[Prevention of coronary heart disease: smoking]

Smoking is the leading preventable cause of illness and premature death in Germany, claiming over 110,000 lives a year because it directly increases the risk of dying from heart disease, stroke, emphysema and a variety of cancers. The overwhelming majority of smokers begin tobacco use before they reach adulthood. Among those young people who smoke, the average age is now 13-14. In Germany, about 39% of male and 31% of female adults (age 18-60 years) continue to smoke, despite information about the unequivocally negative health consequences of smoking. The exact mechanisms of smoking-related vascular disease are not yet known. Smoking causes acute hemodynamic alterations such as increase in heart rate, systematic and coronary vascular resistance, myocardial contractility, and myocardial oxygen demand. These short-term effects could lower the ischemic threshold in smokers with coronary artery disease and contribute to the increased risk for acute cardiovascular events. Endothelial damage is thought to be an initiating event in atherosclerosis and early studies have demonstrated that long-term smoking has direct toxic effects with structural changes of human endothelial cells. Recent research has shown the importance of the functional role of the endothelium in regulating vascular tone, platelet-endothelial interactions, leukocyte adhesion and smooth muscle cell proliferation via synthesis and release of a variety of substances such as nitric oxide. There is strong evidence that smoking leads to endothelial dysfunction mainly by increased inactivation of nitric oxide by oxygen-derived free radicals. Smoking also increases oxidative modification of LDL and is associated with lower HDL plasma levels. Smoking induces a systemic inflammatory response with increased leukocyte count and elevation of the C-reactive protein level. Importantly, the prothrombotic effects of smoking have been repeatedly demonstrated to cause alterations in platelet function, imbalance of antithrombotic vs prothrombotic factors, and decrease of fibrinolytic activity. Given the enormous health hazard of tobacco use, complete abstinence from smoking should be achieved. Smoking cessation counselling should be given to healthy subjects and even more vigorously to patients with manifested disease. Every effort should be undertaken to prevent children and adolescents from starting to smoke. Brief tobacco dependence treatment is effective, and every smoker should be offered at least brief treatment at every office visit. More intensive treatment is more effective in producing long-term abstinence from tobacco. Nicotine replacement therapy (nicotine patches or gum), clinician-delivered social support, and skills training are the three most effective components of smoking cessation treatment. A framework for tobacco control measures is necessary to reduce tobacco consumption and exposure to tobacco smoke. Recommendations on specific tobacco control interventions are: 1. increase in tobacco taxes; 2. comprehensive tobacco advertising bans; 3. legislation prohibiting smoking in work and public places; 4. prohibiting the sales of tobacco products to persons under 18; 5. comprehensive disclosure of the physical, chemical and design characteristics of all tobacco products; 6. training of health professionals to promote smoking prevention and cessation interventions; and 7. development of a national network of smoking cessation treatment services.

[Primary and secondary prevention of coronary heart disease: smoking]

Although smoking is one of the major risk factors for the development of atherosclerosis, the exact mechanism of smoking-related vascular disease is not known. Smoking causes acute hemodynamic alterations such as increase in heart rate, systemic and coronary vascular resistance, myocardial contractility, and myocardial oxygen demand. These short-term effects could lower the ischemic threshold in smokers with coronary artery disease and contribute to the increased risk for acute cardiovascular events. Endothelial damage is thought to be an initiating event in atherosclerosis and early studies have demonstrated that long-term smoking has direct toxic effects with structural changes of human endothelial cells. Recent research has shown the importance of the functional role of the endothelium in regulating normal vascular tone, platelet-endothelial interactions, leukocyte adhesion and smooth muscle cell proliferation via synthesis and release of a variety of substances such as nitric oxide. There is strong evidence that smoking leads to endothelial dysfunction in both conductance and resistance vessels. This effect seems to be dose-related and reversible. The mechanism of endothelial dysfunction in smokers is not known, but increased degradation of nitric oxide by oxygen-derived free radicals has been suggested. In addition, smoking could cause oxidative inactivation of tetrahydrobiopterin, a critical cofactor of nitric oxide, leading to an uncoupling of the endothelial nitric oxide synthase with increased superoxide production and decreased nitric oxide bioactivity. Other pro-atherosclerotic effects of smoking are discussed. Given the enormous health hazard of tobacco use, complete abstinence from smoking should be achieved. Smoking cessation counseling should be given to healthy subjects and even more vigorously to patients with manifested disease. Every effort should be undertaken to prevent children and adolescents from starting to smoke. Brief tobacco dependence treatment is effective, and every tobacco user should be offered at least brief treatment at every office visit. More intensive treatment is more effective in producing long-term abstinence from tobacco. Nicotine replacement therapy (nicotine patches or gum), clinician-delivered social support, and skills training are the three most effective components of smoking cessation treatment.

Endothelial dysfunction, oxidative stress, and risk of cardiovascular events in patients with coronary artery disease

BACKGROUND

Endothelial function is impaired in coronary artery disease and may contribute to its clinical manifestations. Increased oxidative stress has been linked to impaired endothelial function in atherosclerosis and may play a role in the pathogenesis of cardiovascular events. This study was designed to determine whether endothelial dysfunction and vascular oxidative stress have prognostic impact on cardiovascular event rates in patients with coronary artery disease.

METHODS AND RESULTS

Endothelium-dependent and -independent vasodilation was determined in 281 patients with documented coronary artery disease by measuring forearm blood flow responses to acetylcholine and sodium nitroprusside using venous occlusion plethysmography. The effect of the coadministration of vitamin C (24 mg/min) was assessed in a subgroup of 179 patients. Cardiovascular events, including death from cardiovascular causes, myocardial infarction, ischemic stroke, coronary angioplasty, and coronary or peripheral bypass operation, were studied during a mean follow-up period of 4.5 years. Patients experiencing cardiovascular events (n=91) had lower vasodilator responses to acetylcholine (P<0.001) and sodium nitroprusside (P<0.05), but greater benefit from vitamin C (P<0.01). The Cox proportional regression analysis for conventional risk factors demonstrated that blunted acetylcholine-induced vasodilation (P=0.001), the effect of vitamin C (P=0.001), and age (P=0.016) remained independent predictors of cardiovascular events.

CONCLUSIONS

Endothelial dysfunction and increased vascular oxidative stress predict the risk of cardiovascular events in patients with coronary artery disease. These data support the concept that oxidative stress may contribute not only to endothelial dysfunction but also to coronary artery disease activity.

Beneficial effects of alpha-lipoic acid and ascorbic acid on endothelium-dependent, nitric oxide-mediated vasodilation in diabetic patients: relation to parameters of oxidative stress

The impairment of nitric oxide (NO)-mediated vasodilation in diabetes has been attributed to increased vascular oxidative stress. Lipoic acid has been shown to have substantial antioxidative properties. The aim of this study was to assess the effect of lipoic acid on NO-mediated vasodilation in diabetic patients in comparison with the well-recognized effect of ascorbic acid. Using venous occlusion plethysmography, we examined the effects of lipoic acid (0.2 mM) and ascorbic acid (1 and 10 mM) on forearm blood flow responses to acetylcholine, sodium nitroprusside and concomitant infusion of the NO-inhibitor, N(G)-monomethyl-L-arginine, in 39 diabetic patients and 11 control subjects. Plasma levels of antioxidants and parameters of lipid peroxidation were measured and correlated to endothelial function tests. Lipoic acid improved NO-mediated vasodilation in diabetic patients, but not in controls. NO-mediated vasodilation was improved by ascorbic acid at 10 mM, but not 1 mM. Improvements of endothelial function by ascorbic acid and lipoic acid were closely related. The beneficial effects of lipoic acid were positively related to plasma levels of malondialdehyde and inversely related to levels of ubiquinol-10. These findings support the concept that oxidative stress contributes to endothelial dysfunction and suggest a therapeutic potential of lipoic acid particularly in patients with imbalance between increased oxidative stress and depleted antioxidant defense.

Tetrahydrobiopterin improves endothelium-dependent vasodilation by increasing nitric oxide activity in patients with Type II diabetes mellitus

AIMS/HYPOTHESIS

Tetrahydrobiopterin is an essential cofactor of nitric oxide synthase, and its deficiency decreases nitric oxide bioactivity. Our aim was to find whether supplementation of tetrahydrobiopterin could improve endothelial dysfunction in diabetic patients.

METHODS

Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine (0.75-3.0 microg x 100 ml(-1) x min(-1)) and to the endothelium-independent vasodilator sodium nitroprusside (0.1-1.0 microg x 100 ml(-1) x min(-1)) before and during concomitant intra-arterial infusion of tetrahydrobiopterin (500 microg/min) were measured by venous occlusion plethysmography in 12 control subjects and 23 patients with Type II (non-insulin-dependent) diabetes mellitus.

RESULTS

In control subjects, tetrahydrobiopterin had no effect on the dose-response curves to acetylcholine and sodium nitroprusside. In contrast, in diabetic patients, the attenuated endothelium-dependent vasodilation to acetylcholine was considerably improved by concomitant treatment with tetrahydrobiopterin, whereas the endothelium-independent vasodilation was not affected. This beneficial effect of tetrahydrobiopterin in diabetic patients could be completely blocked by N(G)-monomethyl-L-arginine.

CONCLUSION/INTERPRETATION

These findings suggest the possibility that endothelial dysfunction in Type II diabetes might be related to decreased availability of tetrahydrobiopterin.

Tetrahydrobiopterin improves endothelium-dependent vasodilation in chronic smokers : evidence for a dysfunctional nitric oxide synthase

Conditions associated with impaired nitric oxide (NO) activity and accelerated atherosclerosis have been shown to be associated with a reduced bioavailability of tetrahydrobiopterin (BH4). We therefore hypothesized that BH4 supplementation may improve endothelial dysfunction of chronic smokers. Forearm blood flow (FBF) responses to the endothelium-dependent vasodilators acetylcholine (ACh; 0.75, 1.5, and 3.0 microg/100 mL tissue/min) or serotonin (5-HT; 0.7, 2.1, and 6.3 ng/100 mL tissue/min), to the inhibitor of endothelial nitric oxide synthase (NOS) N(G)-monomethyl-L-arginine (L-NMMA; 2, 4, and 8 micromol/min), and to the endothelium-independent vasodilator sodium nitroprusside (SNP; 0.1, 0.3, and 1.0 microg/100 mL tissue/min) were measured by venous occlusion plethysmography in controls and chronic smokers. Drugs were infused into the brachial artery, and FBF was measured before and during concomitant intra-arterial infusion of BH4, tetrahydroneopterin (NH4; another reduced pteridine), or the antioxidant vitamin C (6 and 18 mg/min). In control subjects, BH4 had no effect on FBF in response to ACh, 5-HT, and SNP. In contrast, in chronic smokers, the attenuated FBF responses to ACh and 5-HT were markedly improved by concomitant administration of BH4, whereas the vasodilator responses to SNP were not affected. L-NMMA-induced vasoconstriction was significantly reduced in smokers compared with controls, suggesting impaired basal NO bioactivity. BH4 improved L-NMMA responses in smokers while having no effect on L-NMMA responses in controls. Pretreatment with vitamin C abolished BH4 effects on ACh-dependent vasodilation. In vitro, NH4 scavenged superoxide created by the xanthine/xanthine oxidase reaction equipotent like BH4 but failed to modify ACh-induced changes in FBF in chronic smokers in vivo. These data support the concept that in addition to the free radical burden of cigarette smoke, a dysfunctional NOS III due to BH4 depletion may contribute at least in part to endothelial dysfunction in chronic smokers.

Role for NADPH/NADH oxidase in the modulation of vascular tone

The endothelium modulates vascular tone by producing vasodilator and vasconstrictor substances. Of these, the best characterized and potentially most important are nitric oxide (NO.) and O2-.. These small molecules exhibit opposing effects on vascular tone and chemically react with each other in a fashion that negates their individual effects and leads to the production of potentially toxic substances, such as peroxynitrite (ONOO-). These dynamic interactions may likely have important implications, altering not only tissue perfusion but also contributing to the process of atherosclerosis. The precise O2-. source within vascular tissue remains to be determined. Recent work demonstrated that in endothelial cells as well as in vascular smooth muscle cells, a membrane-associated NAD(P)H-dependent oxidase represents the most significant O2-. source. Interestingly, this oxidase is activated upon stimulation with angiotension II, suggesting that under all conditions of an activated circulating and/or local renin-angiotensin system endothelial dysfunction secondary to increased vascular O2-. production is expected.

Increased NADH-oxidase-mediated superoxide production in the early stages of atherosclerosis: evidence for involvement of the renin-angiotensin system

BACKGROUND

Angiotensin II activates NAD(P)H-dependent oxidases via AT1-receptor stimulation, the most important vascular source of superoxide (O2*-). The AT1 receptor is upregulated in vitro by low-density lipoprotein. The present study was designed to test whether hypercholesterolemia is associated with increased NAD(P)H-dependent vascular O2*- production and whether AT1-receptor blockade may inhibit this oxidase and in parallel improve endothelial dysfunction.

METHODS AND RESULTS

Vascular responses were determined by isometric tension studies, and relative rates of vascular O2*- production were determined by use of chemiluminescence with lucigenin, a cypridina luciferin analogue, and electron spin resonance studies. AT1-receptor mRNA was quantified by Northern analysis, and AT1-receptor density was measured by radioligand binding assays. Hypercholesterolemia was associated with impaired endothelium-dependent vasodilation and increased O2*- production in intact vessels. In vessel homogenates, we found a significant activation of NADH-driven O2*- production in both models of hyperlipidemia. Treatment of cholesterol-fed animals with the AT1-receptor antagonist Bay 10-6734 improved endothelial dysfunction, normalized vascular O2*- and NADH-oxidase activity, decreased macrophage infiltration, and reduced early plaque formation. In the setting of hypercholesterolemia, the aortic AT1 receptor mRNA was upregulated to 166+/-11%, accompanied by a comparable increase in AT1-receptor density.

CONCLUSIONS

Hypercholesterolemia is associated with AT1-receptor upregulation, endothelial dysfunction, and increased NADH-dependent vascular O2*- production. The improvement of endothelial dysfunction, inhibition of the oxidase, and reduction of early plaque formation by an AT1-receptor antagonist suggests a crucial role of angiotensin II-mediated O2*- production in the early stage of atherosclerosis.

Effect of vitamin E on endothelial vasodilator function in patients with hypercholesterolemia, chronic smoking or both

OBJECTIVES

The purpose of this study was to test the hypothesis that long-term supplementation with Vitamin E improves endothelium-dependent relaxation in hypercholesterolemia patients and/or chronic smoking, two risk factors that have been shown to be associated with increased radical formation.

BACKGROUND

Experimental evidence suggests that oxidized low density lipoprotein (LDL) impairs endothelium-dependent relaxation, and vitamin E, a lipid-soluble antioxidant, reduces the oxidation of LDL.

METHODS

Thirteen subjects with hypercholesterolemia, 14 smokers and 15 hypercholesterolemic smokers were enrolled in a double-blind, placebo-controlled study. After baseline measurements of plasma autoantibodies against oxidized LDL and assessment of endothelium-dependent relaxation using intra-arterial forearm infusions of acetylcholine, participants within each group were randomly assigned in a 1:2 fashion to receive either placebo or vitamin E for 4 months, when plasma levels of autoantibodies against oxidized LDL and vascular function were reassessed.

RESULTS

Vitamin E significantly augmented endothelium-dependent relaxation in hypercholesterolemic smokers but not in patients with either hypercholesterolemia or chronic smoking. At baseline, hypercholesterolemic smokers had significantly higher autoantibody levels against oxidized LDL (compared with the other two groups), which were significantly reduced after 4 months of vitamin E supplementation. There was a significant relationship between improvement in acetylcholine-induced vasodilation and the change in autoantibody titer against oxidized LDL (r = -0.59; p = 0.002).

CONCLUSIONS

Long-term vitamin E supplementation improves endothelium-dependent relaxation in forearm resistance vessels of hypercholesterolemic smokers, which are characterized by increased levels of autoantibodies against oxidized LDL. These findings may suggest that the beneficial effect of vitamin E is confined to subjects with increased exposure to oxidized LDL.

Increased NAD(P)H oxidase-mediated superoxide production in renovascular hypertension: evidence for an involvement of protein kinase C

BACKGROUND

Angiotensin II infusion has been shown to cause hypertension and endothelial dysfunction and to increase superoxide (O-.2) production in vascular tissue, mainly via an activation of nicotinamide adenine dinucleotide (phosphate) [NAD(P)H]-dependent oxidase, the most significant O-.2 source in endothelial and/or smooth muscle cells. With these studies, we sought to determine whether endothelial dysfunction in renovascular hypertension is secondary to an activation of these oxidases.

METHODS

Endothelial function in aortas from rats with two kidney-one clip (2K-1C) hypertension and age-matched controls was assessed using isometric tension studies in organ chambers. Changes in vascular O-.2 production were measured using lucigenin-enhanced chemiluminescence and electron spin resonance spectroscopy.

RESULTS

In hypertensive animals, relaxation to endothelium-dependent (acetylcholine) and endothelium-independent nitrovasodilators (nitroglycerin) was impaired. Constriction to a direct activator of protein kinase C (PKC) phorbol ester 12,13 dibutyrate (PDBu) was enhanced, and vascular O-.2 was significantly increased compared with controls. Vascular O-.2 was normalized by the PKC inhibitor calphostin C, by the inhibitor of flavin-dependent oxidases, diphenylene iodonium, and recombinant heparin-binding superoxide dismutase, whereas inhibitors of the xanthine oxidase (oxypurinol), nitric oxide synthase (NG-nitro-l-arginine) and mitochondrial NADH dehydrogenase (rotenone) were ineffective. Studies of vascular homogenates demonstrated that the major source of O-.2 was a NAD(P)H-dependent oxidase. Incubation of intact tissue with PDBu markedly increased O-. 2, the increase being significantly stronger in vessels from hypertensive animals as compared with vessels from controls. Endothelial dysfunction was improved by preincubation of vascular tissue with superoxide dismutase and calphostin C.

CONCLUSIONS

We therefore conclude that renovascular hypertension in 2K-1C rats is associated with increased vascular O-.2 leading to impaired vasodilator responses to endogenous and exogenous nitrovasodilators. Increased vascular O-.2 is likely secondary to a PKC-mediated activation of a membrane-associated NAD(P)H-dependent oxidase.

Long-term nitroglycerin treatment is associated with supersensitivity to vasoconstrictors in men with stable coronary artery disease: prevention by concomitant treatment with captopril

OBJECTIVES

We examined whether long-term nitroglycerin (NTG) treatment leads to an increase in sensitivity to vasoconstrictors. To assess a potential role of the renin-angiotensin system in mediating this phenomenon, we treated patients concomitantly with the angiotensin-converting enzyme (ACE) inhibitor captopril.

BACKGROUND

The anti-ischemic efficacy of organic nitrates is rapidly blunted by the development of nitrate tolerance. The underlying mechanisms are most likely multifactorial and may involve increased vasoconstrictor responsiveness.

METHODS

Forearm blood flow and vascular resistance were determined by using strain gauge plethysmography. The short-term responses to intraarterial angiotensin II (1, 3, 9 and 27 ng/min) and phenylephrine (an alpha-adrenergic agonist drug, 0.03, 0.1, 0.3 and 1 microg/min) were studied in 40 male patients with stable coronary artery disease. These patients were randomized into four groups receiving 48 h of treatment with NTG (0.5 microg/kg body weight per min) or placebo with or without the ACE inhibitor captopril (25 mg three times daily).

RESULTS

In patients treated with NTG alone, the maximal reductions in forearm blood flow in response to angiotensin II and phenylephrine were markedly greater (-64 +/- 3% and -53 +/- 4%, respectively) than those in patients receiving placebo (-41 +/- 2% and -42 +/- 2%, respectively). Captopril treatment completely prevented the NTG-induced hypersensitivity to angiotensin II and phenylephrine (-33 +/- 3% and -35 +/- 3%, respectively) but had no significant effect on blood flow responses in patients without NTG treatment (-34 +/- 2% and -37 +/- 3%, respectively).

CONCLUSIONS

We conclude that continuous administration of NTG is associated with an increased sensitivity to phenylephrine and angiotensin II that is prevented by concomitant treatment with captopril. The prevention of NTG-induced hypersensitivity to vasoconstrictors by ACE inhibition indicates an involvement of the renin-angiotensin system in mediating this phenomenon.

The physiology and pathophysiology of the nitric oxide/superoxide system

The endothelium modulates vascular tone by producing vasodilator vasoconstrictor substances. Of these, the most well characterized and potentially important are .NO and .02-. These small molecules exhibit opposing effects on vascular tone, and chemically react with each other in a fashion which negates their individual effects and leads to the production of potentially toxic substances. These dynamic interactions may likely have important implications, altering not only tissue perfusion but also contributing to the process of atherosclerosis. .NO is produced in endothelial cells by an enzyme termed nitric oxide synthase. The endothelial .NO-synthase is activated when the intracellular level of calcium is increased. This occurs in response to neurohormonal stimuli and in response to shear stress. Acetylcholine and substance P are examples of neurohumoral substances that are able to stimulate the release of nitric oxide and to assess endothelial regulation of vasomotor tone. Importantly, the vasodilator potency of nitric oxide released by the endothelium is abnormal in a variety of diseased states such as hypercholesterolemia, atherosclerosis and diabetes mellitus. This may be secondary to decreased synthesis of nitric oxide or increased degradation of nitric oxide due to superoxide anions. More recent experimental observations demonstrate increased production of superoxide in atherosclerosis, diabetes mellitus and high renin hypertension suggesting that endothelial dysfunction in these states is rather secondary to increased .NO metabolism rather than due to decreased synthesis of .NO. Superoxide rapidly reacts with nitric oxide to form the highly reactive intermediate peroxynitrite (ONOO-). Peroxynitrite can be protonated to form peroxynitrous acid which in turn can yield the hydroxyl radical (OH.). These reactive species can oxidize lipids, damage cell membranes, and oxidize thiol groups. .NO given locally, exerts potent antiatherosclerotic effects such as inhibition of platelet aggregation, inhibition of adhesion of leukocytes and the expression of leukocyte adhesion molecules. It is important to note, however, that in-vivo treatment with .NO (via organic nitrates) increases rather than decreases oxidant load within endothelial cells. It remains therefore questionable whether systemic treatment with .NO may have antiatherosclerotic properties or whether .NO may initiate or even accelerate the atherosclerotic process.

Antioxidant vitamin C improves endothelial dysfunction in chronic smokers

BACKGROUND

Chronic smoking is associated with endothelial dysfunction, an early stage of atherosclerosis. It has been suggested that endothelial dysfunction may be a consequence of enhanced degradation of nitric oxide secondary to formation of oxygen-derived free radicals. To test this hypothesis, we investigated the effects of the antioxidant vitamin C on endothelium-dependent responses in chronic smokers.

METHODS AND RESULTS

Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine (7.5, 15, 30, and 60 micrograms/min) and the endothelium-independent vasodilator sodium nitroprusside (1, 3, and 10 micrograms/min) were measured by venous occlusion plethysmography in 10 control subjects and 10 chronic smokers. Drugs were infused into the brachial artery, and forearm blood flow was measured for each drug before and during concomitant intra-arterial infusion of the antioxidant vitamin C (18 mg/min). In control subjects, vitamin C had no effect on forearm blood flow in response to acetylcholine and sodium nitroprusside. In contrast, in chronic smokers the attenuated forearm blood flow responses to acetylcholine were markedly improved by concomitant administration of vitamin C, whereas the vasodilator responses to sodium nitroprusside were not affected.

CONCLUSIONS

The present studies demonstrate that the antioxidant vitamin C markedly improves endothelium-dependent responses in chronic smokers. This observation supports the concept that endothelial dysfunction in chronic smokers is at least in part mediated by enhanced formation of oxygen-derived free radicals.

New insights into mechanisms underlying nitrate tolerance

The hemodynamic and anti-ischemic efficacy of organic nitrates is rapidly blunted due to the development of nitrate tolerance. The mechanisms underlying this phenomenon remain poorly understood and likely involve several independent factors. More recent experimental observations suggest that tolerance may be the consequence of intrinsic abnormalities of the vasculature, including enhanced vascular superoxide and endothelin production. Superoxide anions degrade nitric oxide derived from nitroglycerin, whereas autocrine-produced endothelin within vascular smooth muscle sensitizes the vasculature to circulating neurohormones, such as catecholamines and angiotensin II, all of which may compromise the vasodilator potency of nitroglycerin. Interestingly, these vascular consequences of in vivo nitroglycerin treatment can be mimicked by incubating cultured endothelial and smooth muscle cells with angiotensin II. Further, nitrate tolerance and rebound following sudden cessation of prolonged nitroglycerin therapy can be prevented by concomitant treatment with high-dose angiotensin-converting enzyme inhibition or angiotensin-I receptor blockade. These data strongly suggest that increased circulating levels of angiotensin II, which are encountered during in vivo nitroglycerin treatment, initiate cellular events that ultimately attenuate the nitroglycerin vasodilator effects during prolonged treatment periods.

Cigarette smoking potentiates endothelial dysfunction of forearm resistance vessels in patients with hypercholesterolemia. Role of oxidized LDL

BACKGROUND

Risk factors for atherosclerosis such as hypercholesterolemia and hypertension are associated with endothelial dysfunction of conduit and resistance vessels; however, the interaction of these risk factors and underlying mechanisms affecting endothelial function remain to be determined. The present study investigated the role of long-term smoking and hypercholesterolemia and their impact on endothelial function of peripheral resistance vessels in relation to plasma levels of autoantibodies against oxidized LDL, which has been implicated in the development of endothelial dysfunction and atherosclerosis.

METHODS AND RESULTS

The vascular responses to the endothelium-dependent agent acetylcholine (7.5, 15, 30, and 60 micrograms/min) and the endothelium-independent agent sodium nitroprusside (1,3, and 10 micrograms/min) were studied in normal control subjects (n = 10), patients with hypercholesterolemia (n = 15), long-term smokers (n = 15), and hypercholesterolemic patients who smoked (n = 15). Drugs were infused into the brachial artery, and forearm blood flow (FBF) was measured by venous occlusion plethysmography. The FBF responses to acetylcholine were significantly blunted in all three patient groups compared with normal control subjects (P < .05). The acetylcholine-induced increase in FBF was significantly attenuated in patients with hypercholesterolemia who smoked compared with hypercholesterolemic nonsmokers and normocholesterolemic smokers (P < .05 for both). The response to sodium nitroprusside was not statistically different in all four groups. Plasma levels of autoantibody titer against oxidized LDL were inversely related to acetylcholine-induced changes in FBF (r = -.53, P < .002) and were substantially increased in the group with both risk factors.

CONCLUSIONS

These results demonstrate that cigarette smoking and hypercholesterolemia synergistically impair endothelial function and that their combined presence is associated with increased plasma levels of autoantibodies against oxidized LDL. These observations raise the possibility that long-term smoking potentiates endothelial dysfunction in hypercholesterolemic patients by enhancing the oxidation of LDL.

Dissociation of coronary vascular tolerance and neurohormonal adjustments during long-term nitroglycerin therapy in patients with stable coronary artery disease

OBJECTIVES

We sought to examine whether long-term nitroglycerin treatment causes tolerance in large coronary arteries and whether the loss of vascular effects parallels neurohormonal adjustments.

BACKGROUND

Nitroglycerin therapy is associated with increased plasma renin activity and aldosterone levels and a decrease in hematocrit. It is assumed that nitroglycerin tolerance results in part from these neurohormonal adjustments and intravascular volume expansion.

METHODS

Three groups were studied: group I (n = 10), no prior nitroglycerin therapy; and group II (n = 10) and group III (n = 8), 24- and 72-h long-term nitroglycerin infusion (0.5 micrograms/kg body weight per min), respectively. Coronary artery dimensions were assessed using quantitative angiography. Plasma renin activity, plasma aldosterone and vasopressin levels and hematocrit were monitored before and during nitroglycerin infusions.

RESULTS

In group I, increasing intravenous concentrations of nitroglycerin caused a dose-dependent increase of the midportion of the left anterior descending coronary artery (baseline diameter 2.13 +/- 0.07 mm [mean +/- SEM], maximally by 22 +/- 2%) and left circumflex coronary artery (baseline diameter 2.08 +/- 0.07) mm, maximally by 22 +/- 3%). An intracoronary nitroglycerin bolus (0.2 mg) caused no further significant increase in diameter, indicating maximal dilation. In group II (n = 10), the baseline large coronary artery diameter under ongoing nitroglycerin was significantly larger than that in group I (left anterior descending artery 2.61 +/- 0.08 mm, left circumflex artery 2.57 +/- 0.08 mm). Additional intravenous and intracoronary nitroglycerin challenges did not cause further dilation, indicating maximally dilated vessels. At the same time, plasma renin activity, plasma aldosterone and vasopressin levels were significantly increased, and hematocrit significantly decreased. In group III patients, the baseline diameter of the left anterior descending artery and the left circumflex artery did not differ from that in patients without nitroglycerin pretreatment, indicating a complete loss of nitroglycerin coronary vasodilative effects. These patients showed no significant increase in circulating neurohormonal levels but a significant decrease in hematocrit.

CONCLUSIONS

Within 24 h of continuous nitroglycerin treatment, the coronary arteries were maximally dilated despite neurohormonal adjustments and signs of intravascular volume expansion. Within 3 days of nitroglycerin infusion, tolerance developed in the absence of neurohormonal activation. The dissociation of neurohormonal adjustments and tolerance in large coronary arteries indicates that after long-term nitroglycerin treatment, true vascular tolerance, perhaps from an intracellular tolerance step, may have developed.

Magnetic resonance imaging in the evaluation of treatment in multiple sclerosis

Magnetic resonance scans of 74 patients with multiple sclerosis participating in a controlled trial were compared 6 months before and at the end of a 24-32 months-treatment period with either Cyclosporin A (n = 31) or Azathioprine (n = 43). Both qualitative rating and computation of lesion volume showed deterioration in more than 40% of the patients, while by clinical criteria only 10-30% were worse. No significant difference was noted when the two treatment groups were compared. If careful repositioning and standardized image parameters are used, MRI is an indispensable tool for the objective determination of disease progression in MS although it cannot replace clinical examination.

An attempt to quantify magnetic resonance imaging in multiple sclerosis--correlation with clinical parameters

The diagnostic value of magnetic resonance imaging (MRI) in multiple sclerosis (MS) is uncontested. But only little information exists on its usefullness in monitoring disease activity. We describe a method of quantification that can be performed in longitudinal MRI-investigations. We used a standardized method of scanning and determined the area of demyelinating lesions with an interactive planimetric computer system. In order to determine the approximate lesion volumes, the computed area was multiplied by the slice thickness. In 89 patients with clinically definite MS we found an average lesion volume of 11900 mm3. The mean score in Kurtzke's expanded disability scale was 3.0. The correlation between computed lesion volume and neurological deficit was significant, but only weak (rho = 0.3). We conclude, that planimetric evaluation of MRI can be a valuable supplement to clinical rating scales in MS patients. The method described here, used in combination with high spacial resolution and better tissue specificity of latest generation MRI scanners, could be helpful in the evaluation of treatment in many other CNS diseases.