypoxia is mediated by adenosine acting on A(1) receptors. It is also nitric oxide (NO) dependent: it is attenuated by NO synthase (NOS) inhibition, but restored when baseline FVC is restored by sodium nitroprusside (SNP), a NO donor. However, under these conditions there was in increase in the critical O(2) delivery (D(O2,crit)) at which hindlimb O(2) consumption (V(O2)) becomes directly dependent upon O(2) delivery (D(O2)), indicating that V(O2) is regulated by newly synthesised NO. 2. In the present study, after NOS inhibition, when baseline FVC was restored with SNP infusion, the increases in FVC evoked by breathing 12 and 8 % O(2) were reduced by the A(1) receptor antagonist DPCPX, by 60 and 40 %, respectively (n = 8). The A(2A) receptor antagonist ZM241385 reduced the FVC increase evoked by 12 % O(2) (by 45 %, n = 8), but did not alter that evoked by 8 % O(2). 3. DPCPX also reduced the increases in FVC evoked by graded systemic hypoxia, breathing 14-6 % O(2) and increased D(O2,crit), from 0.64 +/- 0.06 to 0.95 +/- 0.07 ml O(2) min(-1) kg(-1) (control vs. DPCPX). However, ZM241385 (n = 8) had no effect on the FVC increases or on D(O2,crit) (0.70 +/- 0.02 ml O(2) min(-1) kg(-1), n = 8). 4. Thus, the increases in FVC evoked by mild to severe systemic hypoxia are mediated by A(1) receptors. These responses, which are attributable to proximal arteriolar dilatation, help maintain D(O2). Even after NOS inhibition, adenosine still increases FVC via A(2A) (moderate hypoxia only) and A(1) receptors, providing baseline levels of NO are present. Furthermore, adenosine, acting via A(1) receptors, is important in determining D(O2,crit) and therefore in maintaining V(O2). We propose that this is achieved by A(1)-evoked dilatation of terminal arterioles and is mediated by increased synthesis of NO.

Hypoxia-induced upregulation of eNOS gene expression is redox-sensitive: a comparison between hypoxia and inhibitors of cell metabolism

Several papers report a hypoxia-induced upregulation of the endothelial nitric oxide synthase (eNOS) mRNA expression. Since there is no known hypoxia-sensitive element binding site in the eNOS promoter, we reasoned that the effect of hypoxia could be simulated by a metabolically elicited alteration of the redox state. Therefore, cultured porcine aortic endothelial cells (PAEC) were exposed to hypoxia (1-10% O(2)) or inhibitors of cellular energy metabolism including rotenone, 2, 4 dinitrophenol (DNP) and 2-deoxyglucose for 6 to 24 h. Additionally, cells were treated with lactate and nicotinic acid to alter the cellular NAD(P)H/NAD(P) ratio without changes of energy supply. The cellular NAD(P)H/NAD(P) ratio was used as an index of the cellular redox state and determined using the MTT-assay. Hypoxia increased eNOS mRNA transcription and MTT-reduction in a manner inversely proportional to pO(2). Exposure to rotenone, DNP, and lactate increased the NAD(P)H/NAD(P) ratio, MTT-reduction, and eNOS mRNA also in parallel. In contrast, 2-deoxyglucose and nicotinic acid attenuated both MTT-reduction and eNOS mRNA expression. In order to study a potential role of the redox regulated transcription factor complex AP-1 in hypoxia-induced eNOS mRNA transcription, c-jun expression was determined and decoy experiments were performed. c-jun expression paralleled changes of eNOS mRNA expression and MTT-reduction. Furthermore, in the presence of oligodeoxynucleotides corresponding to the AP-1 binding sites of the eNOS promoter, the hypoxia and chemically induced eNOS mRNA expression was completely abolished. We propose that hypoxia, by altering cellular metabolism, leads to an increase in the cellular NAD(P)H/NAD(P) ratio which favors enhanced eNOS expression by redox-sensitive AP-1 mediated transcriptional control.

In vivo angiogenesis in normal and portal hypertensive rats: role of basic fibroblast growth factor and nitric oxide

BACKGROUND

Angiogenesis plays a pivotal role in many processes. Here, we studied whether angiogenesis to basic fibroblast growth factor (bFGF) in normal and portal hypertensive rats requires nitric oxide (NO).

METHODS

To measure angiogenesis in vivo, two Teflon rings filled with collagen I (Vitrogen 100) were fixed in the mesenteric cavity at day 0, with one supplemented with bFGF (100 ng). Portal hypertension was induced by partial portal vein ligation (PVL). Sham-operated rats served as controls (CON). The role of NO was tested by adding the NO formation antagonist N(omega)-nitro-L-arginine (NNA; 3.3 mg/kg per day) to the drinking water. After 16 days, rings were explanted and embedded, and vessels were morphometrically counted.

RESULTS

bFGF significantly stimulated vessel formation per implant in CON rats (from 624 +/- 97 without stimulation to 1123 +/- 171, n = 11, P < 0.01), but not in PVL rats (from 1106 +/- 174 without stimulation to 1046 +/- 202, n = 9). Without stimulation, numbers of ingrown vessels were significantly (P < 0.05) higher in PVL compared to CON rats. NNA substantially inhibited angiogenesis in both groups (P < 0.01). Vessel numbers were 202 +/- 124 for PVL (n = 5) and 197 +/- 14 for CON (n = 5) animals. bFGF did not reverse angiogenesis prevented by NNA (373 +/- 98 for PVL, 265 +/- 26 for CON, n = 5 per group, NS).

CONCLUSIONS

NO formation inhibition diminishes both unstimulated and bFGF-stimulated angiogenesis in CON rats. Moreover, bFGF cannot rescue NNA-inhibited angiogenesis in PVL rats.

Changes in nitric oxide, superoxide, and blood circulation in muscles over time after warm ischaemic reperfusion in rabbit rectus femoris muscle

We present the sequence of changes in nitric oxide (NO) and superoxide (O2-) over time in reperfusion injuries. We examined both the changes in NO and O2- over time and the blood flow in an isolated ischaemia-reperfusion muscle model in rabbits. The ischaemic group comprised 8 animals which had had vascular pedicles clamped on the their rectus femoris muscles for 4 hours. The control group (n = 6) had a sham operation. Blood samples from the femoral vein proximal to the clamping point were collected before the operation, before clamping, before reperfusion, immediately after reperfusion, and 5, 15, 30, 60, and 120 minutes after reperfusion. NO was measured by Griess' method, and O2- by chemiluminescence. Blood flow was measured with a laser Doppler flowmeter. The amount of NO increased significantly immediately after reperfusion, and 15 and 30 minutes after reperfusion in the ischaemic group, compared with the control group (p < 0.05). O2- increased significantly at 5, 15, 60, 90 and 120 minutes after reperfusion, compared with the control group (p < 0.05). The blood flow volume curve increased by 1.4 times about four minutes after reperfusion compared with previously. After this it gradually decreased. The adverse effects of O2- became apparent when NO was extinguished by O2-.

Role of calcium-sensitive K(+) channels and nitric oxide in in vivo coronary vasodilation from enhanced perfusion pulsatility

BACKGROUND

In vitro studies support K(+)(Ca) channel-induced smooth muscle hyperpolarization as underlying acetylcholine-mediated (or bradykinin-mediated) vasodilation that persists despite combined nitric oxide (NO) and PGI(2) inhibition. We tested the hypothesis that these channels are activated by enhanced pulsatile perfusion in vivo and contribute substantially to vasodilation from this stimulus.

METHODS AND RESULTS

The canine left descending coronary artery was perfused with whole blood at constant mean pressure, and physiological flow pulsatility was set at 40 or 100 mm Hg by computer servo-pump. Cyclooxygenase was inhibited by indomethacin. Mean flow increased +18+/-2% (P:<0.0001) with enhanced pulsatility. This response declined approximately 50% by blocking NO synthase (L-NMMA) or K(+)(Ca) [charybdotoxin (CbTX)+apamin (AP)]. Combining both inhibitors virtually eliminated the flow rise. Inhibiting either or both pathways minimally altered basal coronary flow, whereas agonist-stimulated flow was blocked. Bradykinin-induced dilation declined more with CbTX+AP than with L-NMMA (-66% versus -46%, P:=0.03) and was fully blocked by their combination. In contrast, acetylcholine-induced dilation was more blunted by L-NMMA than by CbTX+AP (-71% versus -44%, P:<0.002) and was not fully prevented by the combination. Substituting iberiotoxin (IbTX) for CbTX greatly diminished inhibition of pulse pressure and agonist flow responses (with or without NOS inhibition). Furthermore, blockade by IbTX+AP was identical to that by AP alone, supporting a minimal role of IbTX-sensitive large-conductance K(+)(Ca) channels.

CONCLUSIONS

K(+)(Ca) activation and NO comodulate in vivo pulsatility-stimulated coronary flow, supporting an important role of a hyperpolarization pathway in enhanced mechanovascular signaling. Small- and intermediate-conductance K(+)(Ca) channels are the dominant species involved in modulating both pulse pressure- and bradykinin-induced in vivo coronary dilation.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Tetrahydrobiopterin impairs the action of endothelial nitric oxide via superoxide derived from platelets

The mechanism by which exogenous tetrahydrobiopterin (BH(4)) impairs the action of endothelial nitric oxide (NO) in the presence of platelets was investigated. The endothelial NO generated by shear stress was determined by the anti-aggregating activity of indomethacin-treated endothelial cells and the cyclic GMP concentration in platelets. The inhibitory effect of exogenous BH(4) was suppressed by superoxide dismutase (SOD), or diclofenac sodium at concentrations inhibiting O(2)(-) generation, but not by allopurinol, a xanthine oxidase inhibitor. BH(4) similarly inhibited the anti-aggregatory effect of sodium nitroprusside (SNP), a NO donor. The inhibitory effect was suppressed by diphenyleneiodonium, a specific inhibitor of NADPH oxidase. Six(S)-BH(4), an inactive diastereoisomer of 6(R)-BH(4), and the 5,6,7,8-tetrahydropterin compounds inhibited the endothelial NO action, whereas sepiapterin and 7,8-dihydrobiopterin (BH(2)), 5,6-double bond pterins, were inactive. These tetrahydropterins, but not sepiapterin and BH(2), scavenged superoxide (O(2)(-)) generated by the hypoxanthine-xanthine oxidase reaction, possibly due to electron transfer during oxidation to its quinonoid-form. BH(4) markedly stimulated the O(2)(-) generation from platelets, in the presence of NADH, rather than that of NADPH. These findings suggest that BH(4) stimulates platelet NAD(P)H oxidase to generate O(2)(-), and inhibits the anti-aggregating effect of NO. SOD activity in the local environment may modify the effect of BH(4) on the endothelial NO activity.

Upregulation of neuronal nitric oxide synthase in skeletal muscle by swim training

Exercise enhances cardiac output and blood flow to working skeletal muscles but decreases visceral perfusion. The alterations in nitric oxide synthase (NOS) activity and/or expression of the cardiopulmonary, skeletal muscle, and visceral organs induced by swim training are unknown. In sedentary and swim-trained rats (60 min twice/day for 3-4 wk), we studied the alterations in NOS in different tissues along with hindquarter vasoreactivity in vivo during rest and mesenteric vascular bed reactivity in vitro. Hindquarter blood flow and conductance were reduced by norepinephrine in both groups to a similar degree, whereas N(G)-nitro-L-arginine methyl ester reduced both indexes to a greater extent in swim-trained rats. Vasodilator responses to ACh, but not bradykinin or S-nitroso-N-acetyl-penicillamine, were increased in swim-trained rats. Ca(2+)-dependent NOS activity was enhanced in the hindquarter skeletal muscle, lung, aorta, and atria of swim-trained rats together with increased expression of neuronal NOS in the hindquarter skeletal muscle and endothelial NOS in the cardiopulmonary organs. Mesenteric arterial bed vasoreactivity was unaltered by swim training. Physiological adaptations to swim training are characterized by enhanced hindquarter ACh-induced vasodilation with upregulation of neuronal NOS in skeletal muscle and endothelial NOS in the lung, atria, and aorta.

Release of nitric oxide after acute hypertension

We have shown that NO production, assessed by measuring changes in plasma nitrate concentration, is down-regulated when blood pressure falls. This study intended to determine first, whether NO-derived plasma nitrate varies in response to increases in blood pressure induced by different mechanical and pharmacologic stimuli, including angiotensin II and catecholamines; and second, specifically to study the interaction between angiotensin II and NO production. An intravenous infusion (4-10 min) of norepinephrine (7.5 microg/kg/min), phenylephrine (30 microg/kg/min), or angiotensin II (0.3 and 3 microg/kg/min) caused hypertension accompanied by an increase in plasma nitrate, as assessed by high-performance capillary electrophoresis. Mechanical hypertension elicited by aortic occlusion also was accompanied by an increase in plasma nitrate. Angiotensin II (0.03, 0.3, and 3 microg/kg/min, 10 min) dose-dependently increased blood pressure. The intermediate and high dose, but not the low dose, of angiotensin II increased plasma nitrate concentration. N(G)-nitro-L-arginine methyl ester (L-NAME) lowered the basal concentration of plasma nitrate, abolished the increase in plasma nitrate elicited by angiotensin II and norepinephrine, and potentiated the pressor effect of the low dose of angiotensin II, although this dose did not increase NO production. L-NAME also potentiated the pressor effects of the intermediate dose of angiotensin II. This study demonstrates that an augmented systemic production of NO, measured as an increase in plasma nitrate, takes place after acute hypertension. The results of this study suggest that an increase in NO generation occurs when angiotensin II hypertension exceeds a certain limit, below which the basal production of NO is sufficient to compensate the vasoconstriction.

The role of nitric oxide in mediating adenosine-induced increases in uterine blood flow in the oophorectomized nonpregnant sheep

OBJECTIVE

Adenosine administration to the uterine vasculature of the nonpregnant oophorectomized sheep results in dose-related increases in uterine blood flow. This study was designed to determine whether these adenosine-induced increases in uterine blood flow are mediated in part by nitric oxide release.

STUDY DESIGN

Five nonpregnant oophorectomized ewes had catheters placed in the femoral artery and vein and in the lateral branches of the right and left main uterine arteries. Adenosine dissolved in isotonic sodium chloride solution was infused into the uterine artery at sequentially increasing doses (1, 3, 10, 30, 100, and 300 microg/min), and a dose-response curve was constructed. After determination of control responses to adenosine a 10-mg/kg dose of the nitric oxide synthase inhibitor N omega-nitro-L -arginine methyl ester was administered into the femoral vein; the dose-response curves to adenosine were then determined again. Responses after N omega-nitro-L -arginine methyl ester administration were compared with those obtained before nitric oxide blockade.

RESULTS

Adenosine increased uterine blood flow in a dose-related fashion, from a baseline of 11 +/- 2 mL/min to 140 +/- 19 mL/min. No further increase was seen with adenosine doses >300 microg/min. There were no significant alterations in systemic arterial pressure or heart rate in response to uterine infusion of adenosine. N omega-nitro-L -arginine methyl ester administration increased baseline blood pressure 24% +/- 4% and decreased heart rate 13% +/- 4%. Responses to adenosine after N omega-nitro-L -arginine methyl ester administration were significantly reduced, from a maximum at the highest dose of 140 +/- 19 mL/min to 95 +/- 13 mL/min (P <.001).

CONCLUSION

A significant portion of adenosine-induced vasodilation in the uterine vasculature appears to be mediated by the release of nitric oxide.

Role of caveolin in hemodynamic force-mediated endothelial changes

BACKGROUND

Caveolin has been shown to play an important role in signal transduction and nitric oxide synthase production. The purpose of this study was to investigate whether caveolin was tyrosine phosphorylated or activated by shear stress or cyclic strain in bovine aortic endothelial cells (BAECs).

MATERIALS AND METHODS

BAECs were subjected to an average of 10% strain at a rate of 60 cycles/min or a laminar shear stress of 10 dyn/cm(2) for up to 4 h. Immunoblotting with anticaveolin antibody was performed to assess activation of caveolin. Coimmunoprecipitation of anticaveolin antibody with anti-tyrosine phosphorylation antibody was performed to detect the tyrosine phosphorylation of caveolin.

RESULTS

Neither cyclic strain nor shear stress at physiologic levels altered the level of caveolin protein. Tyrosine phosphorylation of caveolin could not be observed at any time under either cyclic strain or shear stress condition.

CONCLUSION

Although hemodynamic forces alter nitric oxide synthase production and activate signal transduction, caveolin levels or activity is not altered in endothelial cells exposed to shear stress or cyclic strain.

Ultrasound measurement of brachial flow-mediated vasodilator response

Brachial artery flow-mediated vasodilation is increasingly used as a measure of endothelial function. High resolution ultrasound provides a noninvasive method to observe this flow-mediated vasodilation by monitoring the diameter of the artery over time following a transient flow stimulus. Since hundreds of ultrasound images are required to continuously monitor brachial diameter for the 2-3 min during which the vasodilator response occurs, an automated diameter estimation is desirable. However, vascular ultrasound images suffer from structural noise caused by the constructive and destructive interference of the backscattered signals, and the true boundaries of interest that define the diameter are frequently obscured by the multiple-layer structure of the vessel wall. These problems make automated diameter estimation strategies based on the detection of the vessel wall boundary difficult. We obtain a robust automated measurement of the vasodilator response by automatically locating the artery using a variable window method, which gives both the lumen center and width. The vessel wall boundary is detected by a global constraint deformable model, which is insensitive to the structural noise in the boundary area. The ambiguity between the desired boundary and other undesired boundaries is resolved by a spatiotemporal strategy. Our method provides excellent reproducibility both for interreader and intrareader analyzes of percent change in diameter, and has been successfully used in analyzing over 4000 brachial flow-mediated vasodilation scans from several medical centers in the United States.

Nitric oxide as a signaling molecule in the vascular system: an overview

In retrospect, basic research in the fields of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) during the past two decades appears to have followed a logical course, beginning with the findings that NO and cGMP are vascular smooth muscle relaxants, that nitroglycerin relaxes smooth muscle by metabolism to NO, progressing to the discovery that mammalian cells synthesize NO, and finally the revelation that NO is a neurotransmitter mediating vasodilation in specialized vascular beds. A great deal of basic and clinical research on the physiologic and pathophysiologic roles of NO in cardiovascular function has been conducted since the discovery that endothelium-derived relaxing factor (EDRF) is NO. The new knowledge on NO should enable investigators in this field to develop novel and more effective therapeutic strategies for the prevention, diagnosis, and treatment of numerous cardiovascular disorders. The goal of this review was to highlight the early research that led to our current understanding of the pathophysiologic role of NO in cardiovascular medicine. Furthermore, we discussed the possible mechanism of some drugs interfering with NO signaling cascade.

Bacterial translocation in cirrhotic rats stimulates eNOS-derived NO production and impairs mesenteric vascular contractility

Nitric oxide (NO) has been implicated in the arterial vasodilation and associated vascular hyporesponsiveness to vasoconstrictors observed in liver cirrhosis. Bacteria, potent activators of NO and TNF-alpha synthesis, are found in the mesenteric lymph nodes (MLNs) of ascitic cirrhotic rats. Here, we investigated the impact of bacterial translocation (BT) to MLNs on TNF-alpha production, vascular NO release, and contractility in the mesenteric vasculature of ascitic cirrhotic rats. Vascular response to the alpha-adrenoagonist methoxamine, which is diminished in the superior mesenteric arterial beds of cirrhotic rats, is further blunted in the presence of BT. BT promoted vascular NO release in cirrhotic rats, an effect that depended on pressure-induced shear stress and was blocked by the NO inhibitor N(omega)-nitro-L-arginine. Removing the endothelium had the same effect. Endothelial NO synthase (eNOS), but not the inducible isoform (iNOS), was present in mesenteric vasculature of cirrhotic rats with and without BT, and its expression was enhanced compared with controls. TNF-alpha was induced in MLNs by BT and accumulated in parallel in the serum. This TNF-alpha production was associated with elevated levels of tetrahydrobiopterin (BH(4)), a TNF-alpha-stimulated cofactor and enhancer of eNOS-derived NO biosynthesis and NOS activity in mesenteric vasculature. These findings establish a link between BT to MLNs and increased TNF-alpha production and elevated BH(4) levels enhancing eNOS-derived NO overproduction, further impairing contractility in the cirrhotic mesenteric vasculature.

Pulmonary blood flow distribution in lobar hypoxia--influence of cardiac output and nitric oxide inhalation

Inhaled NO is reported to be less effective in patients with ARDS if cardiac output is high (> 10 L/min). It has also been demonstrated that increased blood flow and increased shear stress cause an enhancement of endogenous NO production. In one-lung ventilation and regional hypoxia, nitric oxide (NO) delivered to the ventilated lung may decrease blood flow to the nonventilated lung and improve arterial oxygenation. So far, however, results have been divergent. The present study was performed with the hypothesis that inhaled NO would be less effective if cardiac output was increased. In the anaesthetized pig, hypoxia (5% O2) was induced in the left lower lobe. NO was delivered consecutively to the hypoxic lobe and to the other, oxygenated parts, of the lungs during continuous measurement of lobar blood flow and total lung blood flow. Bleeding and infusion of dextran caused variation in cardiac output. It was found that lobar hypoxia per se reduced lobar blood flow from 22.9+/-3.1% to 4.7+/-0.9% of cardiac output. An increase (3.2+/-0.3 L x min(-1)) and a decrease (2.2+/-0.2 L x min(-1)) in cardiac output did not alter the relative perfusion of the hypoxic lobe from baseline cardiac output (2.6+/-0.2 L x min(-1)) values. When NO was delivered to the hypoxic lobe, there was a marked increase in relative lobar perfusion to 19.0+/-2.9% during low cardiac output and 16.5+/-2.7% during high cardiac output without any significant difference between the two NO-induced increases of lobar perfusion. The increase in lobar perfusion tended to depend inversely on total pulmonary blood flow when cardiac output had been reduced by bleeding but without reaching statistical significance (r = -0.42, p > 0.05). The decrease in mean pulmonary artery pressure and PaO2 seen during NO inhalation to the hypoxic lobe did not correlate with the level of cardiac output. When NO was delivered to the oxygenated parts of the lungs, no significant effect on relative lobar perfusion or arterial oxygenation was observed, either at raised or at lowered cardiac output. The findings give no further evidence to show that variations in cardiac output alter the effect of NO inhalation.

Effects of shear stress on nitric oxide levels of human cerebral endothelial cells cultured in an artificial capillary system

Nitric oxide (NO) is an important vasodilator with various activities in the cerebral vasculature. Although the response of NO levels to shear stress has been investigated in various models using systemic endothelium, no study has evaluated human cerebral endothelial cells (HCE). We determined the NO levels of HCE cultured in an artificial capillary system in response to changes in shear stress. With direct measurement by a porphyrinic microsensor, we found that NO levels increased immediately with a peak at 7 h after changes in shear stress, and by 24 h dropped to a constant elevated baseline. Shear stress-mediated increases in NO levels were confirmed by the measurement of citrulline, an indirect measure of NO. Furthermore, NO levels by HCE were shown to decrease with decreasing shear stress levels. This study presents a novel system to study NO production by microvascular HCE, and indicates a linear relationship between shear stress and NO levels. As cerebral vessels age and lose transmural compliance, shear stress-mediated production of NO may play a greater role in cerebrovascular function and dysfunction.

Arterial and venous smooth muscle cell proliferation in response to co-culture with arterial and venous endothelial cells

PURPOSE

To determine whether definable differences exist between arterial and venous smooth muscle cells (SMCs), as measured by proliferative response to co-culture with arterial or venous endothelial cells (ECs).

MATERIALS AND METHODS

Human aortic ECs (A-ECs) and saphenous vein ECs (V-ECs) were cultured opposite either aortic SMCs (A-SMCs) or saphenous vein SMCs (V-SMCs). At selected time intervals, SMCs were counted by fluorescence microscopy.

RESULTS

In the presence of an intact EC monolayer, A-ECs induced a 9%-31% increase in A-SMC (P < or = .001) and a 15%-37% increase in V-SMC (P < or = .001) proliferation. Saphenous vein ECs induced a 50%-71% increase in A-SMC (P < or = .001) and a 40%-62% increase in V-SMC (P < or = .001) proliferation. The small proliferative difference between A-SMCs and V-SMCs was significant for co-culture with A-ECs (P < or = .001) and V-ECs (P < or = .001). Of note, compared to A-ECs, V-ECs induced a significantly greater A-SMC (P < or = .001) and V-SMC (P < or = .001) proliferative response.

CONCLUSION

A small, but definable, difference exists between A-SMCs and V-SMCs, as measured by proliferative response in co-culture with A-ECs and V-ECs.

Nitric oxide increases hepatic arterial blood flow in rats with carbon tetrachloride-induced acute hepatic injury

BACKGROUND & AIMS

Little is known about the changes in hepatic blood flow associated with acute hepatic injury. The aim of this study was to investigate the effect of nitric oxide (NO) on hepatic blood flow and the severity of hepatic injury in rats with carbon tetrachloride (CCl4)-induced acute hepatic injury.

METHODS

Rats were pretreated with CCl4 to induce acute hepatic injury. Hepatic blood flow was measured using a radioactive microsphere method. The role of NO in the regulation of hepatic blood flow and the severity of hepatic injury was investigated by administering NG-nitro-L-arginine (L-NNA) and aminoguanidine (AG). Plasma nitrite/nitrate levels, hepatic NO synthase (NOS) activity, and expression of hepatic NOS messenger RNA (mRNA) were measured, and histological examinations were performed.

RESULTS

Hepatic arterial and portal venous blood flow was increased significantly by CCl4, without any change in mean arterial pressure or cardiac output. L-NNA and AG dose-dependently decreased hepatic arterial blood flow, with the highest dose resulting in complete blockade of hepatic arterial dilation, but failed to change portal venous blood flow. Histologically, administration of AG aggravated the hepatic injury in CCl4-treated rats. Plasma nitrite/nitrate levels and hepatic NOS activity were increased significantly by CCl4 treatment. Inducible NOS mRNA was detected in CCl4-treated rats but not in the controls.

CONCLUSIONS

The results of this study suggest that the increased hepatic arterial blood flow in CCl4-induced acute hepatic injury is mediated by excessive NO production and up-regulated by inducible NOS, which plays a role in reducing hepatic injury.

Transmural pressure inhibits prorenin processing in juxtaglomerular cell

Pressure control of renin secretion involves a complex integration of shear stress, stretch, and transmural pressure (TP). This study was designed to delineate TP control of renin secretion with minimal influence of shear stress or stretch and to determine its mechanism. Rat juxtaglomerular (JG) cells were applied to a TP-loading apparatus for 12 h. In cells conditioned with atmospheric pressure or atmospheric pressure + 40 mmHg, renin secretion rate (RSR) averaged 29.6 +/- 3.7 and 14.5 +/- 3.3% (P < 0.05, n = 8 cultures), respectively, and active renin content (ARC) averaged 47.3 +/- 4.6 and 38.4 +/- 3.4 ng of ANG I. h(-1). million cells(-1) (P < 0.05, n = 10 cultures), respectively. Total renin content and renin mRNA levels were unaffected by TP. The TP-induced decrease in RSR was prevented by Ca(2+)-free medium and the Ca(2+) channel blocker verapamil and was attenuated by thapsigargin and caffeine, which deplete intracellular Ca(2+) stores. Thapsigargin and caffeine, but not Ca(2+)-free medium or verapamil, prevented TP-induced decreases in ARC. The adenylate cyclase activator forskolin did not modulate TP-induced decreases in RSR or ARC. These findings suggest that TP not only stimulates Ca(2+) influx but also inhibits prorenin processing through an intracellular Ca(2+) store-dependent mechanism and thus inhibits active renin secretion by JG cells.

Role of nitric oxide in the early renal hemodynamic response after unilateral nephrectomy

We evaluated the involvement of nitric oxide (NO) in the early hemodynamic response to uninephrectomy (UNX) in rats. Animals were uninephrectomized, and 48 h after removal of the kidney, the effect of infusing NG-nitro-L-arginine methyl ester (L-NAME) on renal function was studied. Glomeruli were isolated, and glomerular nitrite and cGMP productions were measured. In addition, endothelial constitutive NO synthase (NOS III) and inducible NO synthase (iNOS) were assessed by Western blot and by measuring the conversion of arginine to citrulline. UNX animals showed an increase in renal plasma flow that was inhibited by L-NAME in a higher proportion than in sham-operated (SO) animals. No differences were observed in systemic NO-dependent vascular tone, since mean arterial pressure showed similar increments in SO and UNX rats. Glomeruli from UNX animals showed an increase in glomerular nitrite production that was blunted by L-NAME addition. Also, cGMP levels were increased in glomeruli from UNX animals, and this increase was inhibited by L-NAME. Western blot analysis showed no differences in NOS III but a higher iNOS amount in glomeruli from UNX than in those from SO rats. No significant differences between UNX and SO rats were found in calcium-dependent NOS enzymatic activity in the renal cortex. However, calcium-independent enzymatic activity was markedly higher in the renal cortex of UNX than in those from SO animals. In conclusion, glomeruli from rats 48 h after UNX had a greater production of NO than those from SO animals. This increased glomerular NO production is based on an increase in the iNOS isoform. Increased glomerular NO synthesis seems to play a role in the decreased renal vascular resistance observed after unilateral nephrectomy in rats.

Both extracellular ATP and shear stress regulate the release of nitric oxide in rat caudal artery

1. To elucidate the physiological role of nitric oxide (NO) in regulating vascular tone, the effects of NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, on the vasoconstrictor response to noradrenaline (NA) in rat caudal artery was examined. 2. NG-Nitro-L-arginine methyl ester significantly potentiated the NA-induced increase in perfusion pressure in the perfused caudal artery, but did not affect the NA-induced contraction in caudal artery ring preparations. In addition, an increase in perfusion pressure mechanically produced by a stepwise increase in flow rate was not affected by L-NAME. 3. Noradrenaline evoked a significant increase in the release of endogenous ATP and its metabolites from the perfused artery, whereas increased perfusion pressure as a result of increased flow rate did not evoke release of endogenous ATP. 4. In the presence of exogenously applied ATP, L-NAME significantly potentiated the increase in perfusion pressure produced by increased flow rate. 5. These results indicate that perfused vascular tone is regulated by endogenous NO and suggest that extracellular ATP may participate in the synthesis and release of NO by shear stress in endothelial cells in the rat caudal artery.