Tolerance to ethanol and cross-tolerance to pentobarbital by isolated hearts from chronic alcoholic rats

Chronic Effects of Ethanol on Pharmacokinetics and Left Ventricular Systolic Function in Rats

BACKGROUND

Observational clinical studies have demonstrated that there is a U-shaped relationship between ethanol consumption and all-cause mortality or risk of ischemic stroke. Although the exact cause of the U-shaped relationship is unclear, the pharmacokinetics of ethanol during the time course of chronic intake of ethanol may be involved, in relation to its cardiotoxic effects. The present study has assessed the cause of the U-shaped relationship between the ethanol consumption and left ventricular (LV) systolic dysfunction in a pharmacokinetic way.

METHODS

Male Wistar rats were paired, and either ethanol or control liquid diet was chronically administered for 7 weeks. Then, these rats were subdivided into 3 groups: control liquid-diet-fed rats [EtOH (-)], 3 g/dL ethanol liquid-diet-fed rats (3%EtOH), and 5 g/dL ethanol liquid-diet-fed rats (5%EtOH). Ethanol's cardiotoxicity on LV systolic function was investigated by echocardiography. Ethanol concentration in blood, ethanol pharmacokinetics, and hepatic alcohol dehydrogenase (ADH) activity were evaluated simultaneously.

RESULTS

The 5%EtOH group revealed LV systolic dysfunction, associated with a higher ethanol concentration in blood, and lower hepatic ADH activity than the EtOH (-) group; however, the 3%EtOH group did not show LV systolic dysfunction. During the acute ethanol stress, LV systolic dysfunction appeared in both EtOH (-) and 5%EtOH groups, with a higher ethanol concentration in blood and lower hepatic ADH activity than the 3%EtOH group. The 3%EtOH group showed a higher ethanol washout rate, less time-integral of ethanol concentration, and shorter mean residence time of ethanol in blood than the EtOH (-) or 5%EtOH group.

CONCLUSIONS

The U-shaped relationship between chronic ethanol consumption and LV systolic dysfunction may be closely related to the pharmacokinetic characteristics of ethanol in blood, which depends on the quantity of chronically drinking alcohol.

Activation of epsilon protein kinase C correlates with a cardioprotective effect of regular ethanol consumption

In addition to decreasing the incidence of myocardial infarction, recent epidemiological data suggest that regular alcohol consumption improves survival after myocardial infarction. We recently found that chronic ethanol exposure induces long-term protection against cardiac ischemia-reperfusion injury, which improves myocardial recovery after infarction. Furthermore, this cardioprotection by ethanol is mediated through myocyte adenosine A1 receptors. We now determine the role of protein kinase C (PKC) in ethanol's protective effect against ischemia-reperfusion injury. Using perfused hearts of ethanol-fed guinea pigs, we find that improved contractile recovery and creatine kinase release after ischemia-reperfusion are abolished by PKC inhibition with chelerythrine. Western blot analysis and immunofluorescence localization demonstrate that regular ethanol consumption causes sustained translocation (activation) of epsilonPKC, but not delta or alphaPKC. This same isozyme is directly implicated in ischemic preconditioning's protection against ischemia-reperfusion injury. Our findings suggest (i) that regular ethanol consumption induces long-term cardioprotection through sustained translocation of epsilonPKC and (ii) that PKC activity is necessary at the time of ischemia to mediate ethanol's protective effect against ischemia-reperfusion injury. Studying this selective effect of ethanol on epsilonPKC activation may lead to new therapies to protect against ischemia-reperfusion injury in the heart and other organ systems.

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.

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.

Effects of ethanol on the contractile function of the heart: a review

Chronic ethanol consumption leads to a number of alterations in the contractile function of the heart and is a leading cause of cardiomyopathy. Ethanol also has an acute negative inotropic effect mediated by direct interaction with cardiac muscle cells, although this action is often masked by indirect actions resulting from enhanced release of catecholamines in vivo. This article reviews the effects of ethanol on the contractile function of the heart. The specific targets affected by ethanol in cardiac muscle cells are discussed in terms of potential mechanisms underlying the depressions of contractility resulting from both acute and chronic actions of ethanol.