Vasopressin does not mediate the inhibition of ethanol drinking by the renin-angiotensin system

Neurokinin Type-3 Receptor Stimulation Impairs Ethanol-Associated Appetitive Behavior in Wistar Rats

OBJECTIVES

Stimulating central neurokinin type-3 (NK-3) receptors decreases ethanol intake in rats. Although paraventricular nucleus of the hypothalamus (PVN) has a high density of NK-3 receptors, their influence on ethanol reinforcement has not been examined. This study's purpose was to assess the effects of intra-PVN infusion of senktide, a NK-3 receptor agonist, on ethanol self-administration. In a follow-up study, senktide's effects on ethanol self-administration after intracerebroventricular (ICV) infusion were examined.

METHODS

Male Wistar rats were trained to self-administer 10% ethanol (10E) in the "Sipper Tube" model described by Samson and colleagues, Guide cannula were then aimed bilaterally at the PVN or unilaterally at the lateral cerebral ventricle. Intra-PVN (5-100 ng/side) or ICV (30-500 ng/rat) effects of senktide on 10E self-administration were also examined as a preliminary test of senktide's selectivity.

RESULTS

Intra-PVN and ICV infusion of senktide reduced the average number of consecutive lever presses and increased the time taken to complete the lever press requirement when 10E served as the reinforcer. Increased duration of the lever-pressing component was observed when senktide was administered prior to 2S self-administration sessions. Neither PVN nor ICV senktide administration significantly altered 10E or 2S consumption.

CONCLUSIONS

These data suggest that stimulation of central neurokinin typ-3 receptors in the Wistar rat reduces appetitive behavior while having little or no impact on consummatory behavior. Ethanol "seeking" appeared more sensitive to disruption by senktide than sucrose "seeking." However, further studies assessing the senktide's effects on sucrose-maintained behavior are needed to verify this hypothesis. Lastly, it is hypothesized that lack of effect of senktide on intake is in part related to the use of outbred Wistar rats in these studies instead of selectively bred rats.

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.

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 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)

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.

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.