Angiotensin II-induced suppression of alcohol intake and its reversal by the angiotensin antagonist Sar-1 Thr-8 angiotensin II

Central Overexpression of Angiotensin AT1AReceptors Prevents Dopamine D2Receptor Regulation of Alcohol Consumption in Mice

BACKGROUND

While angiotensin receptors are found on the soma and terminals of dopaminergic neurons, controversy surrounds the potential role of angiotensin in alcohol consumption.

METHODS

Using a transgenic mouse with a brain-specific overexpression of angiotensin AT(1A) receptors (NSE-AT(1A) mice), we have examined the role of angiotensin in alcohol consumption and alcohol-induced regulation of the dopaminergic system.

RESULTS

The functional relevance of the overexpressed AT(1A) receptors was confirmed by an exaggerated rehydration response following 24-hour dehydration. NSE-AT(1A) mice showed a high preference for alcohol (similar to wild-type mice); yet, raclopride treatment had no effect on alcohol consumption in NSE-AT(1A) mice, while significantly reducing consumption in wild-type mice. In contrast, NSE-AT(1A) mice showed enhanced sensitivity to raclopride compared with wild types in terms of D(2) receptor up-regulation within the ventral mesencephalon. In addition, striatal D(2) receptors in NSE-AT(1A) mice were sensitive to up-regulation by chronic alcohol consumption.

CONCLUSIONS

Collectively, these data imply that while expression of angiotensin AT(1A) receptors on striatal neurons has no impact upon basal alcohol consumption or preference, AT(1A) receptors do modulate the sensitivity of dopamine D(2) receptors to regulation by alcohol and the ability of a D(2) receptor antagonist to reduce consumption.

More vasopressin mRNA in the paraventricular hypothalamic nucleus of alcohol-preferring rats and high alcohol-drinking rats selectively bred for high alcohol preference

Both the selectively bred alcohol-preferring (P) and high alcohol-drinking (HAD) rats exhibit alcohol preference, and develop tolerance to alcohol more quickly than their counterparts, the alcohol-nonpreferring (NP) and low alcohol-drinking (LAD) rats, respectively. It has been shown that the P rats retain developed tolerance longer than do NP rats, and alcohol drinking increases concurrently with the development of tolerance. Although alcohol preference and tolerance are fundamental elements of alcoholism, the exact mechanisms underlying these two phenotypes in P and HAD rats are not well understood. Recent studies have suggested that arginine vasopressin (AVP) may be involved in modulation of alcohol tolerance. Accordingly, this study was designed to examine whether the AVP mRNA level in the hypothalamus differs in rats that have been selectively bred for alcohol preference and nonpreference. A 35S-AVP antisense oligodeoxynucleotide probe was used for in situ hybridization to localize AVP mRNA in the paraventricular hypothalamic nucleus (PVN) and supraoptic nucleus (SON), two major sites for AVP synthesis in the hypothalamus. Quantitative autoradiography demonstrated that P rats had higher levels of AVP mRNA in the PVN than NP rats. Similarly, higher levels of AVP mRNA were also found in the PVN of HAD rats, compared with LAD rats. The AVP mRNA levels in the SON were similar in the alcohol-preferring and alcohol-nonpreferring rat lines. Basal plasma AVP levels were higher in NP rats than in P rats as determined by radioimmunoassay, whereas plasma AVP levels were not significantly different between HAD and LAD rats. The results suggest that increased AVP gene expression in the PVN may contribute to alcohol preference and the development of alcohol tolerance.

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.

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.

Increased alcohol consumption in weight-reduced rats is modulated by the renin-angiotensin system

Weight reduction and food restriction increase the self-administration of alcohol and other drugs of abuse, but the underlying physiological mechanisms have not been identified. Because weight reduction alters angiotensin (ANG) II activity, and ANG II is known to modulate alcohol intake, ANG II may play a role in the enhanced alcohol consumption of food-deprived weight-reduced rats and in the drop in alcohol intake when these rats are refed. Two groups of rats were reduced to and maintained at 80% of their free feeding weights and offered daily 40 min access to a 6% (w/v) alcohol solution and water. Water was available ad lib. After alcohol intake stabilized, one group was given daily injections of the angiotensin converting enzyme inhibitor captopril (5.0 mg/kg) for 6 days while the other group received the saline vehicle. Following this, each group continued to receive either captopril or vehicle injections but was returned to ad lib feeding. Captopril did not alter alcohol intake when the rats were food-deprived and weight-reduced, but did significantly attenuate the decline in alcohol consumption compared to the vehicle group when both groups were refed and regaining weight. These findings suggest that the increase in alcohol intake with food restriction and its decline following refeeding are, in part, related to changes in ANG II activity.

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.

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.

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.

Bestatin, an aminopeptidase B inhibitor, selectively reduces alcohol intake in rats

Extensive research has shown that manipulations that augment activity in the renin-angiotensin system can reduce alcohol intake. Inhibition of aminopeptidase B and M can prolong the action of angiotensin (ANG) II and ANG III by preventing their degradation. This study assessed the ability of bestatin, an aminopeptidase B and M inhibitor, to decrease alcohol intake. Bestatin produced a dose-dependent reduction in alcohol intake without altering water intake. The angiotensin antagonist Sar1Thr3-ANG II, however, did not attenuate the effect of bestatin, suggesting that the reduction in alcohol intake was mediated by a system other than the renin-angiotensin system. Bestatin (Ubenimex) is used extensively in Japan as an anticancer agent. It has a low toxicity and is readily absorbed after oral administration. Although further research is needed to uncover the mechanism of its effect, the potential of this drug as an adjunct for the treatment of alcohol abuse should be evaluated.

Reducing the desire to drink. Pharmacology and neurobiology

The past decade has witnessed major advances in understanding of neural functioning and neurobiological bases of alcohol consumption. Concurrent with this, a range of exciting investigations have been conducted on pharmacologic agents that may curb drinking behavior. Research is reviewed on several promising medications influencing neurotransmitter and endocrine systems with particular attention to the serotonergic and opioid systems. Following this overview, recommendations are offered regarding research methodology to support future pharmacotherapy trials.

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.

Manipulations of the renin-angiotensin system and intake of a sweetened alcoholic beverage among rats

Standard laboratory rats were maintained on a daily regimen involving deprivation of fluids for 22 h followed by a 2-h opportunity to drink water and a sweetened alcoholic beverage. Angiotensin II, in doses ranging from 0.1 to 1.25 mg/kg, dose relatedly decreased rats' mean intake of ethanol. All doses increased rats' mean intake of water. Angiotensin II, 0.25 mg/kg, reliably reduced intake of ethanol when it was presented alone during the 1st h of the daily 2-h drinking session, and reliably increased intake of water when it was subsequently presented alone during the 2nd h. Thus the reduction in intake of ethanol seen when the alcoholic beverage is presented concurrently with water is probably not merely due to the increase in intake of water. Lisinopril, an angiotensin converting enzyme inhibitor, in doses of 0.3, 1.0, and 3.0 mg/kg, dose relatedly decreased intake of ethanol, but only after several days of injections. Concurrent intake of water was increased dose relatedly. When injections of lisinopril ceased, intakes of both ethanol and water took several days to return to control levels. Pretreatment with lisinopril, 3.0 mg/kg, for 8 days, had no effect on subsequent intakes of either water or ethanol. Lisinopril, 3.0 mg/kg, had no effect on rats' intake of a sweet solution without ethanol. These results confirm previous work and extend the data base supporting the idea that the renin-angiotensin system plays a role in modulating intake of ethanol.

The amino acid composition of angiotensin alters its ability to reduce alcohol consumption in rats

The voluntary consumption of alcohol has been shown to be reduced by a variety of manipulations which enhance activity in the renin-angiotensin system, including the administration of the bovine form of angiotensin II-[Val5]-ANG II. The present study investigated the relationship between the amino acid composition of angiotensin II and its ability to reduce alcohol intake by administering a number of different forms or fragments of the parent peptide. [Ile5]-Angiotensin II ([Ile5]-ANG II), two endogenous fragments of angiotensin II [( Des-Asp1]-ANG II and [Des-Phe8]-ANG II) were administered subcutaneously in rats across a range of doses. [Ile5]-ANG II reduced alcohol intake at all doses tested between 20 and 400 micrograms/kg while [Des-Asp1]-ANG II reduced alcohol intake only at the 400 micrograms/kg dose. [Des-Phe8]-ANG II had no effect on alcohol intake at any dose tested. Administration of the antagonist [Sar1-Thr8]-ANG II by itself did not enhance alcohol intake. While the pressor and dipsogenic properties of these fragments sometimes correlated with the reduction in alcohol intake they were not a causal factor in decreasing the intake. These results indicate that variations in the peptide composition of angiotensin can significantly alter its ability to reduce the consumption of alcohol.

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

The renin-angiotensin system has traditionally been associated with the regulation of fluid and electrolyte balance. In this review we summarize the data which ascribes a completely new function to this system, i.e., the regulation of alcohol consumption. In addition, we suggest a possible mechanism for this effect based on the concept of a satiety or stop process. The approach taken was to examine the effect on alcohol intake of a wide variety of drug, genetic, dietary, surgical and neurosurgical manipulations, each of which has a range of biological effects characteristic of that manipulation, but all of which share the common property of altering activity in the renin-angiotensin system. The effect of these manipulations on alcohol intake was most parsimoniously explained by reference to their ability to raise or lower activity in the renin-angiotensin system. Any intervention which modulates activity in this system, either directly or indirectly, is likely to have consequences for alcohol consumption.

Systemic angiotensin II does not act at the area postrema to suppress alcohol intake

The area postrema (AP), a circumventricular organ located in the dorsal medulla, is involved in the coordination of visceral and taste sensory stimuli in the control of ingestive behaviors. This area lacks a blood-brain barrier and is rich in angiotensin receptors. Because systemically administered angiotensin II reduces voluntary alcohol intake, we examined the effect of AP lesions on alcohol intake and on the ability of ANG II reduces alcohol intake. Compared to sham-operated controls, rats with AP lesions consumed significantly more of a palatable 3% alcohol solution, and equal amounts of a less palatable 6% alcohol solution, but the lesion did not alter the ability of ANG II to reduce alcohol intake. These findings indicate that while the AP plays no role in the suppressive effect of ANG II on alcohol consumption, it can modulate alcohol consumption through its responsiveness to orosensory stimuli.

Pharmacology of drug self-administration

Limited access to drugs provides a reliable model for their acute-reinforcing effects and a means by which to explore neuropharmacological mechanisms involved in these effects. In limited access situations intravenous self-administration rates of opiates and psychomotor stimulants is inversely related to dose, and competitive antagonists at low doses increase the number of injections self-administered. Competitive agonists decrease drug self-administration. However noncompetitive antagonists tend to produce decreases in self-administration and the specificity of these results are difficult to interpret. A limited access procedure of ethanol (10% v/v) self-administration using a sucrose or saccharin fade out procedure resulted in reliable and stable ethanol (10% v/v) and water self-administration in a concurrent choice situation using nondeprived unselected Wistar and alcohol preferring P-rats. As observed by others, the opiate antagonist naloxone decreased fluid intake in both strain of rats. However, contrary to earlier results naloxone did not produce a selective decrease in ethanol preference. The serotonin antagonist methysergide had no significant effect on fluid intake or ethanol preference. However, the long-acting dopamine agonist bromocriptine decreased ethanol intake and increased water intake producing a significant decrease in ethanol preference. The results with naloxone suggest that opiate interactions with ethanol may reflect a more general effect on consummatory behavior and the results with bromocriptine suggest that the reinforcing effects of low doses of ethanol may involve a dopaminergic component. Future studies should explore further the interactions of ethanol with competitive antagonists (if possible), and fluid intake or ethanol preference with limbic-extrapyramidal circuitry involved in mediating the reinforcing actions of other drugs of abuse.

Angiotensin converting enzyme inhibitors reduce alcohol consumption: some possible mechanisms and important conditions for its therapeutic use

Alcoholism is a prevalent problem of contemporary society, yet there are virtually no clinically effective drugs for the management of this disorder. A previous study demonstrating the ability of angiotensin-converting enzyme (ACE) inhibitors to attenuate voluntary alcohol intake in rats prompted the suggestion that these drugs, currently marketed for the treatment of hypertension, may also be useful in dealing with human alcohol abuse. The present experiments explored in more detail the effect and possible mechanisms of action of this class of drug on alcohol consumption in rats. Experiment one demonstrated that Abutapril, a new ACE inhibitor, significantly reduced alcohol intake and that this effect could not be blocked by either an ANG II or an opiate receptor antagonist suggesting that neither the peripheral renin-angiotensin system (RAS) nor the endogenous enkephalins are involved in the ability of ACE inhibition to attenuate alcohol intake. Experiments two and three showed that ACE inhibition effectively reduced alcohol drinking faster in animals with elevated RAS activity and not at all in animals with suppressed RAS activity indicating that initial levels of RAS activity may determine the speed and ability of ACE inhibition to attenuate alcohol intake. ACE inhibitors may reduce alcohol intake by elevating a nonapeptide fragment or by elevating central ANG II levels. The assessment of this class of drugs to reduce alcohol intake in humans should include a monitoring of the initial level of activity in the renin-angiotensin system since this may be a predictor of the effectiveness of treatment with the ACE inhibitors.

Systemic angiotensin II acts at the subfornical organ to suppress voluntary alcohol consumption

The subfornical organ plays a role in a number of the effects of blood-borne angiotensin II (ANG II) including the increase in water drinking and blood pressure and the release of vasopressin from the pituitary. Recently it has been shown that systemically administered ANG II also reduces voluntary alcohol intake. The present study assessed the role of the SFO in alcohol consumption by examining the effects of SFO lesions on voluntary alcohol intake and on the suppression of voluntary alcohol intake by ANG II. Whereas the lesion did not alter alcohol consumption per se, it did significantly attenuate the ability of ANG II to reduce alcohol intake. This effect was not due to a lesion-induced change in the pharmacokinetics of alcohol and was observed only in those animals whose lesions produced a functional deficit, i.e., abolishing the increase in water drinking produced by ANG II. These results indicate that the SFO mediates the effect of systemically administered ANG II on alcohol intake but does not otherwise affect the regulation of alcohol consumption.

The beta adrenergic agonist isoproterenol suppress voluntary alcohol intake in rats

The effects of isoproterenol on alcohol consumption were examined to investigate whether beta adrenergic stimulation can reduce voluntary alcohol intake. Two and one-half, 5 and 10 micrograms/kg isoproterenol administered subcutaneously (SC) just prior to alcohol availability produced a dose-dependent reduction in alcohol intake and elevation in water intake. Blood alcohol levels measured subsequent to a SC injection of 5 micrograms/kg isoproterenol or vehicle followed by an intraperitoneal injection of 2.5 g/kg alcohol showed that the adrenergic agonist did not alter the distribution or metabolism of alcohol. Since beta adrenergic agonists such as isoproterenol are potent releasers of renin, these findings support previous work showing that different kinds of interventions which share the common property of elevating activity in the renin-angiotensin system (beta adrenergic stimulation in the present case) consistently result in the reduction of voluntary alcohol intake.

Alcohol intake is inversely related to plasma renin activity in the genetically selected alcohol-preferring and -nonpreferring lines of rats

Studies involving both animals and humans strongly suggest that alcoholism is, in part, genetically determined. One approach to studying this genetic component is to determine whether rats, genetically selected to prefer (P line) or avoid (NP line) alcohol, show differences in those physiological systems which modulate alcohol intake. It has previously been shown that alcohol intake in randomly bred stock rats is sensitive to and inversely related to manipulations which alter activity in the renin-angiotensin (R-A) system. In the present report the basal level of activity in the R-A systems of the P and NP rats as measured by plasma renin activity (PRA) was first assessed following which continuous access to alcohol (10% v/v) and water was offered for a period of five days. PRA was found to be inversely related to the amount of alcohol that was consumed. The P rats drank significantly larger amounts of alcohol than the NP rats who basically avoided the drug. The P rats had a significantly lower PRA than the NP rats. It is suggested that the genetic selection that favored different levels of alcohol consumption in the P and NP rats may have brought about this effect through differences in the activity of the renin-angiotensin systems in the two lines.

Ethanol as a reinforcer for rats: factors of facilitation and constraint

This review examines some particular approaches that have been used to investigate factors that facilitate or constrain the self-administration of ethanol by rats. A technique for increasing ethanol self-administration in rats, the prandial drinking method, was examined and the effect of body-weight reduction on drug intake was discussed. Emphasis was placed on how ethanol intake may be controlled by processes in addition to the direct pharmacological actions of the drug in the CNS. These processes may be physiological. Evidence was presented for a relationship between activity in the renin-angiotensin system and the self-administration of ethanol. These processes may also be environmental. Using the place-conditioning technique, demonstrations were presented of how the context or situation in which ethanol is experienced may determine whether preference or aversion for the drug develops. Such a diversity in the factors that can potentially control ethanol intake may complicate the identification of the causes of alcohol abuse, but this same diversity also holds out greater hope that manipulations may be found to reduce excessive drinking in humans.