This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kaufmann, P. A. Articles by Camici, P. G. Search for Related Content PubMed PubMed Citation Articles by Kaufmann, P. A. Articles by Camici, P. G. Related Collections Nuclear cardiology and PET Mechanism of atherosclerosis/growth factors

(Circulation. 2000;102:1233.)
© 2000 American Heart Association, Inc.

Clinical Investigation and Reports

Coronary Heart Disease in Smokers

Vitamin C Restores Coronary Microcirculatory Function

Philipp A. Kaufmann, MD; Tomaso Gnecchi-Ruscone, MD; Marco di Terlizzi, MD; Klaus P. Schäfers, MSc; Thomas F. Lüscher, MD, FESC, FACC, FRCP; Paolo G. Camici, MD, FESC, FACC, FRCP

From MRC Clinical Sciences Centre (P.A.K., T.G.-R., M. di T., K.P.S., P.G.C.), Imperial College School of Medicine, Hammersmith Hospital, London, UK; and Cardiology (P.A.K., T.F.L.), University Hospital, Zürich, Switzerland. Dr Schäfers’ current address is Klinik und Poliklinik fur Nuklearmedizin, Universitat Muenster, Muenster, Germany.

Correspondence to Paolo G. Camici, MD, MRC Clinical Sciences Centre, Hammersmith Hospital, London W12 ONN, UK. E-mail paolo.camici{at}csc.mrc.ac.uk

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
Background—Coronary endothelial function and vasomotion are impaired in smokers without coronary disease, and this is thought to be due to increased oxidative stress.

Methods and Results—We used positron emission tomography to measure the coronary flow reserve, an integrated measure of coronary flow, through both the large epicardial coronary arteries and the microcirculation in 11 smokers and 8 control subjects before and after administration of the antioxidant vitamin C. At baseline, coronary flow reserve was reduced by 21% in smokers compared with control subjects (P<0.05) but was normalized after vitamin C, whereas the drug had no effect in control subjects.

Conclusions—The present study is the first to demonstrate that the noxious prooxidant effects of smoking extend beyond the epicardial arteries to the coronary microcirculation and affect the regulation of myocardial blood flow. Vitamin C restores coronary microcirculatory responsiveness and impaired coronary flow reserve in smokers, which provides evidence that the damaging effect of smoking is at least in part accounted for by an increased oxidative stress.

Key Words: blood flow • coronary arteries • circulation • tomography • smoking • vitamins

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
Cigarette smoking is a well established risk factor for cardiovascular disease,¹ and it affects both the coronary and the peripheral circulation.² Because cigarette smoke contains a large number of oxidants,³ it has been hypothesized that the adverse effects of smoking may result from oxidative damage to vascular endothelium. Indeed, endothelial dysfunction in brachial⁴ and coronary⁵ arteries has been demonstrated in long-term smokers and even in passive smokers.^{6 7}

Ascorbic acid, or vitamin C, is the main water-soluble antioxidant in human plasma⁸ ; it protects lipids against peroxidative damage by scavenging superoxide and other reactive oxygen species.⁹ In smokers, plasma¹⁰ and tissue¹¹ vitamin C levels are lower than in nonsmokers. In addition, vitamin C has been reported to improve endothelium-dependent vasodilation in the forearm of smokers.¹² In hypertensives, vitamin C improved endothelium-dependent vasomotion of epicardial coronary arteries,¹³ providing evidence that their coronary dysfunction is at least in part caused by increased oxidative stress.

We hypothesized that the noxious prooxidant effects of smoking extend beyond the epicardial arteries to the coronary microcirculation and affect the regulation of myocardial blood flow (MBF). To test this hypothesis, we measured MBF and coronary flow reserve (CFR) with PET in asymptomatic smokers and in nonsmoking control subjects before and after the administration of vitamin C.

	Methods

Top Abstract Introduction Methods Results Discussion References

 
Study Population
We studied 8 male healthy nonsmokers (control subjects) with a mean age of 42±5 years (range 36 to 50 years) and 11 asymptomatic male smokers with a mean age of 43±4 years (range 38 to 50 years). Smokers were included if they had been smoking 1 pack of cigarettes for at least the past consecutive 10 years. They had to refrain from smoking for 3 hours before the study to minimize any relevant effect of acute smoking and short-term cessation of smoking compared with the effect of vitamin C. As a consequence of their smoking habit, the smokers’ carboxyhemoglobin level was 3.5±0.9% of the total hemoglobin versus 0.7±0.3% in nonsmokers (P<0.001). None of the subjects had a history of cardiovascular disease or coronary risk factors (except for smoking). Entry criteria included normal heart rate, blood pressure, ECG, and 2-dimensional echocardiogram, as well as low clinical probability for coronary artery disease.¹⁴ The lipid profile was assessed in all individuals, and those with a total cholesterol level of >6.4 mmol/L (250 mg/100 mL) were excluded from the present study according to the exclusion criteria used in the West of Scotland (WOSCOP) Study.¹⁵ In addition, all subjects were carefully instructed to refrain from the intake of caffeine-containing beverages within 24 hours before the study. A screening test for caffeine was performed on a blood sample taken immediately before the PET scan from each subject; caffeine was not detectable in any of the blood samples.

PET Scanning
Scanning was performed with an ECAT 931-08/12 15-slice tomograph that gave a 10.5-cm axial field of view (CTI/Siemens); characteristics of this tomograph have been reported previously.¹⁶ MBF was measured with ¹⁵O-labeled water (H₂¹⁵O) as reported elsewhere.¹⁷ Briefly, H₂¹⁵O (700 to 900 MBq) was injected as an IV bolus over 20 seconds at an infusion rate of 10 mL/min, and then the venous line was flushed for an additional 2 minutes with saline. The following acquisition frame times were used: 14x5 seconds, 3x10 seconds, 3x20 seconds, and 4x30 seconds.

To define regions of interest, myocardial and blood pool images were then generated directly from the dynamic H₂¹⁵O study as reported previously.¹⁸ Subsequently, regions of interest were drawn within the left atrium and ventricular myocardium on consecutive image planes. These were projected onto the dynamic H₂¹⁵O images to generate blood and tissue time activity curves. Arterial and tissue activity curves were fitted to a single tissue compartment tracer kinetic model to give values of MBF (in mL · g^-1 · min^-1) as previously described.¹⁹

CFR Calculations
MBF was measured at rest and during pharmacologically induced hyperemia with adenosine at a standardized rate²⁰ of 140 µg · kg body wt^-1 · min^-1 IV during 7 minutes. This dosage is in line with the guidelines of the American College of Cardiology and the American Heart Association²¹ for the application of adenosine in nuclear cardiac perfusion studies, and it has been shown to induce maximal myocardial hyperemia²² comparable to that achieved with intracoronary papaverine. PET flow studies have been shown to be accurate and reproducible,²³ even in patients with coronary artery disease,^{24 25 26} of whom many are smokers.

CFR, which is an integrated parameter of endothelial function and vascular smooth muscle relaxation, was calculated as the ratio of hyperemic to baseline MBF. In normal human subjects, myocardial oxygen consumption is linearly related to the heart rate–blood pressure product (RPP), an index of external cardiac work, and both are related to coronary blood flow.²⁷ To allow meaningful interpretation of the quantitative data, it has been proposed that resting MBF be corrected for RPP.²⁸ To account for the variability of coronary driving pressure, coronary resistance (mm Hg · min · g · mL^-1) was also calculated as the ratio of mean arterial pressure to MBF.

Arterial blood pressure was recorded with automatic cuff sphygmomanometry at 1-minute intervals, and the ECG was monitored continuously throughout the procedure. A 12-lead ECG was recorded at baseline and every minute during adenosine administration.

Study Protocol
A baseline CFR was assessed in all subjects. Fifteen minutes later, a repeat measurement of CFR was carried out after a 10-minute infusion of 3 g vitamin C IV (Figure 1). The dose of vitamin C was chosen to reach plasma concentrations that have been demonstrated to inhibit superoxide anion–mediated lipid peroxidation⁸ and to improve brachial²⁹ and coronary¹³ endothelial function in patients with hypertension and brachial endothelial function in smokers.¹²

View larger version (15K): [in this window] [in a new window]   Figure 1. Study protocol.

Dose-Finding Substudy
Because smoking could alter the sensitivity of the coronary smooth muscles to adenosine, a dose that causes maximal dilation in nonsmoking patients may not produce the same maximal dilation in smokers. Therefore, we performed a dose-finding study to test the MBF responsiveness for 3 different doses of adenosine. In 8 additional age-matched (mean age 43±6 years) male smokers, flow was measured at rest and during the standard 140 µg · min^-1 · kg^-1 adenosine dosage. Thereafter, a second resting flow measurement was carried out followed by a second hyperemic flow measurement with a dose of adenosine that was 20% (ie, 170 µg · min^-1 · kg^-1, n=4) or 40% (ie, 200 µg · min^-1 · kg^-1, n=4) higher, with both administered as a 7-minute infusion.

The study protocol was approved by the Research Ethics Committee of Hammersmith Hospital, and radiation exposure was licensed by the UK Administration of Radioactive Substances Advisory Committee. All patients gave informed and written consent before the study.

Statistical Analysis
The comparison of hemodynamic data, MBF, and CFR between baseline and drug infusion was carried out by a 1-way ANOVA for repeated measurements, with Scheffé’s procedure applied when the t test result was statistically significant. Data are reported as mean±SD values.

	Results

Top Abstract Introduction Methods Results Discussion References

 
All procedures were well tolerated apart from the common side effects caused by adenosine, such as flushing and feeling of tightness in the chest. None of the subjects experienced any symptoms or had any ECG change during or after the infusion of vitamin C.

Hemodynamics
At the baseline study, heart rate and mean arterial blood pressure were similar in control subjects and smokers both at rest and during adenosine infusion. They remained unchanged after vitamin C infusion (Table 1). The RPP did not differ between the 2 groups during all study conditions.

View this table: [in this window] [in a new window]   Table 1. Hemodynamic Measurements

MBF, CFR, and Resistance
Mean values of MBF and CFR for both groups are summarized in Table 2. At baseline, resting MBF was similar in control subjects and smokers. In smokers, adenosine-induced hyperemia was reduced by 17% compared with control subjects (P<0.05) (Figure 2). After vitamin C infusion, resting MBF was unchanged in control subjects but significantly increased in smokers (+11%, P<0.05 versus baseline). Similarly, vitamin C did not affect hyperemic flow in control subjects but significantly increased hyperemic flow in smokers (+25%, P<0.001 versus baseline), to a value comparable to that for the control subjects (Figure 2). At baseline, CFR was reduced by 21% in smokers compared with control subjects (P<0.05). Coronary vasodilator reserve in smokers was normalized after vitamin C, whereas the drug had no effect in control subjects (Figure 3). Because of the similarity of RPPs between the 2 groups, correction of resting MBF and CFR for this parameter did not change the significance of these findings.

View this table: [in this window] [in a new window]   Table 2. PET Measurements

View larger version (14K): [in this window] [in a new window]   Figure 2. Individual MBF values. Ado indicates adenosine. *P<0.05 vs control subjects. ***P<0.001 vs baseline.

View larger version (50K): [in this window] [in a new window]   Figure 3. CFR values.

Resting coronary resistance (Table 3) was comparable in control subjects and smokers at baseline and after vitamin C infusion. Adenosine induced a greater reduction in coronary resistance in control subjects than in smokers. Vitamin C infusion significantly decreased the resistance in response to adenosine in smokers to a value comparable to that of control subjects.

View this table: [in this window] [in a new window]   Table 3. Coronary Resistance

Dose-Finding Substudy
In the substudy, coronary resistance fell from 102±20 mm Hg · min · g · mL^-1 to 26±6, 27±6, and 29±6 mm Hg · min · g · mL^-1 after the infusion of 140, 170, and 200 µg · min^-1 · kg^-1 adenosine during 7 minutes, respectively. There was no significant difference between the minimal resistance at the 3 different adenosine doses (Figure 4).

View larger version (20K): [in this window] [in a new window]   Figure 4. Dose-finding study. Ado indicates adenosine; Res, coronary resistance. ***P<0.0001 vs rest.

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The present study is the first to demonstrate that the noxious prooxidant effects of smoking extend beyond the epicardial arteries to the coronary microcirculation to affect the regulation of MBF and that a normal CFR can be restored with vitamin C. This suggests that increased production or activity of oxygen-derived free radicals contributes to vascular damage and heart disease in chronic smokers.

CFR, defined as the ratio of near-maximal to basal MBF, has been proposed as an indirect parameter to evaluate the function of the coronary circulation.³⁰ It is an integrated measure of coronary flow through both the large epicardial coronary arteries and the microcirculation. Therefore, an abnormal CFR can be due to narrowing of the epicardial arteries,¹⁹ as well as to dysfunction of the microcirculation.³¹ The latter can be caused by structural (eg, vascular remodeling with reduced lumen-to-wall ratio)³² or functional changes, which may involve neurohumoral factors or endothelial dysfunction.³³ Endothelial dysfunction has been found to be caused by coronary risk factors such as hypercholesterolemia,³⁴ essential hypertension,³⁵ diabetes mellitus,³⁶ and smoking.⁵

Endothelium-Dependent and -Independent Coronary Hyperemic Responses to Adenosine
Until recently, the vasodilator effect of adenosine was thought to be based solely on the direct stimulation of A₂ adenosine receptors on vascular smooth muscle cells, which mediate an increase in the second-messenger cAMP by stimulating adenylate cyclase. Therefore, this agent has been used frequently in animal and human studies to evaluate endothelium-independent vasodilation.³⁷ However, in the past decade, it has been appreciated that adenosine also acts as an endothelium-dependent vasodilator,³⁸ both via flow-mediated dilation³⁹ and via direct stimulation of A₁ adenosine⁴⁰ and other purinergic⁴¹ receptors on endothelial cells. Although our results reflect coronary microcirculatory function,⁴² with the use of adenosine, no definite evidence can be provided on whether the reduction in flow reserve in smokers is due to endothelium-dependent or -independent mechanisms. However, based on experimental data, it is most likely that the endothelium is the source of the oxidative stress.⁴³

Mechanisms of Smoking-Associated Vascular Damage
Our findings are in agreement with previous observations in smokers that show blunted endothelium-dependent vasodilation in the coronary⁵ and brachial^{4 6} arteries. The findings of the present study extend these observations and demonstrate that smoking leads to a dysfunction of the coronary microcirculation.

Although the mechanisms of smoking-associated vascular damage are not yet fully established, several factors have been proposed. Nicotine has been shown to produce structural damage in aortic endothelial cells of animals.⁴⁴ Smoking is associated with a direct toxic effect on human endothelial cells.⁴⁵ The gas phase of cigarette smoke contains large amounts of free radicals and prooxidants, and the particulate phase contains high concentrations of lipophilic quinones,³ which can form the highly reactive hydroxyperoxide radical (OH·). In addition, the vasoactive level of nitric oxide can be reduced by superoxide anion (O2) that directly originates from cigarette smoke and results in the formation of peroxynitrite anion (ONOO·), a highly reactive compound with strong cytotoxic potency.⁴⁶ In addition, these oxidants may increase the amount of oxidized LDL, which is markedly more effective than native LDL in causing endothelial⁴⁶ and microcirculatory dysfunction through the reduction in nitric oxide synthesis.⁴⁷

In the present study, we have shown that the short-term administration of the antioxidant vitamin C restores coronary microcirculatory responsiveness and impaired CFR in smokers without having an effect in nonsmoking control subjects. This supports the hypothesis⁴⁸ that the damaging effect of smoking is at least in part explained by an increased oxidative stress and is in line with the results of a recent study⁴⁹ in which reduced glutathione, another antioxidant, was shown to improve endothelial dysfunction in patients with cardiovascular risk factors but had no effect in subjects without risk factors. Similarly, vitamin C has been reported to attenuate abnormal coronary vasomotor reactivity in patients with vasospastic angina by scavenging oxygen free radicals.⁵⁰

A shift of the dose-response curve to adenosine in smokers as a cause for the reduced hyperemic response can be excluded on the basis of our dose-finding study.

Study Limitations
It cannot be entirely excluded that some of the smokers had epicardial coronary artery disease (albeit without significant stenosis), which in turn would have induced endothelial dysfunction. This could have been ruled out with certainty only with coronary angiography, which seemed unjustified in these asymptomatic volunteers. With current techniques, the distinction between endothelial dysfunction due to early and nonobstructive coronary artery disease and endothelial dysfunction due to the effect of smoking cannot be made with absolute certainty. However, endothelial dysfunction due to smoking may represent an early stage in the development of coronary artery disease. None of the subjects had hypertension, diabetes, hyperlipidemia, or a history of coronary artery disease or atherosclerosis (determined by the absence of angina, intermittent claudication, and cerebrovascular disease). Thus, their clinical risk for coronary artery disease was assessed as low.¹⁴ In addition, it has been recently demonstrated that even in patients with mild coronary artery disease, CFR assessed with PET can still be used to evaluate and follow up the functional response of the coronary circulation.²⁶

Clinical Implications
Our findings provide evidence that the short-term administration of vitamin C almost completely reverses microcirculatory dysfunction in asymptomatic smokers. Because PET flow studies have been shown to be accurate,^{51 52 53} the method appears appropriate for the study of the effects of any intervention with each subject used as his or her own control. This was confirmed in a recent reproducibility study from our laboratory.²³

Although our study design does not allow us to comment on long-term effects of vitamin C, these effects might be worth testing in a large-scale trial of whether daily oral vitamin C as a dietary supplement has preventive effects on the development of coronary artery disease in smokers. In fact, the larger amount of vitamin C in the Mediterranean diet⁵⁴ could contribute to the fact that in northern Europe, the absolute risk of coronary artery disease is higher than that in the Mediterranean area,⁵⁵ despite the higher prevalence of smoking among the Mediterranean populations.⁵⁶ Although a recent report found prooxidant properties of vitamin C when given as a dietary supplement at a dosage of 500 mg/d in healthy volunteers,⁵⁷ this does not necessarily apply to smokers because the latter have reduced plasma¹⁰ and tissue¹¹ levels of vitamin C due to dietary differences⁵⁸ and to increased consumption as the result of a greater oxidative stress.⁵⁹

	Acknowledgments

 
Dr Kaufmann was funded by a grant from the Swiss National Science Foundation (SCORE B, grant 3232-055002.98). Dr Schäfers was funded by a grant from the "Interdisziplinaere Medizinische Forschung" (grant Sc-1-5-II/96-20) of the University of Muenster. We are grateful to Flemming Hermansen for the use of his software and to the staff of the MRC Cyclotron Unit, especially the radiographers Andy Blyth and Hope McDevitt, for their excellent technical assistance.

Received January 21, 2000; revision received April 10, 2000; accepted April 13, 2000.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Sackett DL, Gibson RW, Bross IDJ, et al. Relation between aortic atherosclerosis and the use of cigarettes and alcohol: an autopsy study. N Engl J Med. 1968;279:1413–1420.
   
2. Jonas MA, Oates JA, Ockene JK, et al. Statement on smoking and cardiovascular disease for health care professionals. Circulation. 1992;86:1664–1669.[Free Full Text]
   
3. Church DF, Pryor WA. Free radical chemistry of cigarette smoke and its toxicological implications. Environ Health Perspect. 1985;64:111–126.[Medline] [Order article via Infotrieve]
   
4. Celermajer DS, Sorensen KE, Georgakopoulos D, et al. Cigarette smoking is associated with dose-related and potentially reversible impairment of endothelium-dependent dilation in healthy young adults. Circulation. 1993;88:2149–2155.[Abstract/Free Full Text]
   
5. Zeiher AM, Schachinger V, Minners J. Long-term cigarette smoking impairs endothelium-dependent coronary arterial vasodilator function. Circulation. 1995;92:1094–1100.[Abstract/Free Full Text]
   
6. Celermajer DS, Adams MR, Clarkson P, et al. Passive smoking and impaired endothelium-dependent arterial dilation in healthy young adults. N Engl J Med. 1996;334:150–154.[Abstract/Free Full Text]
   
7. Sumida H, Watanabe H, Kugiyama K, et al. Does passive smoking impair endothelium-dependent coronary artery dilation in women? J Am Coll Cardiol. 1998;31:811–815.[Abstract/Free Full Text]
   
8. Frei B, England L, Ames BN. Ascorbate is an outstanding antioxidant in human blood plasma. Proc Natl Acad Sci U S A. 1989;86:6377–6381.[Abstract/Free Full Text]
   
9. Bendich A, Machlin IJ, Scandurra O, et al. The antioxidant role of vitamin C. Adv Free Radic Biol Med. 1986;2:419–444.
   
10. Schectman G, Byrd JC, Gruchow HW. The influence of smoking on vitamin C status in adults. Am J Public Health. 1989;79:158–162.[Abstract/Free Full Text]
    
11. Mezzetti A, Lapenna D, Pierdomenico SD, et al. Vitamins E and C and lipid peroxidation in plasma and arterial tissue of smokers and non-smokers. Atherosclerosis. 1995;112:91–99.[Medline] [Order article via Infotrieve]
    
12. Heitzer T, Just H, Münzel T. Antioxidant vitamin C improves endothelial dysfunction in chronic smokers. Circulation. 1996;94:6–9.[Abstract/Free Full Text]
    
13. Solzbach U, Hornig B, Jeserich M, et al. Vitamin C improves endothelial dysfunction of epicardial coronary arteries in hypertensive patients. Circulation. 1997;96:1513–1519.[Abstract/Free Full Text]
    
14. Diamond G, Forrester J. Analysis of probability as an aid in the clinical diagnosis of coronary artery disease. N Engl J Med. 1979;300:1350–1358.[Abstract]
    
15. Shepherd J, Cobbe SM, Ford I, et al. Prevention of coronary heart disease with pravastatin in men with hypercholesterolemia. N Engl J Med. 1995;333:1301–1307.[Abstract/Free Full Text]
    
16. Spinks TJ, Jones T, Gilardi MC, et al. Physical performance of the latest generation of commercial positron scanner. IEEE Trans Nucl Sci. 1988;35:721–725.
    
17. Hermansen F, Rosen SD, Fath-Ourdubadi F, et al. Measurement of myocardial blood flow with oxygen-15 labelled water: comparison of different administration protocols. Eur J Nucl Med. 1998;25:751–759.[Medline] [Order article via Infotrieve]
    
18. Hermansen F, Ashburner J, Spinks TJ, et al. Generation of myocardial factor images directly from the dynamic H₂¹⁵O scan without use of a C¹⁵O blood pool scan. J Nucl Med. 1998;39:1696–1702.[Abstract/Free Full Text]
    
19. Uren NG, Melin JA, De BB, et al. Relation between myocardial blood flow and the severity of coronary artery stenosis. N Engl J Med. 1994;330:1782–1788.[Abstract/Free Full Text]
    
20. Cerqueira MD, Verain MS, Schwaiger M, et al. Safety profile of adenosine stress perfusion imaging: results from the Adenoscan Multicenter Trial Registry. J Am Coll Cardiol. 1994;23:384–389.[Abstract]
    
21. Ritchie Jl, Bateman TM, Bonow RO, et al. Guidelines for clinical use of cardiac radionuclide imaging. A report of the American Heart Association/American College of Cardiology Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures, Committee on Radionuclide Imaging, developed in collaboration with the American Society of Nuclear Cardiology. Circulation. 1995;91:1278–1303.
    
22. Wilson RF, Wyche K, Christensen BV, et al. Effects of adenosine on human coronary circulation. Circulation. 1990;82:1595–606.[Abstract/Free Full Text]
    
23. Kaufmann PA, Gnecchi-Ruscone T, Yap JT, et al. Assessment of the reproducibility of baseline and hyperemic myocardial blood flow measurement with O¹⁵-labeled water and PET. J Nucl Med. 1999;40:1848–1856.[Abstract/Free Full Text]
    
24. Dayanikli F, Grambow D, Muzik O, et al. Early detection of abnormal coronary flow reserve in asymptomatic men at high risk for coronary artery disease using positron emission tomography. Circulation. 1994;90:808–817.[Abstract/Free Full Text]
    
25. Beanlands RS, Muzik O, Melon P, et al. Noninvasive quantification of regional myocardial flow reserve in patients with coronary atherosclerosis using nitrogen-13 ammonia positron emission tomography: determination of extent of altered vascular reactivity. J Am Coll Cardiol. 1995;26:1465–1475.[Abstract]
    
26. Guethlin M, Kasel AM, Coppenrath K, et al. Delayed response of myocardial flow reserve to lipid-lowering therapy with fluvastatin. Circulation. 1999;99:475–481.[Abstract/Free Full Text]
    
27. Camici P, Marraccini P, Marzilli M, et al. Coronary hemodynamics and myocardial metabolism during and after pacing stress in normal humans. Am J Physiol. 1989;257:E309–E317.[Abstract/Free Full Text]
    
28. Nagamachi S, Czernin J, Kim AS, et al. Reproducibility of measurements of regional resting and hyperemic myocardial blood flow assessed with PET. J Nucl Med. 1996;37:1626–1631.[Abstract/Free Full Text]
    
29. Taddei S, Virdis A, Ghiadoni L, et al. Vitamin C improves endothelium-dependent vasodilation by restoring nitric oxide activity in essential hypertension. Circulation. 1998;97:2222–2229.[Abstract/Free Full Text]
    
30. Gould KL, Lipscomb K, Hamilton GW. Physiologic basis for assessing critical coronary stenosis. Am J Cardiol. 1974;33:87–92.[Medline] [Order article via Infotrieve]
    
31. de Silva R, Camici PG. Role of positron emission tomography in the investigation of human coronary circulatory function. Cardiovasc Res. 1994;28:1595–1612.[Medline] [Order article via Infotrieve]
    
32. Folkov B. ‘Structural factor’ in primary and secondary hypertension. Hypertension. 1990;16:89–101.
    
33. Camici PG. Microcirculation: what is the role of calcium antagonists? Eur Heart J 1997;18(suppl A):A51–A55.
    
34. Seiler C, Hess OM, Buechi M, et al. Influence of serum cholesterol and other coronary risk factors on vasomotion of angiographically normal coronary arteries. Circulation. 1993;88:2139–2148.[Abstract/Free Full Text]
    
35. Frielingsdorf J, Seiler C, Kaufmann P, et al. Normalization of abnormal coronary vasomotion by calcium antagonists in patients with hypertension. Circulation. 1996;93:1380–1387.[Abstract/Free Full Text]
    
36. Nitenberg A, Valensi P, Sachs R, et al. Impairment of coronary vascular reserve and ACh-induced coronary vasodilation in diabetic patients with angiographically normal coronary arteries and normal left ventricular systolic function. Diabetes. 1993;42:1017–1025.[Abstract]
    
37. Treasure CB, Vita JA, Cox DA, et al. Endothelium-dependent dilation of the coronary microvasculature is impaired in dilated cardiomyopathy. Circulation. 1990;81:772–729.[Abstract/Free Full Text]
    
38. Headrick JP, Berne RM. Endothelium-dependent and -independent relaxations to adenosine in guinea pig aorta. Am J Physiol. 1990;259:H62–H67.[Abstract/Free Full Text]
    
39. Zanzinger J, Bassenge E. Coronary vasodilation to acetylcholine, adenosine and bradykinin in dogs: effects of inhibition of NO-synthesis and captopril. Eur Heart J. 1993;14(suppl 1):164–168.
    
40. Smits P, Williams SB, Lipson DE, et al. Endothelial release of nitric oxide contributes to the vasodilator effect of adenosine in humans. Circulation. 1995;92:2135–2141.[Abstract/Free Full Text]
    
41. Nees S. The adenosine hypothesis of metabolic regulation of coronary flow in the light of newly recognized properties of the coronary endothelium. Z Kardiol. 1989;6:42–49.
    
42. Reis SE, Holubkov R, Lee JS, et al. Coronary flow velocity response to adenosine characterizes coronary microvascular function in women with chest pain and no obstructive coronary disease. J Am Coll Cardiol. 1999;33:1469–1475.[Abstract/Free Full Text]
    
43. Rajagopalan S, Kurz S, Munzel T, et al. Angiotensin II-mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation: contribution to alterations of vasomotor tone. J Clin Invest. 1996;97:1916–1923.[Medline] [Order article via Infotrieve]
    
44. Booyse FM, Osikowicz G, Quaarfoot AJ. Effect of chronic oral consumption of nicotine on the rabbit aortic endothelium. Am J Pathol. 1981;102:229–238.[Abstract]
    
45. Asmussen G, Kjeldsen K. Intimal ultrastructure of human umbilical arteries: observation on arteries from newborn children of smoking and nonsmoking mothers. Circ Res. 1975;36:579–589.[Abstract/Free Full Text]
    
46. Simon BC, Cunningham LD, Cohen RA. Oxidized low density lipoproteins cause contraction and inhibit relaxation in the pig coronary artery. J Clin Invest. 1990;86:75–79.
    
47. Hein WH, Kuo L. LDLs impair vasomotor function of the coronary microcirculation: role of superoxide anions. Circ Res. 1998;83:404–414.[Abstract/Free Full Text]
    
48. Campisi R, Czernin J, Schröder H, et al. L-Arginine normalizes coronary vasomotion in long-term smoker. Circulation. 1999;99:491–497.[Abstract/Free Full Text]
    
49. Kugiyama K, Ohgushi M, Motoyama T, et al. Intracoronary infusion of reduced glutathione improves endothelial vasomotor response to acetylcholine in human coronary circulation. Circulation. 1998;97:2299–2301.[Abstract/Free Full Text]
    
50. Kugiyama K, Motoyama T, Hirashima O, et al. Vitamin C attenuates abnormal vasomotor reactivity in spasm coronary arteries in patients with coronary spastic angina. J Am Coll Cardiol. 1998;32:103–109.[Abstract/Free Full Text]
    
51. Hutchins GD, Schwaiger M, Rosenspire KC, et al. Noninvasive quantification of regional blood flow in the human heart using N-13 ammonia and dynamic positron emission tomographic imaging. J Am Coll Cardiol. 1990;15:1032–1042.[Abstract]
    
52. Nitzsche EU, Choi Y, Czernin J, et al. Noninvasive quantification of myocardial blood flow in humans: a direct comparison of the [¹³N]ammonia and the [¹⁵O]water techniques. Circulation. 1996;93:2000–2006.[Abstract/Free Full Text]
    
53. Muzik O, Beanlands RS, Hutchins GD, et al. Validation of nitrogen-13-ammonia tracer kinetic model for quantification of myocardial blood flow using PET. J Nucl Med. 1993;34:83–91.[Abstract/Free Full Text]
    
54. de Lorgeril M, Salen P, Martin JL, et al. Mediterranean dietary pattern in a randomized trial: prolonged survival and possible reduced cancer rate. Arch Intern Med. 1998;158:1181–1187.[Abstract/Free Full Text]
    
55. Verschuren WM, Jacobs DR, Bloemberg BPM, et al. Serum total cholesterol and long-term coronary heart disease mortality in different cultures: twenty-five–year follow-up of the Seven Countries Study. JAMA. 1995;274:131–136.[Abstract]
    
56. Gensini GF, Comeglio M, Colella A. Classical risk factors and emerging elements in the risk profile for coronary artery disease. Eur Heart J. 1998;suppl A:A53–A61.
    
57. Podmore ID, Griffiths HR, Herbert KE, et al. Vitamin exhibits pro-oxidant properties. Nature. 1998;392:559.[Medline] [Order article via Infotrieve]
    
58. Kritchevsky SB, Shimakawa T, Tell GS, et al. Dietary antioxidants and carotid artery wall thickness. The ARIC Study. Atherosclerosis Risk In Communities Study. Circulation. 1995;92:2141–2150.
    
59. Duthie GG, Wahle KJ. Smoking, antioxidants, essential fatty acids and coronary heart disease. Biochem Soc Trans. 1990;18:1051–1054.[Medline] [Order article via Infotrieve]
    

This article has been cited by other articles:

				B. I. Levy, E. L. Schiffrin, J.-J. Mourad, D. Agostini, E. Vicaut, M. E. Safar, and H. A.J. Struijker-Boudier Impaired Tissue Perfusion: A Pathology Common to Hypertension, Obesity, and Diabetes Mellitus Circulation, August 26, 2008; 118(9): 968 - 976. [Full Text] [PDF]

				H. A.J. Struijker-Boudier, A. E. Rosei, P. Bruneval, P. G. Camici, F. Christ, D. Henrion, B. I. Levy, A. Pries, and J.-L. Vanoverschelde Evaluation of the microcirculation in hypertension and cardiovascular disease Eur. Heart J., December 1, 2007; 28(23): 2834 - 2840. [Abstract] [Full Text] [PDF]

				R. P. Naoumova, H. Kindler, L. Leccisotti, M. Mongillo, M. T. Khan, C. Neuwirth, M. Seed, P. Holvoet, J. Betteridge, and P. G. Camici Pioglitazone Improves Myocardial Blood Flow and Glucose Utilization in Nondiabetic Patients With Combined Hyperlipidemia: A Randomized, Double-Blind, Placebo-Controlled Study J. Am. Coll. Cardiol., November 20, 2007; 50(21): 2051 - 2058. [Abstract] [Full Text] [PDF]

				Y. Li and H. E. Schellhorn New Developments and Novel Therapeutic Perspectives for Vitamin C J. Nutr., October 1, 2007; 137(10): 2171 - 2184. [Abstract] [Full Text] [PDF]

				P. A. Kaufmann, O. E. Rimoldi, T. Gnecchi-Ruscone, T. F. Luscher, and P. G. Camici Systemic nitric oxide synthase inhibition improves coronary flow reserve to adenosine in patients with significant stenoses Am J Physiol Heart Circ Physiol, October 1, 2007; 293(4): H2178 - H2182. [Abstract] [Full Text] [PDF]

				P. G. Camici and F. Crea Coronary Microvascular Dysfunction N. Engl. J. Med., February 22, 2007; 356(8): 830 - 840. [Full Text] [PDF]

				K. Morita, T. Tsukamoto, M. Naya, K. Noriyasu, M. Inubushi, T. Shiga, C. Katoh, Y. Kuge, H. Tsutsui, and N. Tamaki Smoking Cessation Normalizes Coronary Endothelial Vasomotor Response Assessed with 15O-Water and PET in Healthy Young Smokers J. Nucl. Med., December 1, 2006; 47(12): 1914 - 1920. [Abstract] [Full Text] [PDF]

				P. T. Siegrist, O. Gaemperli, P. Koepfli, T. Schepis, M. Namdar, I. Valenta, F. Aiello, S. Fleischmann, H. Alkadhi, and P. A. Kaufmann Repeatability of Cold Pressor Test-Induced Flow Increase Assessed with H215O and PET J. Nucl. Med., September 1, 2006; 47(9): 1420 - 1426. [Abstract] [Full Text] [PDF]

				M. Namdar, P. Koepfli, R. Grathwohl, P. T. Siegrist, M. Klainguti, T. Schepis, R. Delaloye, C. A. Wyss, S. P. Fleischmann, O. Gaemperli, et al. Caffeine Decreases Exercise-Induced Myocardial Flow Reserve J. Am. Coll. Cardiol., January 17, 2006; 47(2): 405 - 410. [Abstract] [Full Text] [PDF]

				M. L. E. Vicario, L. Cirillo, G. Storto, T. Pellegrino, N. Ragone, L. Fontanella, M. Petretta, D. Bonaduce, and A. Cuocolo Influence of Risk Factors on Coronary Flow Reserve in Patients with 1-Vessel Coronary Artery Disease J. Nucl. Med., September 1, 2005; 46(9): 1438 - 1443. [Abstract] [Full Text] [PDF]

				P. A. Kaufmann, M. Namdar, F. Matthew, M. Roffi, S. V. Aschkenasy, B. van der Loo, G. Sutsch, T. F. Luscher, and R. Jenni Novel Doppler Assessment of Intracoronary Volumetric Flow Reserve: Validation Against PET in Patients With or Without Flow-Dependent Vasodilation J. Nucl. Med., August 1, 2005; 46(8): 1272 - 1277. [Abstract] [Full Text] [PDF]

				T. H. Schindler, E. U. Nitzsche, H. R. Schelbert, M. Olschewski, J. Sayre, M. Mix, I. Brink, X.-L. Zhang, M. Kreissl, N. Magosaki, et al. Positron Emission Tomography-Measured Abnormal Responses of Myocardial Blood Flow to Sympathetic Stimulation Are Associated With the Risk of Developing Cardiovascular Events J. Am. Coll. Cardiol., May 3, 2005; 45(9): 1505 - 1512. [Abstract] [Full Text] [PDF]

				P. A. Kaufmann and P. G. Camici Myocardial Blood Flow Measurement by PET: Technical Aspects and Clinical Applications J. Nucl. Med., January 1, 2005; 46(1): 75 - 88. [Full Text] [PDF]

				P. A. Kaufmann, O. Rimoldi, T. Gnecchi-Ruscone, R. S. Bonser, T. F. Luscher, and P. G. Camici Systemic Inhibition of Nitric Oxide Synthase Unmasks Neural Constraint of Maximal Myocardial Blood Flow in Humans Circulation, September 14, 2004; 110(11): 1431 - 1436. [Abstract] [Full Text] [PDF]

				C. A. Wyss, P. Koepfli, G. Fretz, M. Seebauer, C. Schirlo, and P. A. Kaufmann Influence of Altitude Exposure on Coronary Flow Reserve Circulation, September 9, 2003; 108(10): 1202 - 1207. [Abstract] [Full Text] [PDF]

				T. H. Schindler, E. U. Nitzsche, T. Munzel, M. Olschewski, I. Brink, M. Jeserich, M. Mix, P. T. Buser, M. Pfisterer, U. Solzbach, et al. Coronary vasoregulation in patients with various risk factors in response to cold pressor testing: Contrasting myocardial blood flow responses to short- and long-term vitamin C administration J. Am. Coll. Cardiol., September 3, 2003; 42(5): 814 - 822. [Abstract] [Full Text] [PDF]

				M. F. Carroll and D. S. Schade Timing of Antioxidant Vitamin Ingestion Alters Postprandial Proatherogenic Serum Markers Circulation, July 8, 2003; 108(1): 24 - 31. [Abstract] [Full Text] [PDF]

				B. De Bruyne, N. H.J. Pijls, E. Barbato, J. Bartunek, J.-W. Bech, W. Wijns, and G. R. Heyndrickx Intracoronary and Intravenous Adenosine 5'-Triphosphate, Adenosine, Papaverine, and Contrast Medium to Assess Fractional Flow Reserve in Humans Circulation, April 15, 2003; 107(14): 1877 - 1883. [Abstract] [Full Text] [PDF]

				G. E. Drossos, I. K. Toumpoulis, D. G. Katritsis, J. P. A. Ioannidis, P. Kontogiorgi, E. Svarna, and C. E. Anagnostopoulos Is vitamin C superior to diltiazem for radial artery vasodilation in patients awaiting coronary artery bypass grafting? J. Thorac. Cardiovasc. Surg., February 1, 2003; 125(2): 330 - 335. [Abstract] [Full Text] [PDF]

				C. A. Wyss, P. Koepfli, K. Mikolajczyk, C. Burger, G. K. von Schulthess, and P. A. Kaufmann Bicycle Exercise Stress in PET for Assessment of Coronary Flow Reserve: Repeatability and Comparison with Adenosine Stress J. Nucl. Med., February 1, 2003; 44(2): 146 - 154. [Abstract] [Full Text] [PDF]

				D. Zhang, Y. Tao, J. Gao, C. Zhang, S. Wan, Y. Chen, X. Huang, X. Sun, S. Duan, F. Schonlau, et al. Pycnogenol(R) in cigarette filters scavenges free radicals and reduces mutagenicity and toxicity of tobacco smoke in vivo Toxicology and Industrial Health, June 1, 2002; 18(5): 215 - 224. [Abstract] [PDF]