Endothelin-dependent effects limit flow-induced dilation of conductance coronary vessels after blockade of nitric oxide formation in conscious dogs

OBJECTIVE: To determine whether endothelin (ET)-dependent effects limit shear stress-induced dilation of large epicardial coronary arteries after blockade of nitric oxide (NO) formation. METHODS: In conscious dogs instrumented for measuring coronary blood flow (CBF) and external diameter (CD) of the circumflex coronary artery, flow-dependent CD dilation was elicited by intracoronary (i.c.) adenosine (500 ng kg-1 min-1). RESULTS: I.c. adenosine increased CBF by 28 +/- 4 from 38 +/- 5 ml min-1 and CD by 0.25 +/- 0.03 from 3.53 +/- 0.07 mm without other hemodynamic effects. After N omega-nitro-L-arginine methyl ester (L-NAME), baseline CD fell (P < 0.01) to 3.35 +/- 0.08 mm but CBF was not significantly altered (36 +/- 5 ml min-1). CBF increases caused by adenosine were smaller (17 +/- 2 ml min-1, P < 0.05) and CD responses were nearly abolished (0.02 +/- 0.01 mm, P < 0.01). I.c. Ro 61-1790, an ETA receptor blocker, given after L-NAME did not significantly influence baseline CBF (36 +/- 5 ml min-1) but increased (P < 0.01) CD to 3.45 +/- 0.09 mm. CBF responses to adenosine were not significantly altered by Ro 61-1790 but CD responses (0.10 +/- 0.01 mm) were partially restored (P < 0.01). In contrast, blockade of ETB receptors with Ro 46-8443 after L-NAME had no further effects on CD and CBF responses to adenosine. CONCLUSION: ETA receptor-mediated effects limit flow-dependent dilation of large epicardial coronary arteries in conscious dogs. Suppression of the L-arginine/NO-dependent pathway with L-NAME reveals significant ET-dependent effects.     

A study on coronary hemodynamics during acetylcholine-induced coronary spasm in patients with variant angina: endothelium-dependent dilation in the resistance vessels.

The epicardial coronary artery of patients with variant angina is hyperreactive to the constrictive effect of acetylcholine, but it is not known whether the coronary microvasculature also constricts in response to acetylcholine. Incremental doses of acetylcholine were injected into the left coronary artery of 57 patients with variant angina and with spasm in this artery. By measuring coronary sinus blood flow, coronary hemodynamic status just before angiographic documentation of spasm was examined. Acetylcholine induced spasm in the left coronary artery in all patients. It also decreased the diameter of the nonspasm artery by 36 +/- 19% from baseline. For all patients, coronary sinus blood flow was 89 +/- 38 ml/min at baseline and increased to 104 +/- 61 ml/min during an acetylcholine-induced anginal attack (p less than 0.01). In 10 patients with spasm in both the left anterior descending and left circumflex arteries (that is, multivessel spasm), coronary sinus blood flow decreased from 84 +/- 21 to 52 +/- 26 ml/min (p less than 0.01). In the other 47 patients with spasm in only one of these two arteries (that is, single-vessel spasm), coronary sinus blood flow increased from 90 +/- 41 to 115 +/- 61 ml/min (p less than 0.01) without change in the rate-pressure product. It is concluded that in patients with variant angina, acetylcholine induces spasm and constriction in the epicardial coronary artery, whereas it dilates the resistance vessels presumably through the release of the endothelium-dependent relaxing factor.     

Prostaglandins mediate bradykinin-induced reduction of exhaled nitric oxide in asthma.

Bradykinin (BK) is a mediator of inflammation in asthma with potent bronchoconstrictor actions. Endogenous release of nitric oxide may inhibit BK-induced bronchoconstriction. This study investigated whether bradykinin inhalation could modulate exhaled NO levels in normal and asthmatic subjects, and whether the bradykinin-induced effects were mediated through the production of cyclo-oxygenase products in patients with asthma, by studying the effect of the cyclo-oxygenase inhibitor, L-acetylsalicylic acid (L-ASA). Exhaled NO concentration and forced expiratory volume in one second (FEV1) were measured by chemiluminescence following inhalation of increasing concentrations of BK. In asthmatics (n=11), BK induced a dose-dependent decrease in exhaled NO concentration from 21.3+/-1.6 to 6.+/-0.5 parts per billion (ppb) (p<0.01) at the highest concentration, associated with a significant fall in FEV1. In normal subjects (n=10), the exhaled NO concentration fell from 7.2+/-0.13 to 4.3+/-0.51 ppb (p<0.001) 15 min, after a single inhalation of BK, but without a significant change in FEV1. In asthmatic subjects, pretreatment with inhaled L-ASA (90 x mg x mL(-1), 4 mL) did not alter exhaled NO levels, but prevented a BK-induced fall in exhaled NO concentration, as indicated by a significant increase in exhaled NO levels at the provocative concentration of BK causing a 20% fall in FEV1, (5.7 +/- 0.94 ppb after placebo and 12.0 +/- 1.8 ppb after L-ASA; p<0.05). L-ASA significantly reduced bronchial responsiveness to BK 3.9-fold (p<0.01). Inhaled bradykinin induced bronchoconstriction and a reduction in exhaled nitric oxide levels in asthmatic subjects, an effect that is partly mediated by cyclo-oxygenase products.     

Coexistence of impairment of endothelium-derived nitric oxide and platelet-derived nitric oxide in patients with coronary risk factors.

Impairment of endothelium-derived nitric oxide (EDNO) has been demonstrated in patients with coronary risk factors in some studies, as well as impaired platelet-derived nitric oxide (PDNO) in other studies. However, no study has examined whether these impairments coexist. In 24 patients with coronary risk factors, femoral vascular endothelial function was assessed with acetylcholine (ACh: 50, 100, 200 and 400 microg/min) and endothelium-independent vascular function with nitroglycerin (NTG; 50, 100, 200 microg/min) using a Doppler flow-wire technique, as well as ADP (5 micromol/L)-induced PDNO release with an NO-specific electrode. The ACh-mediated percent change in femoral vascular resistance index (% change of FVRI) and PDNO release had a significant correlation with the number of risk factors. The ACh-mediated % change of FVRI, but not that with NTG, significantly correlated with the PDNO release. Both EDNO and PDNO bioactivities are impaired in patients with coronary risk factors and there is a common mechanism.     

Impact of hypercholesterolemia on acidosis-induced coronary microvascular dilation

An increase in coronary flow conductance during acidosis is an important compensatory mechanism in various diseased conditions. On the other hand, hypercholesterolemia causes microvascular dysfunction as well as macrovascular disorders. We investigated the impact of hypercholesterolemia on the coronary microvascular response to acidosis. Coronary arterioles (< 150 μm) isolated from rabbit hearts were cannulated to micropipettes in a vessel chamber and the microvascular responses were observed. After preconstriction was established, the extravascular pH was gradually reduced from 7.4 to 7.0. The effects of glibenclamide, ATP-sensitive K⁺ (K_ATP) channel blocker, (1 μM, n = 4) or pertussis toxin (100 ng/mL, n = 7) on the acidosis-induced microvascular responses were examined. In another set of experiments, rabbits were randomly assigned to normal chow (NC group, n = 18) or high cholesterol (2 %) diet (HC group, n = 20). After 8 weeks of feeding, the responses of isolated coronary arterioles to acidosis, ADP, nitroprusside, and levcromakalim were examined in the two groups. Coronary arterioles significantly dilated as the pH was reduced and the dilation was significantly inhibited by glibenclamide or pertussis toxin. Acidosis-induced dilation in the HC group was significantly attenuated compared to the NC group (36.5 ± 2.1 % vs 73.7 ± 4.8 % at pH = 7.0 P < 0.05). There were no significant differences in the dilations by ADP, nitroprusside and levcromakalim between the two groups. In conclusion, acidosis-induced dilation of rabbit coronary arterioles is mediated by the activation of the pertussis toxin-sensitive G protein and K_ATP channels, and the dilation of coronary arterioles is impaired in hypercholesterolemia. The impairment occurs upstream of K_ATP channel opening. Received: 19 July 2002, Returned for revision: 1 August 2002, Revision received: 25 September 2002, Accepted: 14 October 2002 Correspondence to: T. Komaru, M.D.     

Rosuvastatin improves basal nitric oxide activity of the renal vasculature in patients with hypercholesterolemia

ObjectiveImpaired endothelium-dependent vasodilation represents an early manifestation of atherosclerosis. Prospective studies have demonstrated that impaired endothelial function in the peripheral circulation of hypercholesterolemic patients predicts CV events and can be restored by statin treatment. Whether this also holds true in the renal circulation has not yet been adequately addressed.MethodsIn a double-blind, randomized, placebo-controlled cross-over trial, 40 hypercholesterolemic patients were randomly assigned to receive rosuvastatin (10 mg/day) and matching placebo. The primary objective of the study was to assess the effect of 6-week treatment with rosuvastatin on basal NOS activity of the renal vasculature, as assessed by measuring renal plasma flow (RPF) both before and after blockade of NOS with systemic infusion of N^G-monomethyl-l-arginine (l-NMMA). In a subgroup of 20 patients we also studied the effects of a 3-day treatment regimen.ResultsCompared to placebo treatment, rosuvastatin decreased LDL-cholesterol levels both after 3 days and 6 weeks of treatment. The decrease in RPF in response to l-NMMA was significantly more pronounced after 6-week therapy with rosuvastatin compared to placebo (?13.7 ± 1.0% versus ?11.3 ± 0.7%; p = 0.046), indicating increased basal NOS activity with rosuvastatin treatment. A trend towards improved basal NOS activity was already evident after 3-day treatment.ConclusionTreatment with rosuvastatin improved basal NOS activity in the renal circulation of hypercholesterolemic patients, suggestive of a nephroprotective effect. In view of the close relation between altered renal function and cardiovascular events, these nephroprotective effects may contribute to the improved CV prognosis associated with statin treatment.     

The role of nitric oxide

When studying the impact of endothelins (ETs) on physiology and pathophysiology, this needs to be done in the context of nitric oxide (NO) synthesis and action, since these two are closely intertwined in their action. Here, we will review the work demonstrating the crosstalk between endothelin-1 (ET-1) and NO, and the recent developments regarding the role of these two mediators in inflammatory processes. Moreover, we will discuss the role of NO in pro-inflammatory diseases and the potential mechanisms of the anti-inflammatory activity of ET receptor antagonism.     

冠状动脉痉挛患者血清一氧化氮含量的变化

目的测定冠状动脉痉挛患者乙酰胆碱试验前后血清一氧化氮(NO)含量,以探讨冠状动脉痉挛的发生机制。方法选择临床上具有胸痛表现,但冠状动脉造影无显著狭窄的患者进行乙酰胆碱试验。在术前及乙酰胆碱试验后即刻取动脉血,采用Griess法检测NO含量,比较痉挛与非痉挛患者血液中NO水平。结果34例患者接受了乙酰胆碱试验,其中21例乙酰胆碱试验阳性(A组),13例阴性(B组)。乙酰胆碱试验前,A组血清中NO含量略低于B组(P>005);乙酰胆碱试验后,A组血清中NO含量略有下降,B组明显升高,B组NO水平显著高于A组(P<001)。结论冠状动脉痉挛患者血管壁NO储备量明显低于正常,NO减少参与了冠状动脉痉挛的发生。     

The relationship between insulin resistance and polymorphisms of the endothelial nitric oxide synthase gene in patients with coronary artery disease

Nitric oxide (NO) regulates endothelial function and is believed to prevent atherogenesis. In endothelial cells, endothelial nitric oxide synthase (eNOS) is expressed constitutively, and regulates NO synthesis. A mutation of the eNOS gene has been associated with the development of coronary artery disease (CAD). The development of CAD is also influenced by insulin resistance, and recent studies suggest that NO might affect cellular insulin activity. We investigated the association between eNOS polymorphisms and insulin resistance in patients with CAD. We screened 45 patients with a history of myocardial infarction (MI), angina pectoris (AP), or coronary spasm. Genotypes were determined by polymerase chain reaction-restriction fragment-length polymorphism analysis. We examined two polymorphisms of the eNOS gene (The T(-786)-->C variant and the missense Glu298Asp variant). Insulin resistance was measured by determining the plasma immunoreactive insulin concentration at the 120 min time point (IRI 120) of a 75 g oral glucose tolerance test. The IRI 120 of the T(-786)-->C variant group was higher than that for the control group (p<0.05). This finding demonstrates that the T(-786)-->C mutation in the eNOS gene decreases insulin sensitivity.     

The role of measurement of exhaled nitric oxide in asthma patients

The aim of the study was to evaluate exhaled nitric oxide levels (F(ENO)) in asthmatics and to establish the possible correlation of these measurements with clinical symptoms, disease severity, anti-inflammatory treatment and spirometric indices. The measurement of exhaled NO was performed using NO analyser model 280i, Sievers Instruments, Inc., USA. This measurement was based on the gas phase chemiluminescence reaction between NO and ozone. The investigations were performed on the group of 85 asthmatic patients (34 with chronic mild asthma, 31 with chronic moderate asthma, 20 with chronic severe asthma). F(ENO) level in healthy, non-smoking volunteers (46 persons--control group) was mean 12.9 +/- 4.6 ppB and it was statistically significant lower than in all groups of asthmatics. The highest F(ENO) levels were observed in patients with severe asthma (74 +/- 72 ppB). Statistically significant lower levels of ENO were obtained in patients with moderate (42 +/- 31 ppB) and mild asthma (49 +/- 43 ppB). In all groups of asthmatic patients higher levels of F(ENO) were observed in subjects with allergic asthma. In patients with mild and moderate asthma ENO levels were negatively correlated with the used dosage of inhaled steroids. Similar dependences were not noticed in patients with severe asthma. The measurement of exhaled nitric oxide levels provides a rapid, reproducible, non-invasive and reliable test, which is very useful in diagnosis and treatment monitoring in asthmatic patients.     

cAMP-independent dilation of coronary arterioles to adenosine : role of nitric oxide, G proteins, and K(ATP) channels.

Adenosine is known to play an important role in the regulation of coronary blood flow during metabolic stress. However, there is sparse information on the mechanism of adenosine-induced dilation at the microcirculatory levels. In the present study, we examined the role of endothelial nitric oxide (NO), G proteins, cyclic nucleotides, and potassium channels in coronary arteriolar dilation to adenosine. Pig subepicardial coronary arterioles (50 to 100 microm in diameter) were isolated, cannulated, and pressurized to 60 cm H(2)O without flow for in vitro study. The arterioles developed basal tone and dilated dose dependently to adenosine. Disruption of endothelium, blocking of endothelial ATP-sensitive potassium (K(ATP)) channels by glibenclamide, and inhibition of NO synthase by N(G)-nitro-L-arginine methyl ester and of soluble guanylyl cyclase by 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one produced identical attenuation of vasodilation to adenosine. Combined administration of these inhibitors did not further attenuate the vasodilatory response. Production of NO from coronary arterioles was significantly increased by adenosine. Pertussis toxin, but not cholera toxin, significantly inhibited vasodilation to adenosine, and this inhibitory effect was only evident in vessels with an intact endothelium. Tetraethylammonium, glibenclamide, and a high concentration of extraluminal KCl abolished vasodilation of denuded vessels to adenosine; however, inhibition of calcium-activated potassium channels by iberiotoxin had no effect on this dilation. Rp-8-Br-cAMPS, a cAMP antagonist, inhibited vasodilation to cAMP analog 8-Br-cAMP but failed to block adenosine-induced dilation. Furthermore, vasodilations to 8-Br-cAMP and sodium nitroprusside were not inhibited by glibenclamide, indicating that cAMP- and cGMP-induced dilations are not mediated by the activation of K(ATP) channels. These results suggest that adenosine activates both endothelial and smooth muscle pathways to exert its vasodilatory function. On one hand, adenosine opens endothelial K(ATP) channels through activation of pertussis toxin-sensitive G proteins. This signaling leads to the production and release of NO, which subsequently activates smooth muscle soluble guanylyl cyclase for vasodilation. On the other hand, adenosine activates smooth muscle K(ATP) channels and leads to vasodilation through hyperpolarization. It appears that the latter vasodilatory process is independent of G proteins and of cAMP/cGMP pathways.     

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.     

The role of nitric oxide in mediating endothelium dependent relaxations in the human epicardial coronary artery.

We have examined the ability of the endothelium of human epicardial coronary arteries to secrete vasorelaxant substances in response to pharmacological stimulation and under basal conditions. In addition, we have attempted to characterise the chemical identity and biochemical pathway for the synthesis of endothelial derived relaxing factor. Human epicardial coronary arteries were removed from patients who were undergoing heart transplantation for reasons other than ischaemic heart disease. Arteries were cut into segments and suspended in 5 ml organ baths containing a modified Tyrodes solution at 37 degrees C, and gassed with a mixture of 95% oxygen and 5% carbon dioxide. Substance P (10(-10) - 10(-7) M) elicited a dose-dependent relaxation of the coronary segments but this action of substance P was dependent upon an intact endothelium. The maximum response of substance P was equivalent to 89 +/- 8.5% of the maximum effect induced by 1 microgram/ml glyceryl trinitrate. This vasorelaxant effect of substance P was unaffected by the presence of 10(-6) M indomethacin. L-NG-monomethyl-arginine (10(-4) M), a specific inhibitor of formation of nitric oxide from L-arginine, antagonised the relaxations induced by substance P, decreasing the maximum response of substance P to 34 +/- 10.5% of the response to glyceryl trinitrate. Upon application, L-NG-monomethyl-arginine caused a further 23.1 +/- 3.0 increase in tension on preconstricted vessels. This increase in tension was reversed with the addition of L-arginine, but was unaffected by D-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of nitric oxide in articular cartilage damage.

The production of large amounts of NO in vitro by cytokine-activated chondrocytes has been established. In vitro studies suggest that NO compromises chondrocyte survival. The role of NO in regulating matrix biosynthesis and degradation has received much attention. Most studies indicate that NO is at least partly responsible for IL-1-induced suppression of glycosaminoglycan and collagen synthesis. NO also may be involved as a mediator of IL-1-induced expression of MMP, mRNA, and protein and may contribute as an activator of the latent forms of the enzymes. Although the interaction of NO and prostaglandins is of considerable interest, current data are inconclusive with respect to the role of NO in the regulation of prostaglandin synthesis, although it seems clear that prostaglandin is not involved in NO synthesis. It is important to note that NO does have protective effects in cartilage and other tissues. Under certain conditions, NO may have anabolic and anticatabolic effects in cartilage. In other tissues, notably in skin and muscle, NO has been found to have a stimulatory role in extracellular matrix repair. In antimicrobial defense, in general, and in bacterial arthritis specifically, NO is an important protective molecule. Production of NO in arthritis-affected cartilage and synovium is a consistent feature of human and experimentally induced arthritis. The production of NO is associated with matrix degradation and chondrocyte apoptosis. The administration of NO synthase inhibitors in experimentally induced arthritis has resulted in reduction of synovial inflammation and destruction of cartilage and bone.     

Sickle cell anemia is associated with reduced nitric oxide bioactivity in peripheral conduit and resistance vessels

The purpose of the study was to examine endothelium-dependent and -independent vasodilation of conduit and resistance vessels in sickle cell anemia (HbSS). We measured the effects of intra-arterial infusion of methacholine, sodium nitroprusside, and NG-monomethyl-L-arginine (L-NMMA) on forearm blood flow using venous occlusion plethysmography in eight patients with HbSS and 11 HbAA controls. We assessed vasodilation of the conduit brachial artery using ultrasound in 17 patients with HbSS and 41 nonanemic controls. Forearm blood flow response to methacholine was similar in HbSS and HbAA, while the response to sodium nitroprusside was greater in those with HbSS. Nitric oxide synthase inhibition with L-NMMA attenuated methacholine-induced forearm blood flow to a lesser extent in HbSS compared to HbAA, suggesting diminished nitric oxide (NO) contribution to endothelium-dependent vasodilation. Flow-mediated and nitroglycerin-induced dilation were impaired in HbSS compared to controls and were not affected by the antioxidant vitamin C or the precursor substrate for NO synthesis L-arginine. NO bioactivity is reduced but differs in peripheral conduit and resistance vessels in HbSS. Resistance vessels have preserved response to exogenous NO donors but have diminished contribution of NO to endothelium-dependent vasodilation. Conduit vessels demonstrate impaired vasodilation to endogenous and exogenous NO.     

冠心病患者一氧化氮分泌周期的初步研究

目的 :了解冠心病 ( CAD)患者及正常人 2 4h6个时间位点血浆和淋巴细胞中一氧化氮( NO)的周期性分泌特点。方法 :CAD组 63例 ,正常组 2 5例 ,二组于 6Am、10 Am、2 Pm、6Pm、10 Pm及次日 2 Am,每隔 4h6个时间位点分别采取肘静脉血 3ml,分离血浆及淋巴细胞 ,高效液相色谱仪间接紫外光度法测定 NO-2 含量 ,以表示 NO值。结果 :1正常人 2 4h血浆和淋巴细胞中 NO分泌呈上午高、下午低的趋势 ,晨 6时最高 ,下午 6时呈低谷 ,晚 10时起又渐升高至早晨 ;2 CAD心绞痛患者血浆和淋巴细胞中 NO含量明显低于正常人 ,其差异具有统计学意义 ( P<0 .0 1) ;3CAD患者失去了正常的 NO生理性分泌曲线 ,血浆和淋巴细胞中 2 4h均在较低水平 ,波动范围不大。结论 :NO在正常人体中并非 2 4h均衡分泌 ,而存在着晨高午低趋势。CAD心绞痛患者不仅 NO分泌减少 ,分泌周期也消失。     

C-reactive protein levels determine systemic nitric oxide bioavailability in patients with coronary artery disease.

AIM: Elevated C-reactive protein (CRP) levels are associated with impaired endothelial vasoreactivity in patients with coronary artery disease (CAD). Because inflammatory cytokines experimentally reduce basal and stimulated endothelial nitric oxide (NO) release, we hypothesised that patients with elevated CRP-levels are characterised by a systemic impairment in NO bioavailability. METHODS AND RESULTS: Forearm blood flow (FBF) responses were measured by venous occlusion plethysmography in 75 male patients with documented CAD. Inhibition of NO synthesis by infusion of L-NMMA significantly reduced baseline FBF (2.2 +/- 0.5 vs. 1.9 +/- 0.5 mL/min/100 mL of forearm tissue, P < 0.001) and acetylcholine-stimulated FBF responses (AUC: 35.0 +/- 16.0 vs. 25.9 +/- 11.9; P < 0.001). CRP serum levels were inversely correlated with L-NMMA-induced decreases in baseline as well as acetylcholine-stimulated FBF responses. Co-infusion of the oxygen-derived free radical scavenger vitamin C significantly increased baseline FBF from 2.0 +/- 0.5 to 2.5 +/- 0.7 (mL/min/100 mL forearm tissue (P < 0.001)) and acetylcholine-stimulated FBF responses in patients with elevated CRP, but not in patients with low CRP serum levels. Vitamin C-induced increases in baseline FBF and in acetylcholine-stimulated FBF responses were significantly correlated with CRP serum levels. By multivariable analysis, CRP serum levels remained the only statistically significant independent predictor of NO bioavailability in the systemic circulation of patients with CAD. CONCLUSIONS: In patients with CAD, low grade systemic inflammation is associated with increased in vivo oxidative stress leading to impaired systemic bioavailability of NO, which might significantly contribute to the transition from stable coronary artery disease to acute coronary syndromes.