Alcohol 36 (2005) 55–61

Different stages in the temporal course of estrogentreatment produce opposite effects on voluntary

alcohol consumption in male rats

Jorge Juarez*, Cristina Vazquez-Cortes, Eliana Barrios-De TomasiLaboratorio de Farmacologıa y Conducta, Instituto de Neurociencias, Universidad de Guadalajara, Rayo 2611,

Col. Jardines del Bosque, C.P. 44520, Guadalajara, Jal., Mexico

Received 10 November 2004; received in revised form 31 May 2005; accepted 7 June 2005

Abstract

The purpose of this study was to examine alcohol consumption in different stages of the estrogen treatment. Three groups of castratedmale Wistar rats were used. One group was treated with 5 mg of estradiol benzoate (E) per day per rat for 6 days and oil from days 7 to 12(EO group). The second group was treated with oil for 6 days and E from days 7 to 12 (OE) and the third with E for 12 consecutive days(EE). The three groups were exposed to a choice of both water and ethanol (10%) before treatment (PreT), from days 7 to 12 of the oil or theE treatment (T2), and during 6 additional days in the post-treatment period (PosT). Alcohol was not available from days 1 to 6 of the oil orthe E treatment (T1). Alcohol consumption in the EO group during T2 was higher than in PreT and PosT periods and all periods in the othertwo groups. In contrast, alcohol consumption during T2 was significantly lower than during the PreT of the OE group and T2 of the EEgroup. At the same time in the EE group, alcohol intake in the T2 was higher than in the PreT and the PosT periods. These results reveal theopposite effects of estrogen treatment on alcohol consumption, which apparently depended on the physiological conditions produced by thetemporal course of hormone treatment. � 2005 Elsevier Inc. All rights reserved.

Keywords: Alcohol; Estrogens; Sexual hormones; Estradiol benzoate; Ethanol; Male rats; Voluntary alcohol intake

1. Introduction

Estrogen is a steroid hormone involved in manyfunctions in females and males. Aromatization, a processthat converts androgens into estrogens irreversibly usingenzyme aromatase, plays an important role in regulatinggene transcription to promote the sexual brain differenti-ation during critical periods of development (Lancaster,1994; Lieberburg et al., 1977; Rhoda, et al., 1984). Thismetabolic transformation has been clearly demonstrated inthe brain of adult male rats (Hojo et al., 2004) and malegonads of humans and rodents (Carreau et al., 2003). Inaddition to playing an important role in the female anatomyand physiology, estrogens have an influence on thefunctionality of the male reproductive tract (Hess, 2003),the general metabolism (Meinhardt & Mullis, 2002), andthe regulation of neural structure and function in the malebrain (Bloch & Gorski, 1988; Plumari et al., 2002; Zhanget al., 2002). Changes in estrogen levels as a consequence

* Corresponding author. Tel.: 152-3-6-47-77-76, ext. 106; fax: 152-3-

6-47-77-76, ext. 102.

E-mail address: jjuarez@cencar.udg.mx (J. Juarez).

0741-8329/05/$ – see front matter � 2005 Elsevier Inc. All rights reserved.

doi: 10.1016/j.alcohol.2005.06.003

of alcohol intoxication have been extensively studied. Apositive correlation between estrogens and alcohol intake inwomen has been documented (Gavaler et al., 1991; Gavaler& Van Thiel, 1992; Muti et al., 1998), and there is evidencethat estrogen levels increase after alcohol treatment in men(Couwenbergs, 1988), women (Mendelson et al., 1988),and male rats (Esquifino et al., 1989). On the other hand,the study of estrogens affecting alcohol consumption hasreceived little attention. The few studies in this respectdescribe a decrease in voluntary alcohol consumption inovariectomized females treated with estrogens (Almeidaet al., 1998; Sandberg et al., 1982; Sandberg & Stewart,1982) and resumption of alcohol intake to baseline levelsafter approximately 14 days of estrogen treatment (Sand-berg et al., 1982; Sandberg & Stewart, 1982). In contrast,it has been described that ovariectomy decreases ethanolconsumption in rats, and hormonal replacement withestradiol restores ethanol intake to presurgical baselinelevels (Ford et al., 2002). Studies in male rats have alsoshown that acute treatment with estrogens reduces alcoholconsumption (Juarez et al., 2002; Messiha, 1981). Incontrast, it has been described that in male mice after 15days of chronic estrogen treatment, there is no effect on

56 J. Juarez et al. / Alcohol 36 (2005) 55–61

voluntary alcohol intake with respect to a placebo group(Hilakivi-Clarke, 1996).

It has been reported that estrogens produce an increasein the internalization of opioid receptors (Eckersell et al.,1998; Micevych et al., 1997, 2003; Sinchak & Micevych,2003), which is a mechanism for receptor downregulationthat produces a reduction in receptor availability. It is wellknown that reduced receptor availability can induce anincrease in the number of receptors (upregulation) in theshort term as a compensatory mechanism. This phenome-non changes the availability of opioid receptors from low tohigh. On the other hand, it is well known that alcohol intakeincreases the endogenous b-endorphin levels (De Waele &Gianoulakis, 1994; Gianoulakis, 1990), which has beenpostulated to produce the rewarding effects of alcohol(Gianoulakis, 1996; Gianoulakis et al., 1996). Taking intoaccount these data, it is possible that estrogens couldinitially produce a decrease in the alcohol consumption dueto a low availability of opioid receptors as a consequence oftheir increased internalization, which would decrease thealcohol rewarding effects. As estrogen treatment pro-gresses, the surge of opioid receptor upregulation wouldincrease the receptor availability, enhancing the rewardingeffects of alcohol and producing an increase in itsconsumption. However, the possible changes in alcoholconsumption could be attenuated if alcohol is continuouslyoffered in both conditions: when initially alcohol has lowrewarding effects and afterward when the rewardingproperties are increased in the course of time during theestrogen treatment. In other words, the recent experience ofa low alcohol intake, which is related to a low reinforcingeffect of alcohol, could affect the subsequent liking foralcohol. Therefore, the changes in alcohol consumptionwould be more evident if alcohol is offered in differentstages of the estrogen treatment instead of throughout. Onthe basis of above mentioned data, we show that the scopeof this study was to give experimental support to dual andopposing effects of estrogen on alcohol consumption,which would depend on the hormonal status at the momentin which alcohol is offered.

2. Materials and methods

Male Wistar rats were obtained from a colony bred inthe Institute of Neurociencias, Universidad de Guadalajara.Subjects were maintained on a 12–12-h light–dark cycle,lights on at 8:00 a.m., and water and food pellets availablead libitum. Temperature, feeding, and light–dark cycleconditions were maintained constant in the course of thestudy.

Males belonging to different litters were housed ingroups of 4, each aged from weaning to 75 days. Malesaged 76–79 days were surgically castrated under pentobar-bital anesthesia (35 mg/kg) and a period of at least 10 daysof recuperation was permitted after the surgical procedure.

Subjects were housed in individual cages with food andwater ad libitum. Alcohol was not available during thispostsurgical period. The testes were removed to eliminatethe main endogenous source of sexual hormones andminimize the conversion from androgens to estrogens.

2.1. Alcohol consumption in the pretreatment period

At 90 days of age, 27 castrated male rats were exposedto alcohol under a free-choice drinking procedure: twobottles were placed in the cages, one containing tap waterand the other a solution of water plus ethanol (MERCK,Darmstadt, Germany). The initial concentration of alcoholpresented was 2% vol/vol and it was increased by 2% everyother day until a final concentration of 10% vol/vol wasreached. One week of continuous free-choice drinkingprocedure with alcohol at 10%, 24 h/day was permitted forhabituation purposes and the following 6 days were used toestablish the baseline alcohol intake before hormonaltreatment (PreT). Consumption of alcohol, water, and foodwas measured every 24 h. Rats were ordered by hierarchyconsidering their baseline alcohol intake and alternatelyassigned to three groups of 9 each. This procedure was donewith the purpose of having similar values of alcohol intakebefore hormonal treatment in rats of the three groups.

2.2. Hormonal and vehicle treatment

Forty-eight hours after the baseline period, one group of9 rats were injected subcutaneously with 0.05 ml of cornoil/day/rat from days 1 to 6 and 5 mg of estradiol benzoate(E)/day/rat from days 7 to 12 (group OE). A second groupof 9 males were injected subcutaneously with 5 mg ofE/day/rat from days 1 to 6 and 0.05 ml of corn oil/day/ratfrom days 7 to 12 (group EO). The males of the third groupwere injected subcutaneously with 5 mg of E/day/rat fromdays 1 to 12 (group EE). The rats of the three groups werenot exposed to alcohol during days 1–6 (T1) regardless oftheir treatment with E or oil. Afterwards, a bottle withethanol 10% was added in each cage from days 7 to 18;therefore, the rats were exposed to free-choice drinking ofalcohol and water, a method similar to that performed in thepretreatment period. In each group, the rats were undereither E or oil treatment from days 7 to 12 (T2) aspreviously indicated, and days 13–18 were recorded toassess alcohol intake in the post-treatment period (PosT).The three groups of rats had free access to food and waterthroughout the study. Consumption of alcohol, water, andfood was measured every 24 h and body weight wasrecorded three times a week.

2.3. Statistical analyses

A mixed three-way ANOVA [treatment as a groupingfactor (OE, EO, and EE) 3 period (PreT, T2, and PosT) 3days as a repeated measure in each period (days 1–6)] wasperformed for alcohol consumption (T1 was not considered

57J. Juarez et al. / Alcohol 36 (2005) 55–61

in this analysis because alcohol was not available in thisperiod). Taking into account the means in each 6-dayperiod/animal, food intake was analyzed through a mixedtwo-way ANOVA [treatment as a grouping factor (OE, EO,and EE) 3 period as a repeated measure (PreT, T2, andPosT)] and T1 was added in the period factor in thisanalysis. Change in the body weight was calculated forevery subject in each period by dividing the differencebetween the body weight measured at the start and thatmeasured at the end by the number of days in that period.These body weight data were analyzed through a mixedtwo-way ANOVA [groups (OE, EO, and EE) 3 periods(PreT, T1, T2, and PosT)]. Duncan’s post hoc test was usedto compare pairs when the main effects or interactions ofANOVA were significant. A p value of #0.05 wasconsidered statistically significant.

Procedures involving the use and care of animals in thisstudy were performed in accordance with the Guide for theCare and Use of Laboratory Animals (Institute ofLaboratory Animal Resources, Commission on LifeSciences, National Research Council, 1996).

3. Results

3.1. Alcohol consumption

Three-way ANOVA for alcohol consumption in (g/kg ofbody weight) indicated the following significant differ-ences: between treatments [F(2,24) 5 4.33, p5 .024];between periods [F(2,48) 5 11.14, p5 .0001]; interaction,treatment 3 periods [F(4,48) 5 11.73, p! .0001]; betweendays [F(5,120) 5 6.74, p! .0001]; interaction, periods 3

days [F(10,240) 5 3.0, p5 .0014]; and interaction, treat-ment 3 periods 3 days [F(20,240) 5 1.95, p5 .01]. Toavoid redundancy and description of irrelevant compar-isons, only the relevant significant differences are de-scribed: Treatment main effect showed that alcoholconsumption was higher in the EO than in the OE groupregardless of period and days. The treatment 3 periodsinteraction indicated higher alcohol consumption in the oilperiod (T2) after the estrogen treatment in the EO groupthan in the PreT, T2, and PosT periods as much in the OE asin the EE group (Fig. 1). At the same time, the alcoholintake in the T2 period was higher than in the PreT andPosT of the EO group. Contrarily, alcohol consumption inthe estrogen period (T2) after the oil treatment wassignificantly lower than in the PreT of the OE group andthe estrogen period (T2) of the EE group (Fig. 1). At thesame time, alcohol intake in the PosT was lower than in thePreT of the OE group. Alcohol consumption in the secondhalf of the estrogen treatment (T2) was significantly higherthan in the PreT and the PosT of the EE group and the PosTof the OE group. Alcohol intake in the PosT of the EOgroup was higher than in T2 and PosT of the OE group(Fig. 1).

The treatment 3 periods 3 days interaction indicated thatthe highest values of alcohol consumption in the EO groupwere observed in the first 2 days immediately after the Etreatment; afterward, the alcohol intake decreased graduallyuntil it reached, on the sixth day of this period (T2), a valuesimilar to that observed in the PreT period (Fig. 1). Thisphenomenon is supported by the significantly higheralcohol consumption on days 1, 2, 3, and 4 than on days5 and 6 of the T2 period in the EO group. It is remarkablethat the values of alcohol consumption on the first 3 days ofT2 in the EO group were almost three-fold higher than thebaseline values (PreT) of this group. This increase washigher than that observed on any other day of any period inthe OE and EE groups, except in comparison between thethird day of T2 in the EO group and the first day of T2 inthe EE group (Fig. 1). Similar to that observed in the EOgroup, alcohol intake tended to decrease gradually fromdays 1 to 6 in the EE group; in this case, the consumptionon day 1 was significantly higher than on days 4–6. Incontrast, the values of alcohol consumption during the Eperiod of the OE group were consistently low across thedifferent days.

3.2. Food intake

Analysis of food intake was performed taking intoaccount the differences between the mean of food intake ineach period (T1, T2, and PosT) and the mean of food intakeon the 6 days corresponding to the pretreatment period(baseline). The mixed two-way ANOVA [treatment (OE,EO, EE) 3 period (T1, T2, PosT)] showed significant periodeffect [F(2,48) 5 13.16, p! .0001] and the post hocanalyses indicated lower food intake in T1 and T2 than inPosT regardless of group. The treatment 3 periods in-teraction [F(4,48) 5 6.0, p5 .0005] indicated (based on

0

1

1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

2

3

4

5

6

Days

Alco

hol i

ntak

e (g

/kg)

OEEOEE

PreT T2 PosT

Fig. 1. Daily voluntary alcohol consumption (g/kg) during the pre-

treatment period (PreT), the oil or estrogen treatment (E) when alcohol was

available (T2), and the post-treatment period (PosT) in the groups OE [6

days of oil (T1) followed by 6 days of E (T2)], EO [6 days of E (T1)

followed by 6 days of oil (T2)], and EE [6 days of E (T1) followed by 6

days of E (T2)]. T1 is not shown because alcohol was not offered in this

period. Bars show the mean (6SEM).

58 J. Juarez et al. / Alcohol 36 (2005) 55–61

follow-up analyses) lower food intake during all periods ofestrogen treatment (T1 in EA and EE group; T2 in OE andEE group) than during the oil treatment (T1) in the OEgroup and the PosT periods of the EO and EE groups.Additionally, food intake during the estrogen treatment(T2) was lower than in the PosT of the OE group and the T2of the EO group (Fig. 2).

3.3. Body weight

Variation in the body weight (BW) was calculated foreach rat by dividing the difference between the body weightmeasured at the beginning and that at the end of each studyperiod by the number of days in that period. These datawere analyzed by a mixed two-way ANOVA [treatment(OE, EO, and EE) 3 period (PreT, T1, T2, and PosT)].Significant differences in body weight between periodswere found [F(3,72) 5 77.59, p! .00009] and the post hocanalyses showed that body weight was higher in the(1) PreT period than in the T1, T2, and PosT periods;(2) PosT period than in the T1 and T2 periods; and(3) T1 period than in the T2 period, regardless of group.The groups 3 periods interaction was significant [F(6,72) 518.72, p! .00009] and the follow-up analyses indicateda decrease in body weight during the periods under estrogentreatment of each group, compared with any other periodwithout estrogen treatment. This decrease in BW occurredregardless of the treatment applied in T1 of the EO group,T2 of the OE group, and T1 and T2 of the EE group(Fig. 3). A recovery in the body weight was observed in theperiods subsequent to the estrogen treatment of each group

-5

-4

-3

-2

-1

0

1

2

3

Fo

od

in

ta

ke

(g

)

(d

iffe

re

nc

e in

re

sp

ec

t o

f th

e b

as

e lin

e)

OE

EO

EE

*

+

*

T1 T2 PosT

**

Fig. 2. Food intake in the oil or estrogen (E) treatments when alcohol was

not available (T1), the oil or estrogen treatments when alcohol was

available (T2), and the post-treatment period (PosT) in the groups OE

[6 days of oil (T1) followed by 6 days of E (T2)], EO [6 days of E (T1)

followed by 6 days of oil (T2)], and EE [6 days of E (T1) followed by 6

days of E (T2)]. Bars show the mean (6SEM) of the differences between

the food intake in each period and the food intake during the pretreatment

period. * ! T1 of OE; PosT of EO; PosT of EE; 1 ! PosT of OE; T2 of

EO.

(T2 in the EO and PosT in the OE and EE groups);however, the body weight gain was significantly lower inthese periods following the estrogen treatment than in thePreT periods of each group, respectively.

4. Discussion

The exposure to alcohol in different stages of theestrogen treatment showed clear differences between groupsand produced opposite effects on alcohol consumption.When rats were exposed to alcohol immediately after 6 daysof oil treatment and during 6 days of estrogen treatment,alcohol intake decreased significantly with respect to thebaseline values, supporting the results of previous studies(Juarez et al., 2002; Messiha, 1981). On the contrary, whenrats were exposed to alcohol immediately after 6 days ofestrogen treatment and during 6 days of oil treatment,alcohol consumption increased by more than two-fold incomparison to the baseline levels. The observed values ofalcohol intake in this group are rarely found in rats that havenot been selected for their preference of alcohol. Finally,when the animals were treated with estrogens for 12 daysand exposed to alcohol from days 7 to 12 of this treatment,alcohol intake was significantly increased with respect to thebaseline values. However, this increase was significantlylower than that seen in the corresponding period (T2) of theEO group, in which the only difference was the substitutionof the oil treatment for estrogen treatment from days 7 to 12.

-5

-4

-3

-2

-1

0

1

2

3

4

5

Ch

an

ge

in

th

e b

od

y w

eig

ht (g

)

OE

EO

EE

*

+

+

PreT T1 T2 PosT

**

*

+

Fig. 3. Changes in the body weight (BW) in the pretreatment period

(PreT), the oil or estrogen (E) treatments when alcohol was not available

(T1), the oil or estrogen treatments when alcohol was available (T2), and

the post-treatment period (PosT) in the groups OE [6 days of oil (T1)

followed by 6 days of E (T2)], EO [6 days of E (T1) followed by 6 days of

oil (T2)], and EE [6 days of E (T1) followed by 6 days of E (T2)]. Bars

show the mean (6SEM) of the change in body weight (BW) in grams. This

change was calculated taking into account the differences between the BW

measured at the beginning of each period and that measured at the end of

the same period divided by the number of days in that period. * ! All

periods without estrogens; 1 ! the corresponding PreT period of each

group, and O the corresponding E period of each group.

59J. Juarez et al. / Alcohol 36 (2005) 55–61

These results show that estrogen treatment can producedifferent and opposite effects on alcohol consumptiondepending on the biological conditions that arise because ofthe temporary course of the hormonal treatment. Thesebiological conditions seem to coincide with severalmechanisms in which the opioid system is involved. It iswell documented that the estrogen treatment produces anincrease in the internalization of mu-opioid receptors(Eckersell et al., 1998; Micevych et al., 1997, 2003;Sinchak & Micevych, 2003). On the other hand, it hasbeen described that alcohol intake increases the endoge-nous b-endorphin levels (De Waele & Gianoulakis, 1994;Gianoulakis, 1990), activating delta-opioid and mu-opioid receptors that seem to play an important role inthe rewarding effects of alcohol (Gianoulakis, 1996;Gianoulakis et al., 1996). Therefore, the decline in alcoholintake during the estrogen treatment in the OE group couldbe due to the reduced availability of mu-opioid receptors asa consequence of its increased internalization, which wouldreduce the rewarding properties of alcohol. This reductionin the receptor availability would be similar to thatobserved during the blockage of opioid receptors by opioidantagonists such as naloxone or naltrexone with similarconsequences in alcohol consumption, i.e., it has beenamply described that naltrexone treatment decreasesalcohol intake in rats (Coonfield et al., 2002; Gardellet al., 1996; Parkes & Sinclair, 2000), monkeys (Williamset al., 2001; Williams & Woods, 1999), and humans(Guardia et al., 2002; Romach et al., 2002).

It is well known that low receptor availability producesshort-term receptor upregulation in male rats (Parkes &Sinclair, 2000); in this sense, there is evidence thathormonal priming of ovariectomized rats with estrogenand progesterone produces mu-receptor upregulation(Hammer et al., 1994) and it has been described anincrease in mu-opioid receptor mRNA levels in hypothal-amus, 48 h after a single injection of estradiol in females(Quinones-Jenab et al., 1997). Therefore, the increase inalcohol consumption observed after 6 days of estrogentreatment in the EO and EE groups could be explained bythe subsequent opioid receptor upregulation after the initialestrogen-induced opioid receptor internalization. Takinginto account that alcohol intake increases the b-endorphinlevels (De Waele & Gianoulakis, 1994; Gianoulakis, 1990),the upregulated opioid receptors should increase therewarding properties of alcohol and therefore, increasethe alcohol intake as indeed occurred in these two groups.

After 6 days of estrogen treatment we observed twodifferent effects on alcohol intake: a large increase in thealcohol consumption in the EO group and a significant butmoderate increase in the EE group. The difference in themagnitude of increase in this last group could be explainedin the following terms: notwithstanding the increasedavailability of the upregulated opioid receptors, the in-ternalization of these receptors induced by estrogens wouldpersist when the hormonal treatment is maintained in the

EE group; therefore, a proportion of the available receptorswould be inactive and then the net availability attenuated,which finally would produce a moderate increase in alcoholconsumption.

Taking into account the hormonal treatment, the PosTperiod in the OE group would be equivalent to the T2period in the EO group because in both periods alcoholintake is assessed after 6 days of estrogen treatment;however, in the EO group alcohol was not offered duringthe E treatment, but was in the OE group. The differenteffects on the alcohol intake observed in these groups afterthe E treatment support the notion that the experience ofa low alcohol intake related to a low rewarding effect, whenalcohol exposure and E treatment are initiated at the sametime, could affect the subsequent liking for alcohol,notwithstanding the supposed upregulation of opioidreceptors in both cases.

It has been described that 8 days of naltrexone treatmentproduces opioid receptor upregulation; afterward, thenumber of these receptors declines gradually recoveringthe baseline levels 5 days after the opioid antagonisttreatment has been interrupted (Parkes & Sinclair, 2000). Inthis study, the gradual decrease in alcohol consumptionafter the estrogen period in the EO group could suggestrecovery in the number of opioid receptors similar to thatdescribed with the opioid antagonist treatment, because thealcohol intake showed the highest values in the first daysafter the estrogen treatment, supposedly when the opioidreceptors are upregulated. Later the alcohol consumptiongradually declined until it reached the baseline values onthe sixth day, when, in accordance with the literature(Parkes & Sinclair, 2000), the opioid receptors haverecovered to the baseline values.

Estrogen treatment produced a decrease in food intakeand body weight, which gradually recovered to the initialvalues on completion of the hormonal treatment. Theseeffects occurred in the three groups regardless of theestrogen being administered during 6 or 12 days and beforeor after the oil treatment. Anorexic effects with the estrogentreatment were not surprising because it has been pre-viously described in female (Butera et al., 1990, 1996;Dagnault et al., 1993; Donohoe & Stevens, 1982; Donohoeet al., 1984; Sandberg et al., 1982; Varma et al., 1999) andmale rats (Juarez et al., 2002). This decrease in food intakeseems to be mediated by the action of estrogens on thehypothalamus (Butera et al., 1990, 1996; Donohoe &Stevens, 1982), apparently involving an increase in thesatiety effect of cholecystokinin (Butera et al., 1996). Theanorexic effect of estrogens was reversed when thehormonal action ceased and the food intake recoveredfaster in the PosT period of the EE group than in thecorresponding period of the other two groups. Taking intoaccount that the EE group had a longer E treatment andtherefore a longer anorexic effect, this finding is probablyrelated to the defense of the body weight set point, which isa well-known homeostatic resource across the species.

60 J. Juarez et al. / Alcohol 36 (2005) 55–61

Another possible explanation could be related with differ-ences in the regulation of the opioid receptors due toa longer exposure to estrogens in the EE group.

It is well known that adrenals also synthesize androgens,i.e., dehydroepiandrosterone and androstenedione, whichcan be converted to testosterone or estrogens; however, lessthan 5% of the overall production of plasma testosterone isof adrenal origin. Therefore, the possible influence of theadrenal androgens in the present results would benegligible. As far as we know there is no evidence thatother gonadal hormones such as activin or inhibin, whichwere removed in the castrated animals, have any influenceon drinking behavior.

This study reveals opposite effects of the estrogentreatment on alcohol consumption, which apparentlydepended on the physiological conditions produced by thetemporal course of the hormonal treatment. There issufficient evidence in the literature suggesting thatmechanisms linked to the opioid system can be involvedin the results presented in this study, unfortunately thestudies directed to analyze the action of sexual hormoneson alcohol consumption are very scarce, and the specificmechanisms involved in the effect of estrogens on alcoholconsumption remain to be studied. On the other hand,present results showed that sex hormones could play animportant role in addictive behavior, which acquireadditional relevance considering that sex hormones arepresent in the organism throughout the reproductive lifespan.

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