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1University Health Network and Mount Sinai Hospital Division of Cardiology, Department of Medicine, University of Toronto; and 2Quality Assurance Laboratory, Liquor Control Board of Ontario, Toronto, Ontario, Canada
Submitted 8 October 2007 ; accepted in final form 27 November 2007
| ABSTRACT |
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microneurography; sympathetic nervous system; blood pressure; cardiovascular diseases; risk factors
The potential benefits of alcohol may relate to its metabolic, antithrombotic, anticoagulant, antioxidant, or anti-inflammatory properties or to effects on hemodynamics, vascular endothelial function, and neurohumoral regulation of the circulation; these latter actions are the focus of the present study. Intoxicating doses of ethanol have been shown to dilate conduit arteries, increase heart rate (HR), and stimulate sympathetic nervous system activity, causing an increase in blood pressure that is sustained for hours after vasodilation dissipates (3, 11, 26, 30). These acute sympathoexcitatory and pressor effects, if replicated with each drink, could account in part for the sustained elevations in ambulatory awake blood pressure and asleep HR observed in a randomized crossover trial when 40 g of ethanol was consumed daily for 4 wk as either beer or red wine (35) and could also contribute to the dose-dependent relationship with blood pressure observed when more than two alcoholic drinks daily are consumed chronically (24). In contrast, there has been no systematic dose-response evaluation of the hemodynamic and vascular effects of one and two standard drinks of red wine or ethanol in the same person, or any direct comparison of such responses between red wine and ethanol.
The purpose of this randomized, single-blind, water-controlled study involving healthy subjects was to answer four questions: 1) Does low or moderate red wine and/or alcohol ingestion affect central sympathetic outflow and endothelium-dependent dilation? 2) If so, are these effects dose dependent? 3) What is the relationship between the amount of wine or ethanol ingested and blood pressure or sympathetic nerve traffic? 4) Does a red wine with verified high polyphenol content differ from alcohol in its effects on vascular responsiveness or the sympathetic nervous system?
| METHODS |
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Detailed instructions to abstain from caffeine, alcohol, and flavonoid-rich drinks (such as fruit juices) and food (fruits, dark chocolate, etc.) from the afternoon of the day before each session were provided. Subjects were instructed to eat a light breakfast in the morning before each study.
Protocol. Subjects attended three morning sessions, during which one of red wine, ethanol, or water was administered at random. To rest the fibular nerve between microneurographic recordings these sessions were scheduled at least 2 wk apart, and since muscle sympathetic nerve activity (MSNA) demonstrates between-leg congruence (33), alternate legs were studied on each session to minimize the potential for nerve trauma. Subjects were seated in a reclined chair, and an antecubital vein was canulated for blood sampling. A respiratory belt was wrapped around the abdomen to ensure that all signals were obtained during spontaneous breathing. HR was determined continuously from the ECG. Blood pressure was recorded automatically by an upper-arm cuff (Dinamap Pro 100, Critikon). A microneurographic electrode was placed in a sympathetic efferent fiber of the fibular nerve as previously described (2). After 10 min of quiet rest, stroke distance was determined by Doppler ultrasound directed above the aortic annulus (23). Brachial artery diameter and flow at rest plus increases in these variables following deflation of a lower-arm cuff inflated to 50 mmHg above systolic pressure for 4.5 min were determined by high-resolution ultrasound using a 7- to 10-mHz linear array transducer and Doppler, respectively (5). In brief, the artery was scanned 2–5 cm above the elbow. Postischemic reactive hyperemia was induced by inflating a lower-arm blood pressure cuff to 50 mmHg above systolic pressure for 4.5 min. A second scan was acquired, commencing 30 s before cuff deflation. Doppler flow measurements were obtained during the resting scan and during the first 10 s of reactive hyperemia. Blood was then drawn, and blood pressure, HR, and efferent MSNA were recorded over 8 min of quiet rest.
The first drink was then ingested over 5 min. When a peak blood alcohol concentration (BAC) of 40 mg/dl was achieved, after
10 min, all measurements were repeated (Fig. 1). Once BAC had fallen to 25–30 mg/dl, the second drink was ingested. A third set of data was acquired once BAC peaked, at
90 mg/dl. At the conclusion of the protocol, subjects voided for urinalysis.
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Selection of red wine and controls. The Quality Assurance Laboratory of the Liquor Control Board of Ontario (Toronto), selected a moderately priced pinot noir with high t-resveratrol content (Wolf Blass, Australia, 2001). Ethanol (95%) was provided by the hospital pharmacy, diluted with bottled Perrier water to a volume and concentration equal to the wine, and flavored with a sugar-free artificial flavoring (Crystal-Light, <1.3 g) for palatability. Equal volumes of Perrier water were provided as water control.
Target blood alcohol concentrations. Classical pharmacokinetics were used to calculate the one-drink dose required to achieve a BAC of 40 mg/dl in each subject, e.g., for a 68-kg male, 155 ml of wine with 12% alcohol content (18.6 g of ethanol) (Fig. 1). This was then doubled (310 ml) for the second dose. BAC was assessed with a breathalyzer (Intoxilyzer SD-5, CMI, Owensboro, KY; accuracy <0.5 mg/dl).
Analytic methods. Concentrations of free resveratrol, catechin, and quercetin in the bottle of wine, in venous plasma, and in urine were determined by gas chromatography (29). Plasma epinephrine, norepinephrine (NE), dopamine (DA), atrial natriuretic peptide (ANP), arginine vasopressin (AVP), adrenocorticotropic hormone (ACTH), and cortisol concentrations were determined by HPLC with electrochemical detection.
Continuous data were digitized and stored with LabView (National Instruments, Austin, TX; Ref. 2). Blinded analysis of data was performed after the conclusion of all studies by trained investigators. Stroke volume (SV) was calculated using the mean-time velocity integral and the area of the aortic annulus orifice (23), and cardiac output (CO) was calculated as the product of SV and simultaneous HR. Brachial artery diameter was determined with edge-tracing software (5). Flow-mediated dilation (FMD) was calculated as the percent increase in brachial artery diameter from baseline elicited by hyperemia (5). MSNA was quantified as burst frequency (bursts/min), burst incidence (bursts/100 heartbeats), and integrated nerve activity normalized to the maximum burst amplitude detected during each recording (NIMSNA) (8).
Statistical analysis. Values are expressed as means ± SE. A linear mixed-effects model was used to account for repeated measurement after zero, one, and two drinks on three different days. Comparisons were made by linear contrasts on the results of the fitted model. A linear contrast was also constructed to test for equal trends over time for the ethanol and wine days. Statistical significance was accepted if P < 0.05.
| RESULTS |
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Interventions. The red wine selected was determined to have high t-resveratrol (9.36 mg/l) and catechin (67.2 mg/l) concentrations and an average quercetin concentration (11.4 mg/l). Wine alone caused significant increases in both plasma and urine resveratrols and catechins (Fig. 2; Table 1). Similar BACs were achieved with the two alcohols after one and two drinks (P = 0.58 and 0.07, respectively): for ethanol 36.5 ± 2 and 81.4 ± 2 mg/dl and for wine 36.1 ± 2 and 71.4 ± 2 mg/dl (for 1 and 2 drinks, respectively, P < 0.00001 from baseline for all).
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CO fell by 0.8 ± 0.3 l/min after two drinks of water (P = 0.004) and after one drink of both ethanol (P = 0.008) and wine (P = 0.015), whereas compared with two drinks of water, CO rose significantly after two drinks of both ethanol (+0.8 ± 0.3 l/min; P = 0.009) and wine (+1.2 ± 0.3 l/min; P = 0.0002) (Fig. 3; Tables 2–4). Overall, there was no difference between the effects of ethanol and wine on CO (P = 0.66).
Sympathoneural and neuroendocrine responses. On the water day, MSNA burst frequency fell 3.5 ± 1.7 bursts/min (P = 0.044) after two drinks, whereas MSNA burst incidence did not change (P = 0.64) (Fig. 4; Tables 2–4). There was no effect of one alcoholic drink on burst frequency. In contrast, two drinks of both ethanol and wine increased MSNA from the predrink baseline (+5.1 ± 1.8 and +6.2 ± 1.7 bursts/min, respectively; P < 0.01). Compared with two drinks of water, MSNA was 9.7 ± 2.5 bursts/min higher after two ethanol drinks (P = 0.0002) and 9.6 ± 2.5 bursts/min higher after two wine drinks (P = 0.0003). There was no significant difference between the two alcoholic beverages with respect to burst frequency (P = 0.74).
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Plasma NE concentration was not significantly affected by either beverage, but there was considerable variability within these data. Two wine drinks increased plasma epinephrine concentration by 0.09 pmol/l from baseline (P = 0.048), although there was no significant difference in this effect between ethanol and wine (P = 0.48). Neither water nor ethanol increased plasma DA concentration. In striking contrast, one glass of wine increased plasma DA concentration by 0.44 ± 0.12 pmol/l (P = 0.004), and two glasses increased plasma DA concentration by 0.81 ± 0.12 pmol/l (P < 0.00001). These effects of two red wine drinks on DA were significantly greater than those of both water (P < 0.00001) and ethanol (P = 0.00005), and there was a significant difference for trends over time between wine and ethanol (P = 0.0001).
None of these interventions affected plasma concentrations of ANP or AVP. Plasma ACTH concentrations increased 80% after wine (P = 0.006), but not after ethanol or water. ACTH concentrations after two drinks of wine were significantly greater than after two drinks of ethanol (P = 0.017) or water (P = 0.043). Trends for ACTH over time were significantly different during the wine and ethanol sessions (P = 0.041). With the exception of a fall after one drink of ethanol (P = 0.041), none of the interventions affected plasma cortisol and there was no difference in trends over time between the two alcoholic beverages.
Brachial artery diameter and responsiveness to flow. There was no change in resting brachial arterial diameter after one or two drinks of water (Fig. 5; Tables 2–4). By contrast, there were significant increases in diameter after one and two drinks of both alcoholic beverages, with no difference between ethanol and wine (P = 0.39). Compared with two drinks of water, brachial diameter was 0.39 ± 0.10 mm larger after two drinks of ethanol (P = 0.0001) and 0.40 ± 0.10 mm larger after two drinks of wine (P < 0.0001).
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| DISCUSSION |
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Our principal findings were that 1) there is a U-shaped relationship between BAC and CO; 2) one alcoholic drink induces conduit artery vasodilation without eliciting direct or reflex increases in HR or MSNA; 3) compared with water, two alcoholic drinks evoke significant increases in MSNA, HR, and CO, yet brachial dilation is sustained and blood pressure does not increase; 4) neither alcoholic beverage augments FMD; 5) despite significantly increasing plasma polyphenols, red wine exerts hemodynamic, sympathoneural, and vascular actions similar to those of ethanol alone; and 6) in contrast to ethanol, red wine increases plasma DA and ACTH concentrations.
Hemodynamic actions of alcohols.
There is little information as to the effects of red wine or ethanol in the doses given in the present study on systemic hemodynamics. A dose of ethanol that raised the BAC in normal subjects to 62 ± 7 mg/dl had no effect on CO but increased superior mesenteric and digital skin blood flow (20), whereas a higher dose (BAC 112 ± 4 mg/dl) increased HR, CO, and blood pressure (17). The present observations are in agreement with previous studies demonstrating a fall or no change in blood pressure and a 4–12 beat/min increase in heart rate following acute intake of higher doses (e.g.,
500 ml) of red wine but not dealcoholized red wine (3, 12, 19, 21). We observed similar dilation of the brachial artery with ethanol and red wine, and similar increases in HR, CO, and MSNA, indicating that alcohol, rather than other red wine constituents, elicits these effects.
Sympathoneural effects of alcohol. The present observations concerning MSNA are unique in two respects. First, there are no published data comparing the effects of ingested red wine and ethanol on MSNA in the same person. Second, one standard drink of ethanol or wine did not increase MSNA in our subjects. Thus the concept that ethanol is sympathoexcitatory (31) is based on findings of studies involving higher doses (BACs ranging between 48 and 107 mg/dl) (11, 14, 30). Despite eliciting sympathoexcitation, two drinks of ethanol or red wine did not increase blood pressure, likely because of countervailing vasodilation.
Randin et al. (26) studied twice nine subjects in whom ethanol (0.5 g/kg) was infused intravenously over 45 min. At one session, ethanol infusion followed 2 days of pretreatment with 2 mg dexamethasone, given to inhibit alcohol-induced stimulation of corticotropin-releasing hormone. Although they did not measure this hormone, when their subjects were premedicated with dexamethasone, ethanol infusion did not alter MSNA and induced calf vasodilation (26). In the present study, despite the shorter time between alcohol consumption and blood sampling, two glasses of wine, but not ethanol, increased ACTH significantly (P < 0.006), and cortisol tended to be higher after both wine and ethanol compared with water (P = 0.08 and 0.09, respectively). These present findings are therefore consistent with a centrally mediated contribution to the sympathoexcitatory response to two wine drinks.
Neither alcoholic beverage elicited significant increases in NE or epinephrine, but there was a striking, significant increase in plasma DA concentrations after red wine. The source and functional importance of this effect are as yet uncertain. Platelet content of serotonin and DA is increased in patients with migraine (6). Importantly, red wine, but not white wine or beer, stimulates the release of serotonin from platelets (15), and fractionation of wine components has identified flavonoids as mediators of this action (25).
Brachial artery dilation. Several groups have compared the effects of single doses of wine, dealcoholized wine, ethanol, and water on endothelium- or flow-mediated (FMD) and nitrate-mediated dilation (1, 4, 12, 32). All described an alcohol-induced increase in brachial artery diameter, but the reported effects on FMD were not consistent, possibly because of the influence of a higher baseline diameter on the denominator of this ratio. In the present study, one alcoholic drink increased brachial artery diameter, and a further increase was seen after two drinks, but there was no difference in the effects of red wine and ethanol on this response.
Of the polyphenols in red wine, resveratrol appears to have the greatest impact on vascular endothelial nitric oxide synthase activity (27). In the present study, two drinks of wine increased the plasma concentration of resveratrol 4-fold and urinary concentration 27-fold, but the flow-mediated vasodilation after two drinks of wine was significantly less than after two drinks of water. This attenuated vasodilator response cannot be attributed entirely to a reduction in brachial endothelial sheer stress (4), because ethanol also dilated the brachial artery yet did not reduce FMD significantly. The key conclusion, therefore, is that the polyphenol constituents of red wine do not augment ethanol-induced vasodilation acutely either at rest or in response to a hyperemic stimulus.
Limitations. It is conceivable that the present sample size may have obscured true differences between the acute actions of red wine and ethanol, but it can be argued on the basis of the present paired comparison study design that, if present, these should be quite small and of doubtful biological significance. The report by Randin et al. (26) suggests that further increases in MSNA might have been detected had we continued our recordings for an hour or more after the last drink; however, the protocol had some time constraints imposed by the bladder fullness stimulated by these interventions. Greater vascular or neurohumoral responses might have been elicited by higher oral intake of polyphenols, but these are unlikely to be achieved in a practical way through the medium of red wine as currently produced, and this protocol aimed to replicate normal social use of alcohol.
In conclusion, one drink of alcohol caused conduit artery vasodilation without activating sympathetic outflow, whereas two drinks increased sympathetic nerve firing rate, HR, and CO. Despite the abundant literature describing the potential cardiovascular benefits of polyphenols, and greater increases in plasma DA and ACTH after two wine drinks, there was no evident distinction between the acute cardiovascular actions of red wine and ethanol. The present findings do not exclude the possibility that evidence of such benefit might emerge with chronic red wine consumption.
Increases in HR and sympathetic outflow are well-described risk markers for hypertension, hypertrophy, heart failure, and cardiovascular death (9, 28). Although it is not possible to infer the chronic actions of alcohol ingestion from this acute dose-response comparison, the narrow dose-response relationships demonstrated may sculpt the J-shaped relationship between alcohol consumption and cardiovascular events observed in population studies.
| GRANTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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