Smoking impairs the activity of endothelial nitric oxide synthase in saphenous vein

Role of endothelial dysfunction in insulin resistance

The endothelium regulates vascular tone through the release of vasodilating and vasoconstricting substances. The most important of these vasodilating substances is nitric oxide (NO), which is also vascular protective and inhibits inflammation, oxidation, vascular smooth muscle cell proliferation, and migration. Damage to the endothelium causes endothelial dysfunction with impaired release of NO and loss of its antiatherogenic protection. Traditional risk factors for coronary artery disease, including diabetes, hypercholesterolemia, hypertension, and low levels of high-density lipoprotein cholesterol, are associated with endothelial dysfunction and thus promote the atherogenic process. More recently, insulin resistance in the absence of overt diabetes or the metabolic syndrome has been associated with endothelial dysfunction. This association provides evidence that the atherosclerotic process may actually begin earlier in the spectrum of insulin resistance, ultimately resulting in a progression of the metabolic syndrome to prediabetes and then to type 2 diabetes. Aggressive treatment of dyslipidemia and hypertension, even before the onset of type 2 diabetes, would appear prudent in decreasing the progression of the atherosclerotic process. The thiazolidinediones are peroxisome proliferator-activated receptor-gamma agonists that improve glucose and lipid metabolism. These agents have recently been shown to improve endothelial function in the early stages of insulin resistance. Results from ongoing trials with thiazolidinediones will reveal whether they will also reduce cardiovascular end points.

Metabolism-based inactivation of neuronal nitric-oxide synthase by components of cigarette and cigarette smoke

It has been shown that administration of cigarette smoke to rats leads to loss of neuronal nitric-oxide synthase (nNOS) activity and nNOS protein in penile tissue. The exact mechanism for this loss of activity and protein is not known. In the current study, we investigated whether extracts prepared from cigarette smoke or from the cigarette itself could directly inhibit nNOS activity. We discovered that the cigarette smoke extract and the cigarette extract cause a time-, concentration-, and calmodulin-dependent inactivation of nNOS in an in vitro system containing the purified enzyme. L-Arginine, but not D-arginine, protects nNOS from this time-dependent inactivation, suggesting an active site directed event. The kinetics of inactivation are consistent with the metabolism-based or suicide inactivation of nNOS. Based on studies with other metabolism-based inactivators, this cigarette-mediated inactivation may render nNOS more susceptible to proteasomal degradation and thereby may explain the loss of nNOS protein in vivo. The component(s) responsible for nNOS inactivation is not volatile, is not retained by a 3,000 molecular weight cut-off membrane, binds to activated charcoal, and is highly water-soluble under both acidic and basic conditions. The discovery of a direct inactivation of nNOS by an organic, cationic compound(s) present in tobacco and tobacco smoke provides a basis for further study of not only the mechanisms responsible for the biological effects of tobacco but also a search for a potentially novel inactivator of nNOS.

Tetrahydrobiopterin attenuates homocysteine induced endothelial dysfunction

Homocysteine is an independent risk factor for atherosclerotic vascular disease. It impairs endothelial function via increasing superoxide production and quenching nitric oxide (NO) release. Tetrahydrobiopterin (BH4) is a critical cofactor that couples nitric oxide synthase and facilitates the production of nitric oxide (vs. superoxide anions). In the first study, the effects of hyperhomocysteinemia (0.1 mM, 3 h) on endothelium-dependent vasorelaxation to ACh and A23187 were examined in isolated segments of rat aortae in the presence or absence of BH4 (0.1 mM). In the second study, the effects of hyperhomocysteinemia (24 h) on nitric oxide production and superoxide release (using lucigenin chemiluminescence) were studied in human umbilical vein endothelial cells in the absence or presence of BH4 (10 microM). Homocysteine incubation impaired receptor-dependent and -independent endothelial function to ACh and A23187. This effect was attenuated by BH4. Furthermore, homocysteine exposure increased superoxide production and impaired agonist-stimulated nitric oxide release. These effects were attenuated by BH4 (p < 0.05). Hyperhomocysteinemia impairs endothelial function, in part due to a diminished bioavailability of BH4 with resultant uncoupling of nitric oxide synthase. BH4 may represent an important target for strategies aimed at improving endothelial dysfunction secondary to hyperhomocysteinemia.

Two week nicotine treatment selectively increases bone vascular constriction in response to norepinephrine

This study was designed to determine if nicotine treatment alters the constrictor and/or dilator function of the vessels which regulate blood flow to intact bone. Nicotine (1.7 mg/kg/day) or nicotine-free, phosphate-buffered saline was administered subcutaneously to mature male rats for 2 weeks via osmotic mini-pumps. On the 14th day, the rats were anesthetized and in vivo experiments were performed to quantitate the changes in arterial blood pressure and perfusion of the intact tibia (measured by laser Doppler flowmetry) in response to two constrictor agonists (norepinephrine, NE and arginine vasopressin, AVP) and two vasodilator agents (acetylcholine, ACh and sodium nitroprusside, SNP). Dose-response curves were generated by plotting the change in the bone vascular resistance index (mmHg/bone perfusion units) evoked by each dose of agonist. In addition, bone arteriolar expression of endothelial nitric oxide synthase protein was quantitated by Western blot analysis. Nicotine treatment significantly enhanced the constriction of the bone vasculature in response to NE, but not to AVP. Vascular dilation in response to ACh and SNP was not changed by nicotine. These results indicate that nicotine selectively accentuates the constrictor response of the bone vasculature to exogenous NE. This enhanced constriction to NE is not due to impaired endothelial cell release of nitric oxide or diminished smooth muscle response to nitric oxide. Since NE and AVP activate similar cell signaling mechanisms to induce constriction, the selective enhancement of NE-induced constriction suggests that nicotine alters a mechanism unique to NE signaling; possibly the number or binding affinity of alpha adrenergic receptors. Since endogenous NE regulates basal blood flow to bone, the effect of nicotine to augment NE-induced constriction could lead to a chronic reduction in blood flow to bone.

Genetic influence on cigarette-induced cardiovascular disease

Cigarette smoking as an addictive habit has accompanied human beings for more than 4 centuries. It is also one of the most potent and prevalent environmental health risks human beings are exposed to, and it is responsible for more than 1000 deaths each day in the United States. With recent research progress, it becomes clear that cigarette smoking can cause almost all major diseases prevalent today, such as cancer or heart disease. These detrimental effects are not only present in active smokers who choose the risk, but also to innocent bystanders, as passive smokers, who are exposed to cigarettes not-by-choice. While the cigarette-induced harm to human health is indiscriminate and severe, the degree of damage also varies from individual to individual. This intersubject variability in cigarette-induced pathologies is partly mediated by genetic variants of genes that may participate in detoxification process, eg, cytochrome P450 (CYP), cellular susceptibility to toxins, such as p53, or disease development. Through population studies, we have learned that certain CYP1A1 variants, such as Mspl polymorphism, may render the carriers more susceptible to cigarette-induced lung cancer or severe coronary atherosclerosis. The endothelial nitric oxide synthase intron 4 rare allele homozygotes are more likely to have myocardial infarction if they also smoke. In vitro experimental approach has further demonstrated that cigarettes may specifically regulate these genes in genotype-dependent fashion. While we still know little about genetic basis and molecular pathways for cigarette-induced pathological changes, understanding these mechanisms will be of great value in designing strategies to further reduce smoking in targeted populations, and to implement more effective measures in prevention and treatment of cigarette-induced diseases.

Impairment of nitric oxide synthase-dependent dilatation of cerebral arterioles during infusion of nicotine

The effects of nicotine on nitric oxide synthase (NOS)-dependent reactivity of cerebral arterioles remain uncertain. Our first goal was to examine whether infusion of nicotine alters NOS-dependent reactivity of cerebral arterioles. Our second goal was to examine the mechanisms that may account for the effects of nicotine on cerebral arterioles. We measured the diameter of pial arterioles to NOS-dependent (ADP and acetylcholine) and NOS-independent (nitroglycerin) agonists before and after the infusion of nicotine (2 microg x kg(-1) x min(-1) iv for 30 min, followed by a maintenance dose of 0.35 microg x kg(-1) x min(-1)). ADP- and acetylcholine-induced vasodilatation was impaired after the infusion of nicotine. In contrast, nicotine did not alter vasodilatation to nitroglycerin. Next, we examined whether the impaired responses of pial arterioles during infusion of nicotine may be related to oxygen radicals. We found that application of superoxide dismutase or tetrahydrobiopterin during infusion of nicotine could prevent impaired NOS-dependent vasodilatation. Thus acute exposure of cerebral vessels to nicotine specifically impairs NOS-dependent dilatation via the production of oxygen radicals possibly related to an alteration in the utilization of tetrahydrobiopterin.

Peripheral and central arterial haemodynamic interactions are early abnormalities in young male cigarette smokers

BACKGROUND

smoking, result in endothelial dysfunction and this affects systemic and local haemodynamics. The aim was to assess interactions of the left ventricle and arterial system of smokers at baseline and after a physiological stimulus--the cold pressor test (CPT) which causes a sympathetically driven vasoconstriction that counteracts the normal endothelial dependent vasodilatation.

MATERIALS AND METHODS

male smokers and controls were compared using applanation tonometry. Parameters included systolic and diastolic blood pressure, ejection duration, heart rate, aortic augmentation index (AAI), and sub-endocardial viability ratio (SEVR). The CPT was performed at 1 and 3 min following immersion of the hand in ice.

RESULTS

smokers have abnormal baseline cardiac timing (heart rate and ejection duration), systolic and diastolic blood pressures which are due to increased peripheral wave reflection (AAI) and thus affect the SEVR. Following CPT, the pressure wave differential, dP/dt, was significantly increased in smokers compared to non-smokers who had a decrease at 1 min in ice. Mean systolic and diastolic pressure was significantly increased in both groups at 1 and 3 min as was end systolic pressure in non-smokers.

CONCLUSIONS

baseline ventriculo-vascular dynamics, are abnormal as was the evoked response to CPT. The blunted blood pressure increase of smokers compared to controls following CPT, may represent altered nitric oxide production in the macro and microcirculation through differential upregulation of endothelial nitric oxide synthase (eNOS) and inducible NOS respectively. The potential for therapeutic intervention and prevention of ongoing endothelial injury, requires further investigation.

Different contribution of apoptosis to the antiproliferative effects of L-arginine, enalapril and losartan on neointimal growth inhibition after balloon arterial injury

It remains to be clarified how angiotensin-converting enzyme inhibitor-induced function (ie, increased NO related action or the inhibition of angiotensin II AT1 receptor dependent action) affects apoptosis of smooth muscle cells in the neointima following arterial injury. Saline (control), enalapril, L-arginine, combined enalapril and L-arginine, or losartan was administered for 14 days to Sprague-Dawley rats after balloon carotid injury and the ratio of intima to media areas (I/M), inducible NO synthase (iNOS) concentrations and %TUNEL were measured. I/M decreased similarly in the enalapril, L-arginine and losartan groups, and the combination of enalapril and L-arginine resulted in the largest I/M decrease. TUNEL positivity was increased compared with controls in the following order: losartan, L-arginine, enalapril and combination of enalapril and L-arginine. The intensity of immunostaining for iNOS was increased approximately 1.9-fold compared with the control in the combined enarapril and L-arginine group as well as in the enalapril group. These data suggest that the apoptosis in the neointima is different for L-arginine, losartan and enalapril under similar conditions and was higher under treatment with enalapril, not only via the action of NO or blocking of the AT1, but also by upregulation of iNOS.

Blunted vasodilatory responses in the cutaneous microcirculation of cigarette smokers

OBJECTIVE

The present study was undertaken to investigate whether chronic smoking alters the vasodilatory capacity in the microcirculation.

METHODS

We assessed, in habitual cigarette smokers, the forearm skin blood flow response to iontophoretically applied acetylcholine (endothelium-dependent vasodilator) and sodium nitroprusside. Postocclusive forearm reactive hyperemia was also explored. The skin blood flow responses were determined with a laser-Doppler flowmeter that allowed us to scan the surface after acetylcholine and sodium nitroprusside application.

RESULTS

Forty healthy male volunteers were included. Twenty subjects were aged 20 to 35 years and 20 subjects were aged 40 to 60 years. We studied the following 4 groups of 10 subjects each: group 1, younger smokers (mean of 7.2 pack-years); group 2, older smokers (mean of 30 pack-years); group 3, younger nonsmokers; and group 4, older nonsmokers. On the day of the experiment, the subjects of groups 1 and 2 were asked to smoke at least 15 cigarettes from the morning until the afternoon, when the experiments were performed. No significant difference in the studied parameters was observed between younger smokers and younger nonsmokers. In older smokers, however, both acetylcholine- and sodium nitroprusside-induced skin blood flow increases were significantly attenuated in comparison with nonsmokers. Heart rate also was significantly blunted by long-term cigarette smoking in older subjects.

CONCLUSION

These data show that the vasodilatory response of the skin microvasculature is impaired in subjects who have smoked cigarettes for many years. This abnormality involves both endothelium-dependent and endothelium-independent responses.

Acute and chronic treatment with nicotine impairs reactivity of arterioles in response to activation of potassium channels

Although acute and chronic treatment with nicotine impairs nitric oxide synthase-dependent responses of large and small blood vessels, the effect of nicotine on other vasodilator pathways remains uncertain. The goal of the current study was to determine effects of nicotine on dilatation of arterioles to activation of ATP-sensitive potassium channels. Reactivity of cheek pouch arterioles ( approximately 50 microm) was measured during acute (1-2 h) and chronic (2-to 3-week) exposure to nicotine in response to aprikalim, cromakalim, and nitroglycerin. Acute treatment with nicotine impaired dilatation of arterioles in response to aprikalim and cromakalim but not nitroglycerin. Aprikalim and cromakalim (1.0 microM) dilated arterioles by 37 +/- 5% and 30 +/- 3%, respectively, before, but by only 21 +/- 4% and 16 +/- 3%, respectively, after infusion of nicotine (p < 0.05). Chronic exposure to nicotine did not alter vasodilatation to nitroglycerin but impaired vasodilatation to aprikalim and cromakalim. In vehicle-treated hamsters, aprikalim and cromakalim (1.0 microM) dilated arterioles by 28 +/- 1% and 32 +/- 3%, respectively. However, in nicotine-treated hamsters aprikalim and cromakalim (1.0 microM) dilated arterioles by only 3 +/- 1% and 13 +/- 1%, respectively. Next, the role of superoxide anion in impaired responses of arterioles to aprikalim and cromakalim during acute infusion of nicotine was examined. Treatment with superoxide dismutase attenuated the effects of nicotine on aprikalim and cromakalim. Thus, acute and chronic exposure to nicotine has profound affects on vasodilatation to activation of ATP-sensitive potassium channels, which may be mediated by superoxide anion.

Tetrahydrobiopterin enhances forearm vascular response to acetylcholine in both normotensive and hypertensive individuals

BACKGROUND

A deficiency of tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide (NO) synthase, decreases NO synthesis and increases superoxide production. Supplementation of BH4 has been postulated to improve endothelial function in atherosclerotic patients. The purpose of this study was to determine whether BH4 restores endothelium-dependent vasodilation in patients with essential hypertension.

METHODS

We evaluated the effects of BH4 on forearm vascular responses to acetylcholine (ACh), an endothelium-dependent vasodilator, and isosorbide dinitrate (ISDN), an endothelium-independent vasodilator, both in patients with essential hypertension and in age- and sex-matched normal control subjects. Forearm blood flow (FBF) was measured using strain gauge plethysmography.

RESULTS

The response of FBF to ACh was less in hypertensive patients (n = 8) than in normal control subjects (n = 8). There was no significant difference in FBF response to ISDN in the two groups. During coinfusion of BH4 (500 mg/min), the FBF response to ACh in hypertensive patients increased significantly (14.8 +/- 4.6 to 25.6 +/- 7.3 mL/min/100 mL tissue, P < .05) to the level of normal control subjects. In the control subjects, also, BH4 augmented the FBF response to ACh (27.8 +/- 8.7 to 36.1 +/- 9.6 mL/min/100 mL tissue, P < .05). The increase in FBF after ISDN was not altered by BH4 in either group (each group, n = 6).

CONCLUSION

Supplementation of BH4 augments endothelium-dependent vasodilation in both normotensive and hypertensive individuals.

Mechanisms of dysfunction of the nitric oxide pathway in vascular diseases

Vascular nitric oxide (NO) is involved in many physiologic and pathophysiologic processes throughout the body. Many vascular diseases have a reduction in the activity of endothelium-derived NO as an important component involved in the initiation and/or progression of the disease. It is now known that there are multiple mechanisms for this reduction in NO activity with one or more mechanisms operating depending on the specific condition or stage of a disease. In other instances, the therapy for certain diseases is responsible for the reduction in NO activity and contributes to the acceleration of vascular disease. This review details the known mechanisms of dysfunction of the NO pathway leading to vascular diseases, which provides the rationale for why certain therapies can improve while other therapies adversely affect vascular health.

Secondhand tobacco smoke impairs rabbit pulmonary artery endothelium-dependent relaxation

OBJECTIVES

To determine whether secondhand smoke (SHS) induces pulmonary artery endothelial dysfunction, and whether dietary L-arginine supplementation is preventive.

BACKGROUND

SHS causes coronary and peripheral arterial endothelial dysfunction.

METHODS

The effects of L-arginine supplementation (2.25% solution) and SHS (10 weeks) on pulmonary vascular reactivity were examined in 32 rabbits fed a normal diet. Endothelium-dependent relaxation of precontracted pulmonary artery segments was studied using acetylcholine and calcium ionophore. Endothelium-independent relaxation was studied using nitroglycerin. Endothelial and serum L-arginine levels were measured by chromatography. In eight SHS-exposed and in eight control rats, pulmonary artery nitric oxide synthase (NOS) activity and arginase activity were studied using the titrated arginine to citrulline conversion assay.

RESULTS

SHS reduced maximal acetylcholine-induced (p = 0.04) and calcium ionophore-induced (p = 0.02) relaxation. L-Arginine increased maximal acetylcholine-induced (p = 0.047) vasodilation. SHS and L-arginine did not influence nitroglycerin-induced relaxation. SHS reduced endothelial L-arginine (p = 0.04) but not serum L-arginine. L-Arginine supplementation increased endothelial (p = 0.007) and serum L-arginine (p < 0.0005). Endothelium-dependent relaxation induced by acetylcholine and calcium ionophore varied directly with endothelial (r = 0.67, r = 0.67) and serum L-arginine (r = 0.43, r = 0.45), respectively. SHS reduced constitutive NOS activity (p = 0.03).

CONCLUSIONS

SHS reduces pulmonary artery endothelium-dependent relaxation by decreasing NOS activity and possibly by decreasing endothelial arginine content. L-Arginine supplementation increases serum and endothelial L-arginine stores and prevents SHS-induced endothelial dysfunction. L-Arginine may offset the deleterious effect of SHS on pulmonary arteries by substrate loading of the nitric oxide pathway.

Tetrahydrobiopterin, a cofactor for NOS, improves endothelial dysfunction during chronic alcohol consumption

We sought to investigate mechanisms that may account for impaired nitric oxide synthase (NOS)-dependent dilatation of cerebral arterioles during alcohol consumption. Our goals were to examine 1) the effect of exogenous application of a cofactor for NOS, i.e., tetrahydrobiopterin (BH4) on the reactivity of pial arterioles during alcohol consumption; and 2) endothelial NOS (eNOS) protein in nonalcohol-fed and alcohol-fed rats. Sprague-Dawley rats were fed liquid diets with or without alcohol for 2-3 mo. We measured in vivo diameter of pial arterioles in response to NOS-dependent agonists (ACh and ADP) and a NOS-independent agonist (nitroglycerin) before and during application of BH4. Blood vessels were then harvested for Western blot analysis of eNOS protein. In nonalcohol-fed rats, ACh and ADP produced vasodilatation, which was impaired in alcohol-fed rats. Vasodilatation to nitroglycerin was similar in both groups of rats. Application of BH4 did not alter vasodilatation in nonalcohol-fed rats but improved impaired vasodilatation in alcohol-fed rats. Also, eNOS protein in cerebral cortex microvessels, the basilar artery, and aorta was not different between nonalcohol-fed and alcohol-fed rats. Thus impaired NOS-dependent vasodilatation during alcohol consumption does not appear to be related to an alteration in eNOS protein but may be related to a deficiency and/or alteration in the utilization of BH4.

Vascular endothelial dysfunction: does tetrahydrobiopterin play a role?

Tetrahydrobiopterin is one of the most potent naturally occurring reducing agents and an essential cofactor required for enzymatic activity of nitric oxide synthase (NOS). The exact role of tetrahydrobiopterin in the control of NOS catalytic activity is not completely understood. Existing evidence suggests that it can act as allosteric and redox cofactors. Suboptimal concentration of tetrahydrobiopterin reduces formation of nitric oxide and favors "uncoupling" of NOS leading to NOS-mediated reduction of oxygen and formation of superoxide anions and hydrogen peroxide. Recent findings suggest that accelerated catabolism of tetrahydrobiopterin in arteries exposed to oxidative stress may contribute to pathogenesis of endothelial dysfunction present in arteries exposed to hypertension, hypercholesterolemia, diabetes, smoking, and ischemia-reperfusion. Beneficial effects of acute and chronic tetrahydrobiopterin supplementation on endothelial function have been reported in experimental animals and humans. Furthermore, it appears that beneficial effects of some antioxidants (e.g., vitamin C) on vascular function could be mediated via increased intracellular concentration of tetrahydrobiopterin. In this review, the potential role of tetrahydrobiopterin in the pathogenesis of vascular endothelial dysfunction and mechanisms underlying beneficial vascular effects of tetrahydrobiopterin will be discussed.

Cigarette smoke-induced endothelium dysfunction: role of superoxide anion

OBJECTIVES

Cigarette smoking is strongly associated with coronary artery disease and atherosclerosis. While smoking has been shown to impair endothelium-dependent vasorelaxation, the mechanisms involved are not completely understood. We investigated the role of superoxide anion and vasoconstricting prostanoids in cigarette smoke induced endothelial dysfunction.

METHODS

Endothelial function was assessed in rat aortic rings exposed to cigarette smoke-treated Krebs buffer, by measuring agonist stimulated endothelium-dependent vasorelaxation. Treatment with superoxide dismutase (SOD) as well as ifetroban, thromboxane A2/prostaglandin endoperoxide H2 (TxA2/PGH2) receptor blocker and indomethacin (cyclooxygenase inhibitor) was used to investigate the role of superoxide anion and vasoconstricting eicosanoids on cigarette smoke-induced endothelial dysfunction. The effect of cigarette smoke on endothelial nitric oxide synthase (eNOS) catalytic activity was measured by conversion of L-arginine to L-citrulline in rat aortas and rat endothelial cell homogenates supplemented with eNOS cofactors.

RESULTS

Relaxations to receptor-dependent agonists, acetylcholine and adenosine diphosphate (ADP), as well as to a receptor-independent agonist, A23187 (Ca2+ ionophore) were significantly impaired by cigarette smoke. Cigarette smoke did not impair relaxations to sodium nitroprusside, indicating preserved guanylate cyclase activity. Further, cigarette smoke did not affect eNOS catalytic activity in homogenates from either endothelial cells or aortas previously exposed to cigarette-smoketreated Krebs buffer. Treatment with SOD or ifetroban and in a lesser degree by indomethacin prevented cigarette-smoke-induced endothelial dysfunction.

CONCLUSIONS

Taken together, our results suggest that cigarette smoking causes an increase in vascular superoxide production which results in decreased nitric oxide (NO) bioactivity and concomitantly increases production of cyclooxygenase dependent and independent vasoconstricting eicosanoids.

Dietary modulation of endothelial function: implications for cardiovascular disease

The vascular endothelium is the primary site of dysfunction in many diseases, particularly cardiovascular disease. A variety of risk factors, including smoking, hypercholesterolemia, hyperhomocysteinemia, hypertension, and diabetes mellitus, adversely affect endothelial function. Emerging evidence suggests an important role of dietary factors in modulating endothelial function. In particular, n-3 fatty acids, antioxidant vitamins (especially vitamins E and C), folic acid, and L-arginine appear to have beneficial effects on vascular endothelial function, either by decreasing endothelial activation or by improving endothelium-dependent vasodilation in patients at high risk of cardiovascular disease as well as in healthy subjects. These effects may serve as one potential mechanism through which these nutrients reduce the risk of cardiovascular disease, as observed in epidemiologic studies and several clinical trials. This article reviews clinical and experimental evidence regarding the role of these nutrients in modulating endothelial function and their potential to prevent cardiovascular disease.

Effect of vitamin C on the availability of tetrahydrobiopterin in human endothelial cells

Vitamin C has long been known for its beneficial vascular effects, but its mechanism of action remains unclear. Recent reports suggest that vitamin C may prevent endothelial dysfunction by scavenging free radicals and increasing the bioavailability of nitric oxide. To investigate this area further, we studied the effect of vitamin C (10(-4) M) and Mn(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP; 10(-5) M), a scavenger of superoxide, hydrogen peroxide, and peroxynitrite, on endothelial nitric oxide synthase (eNOS) enzymatic activity in cultured human umbilical vein endothelial cells. L-Citrulline formation (a measure of eNOS enzymatic activity) was significantly increased in cells treated for 24 h with vitamin C. No effect was observed after MnTBAP treatment. Chronic administration of vitamin C also had no effect on eNOS protein expression. Treatment with vitamin C for 24 h significantly increased levels of the eNOS co-factor tetrahydrobiopterin (BH4), whereas MnTBAP did not affect its levels. Sepiapterin (10(-4) M), a precursor of BH4, significantly increased eNOS activity, whereas addition of vitamin C to cells treated with sepiapterin did not cause any further increase in eNOS activity. Our results suggest that the beneficial effect of vitamin C on endothelial function is best explained by increased intracellular BH4 content and subsequent enhancement of eNOS activity. This effect appears to be independent of the ability of vitamin C to scavenge superoxide anions.

Acute administration of nicotine impairs the hypotensive responses to bradykinin in rats

Nicotine may contribute to smoking-induced endothelial dysfunction because of its ability to impair endothelium-dependent vasodilatation. We investigated whether the acute administration of nicotine changes the hypotensive responses to bradykinin in rats. The effects of pre-treatment with losartan or enalapril on the nicotine-induced changes in the responses to bradykinin were also evaluated. In study 1, anesthetized rats were cannulated via carotid artery for the measurement of mean arterial pressure. Dose-response curves to bradykinin (0.1, 0.4, 1.6, 6.4, 25 and 100 microg/kg) were generated before and 10 min after the injection of nicotine (200 microg/kg, i.v.) or saline. The individual dose-response curves were fitted to a four-parameter logistic equation using the ALLFIT program, which provided an estimate of the maximal response (E(max)) and of the dose of bradykinin producing the half-maximal response (ED(50)). In study 2, rats were pre-treated orally with losartan (10 mg/kg/day) or enalapril maleate (25 mg/kg/day) for 2 weeks. Control rats received tap water alone. After pre-treatment, the rats were anesthetized and used as described in study 1. Nicotine decreased the E(max) (from 73.0+/-7.5 to 65.7+/-3.3 mm Hg; P<0.05) but did not affect the ED(50). In study 2, losartan or enalapril did not affect nicotine-induced decrease in responses to bradykinin; E(max) decreased in both groups (from 68.7+/-6.3 to 62.8+/-4.2 mm Hg, and from 53.8+/-13.0 to 43.1+/-7.1 mm Hg, respectively; P<0.05) without significantly changing the ED(50). These results suggest that nicotine impairs the endothelium-dependent hypotensive responses to bradykinin. This effect is not influenced by inhibition of the angiotensin-converting enzyme or by blockade of the angiotensin AT(1) receptors.

Effects of nicotine and cotinine on porcine arterial endothelial cell function

BACKGROUND. There has been a significant amount of research on the effects of nicotine on vascular biology; however, little is known about the effects of cotinine, the metabolic product of nicotine. This study used a novel vascular perfusion system to study the effects of nicotine and cotinine on the vascular endothelial cell function.

METHODS

Porcine common carotid arteries were cultured in a novel vascular perfusion system with nicotine or cotinine or as controls. After 24 h, vessels were precontracted with norepinephrine and subsequently relaxed with acetylcholine. Vessel diameters were recorded and analyzed. After culture, samples were taken for en face, immunohistochemistry, and RT-PCR for eNOS. Porcine coronary arteries were incubated as controls or with nicotine or cotinine and tested on a myograph system to measure contraction and relaxation.

RESULTS

Porcine carotid arteries treated with nicotine and cotinine showed a 27.2% and a 41.2% reduction in endothelial-dependent relaxation, respectively, as compared to control vessels (P<0.05). Rings of coronary arteries treated with nicotine relaxed similarly to control rings while cotinine-treated rings failed to relax to endothelial-dependent stimulation. RT-PCR for eNOS mRNA showed a 23. 2 and a 24.1% reduction in eNOS expression for nicotine- and cotinine-treated vessels, respectively (P<0.01). Additionally, immunohistochemical staining for eNOS showed less dense staining on nicotine- and cotinine-treated vessels as compared to controls. En face preparations showed normal endothelial cell morphology in all groups, but cell density decreased slightly in vessels treated with nicotine and cotinine.

CONCLUSION

These results indicate that cotinine may have even more effect on the impairment of endothelial-dependent vasorelaxation than nicotine for the regulation of vessel tone in porcine carotid and coronary arteries.

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.

Tetrahydrobiopterin improves endothelial function in human saphenous veins

OBJECTIVES

Diminished production of nitric oxide has been linked to saphenous vein endothelial dysfunction. Tetrahydrobiopterin is an obligate cofactor for the oxidation of L -arginine by nitric oxide synthase in the production of nitric oxide by endothelial cells. The objective of the present study was to examine whether the exogenous addition of tetrahydrobiopterin improves endothelial function in saphenous veins from patients undergoing coronary artery bypass graft operations.

METHODS

Vascular segments of saphenous veins were obtained from 17 patients undergoing elective coronary artery bypass grafting, and in vitro endothelium-dependent and endothelium-independent responses to acetylcholine and sodium nitroprusside were assessed. Isometric dose-response curves were constructed in precontracted rings in the presence and absence of tetrahydrobiopterin (0.1 mmol/L) with the use of the organ bath apparatus. The percentages of maximum relaxation and sensitivity were compared between interventions.

RESULTS

Acetylcholine caused dose-dependent endothelium-mediated relaxation in saphenous veins. In the presence of tetrahydrobiopterin, acetylcholine-induced relaxation was significantly augmented (percentage maximum relaxation, 16.8% +/- 2.9% vs control 7.5% +/- 1.8%; P =.003) without an effect on agonist sensitivity. These effects were endothelium-specific because endothelium-independent responses to sodium nitroprusside were preserved.

CONCLUSIONS

These data uncover beneficial effects of acute tetrahydrobiopterin addition on endothelial function in human vessels. Because endothelial dysfunction has been implicated in the development of graft failure, studies aimed at chronic delivery of tetrahydrobiopterin would be useful in determining the contribution of this cofactor toward saphenous vein atherosclerosis.

A simple physiologic pulsatile perfusion system for the study of intact vascular tissue

Perfusion vascular culture models may provide a useful link between cell culture models and animal culture models by allowing a high level of control over important parameters while maintaining physiologic structure. The purpose of this study was to develop and test a new vascular culture system for pulsatile perfusion culture of intact vascular tissue. The system generates a pulsatile component of flow by means of a cam-driven syringe and a peristaltic pump and compliance chamber. Cams were designed, constructed and tested to simulate canine femoral and common carotid artery flows. The mean pressure was adjusted between 60 and 200 mmHg without significantly affecting flow rate, flow waveform, or the pressure waveform. Porcine common carotid artery segments were cultured in this pulsatile perfusion system. The viability of vascular segments was tested after various culture times with a functional assay that demonstrated both smooth muscle cell and endothelial cell response to vasomotor challenge.

Alterations of venous drug reactivity in humans: acquired and genetic factors

Until recently, studies dealing with veins have almost always been the neglected part of vascular research. Recent data show an increasing rate of venous disease, and increasing evidence supports a role for veins in systemic diseases. The authors discuss and comment on findings of recent studies on venous drug reactivity. Alterations in venous reactivity to alpha- and beta-adrenergic, NO-dependent, and other drugs have been shown in many genetically determined and acquired conditions, such as hypertension, smoking, and aging. In some of them, the changes of venous responsiveness are most likely secondary to another process, while in others the they seem to play a primary role in the development of systemic disease states. Studying the drug reactivity of the venous system more extensively provides useful information for clinicians and researchers and will no doubt help to further knowledge of the normal and pathologic processes of the vasculature.

Decreased plasma concentrations of L-hydroxy-arginine as a marker of reduced NO formation in patients with combined cardiovascular risk factors

Patients with metabolic syndrome represent a group with extensive cardiovascular risk factors for the development of atherosclerosis, which may be preceded by an impairment of endothelial function. Endothelial dysfunction is characterized by a reduced availability of bioactive nitric oxide, the principal mediator of endothelium-dependent vasodilation. In the present study we assessed NO synthesis in vivo by measuring the NO-related amino acids L-arginine and L-citrulline and in particular the stable intermediate compound N(omega)-hydroxy-L-arginine (L-NHA) in patients with metabolic syndrome by using high-performance liquid chromatography (HPLC) analysis. As a prerequisite to our study, we measured the amino acid concentrations in 31 healthy volunteers to investigate gender and age differences. To prove whether blood drawn from peripheral veins reflects plasma concentrations of the whole vessel system, several blood samples from different regions were obtained from patients undergoing elective left and right heart catheterization. In the latter group, no significant differences were noted among the plasma concentrations between the different sample sites. In healthy volunteers, there were no significant differences in plasma concentrations of any one specific amino acid between males and females or age groups. The main finding of the study is that the intermediate product of NO synthesis, L-NHA, is significantly reduced in the plasma samples of patients with a metabolic syndrome as compared with samples from healthy control subjects. The plasma concentrations of the NO precursor L-arginine and the end product of NO synthesis, L-citrulline, were unchanged. In conclusion, our results suggest that plasma levels of L-NHA are independent of age and gender and are not different at various locations within the vascular system. In a group of patients at high risk for the development of atherosclerosis, we found reduced plasma concentrations of L-NHA, either caused by a decreased endothelial NO synthase activity or caused by an increased breakdown of L-NHA by pathways independent of NO synthase, resulting in a reduced availability of L-NHA for NO synthesis.

Nitric oxide in the pathogenesis of vascular disease

Nitric oxide (NO) is synthesized by at least three distinct isoforms of NO synthase (NOS). Their substrate and cofactor requirements are very similar. All three isoforms have some implications, physiological or pathophysiological, in the cardiovascular system. The endothelial NOS III is physiologically important for vascular homeostasis, keeping the vasculature dilated, protecting the intima from platelet aggregates and leukocyte adhesion, and preventing smooth muscle proliferation. Central and peripheral neuronal NOS I may also contribute to blood pressure regulation. Vascular disease associated with hypercholesterolaemia, diabetes, and hypertension is characterized by endothelial dysfunction and reduced endothelium-mediated vasodilation. Oxidative stress and the inactivation of NO by superoxide anions play an important role in these disease states. Supplementation of the NOS substrate L-arginine can improve endothelial dysfunction in animals and man. Also, the addition of the NOS cofactor (6R)-5,6,7, 8-tetrahydrobiopterin improves endothelium-mediated vasodilation in certain disease states. In cerebrovascular stroke, neuronal NOS I and cytokine-inducible NOS II play a key role in neurodegeneration, whereas endothelial NOS III is important for maintaining cerebral blood flow and preventing neuronal injury. In sepsis, NOS II is induced in the vascular wall by bacterial endotoxin and/or cytokines. NOS II produces large amounts of NO, which is an important mediator of endotoxin-induced arteriolar vasodilatation, hypotension, and shock.

Tetrahydrobiopterin restores endothelial function in long-term smokers

OBJECTIVES

We sought to test whether tetrahydrobiopterin (BH4) supplementation improves nitric oxide (NO) bioactivity in smokers.

BACKGROUND

In smokers, endothelium-derived NO bioactivity is impaired. BH4 is an essential cofactor of NO synthase, and its deficiency decreases NO bioactivity.

METHODS

Sapropterin hydrochloride, an active analogue of BH4 (2 mg/kg body weight), was administered orally to healthy male smokers and age-matched nonsmokers. Before and 3 and 24 h after sapropterin, we measured plasma levels of BH4 and examined flow-mediated vasodilation (FMV) of the brachial artery by high resolution ultrasonography, a noninvasive test of endothelial function.

RESULTS

Basal plasma levels of BH4 were not different between smokers and nonsmokers. Sapropterin administration increased plasma levels of BH4 by threefold at 3 h, which returned to the baseline at 24 h. Before sapropterin, FMV was significantly smaller in smokers (p = 0.0002). Sapropterin significantly augmented endothelium-dependent vasodilation in smokers, but did not affect it in nonsmokers (p = 0.001 by analysis of variance [ANOVA]). Coadministration of N(G)-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor (20 micromol), into the brachial artery completely abolished the vasodilatory effects of sapropterin (p = 0.002 by ANOVA). Endothelium-independent vasodilation by glyceryl trinitrate was not different between smokers and nonsmokers and was not altered by BH4.

CONCLUSIONS

We demonstrated that BH4 supplementation improved bioactivity of endothelium-derived NO in smokers. These observations strongly suggest that decreased NO-dependent vasodilation in smokers could be related to reduced bioactivity of BH4.

Agonist-induced release of nitric oxide during acute exposure to nicotine

While we have shown that acute infusion of nicotine impairs agonist-induced dilatation of resistance arterioles (Am. J. Physiol. 272:H2337-H2342, 1997), no studies have examined the release of nitric oxide in response to these agonists before and during treatment with nicotine. Thus, the first goal of the present study was to examine agonist-induced release of nitric oxide by the hamster cheek pouch microcirculation under control conditions and during acute infusion of nicotine. We measured the release of nitric oxide (Sievers NO analyzer) in response to repeated topical application of acetylcholine (1.0 microM) and 5'-adenosine diphosphate (ADP; 1.0 microM) during infusion of vehicle and during infusion of nicotine (2.0 microg/kg/min i.v. for 30 minutes followed by a maintenance dose of 0.35 microg/kg/min). In hamsters treated with vehicle, topical application of acetylcholine and ADP elicited reproducible increases in nitric oxide release. In contrast, in hamsters treated with nicotine, there was a marked inhibition of nitric oxide release in response to acetylcholine and ADP. In a previous study (J. Appl. Physiol. 85:1292-1298, 1998) we found that treatment of the hamster cheek pouch microcirculation with superoxide dismutase restored impaired agonist-induced vasodilatation during acute infusion of nicotine. Thus, our second goal was to examine whether superoxide dismutase would restore agonist-induced release of nitric oxide during infusion of nicotine. We found that treatment of the hamster cheek pouch microcirculation with superoxide dismutase prior to infusion of nicotine prevented nicotine-induced impairment of nitric oxide release in response to acetylcholine and ADP. We suggest that nicotine alters dilatation of arterioles via an increased release of superoxide anion and subsequent inactivation of nitric oxide.

The relationship between polymorphisms in the endothelial cell nitric oxide synthase gene and the platelet GPIIIa gene with myocardial infarction and venous thromboembolism in African Americans

STUDY OBJECTIVES

To determine whether the polymorphic dinucleotide repeats found in intron 4 of the endothelial cell nitric oxide synthase (ecNOS) gene and the platelet GPIIIa PLA(1)/A(2) polymorphism are associated with myocardial infarction (MI) and venous thromboembolism (VTE) in African Americans. Because these two genes may interact physiologically, the third objective was to determine if there was a relationship between the polymorphisms with respect to MI and VTE.

DESIGN

A hospital-based case-control study. After informed consent was obtained, blood used for DNA extraction was drawn from the subjects.

SETTING

The study was conducted in the Anticoagulant Clinic and the Cardiology Clinic at Grady Memorial Hospital in Atlanta Georgia.

PATIENTS

Subjects were recruited from African-American patients with a reported history of MI (n = 110) or VTE (n = 91). Control subjects (n = 185) without a history of cardiovascular or venous disease were recruited from an outpatient clinic.

MEASUREMENTS AND RESULTS

The 393 ecNOS allele was more common among MI cases (36%; p = 0.01) and VTE cases (35%; p = 0.04) than among control subjects (26%). There was no association between the GPIIIa genotypes and either MI or VTE. However, among the MI subjects, there was a strong association between the ecNOS 393/393 genotype and the Pl(A2) allele. It was also found that the frequency of the 393 allele was higher in African-American persons (0.26) compared with what has been reported for Australian Caucasians (0. 14) and Japanese (0.10).

CONCLUSIONS

The 393 allele but not the Pl(A2) allele was significantly associated with both MI and VTE in African Americans. Homozygosity for the 393 allele was significantly associated to the diagnosis of MI prior to the age of 45. The combination of the 393 allele and a Pl(A2) allele was also highly associated with MI. The frequency of the 393 allele was significantly higher in African Americans than what has been reported for other populations. This study furthers not only extends the association of the 393 allele to VTE but has demonstrated an interaction with the Pl(A2) allele with respect to MI.

Paradoxically enhanced bradykinin-induced venodilation in young, healthy, short-term smokers

Bradykinin is a nonapeptide, whose mechanism of vasodilation is mediated chiefly through the release of endothelium-derived relaxing factor (EDRF). Diminished vasodilatory response to EDRF has been demonstrated in many pathologic states such as hypertension, atherosclerosis, diabetes, and long-term, heavy smoking. We studied whether the diminished EDRF-mediated vasodilatory response seen in chronic diseases can be demonstrated in young, clinically healthy smokers. We used the dorsal hand-vein compliance technique, an in vivo technique used to measure response to local infusions of vasoactive substances. Full dose-response curves to bradykinin (dosing range, 0.5-500 ng/min) were generated in 11 young, healthy smokers and 11 young, healthy nonsmokers by using hand veins preconstricted with phenylephrine (dosing range, 20-6,800 ng/min). In addition, after a washout period, a single maximal dose of a non-endothelium-dependent vasodilator, isoproterenol (300 ng/min) was infused. Our results demonstrated that smokers had a greater maximal venodilation to bradykinin than did nonsmokers (106 +/- 40% vs. 69 +/- 49%; p < 0.05). The log of the dose that produced half-maximal response to bradykinin was smaller in smokers: -0.10 +/- 0.93 (0.79 ng/min) versus 0.75 +/- 0.84 (5.6 ng/min); p < 0.05. There was no difference in the maximal dilatory response to isoproterenol: 80 +/- 45% (smokers) versus 89 +/- 50% (nonsmokers), nor was there a difference in the log dose of phenylephrine necessary to produce 80% constriction of the hand vein (2.7 +/-0.7 vs. 2.7 +/- 0.9 ng/min) between the two groups. We conclude that young, otherwise healthy smokers have a paradoxic hyperactive response to the endothelium-dependent vasodilator, bradykinin, but maintain a similar response to the nonendothelium-dependent vasodilator, isoproterenol as compared with nonsmokers. Their reactivity to the alpha1-adrenergic agonist phenylephrine was found to be intact. It is possible that a hyperactive response to EDRF in young smokers contributes to endothelium damage seen in chronic disease. To our knowledge, this is the first report on increased reactivity to bradykinin in short-term smokers.

Chronic exposure to nicotine alters endothelium-dependent arteriolar dilatation: effect of superoxide dismutase

The first goal of this study was to determine whether chronic injection of nicotine alters endothelium-dependent arteriolar dilatation. We measured the diameter of cheek pouch resistance arterioles (approximately 50 microm in diameter) in response to endothelium-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in control hamsters and hamsters treated with nicotine (2 microg. kg-1. day-1 for 2-3 wk). In control hamsters, acetylcholine (0.1 and 1.0 microM) dilated arterioles by 13 +/- 2 and 31 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by 18 +/- 1 and 30 +/- 1%, respectively. In contrast, acetylcholine (0.1 and 1.0 microM) dilated arterioles by only 5 +/- 2 and 12 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by only 7 +/- 2 and 13 +/- 3%, respectively, in animals treated with nicotine (P < 0.05 vs. response in control hamsters). Nitroglycerin produced similar dose-related dilatation of cheek pouch arterioles in control and nicotine-treated hamsters. Our second goal was to examine a possible mechanism for impaired endothelium-dependent arteriolar dilatation during chronic treatment with nicotine. We found that superfusion of the cheek pouch microcirculation with superoxide dismutase (150 U/ml) restored impaired endothelium-dependent, but did not alter endothelium-independent, arteriolar dilatation in hamsters treated with nicotine. Superfusion with superoxide dismutase did not alter endothelium-dependent or -independent arteriolar dilatation in control hamsters. We suggest that chronic exposure to nicotine produces selective impairment of endothelium-dependent arteriolar dilatation via a mechanism related to the synthesis/release of oxygen-derived free radicals.

Superoxide dismutase restores endothelium-dependent arteriolar dilatation during acute infusion of nicotine

We previously showed [Am. J. Physiol. 272 (Heart Circ. Physiol. 41): H2337-H2342, 1997] that nicotine impairs endothelium-dependent arteriolar dilatation. However, mechanisms that accounted for the effect of nicotine on endothelium-dependent vasodilatation were not examined. Thus the goal of this study was to examine the role of oxygen radicals in nicotine-induced impairment of arteriolar reactivity. We measured diameter of cheek pouch resistance arterioles (approximately 50 micrometer diameter) in response to endothelium-dependent (ACh and ADP) and -independent (nitroglycerin) agonists before and after infusion of vehicle or nicotine in the absence or presence of superoxide dismutase. ACh, ADP, and nitroglycerin produced dose-related dilatation of cheek pouch arterioles before infusion of vehicle or nicotine. Infusion of vehicle, in the absence or presence of superoxide dismutase (150 U/ml), did not alter endothelium-dependent or -independent arteriolar dilatation. In contrast, infusion of nicotine (2 microgram . kg-1 . min-1) impaired endothelium-dependent, but not -independent, arteriolar dilatation. In addition, the effect of nicotine on endothelium-dependent vasodilatation was reversed by topical application of superoxide dismutase. We suggest that nicotine impairs endothelium-dependent arteriolar dilatation via an increase in the synthesis/release of oxygen-derived free radicals.

Endothelial dysfunction in human hand veins is rapidly reversible after smoking cessation

Cigarette smoking has been shown to impair endothelium-dependent dilation in arteries. We tested the hypothesis that cigarette smoking also impairs endothelium-dependent venodilation and evaluated changes in this response after smoking cessation in a time-course study using the dorsal hand vein technique. Dose-response curves were constructed in smokers and nonsmokers by infusing bradykinin (1-278 ng/min), an endothelium-dependent vasodilator, and nitroglycerin (0.006-1,583 ng/min), an endothelium-independent vasodilator, into hand veins preconstricted with the selective alpha1-adrenergic agonist phenylephrine. The maximal venodilation induced by bradykinin was 89 +/- 5% in controls (n = 16) and 61 +/- 7% in smokers (n = 18; P = 0.02). No difference in nitroglycerin-induced venodilation was observed between the two groups. Coinfusion of L-arginine (0.33 mg/min) markedly improved the bradykinin-induced venodilation in smokers (52 +/- 7 to 90 +/- 9%; P < 0.01). After acute smoking cessation (n = 7), restoration to normal bradykinin-induced venodilation was observed within 24 h, whereas no change in the response to a maximally effective dose of nitroglycerin (1,583 ng/min) was detected. In a human vein model appropriate for testing vascular functional alterations, this study demonstrates that smoking impairs endothelium-dependent venodilation in heavy smokers. Moreover, this endothelial dysfunction appears to be rapidly reversible after smoking cessation. This model may be useful in studies evaluating mechanisms of endothelial dysfunction and interventions to modify it.

Vascular damage from smoking: disease mechanisms at the arterial wall

The products of tobacco combustion are absorbed into the systemic circulation. Absorbed nicotine stimulates the release of catecholamines, whilst other products (perhaps including nicotine) injure the arterial endothelium and promote atherogenesis. Free radicals and aromatic compounds diminish the endothelial synthesis of nitric oxide, causing impaired endothelium-dependent relaxation of arteries, the earliest clinical sign of endothelial dysfunction. Smoking alters the shear forces and rheology at the endothelial surface and these changes enhance the effects of products of tobacco combustion to upregulate leucocyte adhesion molecules on the endothelial surface. The increased oxidation of low density lipoprotein (LDL) in smokers has synergistic effects to promote monocyte adhesion and monocyte migration into the subintimal space. Continued stimulation of intimal cells by oxidized LDL leads to the development of atherosclerosis. Many of these effects are ameliorated by high concentrations of vitamin C. Smoking also potentiates thrombosis at the dysfunctional endothelium by increasing the concentration of plasma fibrinogen and altering the activity of platelets. All these proatherogenic effects of smoking to injure the endothelium also are observed, albeit to lesser extent, in passive smokers.

Cardiovascular effects of L-arginine

Most of the known cardiovascular effects of L-arginine are exerted via its conversion to nitric oxide by nitric oxide synthase. Accumulating evidence indicates that supplemental administration of L-arginine is sufficient to restore endothelium-derived nitric oxide production in many disorders in which endothelium-derived nitric oxide production is altered. L-arginine may enhance nitric oxide production by competing as a substrate with an endogenous antagonist for nitric oxide synthase. In other cases, L-arginine may act by competing with molecular oxygen as a substrate so as to reduce the production of superoxide anion. It is likely that other mechanisms exist by which the nitric oxide synthase pathway can be perturbed. Regardless of the mechanism, a wide array of cardiovascular disorders characterized by endothelial dysfunction are reversible by L-arginine.

Cigarette smoking-induced increase in the risk of symptomatic vasospasm after aneurysmal subarachnoid hemorrhage

Vasospasm following aneurysmal subarachnoid hemorrhage (SAH) is correlated with the thickness of blood within the basal cisterns on the initial computerized tomography (CT) scan. To identify additional risk factors for symptomatic vasospasm, the authors performed a prospective analysis of 75 consecutively admitted patients who were treated for aneurysmal SAH. Five patients who died before treatment or were comatose postoperatively were excluded from the study. Of the remaining 70 patients, demographic (age, gender, and race) and clinical (hypertension, diabetes, coronary artery disease, smoking, alcohol abuse, illicit drug use, sentinel headache, Fisher grade, Hunt and Hess grade, World Federation of Neurological Surgeons grade, and ruptured aneurysm location) parameters were evaluated using multivariate logistic regression to determine factors independently associated with cerebral vasospasm. All patients were treated with hypervolemic therapy and administration of nimodipine as prophylaxis for vasospasm. Cerebral vasospasm was suspected in cases that exhibited (by elevation of transcranial Doppler velocities) neurological deterioration 3 to 14 days after SAH with no other explanation and was confirmed either by clinical improvement in response to induced hypertension or by cerebral angiography. The mean age of the patients was 50 years. Sixty-three percent of the patients were women, 74% were white, 64% were cigarette smokers, and 46% were hypertensive. Ten percent of the patients suffered from alcohol abuse, 19% from sentinel bleed, and 49% had a Fisher Grade 3 SAH. Twenty-nine percent of the patients developed symptomatic vasospasm. Multivariate analysis demonstrated that cigarette smoking (p = 0.033; odds ratio 4.7, 95% confidence interval [CI] 2.4-8.9) and Fisher Grade 3, that is, thick subarachnoid clot (p = 0.008; odds ratio 5.1, 95% CI 2-13.1), were independent predictors of symptomatic vasospasm. The authors make the novel observation that cigarette smoking increases the risk of symptomatic vasospasm after aneurysmal SAH, independent of Fisher grade.

Identification of predictors for lower extremity vein graft stenosis

BACKGROUND

The cause of intrinsic vein graft stenosis, which develops in at least 20% of infrainguinal autogenous bypass grafts during the intermediate follow-up interval, is unknown. We performed standard duplex surveillance of all lower extremity bypass grafts and evaluated the potential of comorbid patient risk factors that might predict development of vein graft flow disturbance or high-grade graft stenosis.

METHODS

Patients with at least 6 months of postoperative duplex surveillance were identified through our vascular registry. The association of clinical and hemodynamic profiles of graft performance were compared with specific patient risk factors, including demographics, cigarette smoking, antihypertensive medical therapy, type and quality of conduit, degree of ischemia, bypass run-off, and presence of infection, using stepwise logistic regression analysis.

RESULTS

Ninety-three patients (55 male, 38 female; mean age 69) underwent 100 infrainguinal bypasses. Twenty-six high-grade graft stenoses (>70%) were identified in 26 patients during follow-up (mean 21 months) by graft-flow peak systolic velocity (PSV) >300 cm/sec on more than one duplex examination, and were electively revised. Graft flow disturbances (180 cm/sec >PSV <300 cm/sec) were identified in an additional 13 grafts (6 regressed, 7 observed). The need for graft revision was associated with an early graft flow disturbance (P = 0.02), or drop in ankle-brachial index >0.15 (P = 0.03), and the use of an alternative conduit in 13 of 100 grafts (P = 0.04). Only smoking was associated with the development of a duplex detected graft flow disturbance during follow up (P = 0.03).

CONCLUSION

Grafts with early flow disturbances warrant close duplex surveillance to identify graft-threatening stenosis. Risk factors that may predict future lower extremity bypass graft stenosis are smoking and the use of alternative bypass conduits.

Tetrahydrobiopterin, nitric oxide and regulation of cerebral arterial tone

Tetrahydrobiopterin is an essential cofactor required for activity of nitric oxide synthases. Existing evidence suggests that, during activation of constitutive and inducible isoforms of nitric oxide synthase, tetrahydrobiopterin is needed for allosteric and redox activation of enzymatic activity. However, precise mechanisms underlying the role of tetrahydrobiopterin in regulation of nitric oxide formation is not fully understood. In cerebral and peripheral arteries, increased availability of tetrahydrobiopterin can augment production of nitric oxide. In contrast, in arteries depleted of tetrahydrobiopterin, production of nitric oxide is impaired. Proinflammatory cytokines enhance mRNA expression of the rate-limiting enzyme of tetrahydrobiopterin biosynthesis, GTP cyclohydrolase I and stimulate production of tetrahydrobiopterin. The ability of vascular tissues to synthesize tetrahydrobiopterin plays an important role in regulation of nitric oxide synthase under physiological conditions as well as during inflammation and sepsis. More recent studies concerning expression and function of recombinant nitric oxide synthases suggest that availability of tetrahydrobiopterin is important for production of nitric oxide in genetically engineered blood vessels. In this review, mechanisms regulating availability of intracellular tetrahydrobiopterin and its role in control of vascular tone under physiological and pathological conditions will be discussed.

Dilatation of saphenous vein grafts by nitric oxide

OBJECTIVES

To investigate firstly whether flow-dependent vasodilation is maintained in vein grafts, and secondly whether nitric oxide donors dilate vein grafts to improve the flow through graft stenoses.

DESIGN, MATERIALS AND METHODS

The vasodilatation of mature patent vein grafts, in response to reactive hyperaemia and glyceryl trinitrate (GTN), was assessed by the change in external diameter using duplex ultrasonography. The severity (ratio of proximal systolic velocity, V1, to peak systolic velocity at the stenosis, V2, of vein graft stenoses was determined by duplex ultrasonography before and after 24 h of local application of GTN patches.

RESULTS

In post-occlusion hyperaemia the diameter of patent distal vein grafts (n = 7) increased to a maximum of 112 +/- 1.9% of resting diameter after 2 min, p = 0.026. The diameter increased further to 117 +/- 2.5% of the resting value 5 min after oral GTN (n = 5), p = 0.007. The velocity ratio, V2/V1, through graft stenoses (n = 6) decreased by 20 +/- 5% after application of GTN patches, principally as a result of reduction in V2, mean difference 0.8, p = 0.15. The changes in response to GTN were more evident for proximal than distal vein graft stenoses.

CONCLUSION

Flow-induced vasodilatation responses, which have been attributed to the endothelial release of nitric oxide, are maintained in patent vein grafts: the grafts dilate even further in response to GTN. The application of GTN patches close to a vein graft stenoses appears to reduce the velocity ratio through vein graft stenoses. GTN patches might be used to reduce the risk of graft occlusion when there is a delay between the detection and the treatment of haemodynamically significant graft stenoses.

Circumferential deformation and shear stress induce differential responses in saphenous vein endothelium exposed to arterial flow

Adaptation of saphenous vein to the hemodynamic stresses of the arterial circulation is critical to the maturation of vein bypass grafts. We have investigated early adaptive responses of venous endothelium by placing excised human saphenous vein in a bypass circuit with either venous or arterial flow conditions, using external stenting to resolve the effects of longitudinal (shear) from circumferential stress. Endothelial protein concentrations were assessed by immunostaining area (ratio of protein/CD31) and Western blotting of endothelial cell lysates (staining ratio protein/vWf). In both unstented and stented veins nitric oxide synthase increased after 90 min of arterial flow: twofold increase of immunostaining area (P = 0.001), four- to fivefold increase by Western blotting (P = 0.02), and increased A23187mediated maximum endothelium-dependent relaxation of vein rings (P = 0.01). In unstented veins, ICAM-1 concentration was increased after 45 min of arterial flow: twofold increase by immunostaining (P = 0.001) and Western blotting (P = 0.038), with maximum fibrinogen-mediated endothelium-dependent relaxation increasing from 55.9+/-4.9 to 97+/-2.1% (P = 0.01). In contrast, in unstented veins there was a threefold decrease of VCAM-1 and no change in P-selectin after arterial flow for 45 and 90 min, respectively. However, no changes in ICAM-1 and VCAM-1 were observed in stented veins. The flow-induced alterations in nitric oxide synthase, ICAM-1, and VCAM-1 were abolished when 3 mM tetraethylammonium ion (K+ channel blocker) was included in the vein perfusate. The very rapid changes in ICAM-1 and VCAM-1 expression are a response to circumferential stress, whereas the slower upregulation of nitric oxide synthase is a response to longitudinal (shear) stress. Similar changes could influence the adhesiveness of endothelium in newly implanted saphenous vein bypass grafts.