Mechanism of inhibitory action of ethanol on endothelium-dependent relaxation in rat aorta

Vasodilatory effects of antivascular endothelium growth factor (VEGF) antibody, corticosteroid, and nitric oxide on the posterior ciliary arteries

PURPOSE

The purpose of this study was to determine whether an antivascular endothelium growth factor (VEGF) antibody, a corticosteroid, and sodium nitroprusside (SNP) [a nitric oxide (NO) donor] are possible treatment agents for nonarteritic ischemic optic neuropathy (NAION) by clarifying their effects on high-K (potassium) solution-induced contraction in isolated rabbit and human posterior ciliary arteries (PCA).

METHODS

Vascular ring segments were cut from the distal section of the PCA and mounted in a double-myograph system. After obtaining the maximal contraction following the administration of high-K solution, bevacizumab as an anti-VEGF antibody, methylprednisolone as a corticosteroid, and SNP were administered separately. When a vasodilatory effect was observed, carboxy-PTIO (a NO scavenger) or L-NAME (a NO synthase inhibitor) was administered.

RESULTS

Bevacizumab did not relax either the rabbit or the human PCA, whereas methylprednisolone relaxed both. Neither carboxy-PTIO nor L-NAME inhibited methylprednisolone-induced relaxation. SNP relaxed the rabbit PCA. Carboxy-PTIO inhibited SNP-induced relaxation, but L-NAME did not. In the human PCA, the vasodilatory effect of SNP was present, but weaker than in the rabbit PCA.

CONCLUSIONS

A corticosteroid has NO-independent vasodilatory effects. Exogenous NO has a weak dilating effect in the human PCA. Therefore, corticosteroid could be effective for the treatment of NAION.

Essential role for smooth muscle BK channels in alcohol-induced cerebrovascular constriction

Binge drinking is associated with increased risk for cerebrovascular spasm and stroke. Acute exposure to ethanol at concentrations obtained during binge drinking constricts cerebral arteries in several species, including humans, but the mechanisms underlying this action are largely unknown. In a rodent model, we used fluorescence microscopy, patch-clamp electrophysiology, and pharmacological studies in intact cerebral arteries to pinpoint the molecular effectors of ethanol cerebrovascular constriction. Clinically relevant concentrations of ethanol elevated wall intracellular Ca(2+) concentration and caused a reversible constriction of cerebral arteries (EC(50) = 27 mM; E(max) = 100 mM) that depended on voltage-gated Ca(2+) entry into myocytes. However, ethanol did not directly increase voltage-dependent Ca(2+) currents in isolated myocytes. Constriction occurred because of an ethanol reduction in the frequency (-53%) and amplitude (-32%) of transient Ca(2+)-activated K(+) (BK) currents. Ethanol inhibition of BK transients was caused by a reduction in Ca(2+) spark frequency (-49%), a subsarcolemmal Ca(2+) signal that evokes the BK transients, and a direct inhibition of BK channel steady-state activity (-44%). In contrast, ethanol failed to modify Ca(2+) waves, a major vasoconstrictor mechanism. Selective block of BK channels largely prevented ethanol constriction in pressurized arteries. This study pinpoints the Ca(2+) spark/BK channel negative-feedback mechanism as the primary effector of ethanol vasoconstriction.

Anandamide vehicles: a comparative study

Among the studies that investigate the vasorelaxation induced by anandamide, one of the most frequent differences is the use of distinct solvents that could modify vascular function and explain the controversial results described. The aims of this study were: to evaluate the influence of different cannabinoid vehicles in vascular function of rat aorta, and to compare the vasorelaxation induced by anandamide dissolved in different vehicles. Vehicles were: ethanol (70%), Tween 80/ethanol (2:1 and 1:1), 1:1:18 (Tween 80/ethanol/saline) and dimethylsulphoxide (DMSO) 0.5%. All the vehicles tested, except DMSO 0.5%, modified the vascular and/or the endothelial function in rat aorta rings. Anandamide caused a time- and concentration-dependent vasorelaxation in all the experimental groups except in ethanol group, but the mechanisms involved in its vasorelaxation appear to be different depending on the vehicle used. The results obtained with vehicles containing Tween 80 suggest a non-endothelial component in the vasorelaxation caused by anandamide, while those obtained with DMSO at 0.5% suggest an endothelial component in this vasorelaxation.

Temporal effect of alcohol consumption on reactivity of pial arterioles: role of oxygen radicals

Chronic alcohol consumption reduces nitric oxide synthase-dependent responses of pial arterioles via mechanisms that remain uncertain. In addition, the temporal effects of alcohol on pial arterioles is unclear. Thus our goals were to examine the role of oxygen-derived free radicals in alcohol-induced impairment of cerebrovascular reactivity and the temporal effect of alcohol on reactivity of pial arterioles. Sprague-Dawley rats were pair-fed a liquid diet with or without alcohol for 2-3 wk, 2-3 mo, or 5-6 mo. We measured the in vivo diameter of pial arterioles in response to nitric oxide synthase-dependent dilators acetylcholine and ADP and the nitric oxide synthase-independent dilator nitroglycerin. In nonalcohol-fed rats, acetylcholine (1.0 and 10 microM) and ADP (10 and 100 microM) produced dose-related dilatation of pial arterioles. Whereas there was no difference in reactivity of arterioles to the agonists in rats fed the nonalcohol and alcohol diets for a period of 2-3 wk, there was a significant impairment in reactivity of arterioles to acetylcholine and ADP, but not nitroglycerin, in rats fed the alcohol diet for longer durations. We then found that treatment with superoxide dismutase did not alter baseline diameter of pial arterioles in nonalcohol-fed or alcohol-fed rats, but significantly improved impaired nitric oxide synthase-dependent dilatation of pial arterioles in alcohol-fed rats. Thus our findings suggest a temporal relationship in the effects of alcohol on reactivity of pial arterioles and that impaired nitric oxide synthase-dependent cerebral vasodilatation during chronic alcohol consumption may be related, in part, to enhanced release of oxygen-derived free radicals.

Influence of chronic ethanol consumption on arterial tone in young and aged rats

The aim of this work was to evaluate the effects of long-term ethanol consumption on arterial responses in vitro in young and aged rats. Therefore, Wistar rats (ages 3 and 29 mo, respectively) were allocated to six groups: control-young, sucrose-young, ethanol-young, control-aged, sucrose-aged, and ethanol-aged. The ethanol-fed groups were given 25% ethanol by intragastric gavage three times a day 4 days a week. Responses of mesenteric arterial rings were examined in standard organ chambers after 5 treatment weeks. In norepinephrine-precontracted arterial rings, endothelium-dependent relaxations to acetylcholine, as well as endothelium-independent relaxations to isoproterenol, were attenuated in aged rats when compared with young controls. Relaxation responses to isoproterenol, but not to acetylcholine and nitroprusside, were clearly improved by ethanol treatment in both young and aged rats. The cyclooxygenase inhibitor diclofenac, which reduces the synthesis of dilating and constricting prostanoids, enhanced the relaxation to acetylcholine in all three aged rat groups but was without significant effect in the young rats. In the presence of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester the relaxation to acetylcholine in control and sucrose-fed aged rats was markedly reduced compared with control rats, whereas in the young controls and in both young and aged ethanol-exposed groups, distinct relaxations to higher concentrations of acetylcholine were still present. The endothelium-independent relaxations to cromakalim, a hyperpolarizing vasodilator acting via ATP-sensitive potassium channels, were also markedly augmented by ethanol feeding in both young and aged rats. In conclusion, ethanol consumption in both young and aged rats was associated with markedly improved arterial relaxations to isoproterenol and cromakalim, as well as clearly augmented relaxation to acetylcholine during inhibition of cyclooxygenase and nitric oxide synthase. These findings suggest that especially the potassium channel-related component of arterial relaxation was augmented by long-term ethanol exposure.

Ethanol modulates induction of nitric oxide synthase in glial cells by endotoxin

Although ethanol has long been recognized as an immunosuppressant, the effects of ethanol on immune functions in the central nervous system (CNS) have not been well characterized. Glial cells function as immune effector cells within the CNS. Nitric oxide (NO), generated by inducible NO synthase (iNOS) of activated glial cells, appears to participate in the immune defense and the pathogenesis of brain injury and several neurologic diseases. The goal of the present study was to examine the effects of ethanol on NO production and mRNA expression of iNOS following its induction by bacterial endotoxin lipopolysaccharide (LPS) in cultured glial cells. After incubation of mixed glia with LPS for 24 hr, the levels of nitrite in the culture medium were assayed by Griess reaction. We found that LPS (10-500 ng/ml) induced a concentration-dependent increase in the production of NO which was abolished by the selective iNOS inhibitor aminoguanidine. While ethanol treatment (25 to 400 mM, 24 hr exposure) had no direct effect on basal NO production, it significantly suppressed the LPS-induced increase of nitrite levels in a concentration-dependent manner. Using a semiquantitative reverse transcriptase polymerase chain reaction, we found that while ethanol by itself was unable to induce iNOS mRNA, it nevertheless suppressed LPS-induced iNOS mRNA expression. Our results that ethanol had no direct effect on NO production but inhibited LPS-induced NO, indicated an immunomodulatory role by ethanol. These findings suggest that ethanol may ameliorate the consequences of overwhelming NO generation through iNOS induction in glial cells following infection, inflammation or CNS injuries.

Cardiovascular effects of alcohol

The ingestion of one or two alcoholic drinks can affect heart rate, blood pressure, cardiac output, myocardial contractility, and regional blood flow. These actions generally are not clinically important. In the presence of cardiovascular disease, however, even such small quantities of alcohol might result in transient unfavorable hemodynamic changes. Moreover, alcohol abuse can produce cardiac arrhythmias, hypertension, cardiomyopathy, stroke, and even sudden death. In contrast, moderate alcohol use produces changes that have an overall favorable effect on atherosclerotic-related vascular diseases. Because cardiovascular disease due to atherosclerosis is the leading cause of death in Western society, this desirable effect of alcohol use outweighs its detrimental actions, resulting in favorable findings in population studies. Nevertheless, the body of evidence argues against encouraging alcohol use for its cardiovascular effects.

Effects of ethanol on responses of isolated rabbit urinary bladder and urethra

BACKGROUND

Acute ethanol ingestion increases the risk of urinary retention in patients with benign prostatic hyperplasia (BPH). To elucidate the mechanism of this effect, we investigated the in vitro effects of ethanol on lower urinary tract function in rabbits.

METHODS

The responses to various stimuli of muscle strips isolated from male rabbit bladder and urethra were determined in the presence of 0%, 0.5%, 1.0%, and 3.0% ethanol.

RESULTS

Basal tension of tissue strips taken from the bladder and the urethra was reduced by ethanol in a dose-dependent manner, as were bladder contractions induced by field stimulation, bethanechol, and ATP. Ethanol also reduced phenylephrine-induced contractions of the prostatic urethra. A high (3%) concentration of ethanol significantly reduced KCl-induced contraction of both the bladder and urethra, as well as urethral relaxation induced by field stimulation following contraction with 200 mumol/L phenylephrine.

CONCLUSION

Responsiveness of the rabbit lower urinary tract was significantly reduced by exposure to ethanol. A similar decrease in tonus and contractility of the detrusor and inhibition of relaxation in the prostatic urethra may lead to urinary retention in men following acute ingestion of ethanol.

Alcohol, hypertension and the cardiovascular system: a critical appraisal

Cross-sectional and longitudinal population studies have provided a considerable corpus of evidence for an inverse association between light to moderate alcohol intake and both coronary artery disease and stroke. The formulation of balanced public health advice on the basis of such studies, however, needs to take into account the full spectrum of the effects of alcohol on the cardiovascular system, particularly its equally well documented effect to increase level of blood pressure and prevalence of hypertension. In this review, the broader implications of the association of alcohol with hypertension are discussed, principally in the context of the effect of higher levels of alcohol consumption to increase ischaemic and haemorrhagic stroke, left ventricular hypertrophy, congestive cardiomyopathy, cardiac arrhythmia and sudden cardiac death.

Effect of chronic alcohol consumption on responses of cerebral arterioles

The goal of this study was to determine whether chronic ingestion of alcohol alters dilatation of cerebral arterioles in response to agonists that produce activation of adenylate cyclase and activation of ATP-sensitive potassium channels. Rats were fed liquid diets with or without ethanol for 2 to 2.5 months. In vivo diameter of pial arterioles was measured in alcohol-fed and nonalcohol-fed rats during superfusion with isoproterenol, forskolin, cromakalim, and nitroglycerin. Dilatation of pial arterioles in response to activation of adenylate cyclase via stimulation of beta-adrenergic receptors using isoproterenol was impaired in alcohol-fed rats. Isoproterenol (1.0 microM) dilated cerebral arterioles by 15 +/- 3% in nonalcohol-fed rats, but by only 7 +/- 2% in alcohol-fed rats. In contrast, dilatation of pial arterioles in response to forskolin was similar in nonalcohol-fed and alcohol-fed rats. Dilatation of pial arterioles in response to activation of ATP-sensitive potassium channels was impaired in alcohol-fed compared with nonalcohol-fed rats. Cromakalim (1.0 microM) dilated pial arterioles by 22 +/- 5% in nonalcohol-fed rats, but by only 5 +/- 2% in alcohol-fed rats (p < 0.05). In contrast, dilatation of pial arterioles in response to nitroglycerin was similar in alcohol and nonalcohol-fed rats. The findings of the present study suggest that chronic alcohol ingestion impairs dilatation of cerebral resistance arterioles in response to activation of adenylate cyclase via stimulation of beta-adrenergic receptors and in response to activation of ATP-sensitive potassium channels. We suggest that impaired vasodilator mechanisms during chronic alcohol consumption may have important implications for the pathogenesis of cerebrovascular abnormalities observed during chronic alcoholism.

Acute effects of ethanol on responses of cerebral arterioles

BACKGROUND AND PURPOSE

Previous studies have suggested that acute exposure of large peripheral arteries to ethanol impairs endothelium-dependent relaxation. The goal of the present study was to determine the acute effects of ethanol exposure on responses of cerebral resistance arterioles in vivo.

METHODS

We prepared a cranial window in rats to expose the cerebral (pial) microcirculation. We measured the diameter of pial arterioles in vivo in response to agonists that presumably stimulate the synthesis/release of nitric oxide from the endothelium (ADP, acetylcholine, and histamine) or neurons (N-methyl-D-aspartate [NMDA]) before and after topical application of various concentrations of ethanol added to the cerebrospinal fluid (20, 40, 60, 80, and 100 mmol/L). In addition, we examined responses of pial arterioles to nitroglycerin before and 1 hour after topical application of ethanol.

RESULTS

Before application of ethanol, ADP, acetylcholine, histamine, NMDA, and nitroglycerin produced dose-related dilatation of pial arterioles. Application of the various concentrations of ethanol did not alter the baseline diameter of pial arterioles. However, application of 80 and 100 mmol/L ethanol inhibited dilatation of pial arterioles in response to agonists that stimulate the synthesis/release of nitric oxide. Dilatation of pial arterioles in response to nitroglycerin was not altered by application of ethanol.

CONCLUSIONS

The findings of the present study suggest that acute exposure of cerebral arterioles to modest-to-moderate concentrations of ethanol (20 to 60 mmol/L) does not alter responses of cerebral arterioles. In contrast, exposure of cerebral arterioles to higher concentrations of ethanol (80 and 100 mmol/L) can produce specific impairment of dilatation to agonists that stimulate the synthesis/release of nitric oxide from endothelium and neurons.

Direct and astrocyte-mediated effects of ethanol on brain-derived endothelial cells

The effects of ethanol have been studied in the central nervous system, however there exists only scarce information about the effects of ethanol on endothelial cells forming the blood-brain barrier. As some properties of brain endothelial cells are modulated by underlying astrocytes, the effect of ethanol on cerebral microvasculature might be indirect and mediated by astrocytes. To analyse this question, we added to rat brain-derived endothelial cells (rbEC) in culture either only ethanol (0, 15 and 150 mM) or ethanol conjointly with soluble factors secreted by astrocytes. Alternatively, astrocytes were exposed to ethanol and the medium was added to rbEC. The effects of treatments were evaluated on cell growth and expression of specific proteolytic markers of rbEC. The experiments showed that while the addition of ethanol alone to rbEC increased the expression of gamma-glutamyltranspeptidase and cell growth following an initial toxic effect, the most significant effects were seen when ethanol was added to rbEC together with astrocytic factors or when medium conditioned by astrocytes exposed to ethanol was added to rbEC. In particular, the expression of angiotensin converting enzyme in endothelial cells was dose-dependently increased. These results indicate that the hypertensive and toxic effects of ethanol are mediated by ethanol and soluble factor(s) secreted by astrocytes and dependent on the expression of angiotensin converting enzyme in the brain endothelium. Thus, when evaluating in vitro the effects of toxic substances such as ethanol on the cerebral endothelium, the modulating effect of cells surrounding cerebral vessels must be accounted for.

Ethanol affects sympathetic cotransmission and endothelium-dependent relaxation in the rat

The influence of ethanol on sympathetic nerve-mediated contractions of rat tail arteries and on endothelium-dependent relaxation of rat mesenteric arteries by acetylcholine was examined using the method of in vitro pharmacology. Ethanol potentiated sympathetic nerve-mediated contractions. Ethanol had no effect on the neurogenic contractions that remained after alpha-adrenoceptor blockade by prazosin. However, after P2x-purinoceptor desensitisation, the residual nerve-mediated contractions were significantly enhanced by ethanol. Contractions to exogenous noradrenaline and alpha,beta-methylene ATP were unaffected by ethanol. It is concluded that ethanol selectively potentiates the noradrenergic component of sympathetic neurotransmission. Ethanol depressed the relaxation by acetylcholine but not that induced by sodium nitroprusside. These results indicate that ethanol can affect both the neural and endothelial control of vascular tone. The potentiated noradrenergic vasoconstrictor response to sympathetic nerve stimulation and the compromised capacity of the endothelium to cause relaxation after ethanol treatment may contribute to the development of vascular diseases associated with alcohol consumption.