Abstract

Aims: Excessive alcohol use in the form of binge drinking is associated with many adverse medical outcomes. Using an animal model, the primary objective of this study was to determine the effects of repeated episodes of binge drinking on myocardial structure, blood pressure (BP) and activation of mitogen-activated protein kinases (MAPKs). The effects of carvedilol, a beta-adrenergic blocker, were also examined in this animal model of binge drinking. Methods: Rats were randomized into three groups: control, binge and binge + carvedilol (20 mg/kg). Animals received intragastric administration of 5 g ethanol/kg in the morning × 4 days (Monday–Thursday) followed by no ethanol on Friday–Sunday. Animals were maintained on the protocol for 5 weeks. BP was measured using radiotelemetry methods. Animals underwent echocardiography at baseline, 2.5 and 5 weeks. Myocardial MAPKs were analyzed at 5 weeks using western blot techniques. Results: Over the course of 5 weeks, binge drinking was associated with significant transient increases in BP that were greater at 4 and 5 weeks compared with earlier time points. Carvedilol treatment significantly attenuated the binge-induced transient increases in BP at 4 and 5 weeks. No significant changes were found in echocardiographic parameters at any time period; however, binge drinking was associated with increased phosphorylation of p38 MAPK, which was blocked by carvedilol treatment. Conclusion: Repeated episodes of binge drinking result in progressive and transient increases in BP, no change in myocardial structure and differential regulation of MAPK activation.

INTRODUCTION

Worldwide, excessive alcohol consumption is one of the greatest preventable causes of death (Centers for Disease Control, 2004). Between 1995 and 2001, there was a 35% increase in binge drinking among US adults >18 years of age (Naimi et al., 2003). There is also evidence that suggests that those defined as ‘binge drinkers’ reported an average number of eight drinks per binge drinking episode (Centers for Disease Control, 2012). Also, more extreme forms of drinking are escalating, for example, 21 drinks on a 21st birthday (Rutledge et al., 2008). And in some settings, such as university/college campuses, binge drinking episodes are often repeated every weekend (Beets et al., 2009).

The cardiovascular (CV) effects of repeated episodes of binge drinking are poorly and incompletely understood. It is well established that ethanol's CV effects are dose-dependent; low-to-moderate levels of ethanol intake are associated with a reduced CV risk, whereas high intake levels are associated with increased risk of coronary artery disease, stroke, hypertension and cardiomyopathy (Thun et al., 1997; Bagnardi et al., 2008). Interestingly, in certain geographical areas where binge and bender drinking are more frequently reported, investigators have failed to find a cardioprotective effect with any level of ethanol consumption (Britton and McKee, 2000). Also, results from a recent systematic review and meta-analysis demonstrate how the cardioprotective effect of moderate alcohol consumption disappears when irregular heavy drinking patterns (>60 g pure alcohol ≥5 drinks/occasion at least monthly) are considered in the analysis (Roerecke and Rehm, 2010).

To date, most of the data regarding the effects of drinking pattern on CV outcomes are from epidemiologic studies and one-time exposure studies. Data from the Prospective Epidemiological Study of Myocardial Infarction (PRIME) revealed that a binge drinking pattern is associated with greater increases in systolic blood pressure (SBP) and higher risk of myocardial infarction on days following the binge drinking episodes (Marques-Vidal et al., 2001). Also, binge drinking is associated with cerebral infarction in young adults (16–40 years) who do not have other CV risk factors (Haapaniemi et al., 1996). Data from other epidemiologic studies support an association between binge drinking and sudden death (Wannamethee and Shaper, 1992; Britton and McKee, 2000; Corrao et al., 2000), ischemic and hemorrhagic stroke (Haapaniemi et al., 1996; Sundell et al., 2008) as well as cardiac arrhythmias (Nguyen et al., 1987; Panos et al., 1988). Some of the latter adverse CV outcomes have been attributed to alcohol-induced changes in BP. Data from epidemiologic studies support a relationship between alcohol consumption and BP; collectively, the findings suggest that regular daily consumption of >30 g/day for men and >20 g/day for women is associated with an increased relative risk of developing hypertension (Klatsky et al., 1986; Witteman et al., 1990). Only a few studies were identified that examined the one-time effect of binge drinking on BP, and these studies enrolled healthy male subjects (22–33 years of age) who consumed >4–5 standard drinks over a designated period of time. All studies reported significant transient increases in BP after alcohol consumption (Potter et al., 1986; Rosito et al., 1999; Seppa and Sillanaukee, 1999).

No studies to date have evaluated the effects of repeated episodes of binge drinking on CV parameters such as myocardial structure and BP. Therefore, using an animal model, the purpose of our study was to determine the effects of repeated binge episodes on cardiac structure and remodeling, BP and mitogen-activated protein kinases (MAPKs). We hypothesized that binge-induced changes in myocardial structure would be associated with activation of stress-associated MAPKs such as p38, extracellular signal-regulated kinase (ERK 1/2) and c-Jun NH2-terminal protein kinase (JNK), because these MAPKS are associated with different forms of cardiac pathology and there is evidence that acute and chronic ethanol exposure activates MAPKs (Ravingerova et al., 2003; Aroor and Shukla, 2004). We also hypothesized that binge-induced CV effects would be antagonized by the beta-adrenergic blocker, carvedilol.

MATERIALS AND METHODS

Animals and experimental groups

Male Sprague-Dawley rats (Charles River, Wilmington, MA, USA), beginning body weight 210–240 gm, 2–3 months old, were used in all experiments. All procedures were performed in accordance with the ‘Guide for the Care and Use of Laboratory Animals’ published by the US National Institutes of Health (NIH Publication No. 85-23, revised 1996) and approved by the Institutional Animal Care and Use Committee (ACC protocol # 09-006). After a 1-week acclimation, animals were randomly divided into three groups: control (CON) [normal saline (NS) or carvedilol] (n = 12), binge (n = 18) and binge + carvedilol (n = 6). Pilot studies revealed that neither NS nor carvedilol alone had an effect on cardiac structure and BP in animals; therefore, values from these groups were combined and referred to as the CON group. Animals in the CON group were divided into: (a) those used only for echocardiographic studies (n = 6) and (b) those used for radiotelemetry/BP studies (n = 6). Animals in the binge group were divided into: (a) rats used only for blood ethanol (BEL) analysis (n = 6) over the 5-week period and (b) those used only for echocardiographic studies (n = 6) and those used for radiotelemetry/BP studies (n = 7). Separate groups for echocardiography and BP were needed to avoid the effects of handling and anesthesia on BP.

Surgery for radiotelemetry

The radiotelemetry system used in this study consisted of transmitters, platform receivers and a dedicated computer system for data recordings (Data Sciences International, St. Paul, MN, USA). All animals were implanted with C50-PXT transmitters. After animals were anesthetized with ketamine/xylazine (75 mg/kg/10 mg/kg), an incision was made in the lower groin to expose the femoral artery. The pressure catheter was inserted into the femoral artery and advanced into the abdominal aorta. Using a trocar catheter, two electrocardiographic leads were subcutaneously tunneled from the abdominal incision to the left of the xiphoid space and caudal to the rib cage. All surgeries were performed using sterile technique. Cefazolin (100 mg/kg) (Sandoz, Princeton, NJ, USA) was administered twice a day for 3 days and buprenorphine (0.1 mg/kg) (Astra Zeneca, Wilmington, DE, USA) once 4 h immediately after surgery. After a 2-week recovery period, animals were randomized into the aforementioned groups.

Binge protocol

Two weeks following telemetry implantation, animals were randomized into groups. Animals in the binge group received intragastric administration of 5 g ethanol//kg (30% w/v solution) at 10 a.m. × 4 days (Monday, Tuesday, Wednesday and Thursday), followed by no ethanol on Friday, Saturday and Sunday. Animals were maintained on the protocol for 5 weeks. This model simulates binge/bender drinking behavior, which is characterized by the consumption of large amounts of ethanol within a limited time frame bringing the BEL to >80 mg/dl followed by a period of abstinence, which mimics the pattern of drinking in human beings (Thombs et al., 2003). Also, our binge protocol was not associated with animal welfare issues (i.e. weight loss, spontaneous seizures or animal mortality). Pilot studies revealed that peak BELs (150–200 mg/dl) were found between 1 and 2 h after ethanol administration, with levels approximating 0 mg/dl at 15 h after ethanol administration (data not shown). Control rats received an equivolume of NS or carvedilol (via intragastric administration). Animals in the binge group received carvedilol (20 mg/kg/day, gavage) 2 days prior to initiation of the binge protocol and then every day thereafter for 5 weeks because others have shown this dose to exert cardioprotective effects (Matsui et al., 1999; Watanabe et al., 2000). Animals in all groups were allowed 24-h free access to water and food.

To prevent the effects of handling on BP, a separate group of rats (n = 6) was used for BEL analysis over the 5-week period (Blood Ethanol Analyzer, Model GL5, Analox Instruments, Lunenburg, MA, USA). Prior to collecting tail vein blood, EMLA cream (Hospira, Lake Forest, IL, USA) was applied to the tail.

BP recordings

Due to the circadian pattern of feeding and activity in the rat (i.e. increases during lights-out due to feeding and physical activity), all animals received ethanol and/or saline in the a.m., which allowed hemodynamic recordings to take place while animals were not moving around or eating (Waki et al., 2006). Baseline SBP and diastolic BP (DBP) were recorded for 30 min prior to each daily intragastric administration of ethanol. In one series of pilot experiments, we measured BP continuously over a 24-h period to determine the effects of ethanol on BP. The 24-h recordings revealed that changes in BP values occurred between 60 and 90 min after ethanol administration and that these changes were transient and paralleled the increases in peak BEL values. Therefore, based on these pilot data, BP was monitored for up to 2 h after ethanol administration. For clarity, in this report, only 90-min BP changes are reported. At the end of the 5-week protocol, 24-h BP recordings were repeated to determine if there were changes in the transient effect of ethanol on the pattern of increases in BP.

Echocardiography

Echocardiograms were performed at baseline, 2.5 and 5 weeks and as previously described by our laboratory and according to the American Society of Echocardiography guidelines (Schiller et al., 1989; Piano et al., 2007). In brief, echocardiograms were performed by the same experienced sonographer using the Sequoia C256 Echocardiography System (Acuson Corporation, Mountain View, CA, USA) and a 15.0 MHz transducer. Before the procedure, animals were anesthetized with an initial dose of methoxyflurane, and a plane of anesthesia was maintained thereafter via intubation with 1% isoflurane, using a Harvard small-animal ventilator (respiratory rate 80 breaths per minute, respiratory volume 2.5 ml). The transducer was placed on the left thorax, and M-mode and 2D echocardiography images were obtained in the parasternal long- and short-axis views by directing the ultrasound beam at the mid-papillary muscle level. The measurements reported herein were obtained after well-defined, continuous interface of the anterior and posterior walls were visualized. Fractional shortening (FS) was calculated as previously described by our laboratory (Piano et al., 2007; Gu et al., 2008).

MAPK western blot analysis

Immunoblots were performed using 40-μg total protein homogenates (Gu et al., 2008). Protein homogenates were prepared from the left ventricle, and total protein concentrations were determined by Lowry (Bio-Rad, Hercules, CA, USA) assay. Equal amounts of protein (40 μg) were loaded onto a 10% sodium dodecyl sulfate–polyacrylamide gel electrophoresis, subjected to gel electrophoresis and electroblotted onto nitrocellulose membranes that were blocked with milk, washed and then incubated with primary antibody. Primary antibodies employed included: rabbit polyclonal anti-phospho-p38 MAPK, anti-phospho-ERK1/2, anti-phospho-JNK anti-p38, anti-ERK1/2 and anti-JNK (Cell Signaling Technology, Inc., Boston, MA, USA) (Gu et al., 2008). Membranes were extensively washed and then incubated with horse-radish peroxidase-conjugated anti-rabbit secondary antibody (Jackson ImmunoResearch, West Grove, PA, USA). Bands were visualized with the ECL system (Amersham, Little Chalfont, UK) and quantified with ChemiDoc XRS (Bio-Rad, Hercules, CA, USA) applying Quantity One software (Gu et al. 2008).

Statistical analysis

All data are expressed as the mean ± SEM. Echocardiographic data were compared using a two-way analysis of variance (ANOVA), and western blot data were compared using a one-way ANOVA. Baseline BPs (mmHg) were recorded on Monday before ethanol administration. The daily BP response to ethanol was expressed as the percent change in BP (e.g. BP after binge—baseline BP/baseline BP mmHg). Within each week, there were no differences in 90-min BP values as a function of day; therefore, the percent change in BP at 90 min was averaged across each week to obtain a mean 90-min BP change value for each week. All data were compared using a two-way repeated-measures ANOVA. When a significant F ratio (P < 0.05) was found, group comparisons were made using a Fisher's post hoc procedure for multiple comparisons (Sigmastat v 3.5, SYSTAT Software, Richmond, CA, USA).

RESULTS

Animal demographics and echocardiography parameters

No significant differences in ending body weights (gm) were found among animals (CON group 367 ± 4, Binge 374 ± 2, Binge + Carvedilol 421 ± 2). Over the 5-week period, BELs were measured daily after ethanol administration. BELs ranged 120–180 mg/dl at 1½ to 2 h post binge and ranged 88–107 mg/dl 4–5 h post ethanol (mean 91 ± 33 mg/dl). As shown in Table 1, no significant differences were found among groups in echocardiography-derived parameters. (Echocardiograms were not performed in the binge + carvedilol group because no changes were found in the binge group.)

Table 1.

Echocardiographic parameters

 Baseline 2.5 Weeks
 
5 Weeks
 
Control Control Binge  Control Binge  
HR (bpm) 335 ± 15 332 ± 11 332 ± 8 NS 316 ± 13 331 ± 13 NS 
LVEDD (mm) 7.6 ± 0.3 8.0 ± 0.06 8.3 ± 0.1 NS 8.6 ± 0.2 8.2 ± 0.2 NS 
LVESD (mm) 4.7 ± 0.2 4.7 ± 0.2 5.2 ± 0.2 NS 5.7 ± 0.2 5.1 ± 0.2 NS 
LVPWd (mm) 1.1 ± 0.02 1.2 ± 0.04 1.1 ± 0.04 NS 0.98 ± 0.03 1.0 ± 0.02 NS 
LVPWs (mm) 1.9 ± 0.02 2.2 ± 0.07 2.1 ± 0.09 NS 1.8 ± 0.08 1.9 ± 0.08 NS 
LV Mass (gm) 0.48 ± 0.02 0.57 ± 0.01 0.59 ± 0.01 NS 0.55 ± 0.05 0.50 ± 0.02 NS 
FS% 38 ± 1.2 41 ± 2.4 38 ± 1.3 NS 36 ± 1.5 37 ± 2.6 NS 
 Baseline 2.5 Weeks
 
5 Weeks
 
Control Control Binge  Control Binge  
HR (bpm) 335 ± 15 332 ± 11 332 ± 8 NS 316 ± 13 331 ± 13 NS 
LVEDD (mm) 7.6 ± 0.3 8.0 ± 0.06 8.3 ± 0.1 NS 8.6 ± 0.2 8.2 ± 0.2 NS 
LVESD (mm) 4.7 ± 0.2 4.7 ± 0.2 5.2 ± 0.2 NS 5.7 ± 0.2 5.1 ± 0.2 NS 
LVPWd (mm) 1.1 ± 0.02 1.2 ± 0.04 1.1 ± 0.04 NS 0.98 ± 0.03 1.0 ± 0.02 NS 
LVPWs (mm) 1.9 ± 0.02 2.2 ± 0.07 2.1 ± 0.09 NS 1.8 ± 0.08 1.9 ± 0.08 NS 
LV Mass (gm) 0.48 ± 0.02 0.57 ± 0.01 0.59 ± 0.01 NS 0.55 ± 0.05 0.50 ± 0.02 NS 
FS% 38 ± 1.2 41 ± 2.4 38 ± 1.3 NS 36 ± 1.5 37 ± 2.6 NS 

Values are mean ± SEM, n = 6–7 rats/group. Echocardiograms were not performed in the binge + carvedilol group because no changes were found in the binge group.

LVEDD, left ventricular end diastolic dimension; LVESD, left ventricular end systolic dimension; LVPWd, left ventricular posterior wall dimension in diastole; LVPWs, left ventricular posterior wall dimension in systole; LV, left ventricle; FS, fractional shortening; NS, non-significant.

Blood pressure

Over the course of 5 weeks, no changes in SBP were found in the CON group (Fig. 1). In contrast, binge alcohol consumption was associated with significant increases in SBP compared with the CON group, and increases were more pronounced at 4 and 5 weeks (Fig. 1). Except for the SBP value at 3 weeks, carvedilol treatment significantly attenuated the binge-induced increase in SBP. No significant difference was found between CON and binge + carvedilol SBP values at 1 and 2 weeks; however, binge + carvedilol SBP values at 3, 4 and 5 weeks were greater than CON SBP values (Fig. 1). Among the groups and over the 5-week period, similar changes were found with DBP (data not shown).

Fig. 1.

Ninety-minute SBP values (% change from baseline) obtained on each animal, aggregated to calculate average weekly results. Values are mean ± SEM, n = 6–7 rats/group. SBP was continuously monitored over a 24-h period following ethanol administration. Over the entire course of the 5-week study, SBP increases were transient and occurred between 60 and 90 min after ethanol binge administration, with SBP returning to pre-ethanol binge values at ∼10–11 h post-ethanol binge. For clarity, in this report, only 90-min BP changes are reported. *Indicates significantly different from values within the same experimental group, P < 0.001. **Indicates binge value significantly greater than CON group at all weeks and binge + carvedilol (20 mg/kg/day) values at 1, 2, 4 and 5 weeks (P < 0.001). #Indicates significantly greater than the CON group at 3, 4 and 5 weeks (P < 0.001).

Fig. 1.

Ninety-minute SBP values (% change from baseline) obtained on each animal, aggregated to calculate average weekly results. Values are mean ± SEM, n = 6–7 rats/group. SBP was continuously monitored over a 24-h period following ethanol administration. Over the entire course of the 5-week study, SBP increases were transient and occurred between 60 and 90 min after ethanol binge administration, with SBP returning to pre-ethanol binge values at ∼10–11 h post-ethanol binge. For clarity, in this report, only 90-min BP changes are reported. *Indicates significantly different from values within the same experimental group, P < 0.001. **Indicates binge value significantly greater than CON group at all weeks and binge + carvedilol (20 mg/kg/day) values at 1, 2, 4 and 5 weeks (P < 0.001). #Indicates significantly greater than the CON group at 3, 4 and 5 weeks (P < 0.001).

To determine the long-term effects of binge/bender drinking, baseline BPs determined on Monday morning (before ethanol administration) were compared among the groups over the 5-week protocol. No significant differences were found in baseline SBP or DBP among the groups (Fig. 2). Also at the end of 5 weeks, there was no change in the pattern of BP changes, in that peak increases were found 1.5–2 h post-ethanol administration and BP returned to baseline levels 20–24 h post-ethanol administration (data not shown).

Fig. 2.

Baseline (prior to intragastric administration of ethanol) SBP and DBP values measured every Monday during the 5-week protocol. Values are mean ± SEM, n = 6–7 rats per group. Control groups received either NS or carvedilol.

Fig. 2.

Baseline (prior to intragastric administration of ethanol) SBP and DBP values measured every Monday during the 5-week protocol. Values are mean ± SEM, n = 6–7 rats per group. Control groups received either NS or carvedilol.

Activation of MAPKs after binge

Myocardial tissue protein levels of total p38, ERK1/2 and JNK were determined using western blotting. Levels were expressed as the ratio of phosphorylated (P)-to-total protein levels. The levels of P-p38 were significantly greater in the binge hearts compared with the CON (P < 0.01) (Fig. 3). The levels of ERK 1/2 and JNK were similar between groups (Fig. 3). Because binge-induced increases were only found in levels of P-p38, we only performed western blot analysis for this MAPK after carvedilol treatment and found that carvedilol treatment significantly blocked ethanol-induced increases in P-p38 levels (Fig. 4).

Fig. 3.

Effects of 5 weeks of binge drinking on myocardial mitogen-activated protein kinase levels. Values are mean ± SEM, n = 6–7 rats/group. Total and phosphorylated (P) levels of p38, extracellular signal-regulated kinase (ERK 1/2) and c-Jun NH2-terminal protein kinase (JNK) were measured. Levels were expressed as the ratio of phosphorylated (P)-to-total protein levels. Representative western blots shown. *Indicates binge values significantly greater than CON group (P < 0.001).

Fig. 3.

Effects of 5 weeks of binge drinking on myocardial mitogen-activated protein kinase levels. Values are mean ± SEM, n = 6–7 rats/group. Total and phosphorylated (P) levels of p38, extracellular signal-regulated kinase (ERK 1/2) and c-Jun NH2-terminal protein kinase (JNK) were measured. Levels were expressed as the ratio of phosphorylated (P)-to-total protein levels. Representative western blots shown. *Indicates binge values significantly greater than CON group (P < 0.001).

Fig. 4.

Effects of 5 weeks of binge drinking on myocardial MAPK levels, p38 levels and effect of carvedilol treatment (20 mg/kg/day). Representative western blots. Carv, Carvedilol.

Fig. 4.

Effects of 5 weeks of binge drinking on myocardial MAPK levels, p38 levels and effect of carvedilol treatment (20 mg/kg/day). Representative western blots. Carv, Carvedilol.

DISCUSSION

This is the first study in an animal model to examine the effects of repeated episodes of binge drinking on cardiac structure and hemodynamics. We found that binge drinking episodes were associated with transient increases in BP that became progressively greater with repeated episodes of binge drinking. The greater pressor response at 4 and 5 weeks was attenuated but not completely blocked by carvedilol treatment. Five weeks of binge drinking was not associated with changes in cardiac structure; however, binge drinking was associated with increased phosphorylation of p38 MAPK, which was blocked by carvedilol treatment. Binge drinking had no long-term effect on BP because baseline BP (before binge) was unchanged after 5 weeks.

To our knowledge, there are also no data from human cross-sectional studies on the CV effects of repeated episodes of binge drinking. Only three studies were identified, all of which were designed to examine the one-time effect of binge drinking on BP in healthy male subjects (22–33 years of age) (Potter et al., 1986; Rosito et al., 1999; Seppa and Sillanaukee, 1999). In two of those studies, similar to our findings, investigators found increases in BP 1–5 h after alcohol consumption (Potter et al., 1986; Seppa and Sillanaukee, 1999), while others found increases in BP 12–16 h post-alcohol consumption (Rosito et al., 1999). Interestingly, in the studies reporting a more immediate pressor effect of alcohol consumption, the amount of alcohol was either consumed over a shorter time (i.e. 5–6 standard drinks/15 min) (Seppa and Sillanaukee, 1999) or the intake was greater (i.e. 12 standard drinks/6 h) (Potter et al., 1986) compared with the study reporting increases in BP 12–16 h post-alcohol consumption (4–5 standard drinks/1 h) (Rosito et al., 1999).

We found a greater pressor response at 4 and 5 weeks that was attenuated but not completely blocked by carvedilol treatment. Because carvedilol antagonizes α1 vascular smooth muscle receptors, it is possible that the more pronounced BP increase at 4 and 5 weeks may be due in part to an increased vascular responsiveness or sensitization of smooth muscle cells to catecholamines. Increased catecholamine release has been reported with alcohol use, and others have demonstrated that ethanol exposure increases the contractile responsiveness (i.e. greater maximum effect) of aortic rings to α1 agonists such as phenylephrine over a period of time (2–6 weeks) (Stewart and Kennedy, 1999; Tirapelli et al., 2007). Another possibility is ethanol-induced increased endothelin-1 (ET-1) levels. Others have reported that alcohol consumption increases ET-1 levels (Nanji et al., 1994). Using cultured human endothelial cells, Soardo et al. found that 14 days of ethanol exposure (140 mmol/l or 645 mg/dl) increased ET-1 levels (Soardo et al., 2008). Interestingly, the addition of carvedilol (60 μmol) to cell culture dishes decreased ET-1 levels (Soardo et al., 2008). We did not measure catecholamine or ET-1 levels; therefore, the mechanisms underlying both the transient and progressive increases in BP remains incompletely understood.

Using echocardiography, we found no effect of 5 weeks of binge drinking on myocardial structure. Using an animal model, we previously reported that long-term (8–12 months) ethanol administration was associated with left ventricular remodeling and development of a dilated cardiomyopathy exemplified by increased left ventricular dimensions and modest wall thickening (Kim et al., 2001). Similarly, the occurrence of alcoholic heart muscle disease in humans correlates with a high daily level and duration of alcohol consumption (Piano, 2002). Zagrosek et al. (2010) recently examined the effects of a one-time binge drinking episode (median peak BEL was 1.3 g/l) in healthy volunteers. No changes in ventricular volumes or systolic function were found 24 h or 1 week after the single binge episode. The present study only involved 5 weeks of binge drinking in adult male rats; therefore, it remains possible that a longer period of repeated binge drinking episodes may be associated with cardiac structural changes. In addition, future studies should consider developmental-specific effects and include young-adolescent animals.

Our data indicate that binge drinking activates myocardial MAPKs such as p38 and that carvedilol treatment blocked activation. Our findings are in line with others who have found ethanol-induced increases in liver and pancreatic p38 activation (Masamune et al., 2003; Aroor and Shukla, 2004). However, in contrast to others (Aroor and Shukla, 2004), we found no effects of binge ethanol exposure on myocardial ERK1/2 or JNK. This may be due to the timing of MAPK measurement after in vivo ethanol administration. We only evaluated MAPK activation at one time point (5 weeks), while others reporting increases in the liver ERK1/2 and JNK have examined these MAPKs following 1 and 4 h of acute ethanol exposure (Aroor and Shukla, 2004). Activation of MAPK signaling is implicated in alcoholic liver injury associated with cirrhosis. Similar to the liver, activation of myocardial MAPKs is associated with cell growth, cell differentiation and cell death, and may play a key role in the pathogenesis of processes such as hypertrophy, heart failure and reperfusion injury (Ravingerova et al., 2003). Increases in myocardial MAPKs following binge drinking could potentially be linked to adverse cellular changes such as myocyte hypertrophy or apoptosis.

Animal models are important for examining the adverse effects of alcohol abuse and allow for the control of confounding factors such as diet and environmental factors. In addition, animal models will allow investigators to concomitantly study the potential effects on other organ systems, allowing for a better understanding of how the brain versus the heart might be adversely affected by binge drinking. However, because most animals find the taste of alcohol aversive, developing a model that allows for a sufficient amount of alcohol consumption and replicates human states is challenging. Our goal was to simulate episodic binge drinking followed by periods of abstinence because this seems to reflect the current trend in young adult drinking patterns (Beets et al. 2009). Animal models (rats and mice) of binge drinking have been highly variable and have included: the one-time administration of large doses of ethanol (Zhou et al., 2001) and the Majchrowicz method of 3–4 daily intragastric administrations of ethanol for 3–4 days (Faingold, 2008). Other models such as ‘drinking in the dark’ (Rhodes et al., 2005) and ‘scheduled high alcohol consumption’ (Finn et al., 2005) have been developed and allow for studying drinking behavior, such as motivation and dependence. Our model resulted in BELs that were in the range of those established by National Institute on Alcohol Abuse and Alcoholism, and (importantly) our animals exhibited normal growth and weight gain over the 5 weeks (National Institute on Alcohol Abuse and Alcoholism, 2005).

We a priori selected to use the beta-adrenergic antagonist carvedilol because others have shown in humans and animal models that carvedilol treatment reduces BP and is associated with attenuation of left ventricular remodeling, associated with long-standing hypertension and myocardial infarction (Weber et al., 2008). It is also established that carvedilol exerts effects on BP by directly decreasing vascular resistance (rather than decreases in heart rate and cardiac output) (Ram, 2010). The use of only carvedilol, however, is a potential limitation of our study. This is because carvedilol is a non-specific beta-blocker. The use of a specific α1 antagonist may more directly establish a role for activation of α1 receptors and vascular responses linked to activation of this adrenergic receptor sub-type. It is also possible that the effects of ethanol may be mediated by changes or activation of areas within the central nervous system that control BP and CV responses.

Another limitation may relate to the 5-week duration of our study. We were not able to ascertain the potential long-term health consequences of the progressive and transient increases in BP. As noted above, binge drinking in human beings has been associated with many adverse CV events. In a prospective evaluation of adults admitted for first-ever brain infarction, Haapaniemi et al. (1996) found that acute intake of >40 g of ethanol during the 24 h preceding the brain infarction on weekends and holidays was significantly associated with cerebral infarction in young (16–40 years) and middle-aged (41–60 years) subjects. In a recent meta-analysis of longitudinal and case–control studies of risk factors for subarachnoid hemorrhage in men and women, Feigin et al. (2005) found that excessive ethanol intake (>150 g ethanol/week) was associated with a 2-fold increase risk of subarachnoid hemorrhage. One mechanism suggested for the binge-associated increased stroke risk is hypertension; however, at least in younger individuals, hypertension prevalence is low, suggesting that other mechanisms may be involved. In our study, we did not find a permanent effect of binge drinking on BP, exemplified by no change in baseline SBP or DBP over 5 weeks. Although speculative, large and transient increases in BP could be an important mechanism in alcohol-induced stroke in younger individuals.

Our data support the use of an animal model to investigate the CV effects of binge drinking. Our data indicate that repeated episodes of binge drinking result in progressive and transient increases in BP. Future research is needed to determine if transient increases in BP are an important mechanism in alcohol-induced strokes and other adverse CV events associated with binge drinking. In addition, more research is required to establish the adverse effects of binge drinking on other organ systems.

Funding

This study was supported by National Institutes of Health grant AA015578.

Acknowledgments

The authors thank Kevin Grandfield, Publication Manager for the UIC Department of Biobehavioral Health Science, for editorial assistance.

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