Contractile, metabolic and electrophysiologic effects of ethanol in the isolated rat heart

Effects of alcohol on intracellular pH regulators and electromechanical parameters in human myocardium

BACKGROUND

Disturbances in intracellular pH (pHi) of the heart can trigger major changes in the strength and rhythm of the heartbeat. It is well known that two extruders, Na+/H+ exchange (NHE) and Na+/HCO3- symporter (NHS), and a monocarboxylic acid transporter (MCT) are involved in acid-equivalent extruding in the human heart. Drinking alcohol has been proven to affect blood pressure and heart contractility and, sometimes, causes cardiac arrhythmia. To assess the effects of alcohol on pHi regulators and electromechanical parameters, various concentrations of alcohol were superfused into human myocardium in the present study.

METHODS

Human atrial myocardium was obtained from hearts of patients undergoing corrective cardiac surgery. Institutional rules for the protection of human subjects were observed. In the whole study, pHi was measured by an epifluorescent, ratiometric microspectrofluorimetry technique with the dye BCECF, while electrophysiological experiments were performed by traditional micropipette. NHE and NHS activities were measured after pHi recovery from intracellular acidosis induced by NH4Cl prepulse, while MCT activity was measured by a lactate adding/removing technique.

RESULTS

In pHi experiments, we demonstrated that alcohol could induce a biphasic, concentration-dependent (30-1000 mM) pHi change (i.e., alkalosis after acidosis) in human atrium in HEPES-buffered Tyrode solution. To a smaller extent, similar results were found when the superfusate was replaced by HCO3- -buffered Tyrode solution. NHE activity was increased by a moderate concentration of alcohol (30 mM), while it was inhibited in a concentration-dependent manner by higher concentrations of alcohol (>100 mM). On the contrary, 30-1000 mM alcohol increased the activity of NHS in a concentration-dependent manner. Surprisingly, MCT activity was not affected by alcohol. In electromechanical experiments, we found that alcohol (30-1000 mM) had a notable concentration-dependent inhibitory effect on the contractile force, while higher concentrations of alcohol (>100 mM) decreased the action potential amplitude, upstroke velocity, duration of repolarization, and force of contractions in a concentration-dependent way. All these alcohol-induced pHi changes and electromechanical inhibitions were reversible.

CONCLUSIONS

To our knowledge, this study provides the first evidence that alcohol can affect pHi in human myocardial tissue by changing the activity of acid extruders (i.e., NHE and NHS).

Alcohol and heart failure

BACKGROUND

Current heart failure (HF) guidelines note that alcohol use should be discouraged or restricted in patients with HF resulting from left ventricular systolic dysfunction. Existing knowledge is limited in the area of HF and alcohol.

METHODS AND RESULTS

The purpose of this article is to review the evidence regarding the acute and long-term use of alcohol in the setting of HF. In addition, general aspects about alcohol and alcoholic beverages that are important for understanding and interpreting alcohol-related literature are reviewed and that can be used when discussing alcoholic beverage use with patients with HF.

CONCLUSIONS

There is some emerging evidence that suggests light drinking (1 to 14 drinks per week) is safe and even beneficial in HF patients with ischemic left ventricular dysfunction (LVD). However, there are no effects of light drinking in HF patients with nonischemic LVD. Clinicians should reinforce the importance of evidence based pharmacologic and nonpharmacologic therapies in HF.

Alcoholic cardiomyopathy: incidence, clinical characteristics, and pathophysiology

In the United States, in both sexes and all races, long-term heavy alcohol consumption (of any beverage type) is the leading cause of a nonischemic, dilated cardiomyopathy, herein referred to as alcoholic cardiomyopathy (ACM). ACM is a specific heart muscle disease of a known cause that occurs in two stages: an asymptomatic stage and a symptomatic stage. In general, alcoholic patients consuming > 90 g of alcohol a day (approximately seven to eight standard drinks per day) for > 5 years are at risk for the development of asymptomatic ACM. Those who continue to drink may become symptomatic and develop signs and symptoms of heart failure. ACM is characterized by an increase in myocardial mass, dilation of the ventricles, and wall thinning. Changes in ventricular function may depend on the stage, in that asymptomatic ACM is associated with diastolic dysfunction, whereas systolic dysfunction is a common finding in symptomatic ACM patients. The pathophysiology of ACM is complex and may involve cell death (possibly due to apoptosis) and changes in many aspects of myocyte function. ACM remains an important cause of a dilated cardiomyopathy, and in latter stages can lead to heart failure. Alcohol abstinence, as well as the use of specific heart failure pharmacotherapies, is critical in improving ventricular function and outcomes in these patients.

Basal and ethanol-induced cardiac contractile response in lean and obese Zucker rat hearts

Obesity plays a pivotal role in metabolic and cardiovascular diseases. Certain types of obesity may be related to alcohol ingestion, which itself leads to impaired cardiac function. This study analyzed basal and ethanol-induced cardiac contractile response using left-ventricular papillary muscles and myocytes from lean and obese Zucker rats. Contractile properties analyzed include: peak tension development (PTD), peak shortening amplitude (PS), time to PTD/PS (TPT/TPS), time to 90% relaxation/relengthening (RT(90)/TR(90)) and maximal velocities of contraction/shortening and relaxation/relengthening (+/-VT and +/-dL/dt). Intracellular Ca(2+) transients were measured as fura-2 fluorescence intensity (DeltaFFI) changes and fluorescence decay time (FDT). In papillary muscles from obese rats, the baseline TPT and RT(90) were significantly prolonged accompanied with low to normal PTD and +/-VT compared to those in lean rats. Muscles from obese hearts also exhibited reduced responsiveness to postrest potentiation, increase in extracellular Ca(2+) concentration, and norepinephrine. By contrast, in isolated myocytes, obesity reduced PS associated with a significant prolonged TR(90), normal TPS and +/-dL/dt. Intracellular Ca(2+) recording revealed decreased resting Ca(2+) levels and prolonged FDT. Acute ethanol exposure (80-640 mg/dl) caused comparable concentration-dependent inhibitions of PTD/PS and DeltaFFI, associated with reduced +/-VT in both groups. Collectively, these results suggest altered cardiac contractile function and unchanged ethanol-induced depression in obesity.

Diminished cardiac contractile response to tetrahydropapaveroline in hypertension: role of beta-adrenoceptors and intracellular Ca(2+)

Tetrahydropapaveroline (THP), a condensation product of ethanol-derived acetaldehyde, potentiates cardiac function through a beta-adrenergic mechanism. It is well established that beta-adrenergic activity is markedly depressed in hypertension. However, little is known about the myocardial action of THP in hypertension. In this study, the effect of THP was examined using left ventricular papillary muscles and ventricular myocytes from 10-week-old normotensive (WKY) and spontaneously hypertensive (SHR) rats. The mechanical parameters evaluated include: peak tension developed (PTD), peak twitch amplitude (PTA), time-to-PTD/PTA (TPT/TPS), time-to-90% relaxation/relengthening (RT(90)/TR(90)), and the maximal velocities of contraction/shortening and relaxation/relengthening (+/-VT/+/-dL/dt). Intracellular Ca(2+) transients were measured as fura-2 fluorescence intensity changes (delta FFI). THP (0.01-100 microM) produced a concentration-dependent increase in myocardial contraction on muscles and myocytes from both groups of animals. However, preparations from the SHR group were generally less responsive to THP than their normotensive counterparts. The increase in contractility by THP was associated with increases in delta FFI and +/-VT, and shortening of TPT/TPS and RT(90)/TR(90). The role of beta-adrenoceptor(s) in the mechanism of action of THP was explored using specific beta-receptor subtype antagonists CGP 207.12A (beta(1)) and ICI 118,551 (beta(2)). In preparations from both WKY and SHR hearts, the THP-induced increase in cardiac contractility was either attenuated or blocked by CGP 207. 12A and ICI 118,551. These results indicate that THP exhibits a positive action on myocardial contraction that is mediated, in part, through both beta(1) and beta(2) adrenergic receptors. This cardiac inotropic response, however, is markedly diminished in hypertension, which is due possibly to alterations in beta-adrenergic signal transduction.

Hypertension augments ethanol-induced depression of cell shortening and intracellular Ca(2+) transients in adult rat ventricular myocytes

Ethanol, a risk factor for myocardial dysfunction, depresses myocardial contraction. This study was to determine whether ethanol-induced myocardial depression is affected by hypertension. Mechanical properties of ventricular myocytes isolated from both normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were evaluated using a video edge-detection system. Myocytes were electrically stimulated to contract at 0.5 Hz. Contractile properties analyzed include peak twitch amplitude (PTA), time-to-PTA (TPS), time-to-90% relengthening (TR(90)), and maximal velocities of shortening/relengthening (+/-dL/dt). Intracellular Ca(2+) transients were measured as fura-2 fluorescence intensity (DeltaFFI) changes. Acute ethanol exposure (80-640 mg/dl) caused a concentration-dependent inhibition of PTA and DeltaFFI in both WKY and SHR myocytes. The extent of maximal inhibition of PTA and FFI was significantly greater in SHRs (53.7 and 38.9%) compared to the WKY group (21.0 and 25.4%). Ethanol did not affect TPS but shortened TR(90) and slowed +/-dL/dt at high concentration ranges. Interestingly, the augmented ethanol-induced inhibition of cell shortening in hypertension was greatly attenuated by Ca(2+) channel opener BayK 8644 (1 microM). These results suggest that ethanol-induced myocardial depression may be augmented in hypertension, possibly due to mechanism(s) involving sarcolemmal Ca(2+) channels.

Influence of age on the inotropic response to acute ethanol exposure in spontaneously hypertensive rats

Acute ethanol exposure depresses cardiac electromechanical function, whereas chronic ethanol consumption leads to the development of a specific myopathic state. Chronic hypertension and aging have similar effects in the impairment of myocardial function. However, little is known about the effects of ethanol on cardiac mechanical function in hypertension. We studied the effect of age on baseline mechanical properties and the inotropic response to clinically relevant concentrations of ethanol (18 to 71 mmol/L) using papillary muscles from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) at 10 and 25 weeks of age. Mechanical parameters measured were peak tension developed, time to peak tension, time to 90% relaxation, and maximal velocities of tension development and tension decline. SHR exhibited elevated systolic pressure and body weight as well as cardiomegaly and hepatomegaly at 10 and 25 weeks of age. Baseline mechanical properties were similar in SHR and WKY muscles at 10 weeks, whereas at 25 weeks, SHR muscles developed less tension, and both maximal velocities of tension development and tension decline were markedly depressed. Ethanol exposure produced concentration-dependent negative inotropic effects in both groups at both ages. Ethanol (> 18 nmol/L) decreased peak tension developed in both groups at 10 weeks, although higher concentrations were required at 25 weeks. The negative inotropic effect of ethanol resulted in the shortening of time to 90% relaxation in both groups at 10 weeks and was associated with a slowing of maximal velocities of both tension development and tension decline. The results suggest that aging depresses baseline mechanical properties when coupled with hypertension. In addition, the magnitude of the negative inotropic effect of ethanol was attenuated in both groups at 25 weeks of age.

Acute and chronic effects of ethanol on papillary muscles from spontaneously hypertensive rats

The effects of chronic ethanol ingestion (12 weeks) on the mechanical properties of hypertrophied papillary muscle and the in vitro effects of ethanol (80-640 mg/dl) was studied. Papillary muscles from spontaneously hypertensive rats (SHRs) and their normotensive controls, the Wistar-Kyoto rat (WKY), were used in this study. Peak-developed tension was significantly less in muscles obtained from SHR compared with WKY even when normalized for muscle cross-sectional area. Chronic ethanol ingestion resulted in a significant shortening of both contraction and relaxation duration in muscles from SHR and WKY. In muscles from SHR and WKY, acute in vitro ethanol exposure produced concentration-dependent negative inotropic effects that were associated with a reduction in the duration of contraction and relaxation and marked slowing in the maximum velocities of tension development and decay. These findings suggest that the contractile response to ethanol exposure, in vitro, is not modified by either chronic ethanol ingestion or hypertension.

Influence of ethanol on circulation in surface-induced hypothermia and subsequent rewarming

Hypothermia and ethanol are often closely linked and in hypothermic accidents ethanol is often a contributing factor. To study the effects of ethanol on the circulation in hypothermic conditions, cardiac catheterization was carried out on 18 anaesthetized beagle dogs. They were divided into two groups. One gram of ethanol/kg of b.wt. diluted in saline was infused into the vena cava superior within 30 min to seven dogs. The dogs were then cooled between ice bags until the blood temperature in the ascending aorta was 25 degrees C and they were then rewarmed. The control group of 11 dogs was cooled and rewarmed without ethanol infusion. The heart rate first increased when cooling down to 33 degrees C and decreased thereafter in the control group. In the ethanol group heart rate increased during the ethanol infusion and remained high when cooling down to 33 degrees C and decreased thereafter. Heart rate was higher in the ethanol group throughout the experiments, and during rewarming the difference was significant. In the control group cardiac output first increased until a body temperature of 33 degrees C was achieved but then decreased. In the ethanol group cardiac output started to decrease after ethanol infusion. During rewarming there was a significantly higher cardiac output in the ethanol group, probably due to the higher heart rate. In the cardiac cycle the systolic period prolonged significantly (p < 0.001) in both groups when the body temperature decreased from 37 degrees C to 25 degrees C whereas the diastolic period remained quite stable. The contraction phase was also affected by the cooling. The changes in contraction force cannot be seen in dP/dt alone because dP/dt values first increased significantly when cooling from 37 degrees C to 33 degrees C but then decreased. Ejection fraction, systolic period, and the systemic vascular resistance increased despite the reduction of the dP/dt and thus we conclude that the contraction force is augmented in hypothermia. In the ethanol group the myocardium seems to be depressed due to ethanol. In the early phase of cooling heart rate increased but cardiac output decreased in the ethanol group, indicating the decreased ability of the heart to respond to cooling in the presence of ethanol. The time constant of exponential pressure fall (tau) increased linearly with cooling from 37 degrees C to 25 degrees C and recovered with rewarming in both groups. Changes in negative dP/dt coincided with the changes in the time constant of exponential isovolumic pressure fall. Ethanol did not influence relaxation. All the parameters we checked recovered to normal during rewarming.

Effect of ethanol on function of the rat heart and skeletal muscles

The present study was undertaken to evaluate the acute effects of ethanol on responses of the rat heart and skeletal muscles both in vivo and in vitro. In the anesthetized rat, intravenous infusion of ethanol at 0.1-0.5 g/kg body weight (33-167 mM) decreased the breathing rate by 8-83%, heart rate by 4-52%, and QRS amplitude by 5-27%, and increased the P-R interval by 1-49%. In the anterior tibialis muscle subjected to repetitive nerve stimulation at 100 Hz for 0.5 sec, ethanol at 0.1 g/kg increased the amplitude of the muscle action potential (AP) by 7%, whereas at 0.5 g/kg it decreased the muscle AP by 32%. The nerve-evoked tetanic tension was reduced by 7-34% at 0.1-0.5 g/kg ethanol. In the isolated rat heart, perfusion of ethanol at 0.1-3.0% (22-651 mM) decreased the heart rate by 8-48% and QRS amplitude by 10-39%, and increased the P-R interval by 5-61%. Left ventricular pressure was increased by 10% at 0.1% ethanol, and decreased by 80% at 3.0% ethanol. In the isolated rat phrenic nerve-diaphragm muscle preparation subjected to repetitive nerve stimulation at 100 Hz for 0.5 sec, 0.1-3.0% ethanol decreased the amplitude of the nerve AP by 5-89%, nerve-evoked muscle AP by 2-96%, and peak tetanic tension by 1-87%. On repetitive direct muscle stimulation at 100 Hz for 0.5 sec, 0.1-3.0% ethanol decreased the amplitude of the muscle-evoked muscle AP by 8-65%, and muscle-evoked tetanic tension by 2-65%. These studies indicate that ethanol causes smaller reduction in responses of the heart and skeletal muscles at clinical concentrations, but marked reduction in these responses at higher concentrations due to direct action on excitability of these tissues. At higher concentrations, ethanol causes greater reduction in excitability of the skeletal muscle than of the heart.

Prolonged consumption of moderate doses of alcohol and in vitro gastro-duodenal and ileal contractility in the rat

The effects of chronic feeding with moderate doses of ethanol (3% vol/vol in drinking water for 8 weeks), which do not induce tolerance, dependence and withdrawal, on the contractility of gastric, duodenal and ileal strips from rats were investigated. Only 50% of ethanol-treated specimens (as compared to 100% of saccharose-fed controls) exhibited antral phasic contractions (frequency decreased by 31% and 27% in the antrum and duodenum, respectively; P < 0.03 vs. controls). The depolarizing agent potassium chloride (KCl, 80 mM) produced less peak active tension in the fundus of ethanol-fed rats (P < 0.01). In alcoholic rats the sensitivity of the antrum to acetylcholine was fourfold less than that of control specimens. It is concluded that, in the rat, moderate doses of ethanol given chronically impair both spontaneous and tonic contractility of the stomach and duodenal muscle without affecting ileal contraction. It is possible that motility defects in the gut exposed to ethanol concentrations which do not cause tolerance, dependence or withdrawal in the rat may be due to a local rather than a systemic effect on the smooth muscle.

Alcoholic cardiomyopathy

Chronic alcoholism is one of the most important causes of dilated cardiomyopathy, and a large proportion of chronic alcoholics demonstrate impairment of cardiac function. The development of cardiac dysfunction is apparently related to the total lifetime dose of ethanol. Studies in experimental animals have demonstrated that both acute and chronic ethanol administration impair cardiac contractility. However, the relationship, if any, between the acute effects of alcohol and the development of irreversible cardiomyopathy remain to be elucidated.

Influences of changes in calcium concentration and verapamil on the cardiac depressant effect of ethanol in cat papillary muscle

1. In isolated cat heart papillary muscle electrically driven at a constant rate the depressant effects of increasing concentrations of ethanol on peak tension developed (PTD) was studied in Ringer-Locke solution with different calcium concentrations and with the addition of verapamil. 2. Ethanol induced a concentration dependent decrease in PTD that was significantly greater for each concentration of ethanol in hypocalcic medium (1.1 mM) than in normocalcic medium (2.2 mM). 3. In normocalcic (2.2 mM) medium, verapamil (5.1 x 10(-4) mM) plus ethanol (48.6 and 97.2 mM) produced a decrease in PTD to values significantly greater than those obtained by the addition of ethanol and verapamil alone. Therefore a potentiation of the effects of ethanol by verapamil was observed when both drugs act simultaneously. 4. In hypercalcic medium (4.4 mM), verapamil plus ethanol (48.6 and 97.2 mM) produced a slight decrease in PTD that was significantly less than that observed in normocalcic and hypocalcic mediums. 5. In hypocalcic medium (1.1 mM) verapamil plus ethanol (48.6 and 97.2 mM) produced a decrease in PTD that was of the same relative magnitude (%) as that observed in normocalcic medium. However no potentiation of the combined effects of verapamil plus ethanol was observed in hypocalcic medium.