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

Pharmacotherapies for alcohol problems: a review of research with focus on developments since 1991

Research on medications to treat alcohol problems has flourished in the last 5 years. Whereas before this time most projects focused on withdrawal agents, at least equal interest has now extended to drugs that may directly reduce urge to drink. The most promising medications in this regard are the opiate antagonists and acamprosate. Considerable attention has also been devoted to serotonergic agents. As aids to detoxification, pharmacologic agents that affect the multiple neural systems disrupted by acute alcohol withdrawal remain under active investigation. Significant progress is also being made in identifying medications to assist alcoholics suffering collateral psychopathology, especially depression and anxiety based disorders. Unfortunately, fewer gains have been realized in the development of medications to assist patients simultaneously dependent on both alcohol and illicit drugs. Also, research to develop amethystic agents remains in its very early stages.

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.

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.

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.

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.