Regulation of alcohol consumption by the renin-angiotensin system: a review of recent findings and a possible mechanism of action

Effect of exercise duration on toluene-induced locomotor sensitization in mice: a focus on the Renin Angiotensin System

RATIONALE

Exercise attenuates addictive behavior; however, little is known about the contribution of exercise duration to this positive effect. The Renin Angiotensin System (RAS) has been implicated both in addictive responses and in the beneficial effects of exercise; though, its role in the advantageous effects of exercise on toluene-induced addictive responses has not been explored.

OBJECTIVES

To evaluate the impact of different exercise regimens in mitigating the expression of toluene-induced locomotor sensitization and to analyze changes in RAS elements' expression at the mesocorticolimbic system after repeated toluene exposure and following voluntary wheel running in toluene-sensitized animals.

METHODS

Toluene-induced addictive-like response was evaluated with a locomotor sensitization model in mice. Toluene-sensitized animals had access to running wheels 1, 2, 4 or 24 h/day for 4 weeks; thereafter, locomotor sensitization expression was evaluated after a toluene challenge. RAS elements (ACE and ACE2 enzymes; AT1, AT2 and Mas receptors) expression was determined by Western blot in the VTA, NAc and PFCx of toluene-sensitized mice with and without exercise.

RESULTS

Individual differences in toluene-induced locomotor sensitization development were observed. Access to wheel running 1 and 2 h/day reduced but 4 and 24 h/day completely blocked locomotor sensitization expression. Repeated toluene exposure changed RAS elements' expression in the VTA, NAc and PFCx, while exercise mainly modified ACE and AT1 in air-exposed and toluene-sensitized mice.

CONCLUSIONS

Inhalant-exposed animals show different sensitization phenotypes. Exercise duration determined its efficacy to attenuate the addictive-like response. Toluene exposure and exercise each modified RAS, the latter also modifying toluene-induced changes.

Role of aldosterone and mineralocorticoid receptor (MR) in addiction: A scoping review

Preclinical and human studies suggest a role of aldosterone and mineralocorticoid receptor (MR) in addiction. This scoping review aimed to summarize (1) the relationship between alcohol and other substance use disorders (ASUDs) and dysfunctions of the aldosterone and MR, and (2) how pharmacological manipulations of MR may affect ASUD-related outcomes. Our search in four databases (MEDLINE, Embase, Web of Science, and Cochrane Library) indicated that most studies focused on the relationship between aldosterone, MR, and alcohol (n = 30), with the rest focused on opioids (n = 5), nicotine (n = 9), and other addictive substances (n = 9). Despite some inconsistencies, the overall results suggest peripheral and central dysregulations of aldosterone and MR in several species and that these dysregulations depended on the pattern of drug exposure and genetic factors. We conclude that MR antagonism may be a promising target in ASUD, yet future studies are warranted.

Sexual Dimorphism in the Expression of Cardiac and Hippocampal Renin-Angiotensin and Kallikrein–Kinin Systems in Offspring from Mice Exposed to Alcohol during Gestation

Prenatal alcohol exposure (PAE) impairs fetal development. Alcohol consumption was shown to modulate the renin–angiotensin system (RAS). This study aimed to analyze the effects of PAE on the expression of the renin–angiotensin system (RAS) and kallikrein–kinin system (KKS) peptide systems in the hippocampus and heart of mice of both sexes. C57Bl/6 mice were exposed to alcohol during pregnancy at a concentration of 10% (v/v). On postnatal day 45 (PN45), mouse hippocampi and left ventricles (LV) were collected and processed for messenger RNA (mRNA) expression of components of the RAS and KKS. In PAE animals, more pronounced expression of AT1 and ACE mRNAs in males and a restored AT2 mRNA expression in females were observed in both tissues. In LV, increased AT2, ACE2, and B2 mRNA expressions were also observed in PAE females. Furthermore, high levels of H2O2 were observed in males from the PAE group in both tissues. Taken together, our results suggest that modulation of the expression of these peptidergic systems in PAE females may make them less susceptible to the effects of alcohol.

Captopril and losartan attenuate behavioural sensitization in mice chronically exposed to toluene

Inhalants are consumed worldwide for recreational purposes. The main component found in many inhalants is toluene. One of the most deleterious behavioural effects caused by chronic exposure to inhalants is addiction. This response has been associated with activation of the mesolimbic dopaminergic pathway, and it is known that the renin angiotensin system plays a role in the modulation of this dopaminergic system. In the present work, we hypothesize that blockade of the RAS with angiotensin converting enzyme inhibitors or angiotensin II type 1 receptor blockers is able to attenuate the addictive response induced by toluene. We exposed mice to toluene for four weeks to induce locomotor sensitization. In the second phase of the work, captopril or losartan were administered for 20 days. Subsequently, the expression of behavioural sensitization was evaluated with a toluene challenge. To exclude false associations between the observed responses and treatments, motor coordination and blood pressure were analysed in animals treated with captopril or losartan. At the end of the behavioural studies, animal brains were harvested and Ang II/Ang-(1-7) and Ang-(1-7)/Ang II ratios were analysed in the nucleus accumbens (NAc) and prefrontal cortex (PFCx). The results showed that toluene induced behavioural sensitization, while captopril or losartan treatment attenuated the expression of this response. No significant differences were observed in motor coordination or blood pressure. Repeated toluene administration decreased Ang-(1-7)/Ang II ratio in the PFCx. On the other hand, treatment with captopril or losartan decreased the Ang II/Ang-(1-7) ratio and enhanced the Ang-(1-7)/Ang II ratio in the NAc. This work suggests that blockade of RAS attenuates the toluene-induced behavioural sensitization.

Role of angiotensin II and the subfornical organ in the pharmacological actions of ethanol

AIMS

The current study was designed to evaluate if angiotensin II mediates the hypothermic effects of ethanol, and to determine if the effects of angiotensin are mediated centrally. We also tested the hypothesis that the subfornical organ (SFO) is a site responsible for the alterations in body temperature and aerial righting reflex mediated by ethanol and for the modulation of ethanol consumption in rats.

METHODS

Male Sprague-Dawley rats were used in a series of experiments to evaluate the role of both peripheral and central administration of losartan, a selective angiotensin type 1 receptor antagonist on ethanol-induced hypothermia. Subsequent studies were undertaken in SFO-lesioned rats to evaluate the effects of SFO-lesion on alcohol intake, the thermal response to alcohol and angiotensin, and the aerial righting reflex.

RESULTS

Selective antagonism of the angiotensin II type 1 receptor, administered either peripherally or centrally, attenuated not only the fall in colonic temperature but also attenuated the transient rise in tail skin temperature that was associated with administration of ethanol. The thermal responses to both angiotensin and ethanol were similarly attenuated in SFO-lesioned rats. Likewise the aerial righting reflex, which has previously been shown to be impaired by losartan treatment, was also significantly attenuated in SFO-lesioned animals. Alcohol intake, as determined by a 48 h, two-bottle preference test also revealed that SFO-lesioned animals consumed significantly less alcohol (ethanolic beer) than did controls.

CONCLUSION

Collectively, the results demonstrate that ethanol-induced temperature responses are mediated by the renin-angiotensin system and that this interaction is mediated centrally. In addition, the results demonstrate that the SFO is a site that mediates several neurobiological effects of ethanol, possibly via the renin-angiotensin system.

Attenuation of the alcohol preference of C57BL/6 mice during chronic renal failure

The C57BL/6 inbred mouse strain is known for its strong, genetically determined preference for alcohol over water. In this study we examined the voluntary alcohol consumption (VAC) of C57BL/6 mice during chronic renal failure (CRF). Two weeks after the surgical induction of renal failure, CRF mice, together with normal and sham-operated control mice, were submitted to a standard 24-day VAC protocol. The mice were offered water for the first 6 days (period of acclimatization), alcohol (10% ethanol solution) for the next 4 days (period of forced alcohol exposure), and a choice between water and alcohol for the last 14 days (VAC period). The results (mean +/- SEM) obtained from the last 8 days of the VAC period were significantly different (P <.05) between CRF mice and the 2 control groups. As expected, CRF mice had a higher total fluid intake than did normal and sham-operated controls (9.5 +/- 0.2 vs 5.4 +/- 0.2 and 5.4 +/- 0.2 g/d). Surprisingly, despite their increased total fluid consumption, CRF mice nearly abolished their absolute alcohol intake compared with that of both control groups (3.2 +/- 0.5 vs 13.1 +/- 0.8 and 14.2 +/- 1.1 g alcohol/kg body wt/d). The resulting alcohol preference ratio (g alcohol/g total fluid) was markedly decreased in the CRF mice compared with that in both control groups (0.09 +/- 0.01 vs 0.62 +/- 0.03 and 0.64 +/- 0.05). We conclude that the innate alcohol preference of C57BL/6 mice is nearly abolished during CRF. Additional studies to clarify the mechanism of this striking change in drinking pattern are required, with special emphasis on the possible role of angiotensin II, which is involved in thirst regulation and known to reduce the alcohol consumption of normal alcohol-preferring rats.

Chemosensory factors influencing alcohol perception, preferences, and consumption

This article presents the proceedings of a symposium at the 2002 RSA/ISBRA Meeting in San Francisco, California, co-organized by Julie A. Mennella and Alexander A. Bachmanov of the Monell Chemical Senses Center. The goal of this symposium was to review the role that chemosensory factors (taste, smell, and chemical irritation) play in the perception, preference, and consumption of alcohol. The presented research focused on both humans and laboratory animals and used a variety of approaches including genetic, developmental, pharmacological, behavioral, and psychophysical studies. The presentations were as follows: (1) Introduction and overview of the chemical senses (Julie A. Mennella and Alexander A. Bachmanov); (2) Taste reactivity as a measure of alcohol palatability and its relation to alcohol consumption in rats (Stephen W. Kiefer); (3) Early learning about the sensory properties of alcohol in laboratory animals (Juan Carlos Molina); (4) Early learning about the sensory properties of alcohol in humans (Julie A. Mennella); (5) Genetic dissection of the ethanol-sweet taste relationship in mice (Alexander A. Bachmanov and Michael Tordoff); and (6) Human genetic variation in taste: connections with alcohol sensation and intake (Valerie B. Duffy and Linda M. Bartoshuk). The symposium concluded with a general discussion.

Gender difference in enzymes related with alcohol consumption in hamster, an avid consumer of alcohol

Syrian golden hamster (Mesocricetus auratus) is extraordinary among laboratory rodents in its ability to drink alcohol. After being given a free choice between 15% ethanol and water for 5 days, both male and female hamsters derived at least 85% of the fluid intake from the ethanol solution. Analysis of the alcohol-metabolizing enzymes in alcohol-naïve hamsters showed that the male had a higher activity of 57%, 58% and 34% in stomach alcohol dehydrogenase, liver cytochrome P450 1A2 and liver aldehyde dehydrogenase, respectively, compared with the female. The activity of lung angiotensin-converting enzyme, which influence fluid intake, was twofold higher in the male. After 4 weeks of ethanol consumption, the activities of the hepatic alcohol-metabolizing enzymes remained unchanged except cytochrome P450 2E1 which increased 42% and 88% in male and female hamsters, respectively. A reduction of approximately 80% in the activity of cytochrome P450 1A2 was observed in both genders. The activities of several other cytochrome P450 enzymes were also decreased. Although ethanol consumption did not increase plasma aminotransferase levels, it caused a significant increase in liver weight in female, but not male hamsters.

Neutral endopeptidase and alcohol consumption, experiments in neutral endopeptidase-deficient mice

Alcohol consumption was investigated in mice which were rendered deficient in the peptide-degrading enzyme neutral endopeptidase (EC 3.4.24.11) (NEP-/-) by gene targeting and compared to alcohol consumption in corresponding wild type mice (NEP+/+). Mice were offered a free choice to drink tap water or 10% alcohol. The NEP-/- mice consumed significantly more alcohol ( approximately 42%) than the NEP+/+ mice, whereas no significant differences were observed in the total fluid consumption. The daily food consumption of alcohol naive NEP-/- animals was elevated ( approximately 29%). Furthermore, the activities of peptidases closely related to neutral endopeptidase were analysed ex vivo in several brain regions from NEP-/- and NEP+/+ mice not treated with alcohol. There was no obvious compensation for the total loss of neutral endopeptidase by the functionally related peptidases angiotensin-converting enzyme and aminopeptidase N. In vitro, the degradation of exogenously applied [Leu(5)]enkephalin was not reduced in membrane preparations of those brain regions assayed in NEP-/- mice. A small reduction in [Leu(5)]enkephalin degradation was detected in striatal membrane preparations of NEP-/- mice, if aminopeptidase N was additionally blocked by bestatin or amastatin.

Angiotensin II stimulates intake of ethanol in C57BL/6J mice

The influence of intracerebroventricular (i.c.v.) infusion of angiotensin II on intake of water and ethanol solutions was determined in C57BL/6J mice. Compared to other mice, C57 mice do not show an aversion to ethanol solutions. With both water and ethanol solutions available, the C57 mice consumed 40-60% of their total daily fluid intake as ethanol solution when the concentration of ethanol solution offered was 4-14%. When given a choice between 0.3 M KCl and either 4 or 10% ethanol solution, the mice clearly preferred the ethanol solution. With water only available, i.c.v. infusion of angiotensin II increased intake from 3-5 mL/day (baseline) to 11-12 mL/ day (Day 4 of infusion). A similar increase in intake occurred in mice with access to a nonpreferred solution of 0.3 M KCl. In comparison, when only 4% ethanol solution was available, angiotensin II increased intake to 7-8 mL/day, and when only 10% ethanol solution was available, intake was transiently increased. The results demonstrated that thirst for water caused by i.c.v. infusion of angiotensin II in C57 mice is similar to that observed in BALB/C mice. Unlike BALB/C mice, however, i.c.v. infusion of angiotensin II stimulated intake of ethanol solution. The failure of angiotensin II to cause a large increase in 4% ethanol solution or a sustained increase in 10% ethanol solution intake does not seem to be caused by an aversion to the taste of ethanol solution, but most likely due to postingestional factors.

Intracerebroventricular infusion of angiotensin II increases water and ethanol intake in rats

The influence of prolonged ingestion of ethanol on stimulation of water or ethanol intake by intracerebroventricular infusion of ANG II was evaluated in rats. Animals were maintained for 5-6 mo with either 10% ethanol solution or water as their only source of fluid. In both groups of rats, infusion of ANG II caused a large increase in water intake (7-fold) and a lesser increase in 10% ethanol intake (2-fold). The effect of ANG II on the volume of ethanol solution ingested, however, was inversely related to the concentration of the ethanol solution. As the concentration of ethanol solution was decreased, frequency and duration of drinking bouts increased. The intake of sweetened 10% ethanol solution or commercially produced wine during infusion of ANG II was similar to the intake of 10% ethanol and not related to taste preference. In conclusion, chronic consumption of ethanol solution did not appear to adversely effect ANG II stimulation of water intake. The intake of ethanol solution during infusion of ANG II was inhibited by a direct effect of ingested ethanol and/or by indirect effect from metabolized ethanol.

Histaminergic activation of endogenous angiotensin II fails to inhibit alcohol intake in rats

Demonstrations that alcohol intake can be inhibited by pharmacological activation of the renal renin-angiotensin system (RRA) or injection of angiotensin II (ANG II) in rats led to this study of a role for endogenous ANG II in inhibition of alcohol intake in rats. Relatively small doses of histamine, above threshold for eliciting drinking of water and activation of the RRA, were injected SC in adult male Sprague-Dawley rats with access to 3.0% alcohol in 45-min one-bottle alcohol tests and in two-bottle tests in which alcohol and water were available at the midpoint of the 12-h dark phase. The 0.312 and 1.25 mg/kg doses of SC histamine elevated plasma renin activity to levels similar to those in rats that had just eaten food. Neither dose of histamine affected alcohol intake in one-bottle tests. A relatively large 10 mg/kg dose of histamine increased alcohol intake in a one-bottle test, but decreased alcohol intake and increased water intake in two-bottle tests. The inhibitory effect of the 10 mg/kg dose of histamine on alcohol intake was completely blocked by SC 10 mg/kg losartan, a selective AT1 angiotensin receptor antagonist. This 10 mg/kg dose of losartan given alone, however, failed to increase alcohol intake in one- or two-bottle tests. These results generally do not support a role for endogenous ANG II as an inhibitory physiological signal in the control of alcohol ingestion in rats, because histaminergic activation of RRA, using small but physiologically meaningful doses of histamine, failed to inhibit alcohol intake.

Effect of captopril on voluntary consumption of ethanol, water and solid food by UChA and UChB rats

Angiotensin converting enzyme inhibitors (ACEI) have been reported to reduce ethanol consumption in rats, but it is unclear whether this effect is specific for ethanol or secondary to effects on appetite or satiation for calories or water. In the present study we assessed the effect of captopril, an ACEI, on the voluntary consumption of 10% ethanol solution, water and solid food in our strain of rats genetically selected for their voluntary consumption of ethanol, namely UChA (low consumer) and UChB (high consumer). Captopril (30 mg/kg) was injected intraperitoneally for 3 consecutive days to UChA and UChB rats and ethanol, water and food intake were measured before, during and after captopril treatment; these results were compared with those produced by a control saline solution. Results showed that captopril produced a significant reduction of alcohol voluntary consumption in UChB but not in UChA rats. However, this effect was not specific for ethanol since captopril also induced a significant decrease in food intake leading to a loss of weight in both rat strains, suggesting that it seems to be secondary to changes in appetite for calories.

Intake of ethanol, sodium chloride, sucrose, citric acid, and quinine hydrochloride solutions by mice: a genetic analysis

Mice of the 129/J (129) and C57BL/6ByJ (B6) strains and their reciprocal F1 and F2 hybrids were offered solutions of ethanol, sucrose, citric acid, quinine hydrochloride, and NaCl in two-bottle choice tests. Consistent with earlier work, the B6 mice drank more ethanol, sucrose, citric acid, and quinine hydrochloride solution and less NaCl solution than did 129 mice. Analyses of each generation's means and distributions showed that intakes of ethanol, quinine, sucrose, and NaCl were influenced by a few genes. The mode of inheritance was additive in the case of ethanol and quinine, for sucrose the genotype of the 129 strain was recessive, and for NaCl it was dominant. Citric acid intake appeared to be influenced by many genes with small effects, with the 129 genotype dominant. Correlations of sucrose consumption with ethanol and citric acid consumption were found among mice of the F2 generation, and the genetically determined component of these correlations was stronger than the component related to environmental factors. The genetically determined correlation between sucrose and ethanol intakes is consistent with the hypothesis that the higher ethanol intake by B6 mice depends, in part, on higher hedonic attractiveness of its sweet taste component.

The dipsogen angiotensin II does not stimulate ethanol intake in mice

Mice that were habituated to drinking ethanol solution and mice that had drunk water only (naive mice) were given an ICV infusion of angiotensin II (Ang II) at 2.9 ng/h for 8 days to determine the effect of chronic ethanol intake on the ingestive response to this potent dipsogen. Ang II infusion in alcohol-naive mice increased daily water intake from 3.7 +/- 0.2 ml (mean +/- SE, n = 6) to 11.0 +/- 1.5 ml on day 4 (p < 0.001) and to 18.3 +/- 2.6 ml on day 8 (p < 0.001). In subsequent experiments, mice had access to 4% ethanol solution up to day 4 and then to water for 4 days during the Ang II infusion. Alcohol-naive mice did not increase daily fluid intake until the water was provided on day 5; intake increased to 17.5 +/- 2.3 ml on day 8 (p < 0.001, n = 7). Mice accustomed to drinking 4% ethanol (4.3 +/- 0.3 ml/day) also did not increase intake until the water was provided; intake reached 22.9 +/- 3.0 ml of water on day 8 (p < 0.001, n = 7). Mice accustomed to drinking 10% ethanol behaved similarly (n = 4). Thus, alcohol-naive or -habituated mice did not respond to this dipsogenic stimulus until water was available; the thirst for water was unimpaired. Preference-aversion tests showed that mice drank little or no 4% ethanol (or even 2% ethanol) when water was also available. Taste aversion, plus previous experience from ingestion of ethanol in habituated mice, may explain the rejection of ethanol to quench Ang II-induced thirst. Experimental results obtained using other aversive solutions, 3 mM quinine and 300 mM KCl, suggest that postingestional, metabolic effects of solutes may also contribute to such rejection.

Angiotensin II reduces alcohol intake and choice in water- or food-restricted rats

Two experiments were conducted to assess the effects of administration of the neuropeptide and hormone angiotensin II (AII) on ethanol intake and choice. First, 18 male Wistar rats were water deprived for 23 h and given access to 5% w/v ethanol for 30 min, followed by 30 min of access to water; food was ad lib. Following adaptation to this schedule, rats were randomly assigned to receive an IP injection of 0, 100, or 200 micrograms/kg of AII at either -30 or 0 min prior to ethanol access. Each AII injection decreased ethanol intake only if injected immediately before access; water and food intake were unaffected. Secondly, rats were given food daily at 2% of body weight with ad lib water and randomly assigned to receive either only water or 4% w/v ethanol ad lib on alternate days. Following adaptation, rats were randomly assigned to receive IP saline or 200 micrograms/kg of AII prior to presentation of a choice of ethanol or water for 1 h. AII reduced ethanol intake and increased water intake at 0-30 min after injection. Results confirm previous reports of inhibition of alcohol consumption by peripheral AII, and indicate a temporal constraint on AII's effect, which is consistent with a role as a short-term satiety factor.

Ethanol consumption and taste preferences in C57BL/6ByJ and 129/J mice

Mice of the C57BL/6ByJ (B6) and 129/J (129) strains were offered different concentrations of taste solutions in 48-hr, two-bottle choice tests. In comparison with the 129 strain, the B6 strain had higher preferences for ethanol, sucrose, and citric acid. They had lower preferences for NaCl and similar preferences for capsaicin and quinine hydrochloride. These data are consistent with the hypothesis that the higher ethanol intake by B6 mice depends, in part, on higher hedonic attractiveness of its sweet taste component.

Acetaldehyde inhibits serum aminopeptidases

Aminopeptidase A (APA)- and aminopeptidase M (APM)-like activity were assayed in Moni-Trol ES with L-alpha-aspartyl-beta-naphthylamide and L-alanyl-beta-naphthylamide, respectively. Upon preincubation of the serum with 89.4, 223.5, and 447 mM acetaldehyde at room temperature for 30 min, a reduction in 26.8%, 55.3%, and 75.8% aminopeptidase A activity was observed. Similarly, aminopeptidase M activity was reduced by 26.5% and 53.1% upon preincubation with 223.5 and 447 mM acetaldehyde. Ethanol at 84.9, 212.3, and 427.9 mM did not significantly affect the enzymic activity. Because aminopeptidase A and aminopeptidase M also degrade the pressor substance, angiotensin II, it is suggested that inhibition of aminopeptidase A- and aminopeptidase M-like activity by acetaldehyde, the product of ethanol metabolism, may lead to higher levels of circulating angiotensin II and, consequently, hypertension, in alcoholics. The hydrolysis of lysine-p-nitroanilide, an aminopeptidase B substrate, was also inhibited upon addition of acetaldehyde to Moni-Trol ES serum.

Intracerebroventricularly infused angiotensin II or III do not alter voluntary alcohol intake in rats

Subcutaneous injections of angiotensin (ANG) II or III in the periphery reduce alcohol intake and raise water intake. These peptides do not cross the blood-brain barrier and cannot reach the angiotensin receptor-rich sites surrounding the lateral and third ventricles. To examine the effect on alcohol intake of ANG II and III at these ventricular sites, groups of rats were first trained to drink alcohol using a limited access procedure, then surgically prepared with chronic indwelling lateral or third ventricular cannulae, and then reoffered daily 40-min access to alcohol. Neither ANG II (25-200 ng) nor ANG III (25-100 ng) had any effect on alcohol consumption at either of the two ventricular sites. Water consumption was significantly enhanced by both peptides at both sites and could be attenuated by prior treatment with the ANG II antagonist Sar1Thr8-ANG II. The SC administration of ANG II was able to produce a significant reduction in alcohol drinking. These findings demonstrate that ICV administered ANG II or ANG III do not modulate alcohol drinking and that changes in alcohol intake do not result from the thirst promoted by ANG II. Sites in the periphery may be more involved in the interaction between angiotensin and alcohol consumption.

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.

Interaction of acetaldehyde with plasma proteins of the renin-angiotensin system

Chronic alcohol abuse may lead to hypertension by stimulating the activity of the renin angiotensin system (RAS). While there are reports on the alcohol associated increase of angiotensin II in rats and increases of plasma renin activity in rats and human alcoholics, the exact mechanisms of stimulation of the RAS activity is not clear. This study provides evidence for a biochemical interaction of acetaldehyde, the primary oxidative metabolite of ethanol, upon bilaterally nephrectomized (NEPEX) rat plasma that contains significant quantities of angiotensinogen and lacks active renin. Rat plasma served as the source of renin in this study. Preincubation of NEPEX plasma with 0.2 M acetaldehyde at 4 degrees C for 2 h resulted in a 21% increase in the angiotensin I (A I) formation by the rat plasma renin and 27% increase in the A I formation by the trypsinized rat plasma renin. When the rat plasma which contains modest quantities of endogenous angiotensinogen in addition to renin was preincubated with 0.2 M acetaldehyde at 4 degrees C for 2 h, the rate of A I formation was increased by 10%. Equivalent amounts of ethanol did not modify the rate of A I generation when added to NEPEX plasma or rat plasma. These results suggest the possibility of a biochemical interaction of acetaldehyde with the renin substrate which may enhance the activity of the RAS cascade, thereby contributing to hypertension in chronic alcoholics.

Dietary salt and voluntary ethanol consumption in golden hamsters

Adult male golden hamsters were maintained on powdered Purina chow and tap water, and were permitted continuous access to either a 15% or a 30% ethanol solution (v/v); after an initial 4-5 weeks of ethanol availability, hamsters had stabilized their intakes and were deriving an average of 1.25 and 1.96 g/day of absolute ethanol from the 15% and 30% solutions, respectively. When salt was added to the diet in increasing concentrations ranging from 4% to 10% over a period of 40 days, hamsters reduced chow-derived calories by up to 35%, increased tap water consumption by up to 50%, and increased consumption of ethanol solutions by up to 100%; when unadulterated Purina chow was reinstated, intakes of chow-derived calories, tap water, and ethanol solutions returned to baseline levels. Hamsters that were continuously maintained on unadulterated Purina chow, but with chow-derived calories matched to that of animals on the salt-adulterated diet, significantly increased their ethanol intake, but not their tap water intake; the increase in their ethanol intake was only about half as large as that of hamsters that had salt added to the diet, but the increase persisted even after ad lib feeding was reinstated. The results indicate that the addition of salt to the diet of hamsters produces large increases in ethanol consumption; furthermore, the increased ethanol intake is not simply the result either of a nonselective increase in fluid consumption or of the reduction in food intake that accompanies the addition of salt to the diet. Results are related to the possible role of the renin-angiotensin system in the control of ethanol consumption in the golden hamster.

The reduction in alcohol intake produced by enalapril is not attenuated by centrally administered angiotensin inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, reduce alcohol intake when injected peripherally. The mechanism by which ACE inhibitors produce this effect on alcohol intake is unknown. A rise in the biosynthesis of angiotensin II in the periphery is known to reduce alcohol intake. In this experiment, we examine the possibility that the reduction in alcohol intake produced by an ACE inhibitor, enalapril, is mediated by a rise in angiotensin II in the brain. Enalapril, 20 mg/kg, injected intraperitoneally, produced a 40% reduction in alcohol intake. This reduction was not attenuated by the concurrent administration into the lateral ventricle of either the ACE inhibitors captopril or ceranapril (1, 10, or 25 micrograms), or the angiotensin II receptor antagonist Sar1-Thr8-Angiotensin II (5 micrograms). These findings suggest that the ACE inhibitors do not reduce alcohol intake by raising angiotensin II in the brain.

Adrenalectomy does not modify the suppressive effect of angiotensin II on voluntary ethanol drinking in rats

Enhancement of activity in the renin-angiotensin system reduces voluntary ethanol consumption in rats. Because angiotensin II, which is a major bioactive component of the renin-angiotensin system, stimulates the release of aldosterone, aldosterone may play a role in the reduction of ethanol intake by angiotensin II. The present study examined ethanol drinking in a group of rats that was bilaterally adrenalectomized and incapable of producing aldosterone, and in a sham group that underwent similar surgery except that the adrenal glands were left intact. Rats were maintained on ad libitum food, water and 1.5% saline solution in their home cages. Access to ethanol (6% weight/volume) was restricted to a daily 40 min period and was always offered as a choice in conjunction with water. Adrenalectomy did not alter the effect of angiotensin II on ethanol intake as subcutaneous injections of angiotensin II (400 micrograms/kg) significantly reduced ethanol intake to the same degree in both the adrenalectomized and sham groups. In the next phase, daily subcutaneous injections of aldosterone (100 micrograms/kg) reduced the home cage intake of 1.5% saline in the adrenalectomized group indicating that this dose of aldosterone was biologically active. These aldosterone injections did not affect ethanol intake in either the adrenalectomized or sham groups. Under the present conditions of testing aldosterone does not appear to play a role in the angiotensin II-induced reduction of ethanol consumption.

Consumption of sweet, salty, sour, and bitter solutions by selectively bred alcohol-preferring and alcohol-nonpreferring lines of rats

To determine whether selective breeding for high or low oral ethanol consumption is associated with different preferences for nonpharmacological solutions with various flavors, the oral intake of a range of concentrations of sucrose (0.5-64.0 g/100 ml), NaCl (0.025-3.2 g/100 ml), citric acid (0.008-2.048 g/liter), and sucrose octaacetate (0.002-0.512 g/liter) was studied in alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. Separate groups of 7-8 rats from each line were tested for consumption of each of the four flavors. The flavored solutions were presented continuously with water and food always available, and the concentrations were doubled every 48 hr. Although rats from both lines showed a strong preference for the sucrose solutions, P rats consumed greater amounts than NP rats [F(7,98) = 5.57, p < 0.001]. Rats of the P line drank less of the NaCl solutions than NP rats [F(7,98) = 3.88, p < 0.001], but the effect was not as robust as the line differences seen with sucrose. The P and NP rats did not differ in citric acid or sucrose octaacetate intake at any of the concentrations tested. Selective breeding for high oral ethanol preference appears to be positively associated with consumption of sweet solutions and negatively associated with intake of salty solutions.

The reduction in alcohol drinking by peripherally injected angiotensin II is selectively mediated by the AT1 receptor subtype

We investigated which of the two angiotensin (ANG) receptor subtypes mediates the reduction in alcohol intake produced by peripheral injections of ANG II. Adult male Wistar rats were trained to self-administer alcohol (6% w/v) using a procedure that, by limiting access to a brief daily availability period (40 min), fosters a bout pattern of alcohol drinking and a pharmacodynamic effect. Water was continuously available. Once intake stabilized, groups received daily injections either 200 micrograms/kg ANG II SC or the control vehicle saline immediately prior to alcohol availability. Alcohol consumption was attenuated and water intake elevated in the groups receiving ANG II and was unaffected by the vehicle injections. Following this, different groups were pretreated with ascending doses (0.25, 0.5, 1.0 mg/kg) of either PD123319, the selective AT2 receptor antagonist, Sar1,Thr8-ANG II (0.25 mg/kg), the nonselective ANG II antagonist, or DuP753 (0.25, 0.5, 1.0 mg/kg), the selective AT1 receptor antagonist. Control groups received antagonist pretreatment followed by the ANG II vehicle. Neither PD123319, DuP753, or Sar1, Thr8-ANG II had any effect of their own on alcohol or water intake. Pretreatment with PD123319 did not alter the suppressive effect of ANG II on alcohol intake. DuP753 produced a dose-dependent attenuation in the suppressive effect of ANG II on alcohol intake and antagonized the dipsogenic effect of ANG II on water intake. The effect of Sar1,Thr8-ANG II was similar to that of DuP753. These findings suggest that the reduction in alcohol intake produced by ANG II is mediated through the AT1 receptor subtype.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

Reduction of voluntary alcohol intake in the rat by modulation of the dopaminergic mesolimbic system: transplantation of ventral mesencephalic cell suspensions

The dopaminergic mesolimbic system plays a major role in the mechanisms of reward and positive reinforcement, and is also known to be a primary target for the action of substances that are self-administered and are considered drugs of abuse. Even though alcohol administration has been shown, by physiological and pharmacological manipulations, to cause changes in the mesolimbic dopaminergic system, it has not yet been determined whether, conversely, experimentally induced changes in this system are effective in regulating the voluntary intake of ethanol. In the present study we assessed the effects of the intrastriatal transplantation of fetal dopaminergic grafts on the regulation of voluntary alcohol intake in the rat. Fetal dopaminergic transplants from ventral mesencephalon--but not dopamine-poor transplants or sham-operated animals--reduced the voluntary intake of ethanol by about 40-50%. These results indicate that the effects obtained are due to the dopaminergic nature of the grafts, and not the consequence of a non-specific effect of the graft, or of the surgical procedure itself. These results support the hypothesis that the dopaminergic mesolimbic system plays an important role in the regulation of the voluntary intake of ethanol.

Reduction of voluntary alcohol consumption in the rat by transplantation of hypothalamic grafts

Stimulation of the peripheral renin-angiotensin system has been shown previously to decrease the voluntary intake of ethanol in the rat. The existence of a separate brain renin-angiotensin system, independent from that of the periphery, has been widely demonstrated. The brain renin-angiotensin system plays an important role in the regulation of water and electrolyte balance and neuroendocrine function. However, the role played by this system in the regulation of voluntary alcohol consumption has not yet been studied. The goal of the present work was to assess the feasibility of decreasing the voluntary alcohol intake in a strain of rats (Rapp SS/Jr rats) that have a genetic deficiency responsible for a low activity of the renin-angiotensin system and elevated alcohol intake. Adult Rapp SS/Jr rats received intraventricular transplants of fetal hypothalamic grafts (from normal donors), known to contain angiotensin-immunoreactive cell bodies. Our studies revealed that angiotensin-immunoreactivity in the cell bodies and fibres in the paraventricular, supraoptic and suprachiasmatic nuclei of the hypothalamus in Rapp SS/Jr rats was markedly reduced. Animals that had surviving grafts containing angiotensin-immunoreactive cell bodies in the dorsal third ventricle--but not in the ventral third ventricle, in the lateral ventricles, or sham operated animals--had a 40% decrease of their voluntary alcohol intake, when compared to their intake before surgery, or to the control group. However, water consumption was not reduced in both the sham and transplanted animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin suppresses alcohol intake and plays a role in the suppression produced by an ACE inhibitor

The possible role of the endogenous kinins in the control of alcohol intake was assessed in two experiments. In Experiment 1, naive rats, maintained on ad lib food and water, were given daily 40-min access to a 6% (w/v) alcohol solution and water. Daily intraperitoneal (IP) injections of captopril (20 mg/kg) significantly reduced alcohol intake, while pretreatment with subcutaneous (SC) injections of the bradykinin antagonist [D-Phe7]-bradykinin (100-300 micrograms/kg) attenuated the suppressive effect of captopril on alcohol intake. The saline vehicle or the bradykinin antagonist alone did not alter alcohol intake. In Experiment 2, bradykinin was administered daily at 100, 200, and 400 micrograms/kg doses SC either alone or in combination with captopril 10 mg/kg IP. Neither bradykinin nor captopril by themselves changed alcohol or water intake. Bradykinin combined with captopril stimulated water intake and reduced alcohol intake by up to 70%. This effect was not due to drug-induced changes in the pharmacokinetics of alcohol. The angiotensin II receptor antagonist [Sar1,Thr8]-angiotensin II at 250 and 500 micrograms/kg SC attenuated the stimulation of water intake but not the reduction in alcohol intake. It is suggested that by inhibiting kininase II, ACE inhibitors extend the duration of action of bradykinin and thereby unmask a potent inhibition of alcohol intake mediated by kinins--an effect that is dissociable from the accompanying stimulation of water intake. Taken together, these results point to an involvement of the kinin system in the regulation of alcohol intake and in particular to a role of bradykinin in the suppressive effect of ACE inhibitors on alcohol intake.

Acetaldehyde inhibits angiotensin-converting enzyme activity of bovine lung

The role of ethanol and its primary metabolite, acetaldehyde, were investigated for their effects upon angiotensin-converting enzyme (ACE) (EC 3.4.15.1), since the enzyme plays a key role in the maintenance of blood pressure homeostasis by transforming angiotensin I into angiotensin II and degrading bradykinin. ACE was extracted from a 38,000 x g pellet of bovine lung homogenate with 0.05-M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) buffer, pH 7.0/0.4 M NaCl/10 microM ZnCl2/0.5% Triton X-100. The solubilized enzyme was preincubated with increasing concentrations of acetaldehyde (0.177-2.213 M) for 30 min at 0 degree C. Progressive inhibition of 41-84% was observed as enzyme aliquots were assayed with hippuryl-L-histidyl-L-leucine (HHL) as the substrate. The interaction of angiotensin-converting enzyme with acetaldehyde was rapid under these conditions. Ethanol appeared to to have no effect upon enzymic activity at comparable concentrations. These results suggest that acetaldehyde-mediated ACE inhibition in vivo may play a contributory role in the development of vasodilation and facial flush reaction consequent to ethanol consumption, thereby accounting for localized hypotension.

Captopril and hydrochlorothiazide (Capozide) combine to enhance the reduction in voluntary alcohol intake in rats

The effect of Capozide, the combination of captopril with a hydrochlorothiazide diuretic, on voluntary alcohol intake was assessed in two experiments. In experiment 1 naive rats who were maintained on ad libitum food and water were given daily 40-min access to a 6% (w/v) alcohol solution and water. Daily intraperitoneal injections of captopril (10 mg/kg) reduced alcohol intake, but the combination of captopril (5 and 10 mg/kg) and hydrochlorothiazide (2.5, 5, and 10 mg/kg) enhanced the reduction in intake. In experiment 2, captopril alone, hydrochlorothiazide alone, and the combination of captopril and hydrochlorothiazide were again administered daily in the limited access procedure. Captopril (10 mg/kg) again reduced alcohol intake as did all three doses of hydrochlorothiazide (2.5, 5, and 10 mg/kg). Compared with the individual effects of captopril and hydrochlorothiazide, Capozide exerted a supra-additive reduction in alcohol intake. These effects were not due to drug-induced changes in the pharmacokinetics of alcohol. Taken together these results demonstrate an enhanced potency of Capozide in suppressing alcohol intake and invite their testing in a population of hypertensive alcoholics and alcohol abusers.

Reduction of ethanol intake by aerosol inhalation of a beta-adrenergic agonist: new route--new treatment approach?

The quick, convenient, unobtrusive administration of a low dose of a drug that effectively reduces alcohol intake could be a useful adjunct to any program that aims to treat alcohol abuse. This study evaluates the ability of isoproterenol, a drug that has previously been shown to reduce ethanol intake, to exercise this action when administered as a metered aerosol mist. Rats were trained to self-administer ethanol using a procedure that limits access to a brief daily availability period. Once intake stabilized, animals were given isoproterenol by metered aerosol inhalation just before ethanol availability. A custom-designed helmet attached to a commercially available mistometer was used to deliver the drug. Isoproterenol produced a dose-dependent reduction in ethanol intake and an increase in water intake replicating the effects of parenterally administered isoproterenol on ethanol and water consumption. These findings demonstrate that the administration of isoproterenol in inhaled aerosol form can effectively reduce voluntary ethanol consumption in rats. The administration of pharmacologically active antialcohol agents via the inhalation route may be useful in the symptomatic treatment of alcohol abuse in humans.

Forebrain circumventricular organs mediate captopril-enhanced ethanol intake in rats

Chronic peripheral treatments with low doses of the angiotensin-converting enzyme inhibitor, captopril, enhance daily intakes of dilute ethanol solutions in rats as they do the intakes of water and saline solutions. Placing captopril into the drinking water or infusing it SC increases daily intake of 6% (v/v) ethanol from 30-100% over 4-12 days of treatment. The present study examined the effects of electrolytic lesions either of the subfornical organ (SFO) or of the organum vasculosum laminae terminalis (OVLT), on captopril-enhanced ethanol intake. Captopril was infused in minipumps at 5 mg/day for 14 days. The intake of 6% (v/v) ethanol was abolished by SFO lesions and was temporarily reduced by OVLT lesions. The SFO, in particular, is essential for the expression of enhanced ethanol intake during low-dose peripheral captopril administration. Local angiotensin II synthesis and receptor activation at the SFO appear to be the mechanism of the enhanced ethanol drinking during captopril.

Angiotensin and captopril increase alcohol intake

Reportedly both angiotensin II (ANG II) and angiotensin-converting enzyme (ACE) inhibitors reduce ethanol intake when they are injected SC into certain chronic experimental conditions in the rat. The ACE inhibitors are suggested to reduce ethanol intake by increasing ANG II synthesis in the brain. The present results show that several different methods can produce opposite effects of ANG II and the ACE inhibitor captopril on ethanol intake. Continuous intraventricular infusions of ANG II for 7 days or low doses of oral or SC-infused captopril for up to 12 days increased the intake of ethanol. The only reduction of ethanol intake resulted from a universal blockade of all ACE in both the brain and periphery, a condition in which ANG II could not possibly mediate the decrease. The results contradict the hypothesis that ethanol intake is suppressed by centrally acting or centrally synthesized ANG II. ACE inhibitors may reduce ethanol intake only when they affect the brain as well as the periphery.

Angiotensin II mediates a conditioned taste aversion in water-replete rats

Many compounds that exert an influence on behavioral processes will, under the unique conditions of the conditioned taste aversion (CTA) procedure, cause animals to avoid consuming an otherwise preferred fluid. While angiotensin II (ANG II) is a peptide with a number of behavioral and physiological actions, previous research did not support its role as an agent capable of inducing a CTA. Those studies used fluid deprivation to induce fluid intake and only a single conditioning trial. Fluid deprivation can elevate endogenous ANG II levels that may have interfered with or masked the ability of ANG II injections to exert an effect as a CTA-inducing agent. The present study reassessed the ability of ANG II to induce a CTA using fully hydrated animals and a number of conditioning trials. ANG II was able to induce a significant taste aversion at a dose five times lower than that used in previous studies.

Effects of angiotensin II and an angiotensin converting enzyme inhibitor on alcohol intake in P and NP rats

While it is known that randomly bred normotensive Wistar stock and hypertensive rats alter their alcohol consumption when activity in the renin-angiotensin (R-A) system is modified, the effect of manipulations to the R-A system on alcohol intake in genetically selected alcohol-preferring P and -nonpreferring NP rats has not been assessed. In Experiment 1, nine P rats and 8 NP rats were injected with the saline vehicle and offered limited access to 10% (v/v) alcohol for 40 min each day for 7 days. When intake stabilized both groups were given daily intraperitoneal injections of the angiotensin converting enzyme inhibitor, ceranapril (20 mg/kg) 45 min prior to alcohol access for 11 days. Ceranapril (SQ 29,852) reduced alcohol intake in both the P and NP animals, while saline had no effect. In Experiment 2, these same two groups of P and NP rats were injected with three doses of angiotensin II (ANG II) (100, 200, 400 micrograms/kg) immediately prior to alcohol access. Each dose was tested for 10 consecutive days, with a 14-day period of no drug preceding and following the ANG II treatments. ANG II reduced alcohol intake in the NP rats and produced a dose-dependent reduction in the alcohol consumption of the P rats. These findings indicate that the renin-angiotensin system can modify alcohol consumption in rats selectively bred for high and low alcohol intake.

Sham ingestion of alcohol in rats

Sprague-Dawley rats were surgically fitted with gastric fistulas and their intakes of 6% ethanol measured first with the fistula closed (normal drinking) and then on three test sessions with the fistula open (sham drinking). The rats were water deprived prior to the 1-h test sessions. On the second and third sham drinking sessions, intakes of alcohol were significantly increased above those in both the closed and first open fistula session. The effectiveness of the sham ingestion preparation to minimize absorption was shown by the much lower blood alcohol levels in sham compared with real drinking rats. Thus, reduction of the postingestive effects of alcohol leads to an acquisition of increased oral consumption. The similarities and differences between sham intakes of water and alcohol are discussed.