Autonomic Modulation of Altered Diurnal Hemodynamic Profiles in Ethanol-Fed Hypertensive Rats

Alcohol suppresses cardiovascular diurnal variations in male normotensive rats: Role of reduced PER2 expression and CYP2E1 hyperactivity in the heart

BACKGROUND AND AIMS

The molecular mechanism of the adverse effects of ethanol on diurnal cardiovascular regulation remains unknown. In separate studies, the cardiac circadian rhythm protein period-2 (PER2) confers cardioprotection and, in other organs, PER2 interaction with the ethanol-metabolizing enzyme CYP2E1 underlies, via heme oxygenase-1 (HO-1) upregulation, tissue injury/dysfunction. Here, we hypothesized that suppressed PER2 expression and elevated CYP2E1/HO-1 levels in the heart underlie the disrupted diurnal cardiovascular rhythm/function in alcohol-fed normotensive rats.

METHODS

In ethanol-fed (5%, w/v; 8 weeks) or isocaloric liquid diet-fed male rats, diurnal changes in blood pressure (BP), heart rate (HR), HR vagal variability index, root mean square of successive beat-to-beat differences in beat-interval duration (rMSSD), and cardiac function were measured by radiotelemetry and echocardiography followed by ex vivo molecular studies.

RESULTS

Radiotelemetry findings showed ethanol-evoked reductions in BP (during the dark cycle), rMSSD (during both cycles), and in diurnal differences in BP and rMSSD. Echocardiography findings revealed significant (p < 0.05) reductions in ejection fraction and fractional shortening (weeks 4-6) in the absence of cardiac remodeling (collagen content). Hearts of ethanol-fed rats exhibited higher (p < 0.05) CYP2E1 activity (50%) and HO-1 expression (63%), along with reduction (p < 0.05) in PER2 levels (29%), compared with the hearts of isocaloric diet-fed control rats.

CONCLUSIONS

Our novel findings implicate upregulations of CYP2E1/HO-1 and downregulation of the circadian rhythm cardioprotective protein PER2, in the heart, in the chronic deleterious diurnal cardiovascular effects of alcohol in male rats.

Heart rate turbulence during acute alcohol withdrawal syndrome

BACKGROUND

Alcohol withdrawal syndrome is associated with an increased incidence of cardiac arrhythmias and sudden cardiac death. Heart rate turbulence (HRT) parameters were applied during withdrawal to estimate cardiac regulation during treatment with clomethiazole.

METHODS

Twenty-two patients suffering from alcohol withdrawal syndrome were included in the study. Heart rate regulation was obtained by means of Holter ECG analyzing time intervals before medication, and 2 and 6h after medication. Slope and onset of HRT were calculated in addition to heart rate variability (HRV) parameters. Furthermore, we calculated the slope and the onset of ectopic beat-like events.

RESULTS

Heart rate variability parameters indicated a minor reduction of vagal modulation during withdrawal syndrome. Especially, the fractal scaling exponent BBI alpha1 (4-16) indicated the autonomic shift. In contrast to HRV parameters, no significant changes were observed in the HRT parameters. Significant correlations were observed between severity of withdrawal, as assessed by the AWS scale, and the fractal scaling exponent BBI alpha2 (16-64), and the onset and the slope of HRT of ectopic beat-like activity.

CONCLUSION

Increased sympathetic modulation during withdrawal and clomethiazole treatment is not associated with changes of heart rate turbulence parameters predictive of cardiac death after myocardial infarction.

Reduced cardiac contractile force due to sympathovagal dysfunction mediates the additive hypotensive effects of limited-access regimens of ethanol and clonidine in spontaneously hypertensive rats

Our previous attempts to investigate the long-term hemodynamic interaction between ethanol and clonidine in telemetered spontaneously hypertensive rats (SHRs) were hampered by the lack of a sustained hypotensive response to continuous clonidine exposure. This limitation was circumvented when we adopted a limited-access clonidine (8:30 AM-4:30 PM) paradigm in a recent study. The latter paradigm was employed here to evaluate the ethanol-clonidine interaction and possible roles of myocardial function and autonomic control in this interaction. Changes in blood pressure (BP), heart rate, maximum rate of rise in BP wave (+dP/dt(max)), and spectral cardiovascular autonomic profiles were measured by radiotelemetry in pair-fed SHRs receiving clonidine (150 μg/kg/day), ethanol [2.5% (w/v)], or their combination during the day for 12 weeks. Ethanol or clonidine elicited long-term decreases in BP, and their combination caused additive hypotensive response. Significant reductions in +dP/dt(max) were observed upon concurrent treatment with ethanol and clonidine, in contrast to no effect for individual treatment. In addition, the combined treatment increased the high-frequency (HF) spectral band of interbeat interval (IBI-HF(nu), 0.75-3 Hz) and decreased low-frequency (IBI-LF(nu), 0.2-0.75 Hz) bands and IBI(LF/HF) ratios. Clonidine-evoked reductions in plasma and urine norepinephrine and BP-LF spectral power (measure of vasomotor sympathetic tone) were not affected by ethanol. In conclusion, concurrent treatment with ethanol and clonidine shifts the sympathovagal balance toward parasympathetic dominance and elicits exaggerated hypotension as a result of a reduction in cardiac contractile force.

Rats in acute withdrawal from ethanol exhibit left ventricular systolic dysfunction and cardiac sympathovagal balance shift

There is strong evidence that sympathovagal balance plays an important role in the progression of cardiac dysfunction in non-alcoholics. The purpose of this investigation was to determine whether a pattern of continuous ethanol intake and withdrawal modulates the cardiac sympathovagal balance and left ventricular (LV) systolic function in rats. Male Wistar rats were treated with a continuous ethanol liquid diet for 49 days, and then subjected to 1-day withdrawal and 21-day abstinence. Cardiac sympathovagal balance and LV systolic function were evaluated based on heart rate variability (HRV), Western blotting, and echocardiography. Longitudinal data obtained from the same rats showed that the 49-day continuous ethanol treatment induced LV systolic dysfunction, expressed by decreased fractional shortening and ejection fraction. At the 1-day withdrawal, LV systolic dysfunction was deteriorated, and the low-frequency power/high-frequency power (LF/HF) ratio in HRV was elevated because of the depressed HF and the increased LF. Western blot analysis showed an increased expression of myocardial tyrosine hydroxylase and a decreased expression of myocardial acetylcholine. All anomalies were recovered to baseline values with 21-day abstinence. We concluded that acute withdrawal from a 49-day continuous ethanol regimen is sufficient to promote the shift of cardiac sympathovagal balance toward sympathetic predominance and reduced vagal tone, contributing to the further deterioration of LV systolic function in rats. Those providing medical care for alcoholics should be aware of this enhanced susceptibility to LV systolic dysfunction with abrupt termination of a continuous ethanol regimen.

Reduced cardio-respiratory coupling in acute alcohol withdrawal

BACKGROUND

Chronic alcoholism represents a risk factor for cardiac arrhythmias. One underlying mechanism is a sympathetically dominated autonomic imbalance. This is especially apparent during acute withdrawal from alcohol. Since linear analysis of heart rate variability may not be entirely adequate to detect such autonomic dysfunction in acute alcohol withdrawal, we applied novel non-linear parameters and measures for cardio-respiratory coupling.

METHODS

20 patients suffering from acute alcohol withdrawal syndrome and 20 controls were included. For patients, heart rate and respiration were recorded on admission, after medication and at discharge. From these data, complexity measures (symbolic dynamics, approximate entropy) of heart rate modulation and respiration as well as parameters for cardio-respiratory coupling (coherence, cross-approximate entropy) which relate to vagal function were calculated.

RESULTS

Heart rate modulation was significantly less complex in patients acutely admitted for alcohol withdrawal. Furthermore, coupling between beat-to-beat (RR) intervals and respiration time series was significantly diminished. Of the parameters assessed, cross-approximate entropy showed a trend for correlation with symptom severity.

CONCLUSION

These data indicate diminished vagal function in acute alcohol withdrawal. Applying the methods described thus allows a sensitive detection of vagal neuropathy in this disease.

Role of Myocardial Contractility and Autonomic Control in the Hypotensive Response to a Limited Access Ethanol Paradigm in SHRs

BACKGROUND

Previous experimental studies that evaluated the chronic hemodynamic effect of ethanol employed the continuous exposure protocol of ethanol, which does not mimic the pattern of alcohol consumption in humans. This study dealt with the long-term hemodynamic and cardiovascular autonomic effects of ethanol, in a limited-access regimen in telemetered spontaneously hypertensive rats (SHRs).

METHODS

Changes in blood pressure (BP), heart rate (HR), myocardial contractility (dP/dt(max)), and spectral cardiovascular autonomic profiles during the ethanol exposure period (2.5 or 5% w/v, 8 h/d, 8:30 am till 4:30 pm) were followed for 12 weeks.

RESULTS

Compared with control pair-fed SHRs, body weight and urine output, osmolality, and potassium levels were decreased in SHRs receiving 5% but not 2.5% ethanol. Blood pressure showed progressive falls during ethanol-feeding periods with a maximum effect observed at week 5. The peak hypotensive effect was maintained thereafter in SHRs receiving 5% ethanol in contrast to steady rises in BP in the 2.5% ethanol group to near-control levels by the conclusion of the study. Heart rate was slightly but significantly increased by ethanol 5% whereas dP/dt(max) showed persistent reductions. Power spectral analysis showed that ethanol attenuated the baroreflex gain of HR as suggested by the reductions in index alpha, the spectral index of spontaneous baroreflex sensitivity (BRS).

CONCLUSIONS

It is concluded that limited access ethanol drinking in SHRs elicited hypotension that was concentration dependent and mediated, at least partly, through reductions in myocardial contractility. Baroreflex sensitivity attenuation by ethanol appeared to have limited the tachycardic response to ethanol and perhaps its capacity to offset the evoked hypotension.

Heart rate variability and sympathetic skin response in male patients suffering from acute alcohol withdrawal syndrome

BACKGROUND

Many symptoms of alcohol withdrawal (AW) such as tachycardia or elevated blood pressure might be explained by increased peripheral and central adrenergic activity. In contrast to many neurochemical studies of sympathetic activation during AW, only very few studies investigated autonomic balance using neurophysiological methods.

METHODS

We investigated heart rate variability (HRV) and sympathetic skin response (SSR) in male patients suffering from mild AW syndrome (n = 20, no treatment required) and in patients with moderate to severe AW syndrome (n = 20, clomethiazole treatment) in the acute stage. Sympathovagal influence was quantified using measures of time and frequency domain of HRV as well as modern nonlinear parameters (compression entropy). Furthermore, we obtained latencies and amplitudes of SSR to quantify isolated sympathetic influence. Measures were obtained during the climax of withdrawal symptomatology before treatment, 1 day after climax, and shortly before discharge from hospital. Alcohol withdrawal scores were obtained and correlated to autonomic measures.

RESULTS

Ambulatory blood pressure and AW scores revealed characteristic withdrawal symptoms in both patient groups. Apart from the nonlinear parameter compression entropy, Hc, measures of HRV revealed no sign of autonomic dysfunction in contrast to the significantly increased heart rates at the time of admission. Latencies and amplitudes of SSR did not indicate any increase of sympathetic activity. A negative correlation was found between Hc and mental withdrawal symptoms.

CONCLUSIONS

We show here that classical measures for autonomic nervous system activity such as HRV and SSR are not suitable for describing the autonomic changes seen in acute AW, although a major role for the sympathetic nervous system has been proposed. This might be due to multiple dysregulation of metabolites in AWS or to subtle alcohol-induced damage to neuronal structures, issues that should be addressed in future studies.