Effect of L-5-Hydroxytryptophan on drinking behavior in Coturnix japonica (Temminck and Schlegel, 1849) (Galliformes: Aves): involvement of renin-angiotensin system.

Abstract

The purpose of this study was to explore the role of L-5-hydroxytryptophan (L-HTP) and its relationship with the renin-angiotensin system (RAS) on the drinking behavior in Japanese quails. Normally-hydrated quails that received injections of L-HTP (12.5; 25 and 50 mg.kg-1) by the intracoelomic route (ic) expressed an increase in water intake, which was inhibited by captopril, an angiotensin converting enzyme (ACE) inhibitor. In addition, captopril also induced such a response in birds under previous fluid deprivation. High doses of captopril (35-70 mg.kg-1, sc) in normally-hydrated quails decreased the spontaneous water intake while low doses of captopril (2-5 mg.kg-1, sc) did not prompt water intake after L-HTP administration. Losartan, an AT1 receptor antagonist in mammals, did not change the water intake levels in normally-hydrated or water-deprivated birds. Serotonin (5-HT) injections did not provoke its known dipsogenic response.

Full text

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Braz. J. Biol., 67(4): 771-776, 2007
771
Effect of L-5-Hydroxytryptophan on drinking behavior in
Coturnix japonica (Temminck and Schlegel, 1849) (Galliformes: Aves):
Involvement of renin-angiotensin system
Cedraz-Mercez, PL., Almeida, AC., Thomaz, CM., Costa-e-Sousa, RH.,
Olivares, EL., Côrtes, WS., Medeiros, MA. and Reis, LC.*
Departamento de Ciências Fisiológicas, Instituto de Biologia, Universidade Federal Rural do Rio de Janeiro – UFRRJ,
BR 465, Km 07, CEP 23890-000, Seropédica, RJ, Brazil
*e-mail: lcreis@ufrrj.br
Received March 14, 2006 – Accepted April 27, 2006 – Distributed November 30, 2007
(With 4 figures)
Abstract
The purpose of this study was to explore the role of L-5-hydroxytryptophan (L-HTP) and its relationship with the renin-
angiotensin system (RAS) on the drinking behavior in Japanese quails. Normally-hydrated quails that received injections
of L-HTP (12.5; 25 and 50 mg.kg-1) by the intracoelomic route (ic) expressed an increase in water intake, which was
inhibited by captopril, an angiotensin converting enzyme (ACE) inhibitor. In addition, captopril also induced such a re-
sponse in birds under previous fluid deprivation. High doses of captopril (35-70 mg.kg-1, sc) in normally-hydrated quails
decreased the spontaneous water intake while low doses of captopril (2-5 mg.kg-1, sc) did not prompt water intake after
L-HTP administration. Losartan, an AT1 receptor antagonist in mammals, did not change the water intake levels in nor-
mally-hydrated or water-deprivated birds. Serotonin (5-HT) injections did not provoke its known dipsogenic response.
Keywords: drinking behavior, renin-angiotensin system, L-5-hydroxytryptophan, thirst, Coturnix japonica.
Efeito do l-5-hidroxi-triptofano no comportamento dipsogênico em Coturnix japonica
(Galliformes: Aves): Envolvimento do sistema renina-angiotensina
Resumo
O objetivo deste estudo foi investigar a influência do L-5-hidroxitriptofano (L-HTP) e sua relação com o sistema
renina-angiotensina (SRA) no comportamento dipsogênico de codornas. Codornas normohidratadas que receberam
L-HTP em diferentes doses (12,5; 25 e 50 mg.kg-1) por via intracelomática (ic) expressaram um aumento na ingestão
de água, o qual foi suprimido pela administração prévia de captopril (inibidor da ECA-enzima conversora de angio-
tensina). Esta ação inibitória do captopril, em menor intensidade, foi também evidenciada em aves previamente sub-
metidas ao jejum hídrico. O tratamento isolado com captopril (35-70 mg.kg-1) reduziu consideravelmente a ingestão
espontânea de água em codornas normohidratadas, enquanto baixas doses (2-5 mg.kg-1) não provocaram aumento na
ingestão de água induzida pelo L-HTP. Losartan, um antagonista de receptores AT1 em mamíferos, não foi capaz de
modificar os níveis de ingestão hídrica, tanto em aves normohidratadas quanto em aves privadas de água. Serotonina
aplicada perifericamente não promoveu a conhecida resposta dipsogênica de mamíferos.
Palavras-chave: comportamento dipsogênico, sistema renina-angiotensina, L-5-hidroxitriptofano, sede, Coturnix
japonica.
1. Introduction
Osmoregulation is dependent on drinking behavior
that is evoked when angiotensin II (ANG II), a phyloge-
netic ubiquitous octapeptide, acts on ANG II receptors in
the subfornical organ (SFO) (Fitzsimons, 1998; Antunes-
Rodrigues et al., 2004). Increase in the circulating ANG
II levels is the outcome of a reduction either blood vol-
ume or sodium plasma levels which induce renal renin
secretion. Renin secretion is also modulated by sympa-
thetic-adrenergic transmission through the β-adrenergic
receptors activation of the juxtaglomerullar cells located
in the renal afferent arterioles and jointly influenced by
the macula densa, juxtaglomerullar apparatus and me-
sangial cells (Fitzsimons, 1998).

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Cedraz-Mercez, PL. et al.
Braz. J. Biol., 67(4): 771-776, 2007
772
in mammals with those reached in quails, we intend to
appraise the influence of L-HTP administration on wa-
ter intake in different experimental paradigms. Initially,
we will investigate the drinking response pattern after
L-HTP administration. In these conditions, it is known
that this amino acid induces serotonin brain synthesis
and decreases solid food ingestion (Reis et al., 2005).
Therefore, we investigated the role of its administration
on water intake in normally-hydrated birds. To assess
the role of ANG II in L-HTP-induced drinking behav-
ior, quails were given the angiotensin converting enzyme
(ACE) inhibitor, captopril treatment. In addition, a previ-
ous objective is to research if ACE of quails is responsive
to captopril, considering that such a protein can be dis-
tinct from that found in mammals. Furthermore, we ex-
amine the contribution of ANG II receptors on drinking
behavior through losartan (ANG II receptor antagonist)
treatment. The drinking action hypothesis of the capto-
pril treatment in low doses added to food and combined
with the L-HTP injection, was also examined. Finally,
we verify the 5-HT drinking behavior in Japanese quails
as prior evidence in pigeons (Brun, 2001).
2. Materials and Methods
2.1. Animals and housing
Male quails (Coturnix japonica) weighing 120-150 g
(3-4 months old) were used in this study and kept in indi-
vidual cages at 27 ± 3 °C with 12 h of light and 12 hours
of darkness. Food (Natural Line-Purina®) and water were
available in metal food containers and plastic graduate
bottles, respectively.
2.2. General and experimental procedures
Male quails weighing 120-150 g were randomly se-
lected from a larger group of animals kept in the labora-
tory under the same temperature conditions (25 ± 5 °C),
lighting cycle (12/12, light/dark) and feeding conditions
(quail chow and distilled water ad libitum). Quails were
housed in individual small wire cages, where the birds
were trained for more than one week to drink from the
graduate plastic tubes. All protocols and evaluations
were performed during the light period (7:00 AM up to
7:00 PM)
A subcutaneous injection (sc) was applied in the dor-
sum, between the two wings, and an intracoelomic injec-
tion (ic) into the thoracic-abdominal-pelvic cavity was
made at a 45º angle in the medium quadrant of the pelvic
wall, both with a 1 mL syringe, attached to a 1 cm long
needle with a 25-gauge diameter. A control group was
included in each experimental protocol where the birds
received injections of saline solution (1 mL.kg-1).
Evaluation of the ingestion of fluids in normally
hydrated quails was carried out at 09:00 AM and in the
water-deprived birds was realized at 01:00 PM. Water in-
take was expressed in mL/bird during 5 hours at 60 min-
utes intervals.
Beyond this physiological stimulus that increases
ANG II production, other peripheral signals (e.g., vis-
cerosensory and humoral) that could induce thirst and,
subsequently, water intake, are still unknown. There are
few reports concerning the peripheral signals which in-
duce water intake in birds (Kraly, 1990; Anderson and
Houpt, 1992; Fitzsimons, 1998). Comparative studies
reveal that serotonin (5-HT) evokes opposite responses
on water intake in birds and mammals (Reis et al., 1990;
Reis et al., 1992; Da Silva et al., 2004; Häckl et al.,
2005). Pigeons exhibit drinking behavior when sero-
tonin (5-HT) is centrally, but not systemically applied,
because such response seems to be mediated by angi-
otensinergic circuits (Steffens et al., 1997; Brun et al.,
2001). Indeed, there are few results that reveal 5-HT and
5-hydroxytryptophan (L-HTP) as initiators of drinking
behavior induced by the renin release mechanism and
further increase of ANG II systemic levels (Fregly et al.,
1980; Kikta et al., 1981; 1983; Rowland et al., 1987;
Fitzsimons, 1998). Thus the brain renin-angiotensin sys-
tem (RAS), like a final pathway for thirst, receives sev-
eral inputs from other neurotransmitters systems.
Serotonergic neurons that were among the first to
develop (Jacobs and Fornal, 1999) conserve the same
anatomy among vertebrates, with neurons in or near the
midbrain midline, implying that interrelations between
serotonergic neurotransmission and behavior were
maintained during evolution (Parent, 1981; Kah and
Chambolle, 1983; Ueda et al., 1984; Meek and Joosten,
1989; Ayala-Guerrero et al., 1991; Cozzi et al., 1991).
During ontogenetic development, brain serotonergic
neurons play an important role facilitating primary mo-
tor function and coordinating autonomic and neuroendo-
crine functions which are implicated to specific behavior.
Behavior, such as drinking and feeding are constantly
monitored by 5-HT-containing neurons in mammals and
birds. Studies in our laboratory evidenced the seroton-
ergic neurons influence in the sodium appetite and food
and water intake behavior (Badauê-Passos Jr et al., 2003;
Olivares et al., 2003; Lima et al., 2004; Cavalcante-Lima
et al., 2005a,b; Reis et al., 2005; Reis and Marinho, 2005;
Cedraz-Mercez et al., 2005; Medeiros et al., 2005). In
rats, peripheral administration of either 5-HT or its pre-
cursor 5-HTP induces water intake via renal renin-angi-
otensin system (RAS) activation (Rowland et al., 1987),
however they display opposed effects when centrally
applied. Besides, the dorsal raphe nucleus, an important
midbrain 5-HT system, maintains reciprocal interactions
with specific thirst inducer areas, such as the subfornical
organ (SFO) (Tanaka et al., 2003). In birds, 5-HT as well
as L-HTP arouses hypophagy and increased water intake
(Denbow, 1989; Brun et al., 2001; Reis et al., 2005).
The purpose of this study was to further physiologi-
cal correlations among relative data for mammals and
other birds with the evidence obtained herein. In stud-
ies realized in our laboratory we observed a drinking
response induced for L-HTP intracoelomic administra-
tion. To examine the correlations among gained response

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Drinking behavior in Coturnix japonica
Braz. J. Biol., 67(4): 771-776, 2007
773
When adequate a post hoc test of Dunnet was applied
after ANOVA. Analysis inside of groups was realized us-
ing the Student “t” parametric test. Values were signifi-
cantly different when P < 0.05.
3. Results
The L-HTP administration induced a powerful
drinking response in normally-fed and -hydrated quails
(Figure 1). At higher doses of L-HTP, dipsogenic re-
sponse was still observed in spite of hypnogenic ac-
tion induced for L-HTP. After 120 minutes all the birds
treated with L-HTP ingested a water volume over 9.4 ±
1.4 mL whereas birds from the control group did not in-
gest over 5.9 ± 0.67 mL (p < 0.05). The isolated treat-
ment with captopril decreased the water intake in nor-
mally-hydrated quails (120 minutes, 3.41 ± 0.37 mL vs.
control, 6.1 ± 0.47 mL, p < 0.05) (Figure 2a). Previous
treatment with captopril in high doses inhibited the intake
response induced by L-HTP to levels below the controls
(6.17 ± 1.04 mL vs. control, 11.6 ± 1.0 mL; 300 minutes)
(p < 0.05) (Figure 2b). Previous administration of a low-
er captopril dose did not modify the drinking response
induced by L-HTP (Figure 3). Lastly, the 5-HT injection
was unable to stimulate water intake (Figure 4).
4. Discussion
The present study evidenced L-HTP as a powerful
stimulus for thirst in the Japanese quail. The drinking
response induced by L-HTP had an angiotensinergic
component inasmuch the captopril powerfully inhibited
the hyperdipsetic response. In addition, the dipsogenic
response provoked by the ACE inhibitor was less than
that from the baseline, indicating that water intake in
these birds is dependent on high ANG II plasma levels.
Probably water intake, in baseline conditions, needs sys-
temic ANG II synthesis from unknown peripheral sig-
nals. In mammals, the main peripheral signals are his-
tamine, insulin and gastrin (Kraly, 1990; Anderson and
Experiment 1. Influence of L-HTP administration
on the water intake in normally- hydrated quails
In this condition normally-hydrated quails received
L-HTP by ic injections in 12.5; 25 and 50 mg.kg-1 doses
(N = 12 for each group) for water intake evaluation as
similarly described in mammals (Fregly et al., 1980;
Kikta et al., 1981; Rowland et al., 1987). The control
group was treated with isotonic saline (1 mL.kg-1, ic,
N = 12). After injections, the quails were immediately
housed in cages.
Experiment 2. Effect of captopril administration
(35 mg.kg-1) in the spontaneous water intake in normally
hydrated quails
Normally-hydrated quails (N = 12) were treated with
captopril (35 mg.kg-1, sc), to evaluate the influence of
peripheral and central ACE inhibition, as employed in
mammals (Elfont et al.,1984; Fregly and Rowland, 1985;
Fitzsimons, 1998) on spontaneous water intake. The
control group (N = 12) was treated with isotonic saline.
Birds had free access to the water after injection.
Experiment 3. Effect of the previous captopril ad-
ministration on water intake induced by L-HTP in nor-
mally-hydrated quails
Two bird groups treated with a dipsogenic dose of
L-HTP (25 mg.kg-1, ic) were previously treated (before
30 minutes) with isotonic saline (1 mL.kg-1, sc, N = 12)
or captopril (35 mg.kg-1, sc, N = 12) to evaluate the influ-
ence of the ACE inhibition in drinking response elicited
by L-HTP. Water was presented just after L-HTP injec-
tion.
Experiment 4. Effect of the previous injection of a
low dose of captopril in water intake induced by L-HTP
in normally-hydrated quails
In this study, quails treated with L-HTP (25 mg.kg-1,
ic) were previously treated (30 minutes before) with
captopril (0.5 and 2 mg.kg-1, sc, N = 12 for each group)
to evaluate the influence of the peripheral ACE inhibi-
tion on the dipsogenic response as witnessed in mam-
mals (Elfont et al., 1984; Fregly and Rowland, 1985;
Fitzsimons, 1998). In this situation an increase in ANG I
plasma levels occurs and subsequent increased brain
availability at the time ANG II takes place. The control
group (N = 12) was treated with saline (1 mL.kg-1, sc)
and L-HTP (25 mg.kg-1, ic). Water was presented after
the L-HTP injection.
Experiment 5. Influence of 5-HT (serotonin) ad-
ministration on spontaneous water intake.
In this study 5-HT was administrated in different
doses (0.125; 1.25 and 2.5 mg.kg-1, sc, N = 12 for each
group) in normally-hydrated quails to evaluate the drink-
ing response such as reported in mammals (Kikta et al.,
1983; Rowland et al., 1987). The control group was
treated with isotonic saline (N = 12). Free access to the
water was allowed immediately after injections.
2.3. Statistical analysis
The results are presented as mean ± standard error.
The analysis involving the various groups was realized
by the ANOVA test to verify the effect of the treatments.
25
20
15
10
00
60120 180240300360
5
Water intake (mL)
Minutes after water presentation
Controls
L-HTP 12.5
L-HTP 25
L-HTP 50
Figure 1. Effect of the serotonin precursor treatment
(L-HTP 12.5, 25 and 50 mg.kg-1, ic, N = 12 for each group)
on water intake of normally-hydrated quails. Data represent
mean ± SE. *P < 0.05 compared with controls (N = 12).

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Cedraz-Mercez, PL. et al.
Braz. J. Biol., 67(4): 771-776, 2007
774
Although mild, water intake inhibition possibly repre-
sents the suppression of the homeostatic mechanisms
displayed during water deprivation, in addition to the os-
motic drinking signals (Fitzsimons, 1998). The hypodip-
sia induced by captopril, in quails, is probably related
to the central and peripheral ACE inhibition which can
support distinct drinking mechanisms.
These results constitute the first report to demon-
strate that the quail’s ACE is responsive to captopril ac-
tion. In this condition, the ACE molecular structure of
the quails, responsible for captopril recognition, perhaps
maintains a high degree of homology, comparatively to
mammals. However, we did not obtain positive results
when we tested the dipsogenic action hypothesis of cap-
topril low doses, widely reproduced in rats (Elfont et al.,
1984; Fregly and Rowland, 1985; Fitzsimons, 1998).
According to that hypothesis, a low dose of captopril
inhibits only peripheral ACE, which would provide in-
creased levels of serum ANG I, which centrally avail-
able, would be converted into ANG II, which is consid-
ered to be an ACE isoform in brain dipsogenic structures
such as SFO. It seems that this mechanism did not occur
in Japanese quails.
The systemic treatment with losartan, an AT1 antago-
nist in mammals, did not change the drinking behavior
in normally-hydrated quails as well as those under water
deprivation.
In pigeons, losartan, administrated by the intracer-
ebroventricular (icv) route, did not provoke a blockade
of the dipsogenic response induced by 5-HT (Brun et al.,
2001). Losartan applied in quails under water depriva-
tion for 6 hours did not change the water and 0.9% NaCl
intake levels. However, losartan treatment in quails under
water and food deprivation for 6 hours induced a com-
plete suppression of the water and salt intake response
for a long period (Cedraz-Mercez et al., 2006).
On the other hand, we cannot attain the 5-HT hyper-
dipsetic response described in rats (Fregly et al., 1980;
Water intake (mL)
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Minutes after water presentation
Figure 2. Effect of the pure captopril (35 mg.kg-1, sc,
N = 12; a) treatment or captopril treatment before L-HTP
(25 mg.kg-1, ic, N = 12; b) administration on water intake
of normally-hydrated quails. Captopril injections were car-
ried out immediately before free water access (a) or 30 min
before L-HTP injections (b) Data represent mean ± SE.
*P < 0.05 compared with controls (N = 12).
15
10
5
00
60120180240300360
Capto
injection
a
Water intake (mL)15
10
20
5
0
0 60120 180240300360
Capto
injection
b
L-HTP 25
L-HTP 25 + Capto 35
Controls
Controls
Capto 35
*
*
*
*
*
*
*
*
L-HTP 25 + Capto 0.5
L-HTP 25 + Capto 2
Minutes after water presentation
Figure 3. Effect of low dose captopril treatment on L-HTP-
induced drinking in normally-hydrated quails. Captopril
(0.5 and 2.0 mg.kg-1, sc, N = 12) injections were carried
out 30 minutes before L-HTP (25 mg.kg-1, ic, N = 12) treat-
ment. Data represent mean ± SE. *P < 0.05 compared with
controls (N = 12).
Water intake (mL)
15
10
5
0
0 60 120180240300360
Controls
L-HTP 25
Capto
injection
*
*
*
*
*
*
*
*
00
60120180240300360
Minutes after water presentation
14
12
10
8
6
4
2
Water intake (mL)
Controls
5-HT 0.125
5-HT 1.25
5-HT 2.25
Figure 4. Influence of the 5-HT (0.125, 1.25 and 2.5 mg.kg-1,
ic, N = 12 for each group) administration in spontaneous wa-
ter intake of normally-hydrated quails. Birds had water free
access immediately after 5-HT injections. Data represent
mean ± SE. *P < 0.05 compared with controls (N = 12).
Houpt, 1992; Fitzsimons, 1998) but no evidence was
achieved in birds.
We had a similar perception with the captopril ad-
ministration in quails after water deprivation stimulus.

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Braz. J. Biol., 67(4): 771-776, 2007
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level which would change the motor pattern of the intake
response. This presumption is supported by the fact of
L-HTP having induced a copious hyperdipsetic response
simultaneously to the hypnogenic response.
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