JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY 2014, 65, 5, 659-671
www.jpp.krakow.pl
P. SOWA1,2, M. ADAMCZYK-SOWA1,3, K. ZWIRSKA-KORCZALA1, K. PIERZCHALA3,
D. ADAMCZYK2, Z. PALUCH2, M. MISIOLEK2
PROOPIOMELANOCORTIN BUT NOT VASOPRESSIN OR RENIN-ANGIOTENSIN SYSTEM
INDUCES RESUSCITATIVE EFFECTS OF CENTRAL 5-HT1A ACTIVATION
IN HAEMORRHAGIC SHOCK IN RATS
Department of Physiology, Medical University of Silesia, Zabrze, Poland; 2ENT Department, Medical University of Silesia,
Zabrze, Poland; 3Department of Neurology, Medical University of Silesia, Zabrze, Poland
1
The aim of this study was to determine the effectory mechanisms: vasopressin, renin-angiotensin system and
proopiomelanocortin-derived peptides (POMC), partaking in the effects of serotonin through central serotonin 1A receptor
(5-HT1A) receptors in haemorrhagic shock in rats. The study was conducted on male Wistar rats. All experimental
procedures were carried out under full anaesthesia. The principal experiment included a 2 hour observation period in
haemorrhagic shock. Drugs used - a selective 5-HT1A agonist 8-OH-DPAT (5 µg/5 µl); V1a receptor antagonist [bmercapto-b, b-cyclo-pentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP (10 µg/kg); angiotensin type I receptor antagonist
(AT1) ZD7155 (0.5 mg/kg, i.v.); angiotensin-converting-enzyme inhibitor captopril (30 mg/kg, i.v.); melanocortin type 4
(MC4) receptor antagonist HS014 (5 µg, i.c.v.). There was no influence of ZD715, captopril or blocking of the V1a receptors
on changes in the heart rate (HR), mean arterial pressure (MAP), peripheral blood flow or resistance caused by the central
stimulation of 5-HT1A receptors (P³0.05). However, selective blocking of central MC4 receptors caused a slight, but
significant decrease in HR and MAP (P<0.05). POMC derivatives acting via the central MC4 receptor participate in the
resuscitative effects of 8-OH-DPAT. The angiotensin and vasopressin systems do not participate in these actions.
K e y w o r d s : hypovolaemia, shock, proopiomelanocortin-derived peptides, serotonin, 5-HT1A, 8-OH-DPAT, serotonin 1A
receptor, hemorrhagic shock, vasopressin
INTRODUCTION
The total blood volume in the human body is a rather
constant value amounting to approximately 7% of the total body
mass (1). In physiological conditions this volume is regulated
primarily by hormonal mechanisms, including the effects of
arginine vasopressin, naturietic peptides, aldosterone,
angiotensin II and III and adrenal cortex glucocorticoids.
Moreover, the balance between the supply and loss of water has
a significant influence on the total body blood volume (2).
The body's response to blood loss is two-phased. In the first
phase, called the sympathoexcitatory phase, the blood pressure
is maintained within the proper range. With further blood loss
it comes to a severe drop in the arterial blood pressure and a
decrease in the heart rate, which is the beginning of the second
phase of the regulation of the circulatory system in
haemorrhagic shock, called the sympathoinhibitory phase (3).
Both phases of the circulatory regulation in haemorrhagic
shock are connected with a considerable increase in
angiotensin II and vasopressin concentration in the blood (4,
5). Vasopressin is a well known vasoconstrictive drug in the
treatment of septic shock, and this effect is connected with a
substantial decrease in the heart rate with a maintained cardiac
output. Moreover, no significant hemodynamic differences
between patients treated with vasopressin and noradrenaline
have been observed (6). Furthermore, in clinical studies it was
shown that vasopressin used together with catecholamines has
a kidney protective function compared with treatment with
catecholamines only, and has no impact on the mortality rate
(7, 8). In an experimental study it was noticed that resuscitative
effects similar to that of vasopressin are triggered by the
stimulation of the serotonergic system. Tiniakov and Scrogin
(9) have noted that the administration of 8-OH-DPAT produces
a stronger resuscitative effect than the one achieved by
vasopressin.
Although noradrenaline, other sympathomimetics and
vasopressin are broadly used in clinical treatment of shock, some
authors suggest, that the renin-angiotensin-aldosterone system
inhibition seems to be more attractive (10). Laboratory
experiments have shown that after the use of angiotensin II, AT1
and AT2 receptor antagonists and angiotensin-convertingenzyme inhibitor (ACE) a considerable decrease in blood
pressure, dependent on the type of the blocked receptor was
observed in hypovolaemia. It was noticed that this effect is
mainly dependent on the AT1 receptor (11).
There is evidence for a close link of the effects of serotonin
with the renin-angiotensin-aldesterone axis (12, 13), and
therefore their interaction in the regulation of blood circulation.
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The precise mechanism of action, however, appears to be
insufficiently understood.
In hypovolaemic animals, especially in critical
hypovolaemia, it comes to an increase in the concentration of
proopiomelanocortin derivatives - adrenocorticotropic hormone
and endorphines in the blood (14, 15). Also, well known is the
resuscitative effect of derivatives of proopiomelanocortin (16-19)
in which melanocortin type 4 receptor is the mediator (20, 21).
The aim of the following study was to determine the
effectory mechanisms, such as: vasopressin, renin-angiotensin
system and proopiomelanocortin-derived peptides (POMC),
partaking in the effects of serotonin through central 5-HT1A
receptors in haemorrhagic shock in rats.
MATERIAL AND METHODS
The study was conducted on male Wistar rats, weighing in the
range of 210–280 g. The animals were kept in metal cages, five
per cage, under the 12 hour day/night cycle, water and food ad
libitum. All experimental procedures were carried out under full
anesthesia. The lateral ventricle cannulation was performed at 5–7
days before the main experiment, using ketamine (100 mg/kg)
(Gedeon Richter, Budapest, Hungary) and ksylazine (10 mg/kg)
(Research Biochemicals Inc., Natick, MA, USA) given
intraperitoneally (i.p.). The 8 mm diameter cannule, after skin
preparation, was placed in the skull according to Hilliard et al.
(22), 4–4.5 mm deep, and fixed with acrylic glue. All substances
administered intracerebroventricularly (i.c.v.) were in the volume
of 5 µl using a Hamilton syringe (type Microliter # 702, HamiltonBonaduz, Switzerland).
On the day of the main experiment the animals were
anesthetized using ethylurethane (Riedel-de Haen, Seelze,
Germany) (1.25 g/kg; i.p.). After superficial tissue preparation
the femoral artery and femoral vein were cannuled with catheters
filled with heparinized 0.9% NaCl (300 IU/ml) (Polfa, Warsaw,
Poland). In animals in which the peripheral blood flow was
measured, the carotid communal artery and internal jugular vein
were cannuled.
For the peripheral blood flow measurement, after previous
laparotomy, the renal artery, upper mesenteric artery and the
distal part of abdominal aorta were preparated.
Systolic, diastolic and mean arterial blood pressure (MAP)
was measured using RMN-201 (Temed, Zabrze, Poland). Heart
rate (HR) was automatically calculated as QRS rate in
electrocardiography Diascope 2 (Unitra Biazet, Bialystok,
Poland). Peripheral blood pressure was measured using
electromagnetic sensors (1RB2006, Hugo Sachs Elektronik,
March-Hugstetten, Germany) connected to Time Flowmeter
Type 700 (Hugo Sachs Elektronik, March-Hugstetten,
Germany).
Peripheral resistance was calculated as a ratio of MAP to
peripheral flow in the renal artery (RBF) - renal vascular
resistance (RVR), upper mesenteric artery (MBF) - mesenteric
vascular resistance (MVR) and the distal part of the abdominal
aorta (hindlimb blood flow - HBF) - hindlimb vascular
resistance (HVR). The principal experiment included a 2 hour
observation period after the stabilisation of cardiovascular
parameters in haemorrhagic shock.
Haemorrhagic shock was evoked according to Guarini et al.
(18-20, 23), by controlled bleeding from the femoral or internal
jugular vein to a calibrated drain at maximal speed of 1 ml/min,
over the period of 15–25 min, reaching and stabilizing MAP at
between 20–25 mmHg. The haemorrhage protocol used has
already been employed in the previous studies by our team (24,
25). The average blood volume required for the indication of
critical hypovolaemia was about 2.19±0.27 ml/100 g body mass.
To examine the influence of the central serotonin 1A receptor
(5-HT1A) in cardiovascular regulation under haemorrhagic
shock conditions, a selective 5-HT1A agonist - 8-hydroxy-2-(din-propylamino)tetralin,
1-(2,5-dimethoxy-4-iodophenyl)aminopropane (8-OH-DPAT) (Riedel-de Haen, Seelze, Germany)
(5 µg/5 µl) was used i.c.v. Similarly to other authors and
according to our previous study we used 8-OH-DPAT in
concentration of 5 µg (24-26).
The role of vasopressin in the effect of 8-OH-DPAT was
examined through the use of V1a receptor antagonist - [b-mercaptob,
b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP
administered intravenously in the dose of 10 µg/kg.
In order to determine the role of the renin-angiotensin system
in the effects of centrally acting 8-OH-DPAT the peripheral blood
flow and vascular resistance after the administration of
angiotensin type I receptor antagonist (AT1) - ZD7155 (0.5 mg/kg,
i.v.) were examined. Furthermore, angiotensin-convertingenzyme inhibitor - captopril (30 mg/kg, i.v.) was used.
The participation of POMC derived peptides in the impact of
8-OH-DPAT on the circulatory regulation in critical
hypovolaemia was observed through the use of melanocortin
type 4 (MC4) receptor antagonist - HS014 (5 µg, i.c.v.).
Chemicals
used:
captopril,
[b-mercapto-b,
bcyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP, HS014
(Ac-Cys-Glu-His-D-2-Nal-Arg-Trp-Gly-Cys-Pro-Pro-Lys-AspNH2) (Sigma Chemical Co., St. Louis, MO, USA), ZD7155
hydrochloride (5,7-Diethyl-3,4-dihydro-1-[[2'-(1H-tetrazol-5yl)[1,1'-biphenyl]-4-yl]methyl]-1,6-naphthyridin-2(1H)-one
hydrochloride) (Tocris Cookson Inc., Ellisville, MO, USA).
Statistical analysis was performed using Statistica 7.0
(StatSoft Inc, USA). The parametric t-Student test and nonparametric U-Man-Whitney, c2 and Wilcoxon tests were used for
significance analysis. The values were presented as mean ±
standard deviation (SD). Values of P<0.05 were accepted as
statistically significant.
All experimental protocols were carried out with measures
to minimize animal pain and discomfort in accordance with the
European Communities Council Directive and were approved by
the local Ethical Committee of Silesian Medical University in
Katowice (No 46/05, 26th of July 2005).
RESULTS
Centrally administrated 8-OH-DPAT caused resuscitative
effects already described before, also by our research team (24,
25). These effects were presented by an increase in HR and
MAP, as well as an increase in peripheral blood flow. Moreover,
survival time of study animals increased from 30 min to 2 hours
(the total study observation time).
The role of angiotensin type II in hemodynamic changes triggered
by central 8-OH-DPAT administration
In the first phase of the experiment the role of angiotensin type
II in the effects of centrally acting 8-OH-DPAT was examined. The
peripheral AT1 receptors were blocked through the intravenous
administration of a selective antagonist of these receptors, ZD7155
(0.5 mg/kg, i.v.), 5 minutes prior to the i.c.v. administration of
8-OH-DPAT. Moreover, the study was expanded by angiotensinconverting-enzyme inhibitor - captopril (30 mg/kg, i.v.)
administered in the same manner.
No influence, of either selective blocking of the AT1
receptor (ZD7155), or the blocking of angiotensin-converting
enzyme (captopril), on the changes in HR (Fig. 1A) and MAP
(Fig. 1B) caused by the central stimulation of 5-HT1A receptors
(P³0.05) was observed. Separate administration of ZD7155 or
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The role of vasopressin in hemodynamic changes triggered by
central 8-OH-DPAT administration
captopril in the control group had no impact on the examined
circulatory parameters (Fig. 1, Fig. 2 and Fig. 3).
Similarly, no influence of the abovementioned substances on
the changes in peripheral vascular flow in the RBF (Fig. 2A),
MBF (Fig. 2B) and HBF (Fig. 2C), as well as peripheral
resistance: renal vascular resistance (RVR) (Fig. 3A), mesenteric
vascular resistance (MVR) (Fig. 3B) and hindlimb vascular
resistance (HVR) (Fig. 3C) was found.
In order to determine the effects of vasopressin in the
resuscitative effect triggered by the central stimulation of 5HT1A receptors, peripheral V1a receptors were inhibited
through the intravenous administration of [b-mercapto-b, ba
cyclopentamethylenepropionyl 1,O-me-Tyr 2,Arg 8]AVP,
Fig. 1. Changes in HR (A) and MAP (B) after i.c.v.
administration of 8-OH-DPAT (5 µg) (˜) and i.v. 0.5
mg/kg of ZD7155 (¢) or i.v. 30 mg/kg of captopril
(p) premedication. In control groups i.v. ZD7155
with i.c.v. 0.9% saline (¤), i.v. captopril with i.c.v.
0.9% saline (r) or i.v. and i.c.v. 0.9% saline (¯)
were used. The moment of i.v. premedication with
ZD7155, captopril or 0.9% saline was marked with
the dashed arrow, while the moment of i.c.v. 8-OHDPAT or 0.9% saline administration was marked as
the solid arrow. The values were presented as mean
± standard deviation (S.D.), n=6, * P<0.05 vs.
control group, # P<0.05 vs. 8-OHDPAT only treated
group.
Table 1. The influence of premedication with examined substances on the changes in the heart rate (HR), mean arterial pressure
(MAP), renal blood flow (RBF), mesenteric blood flow (MBF), and the blood flow in the distal part of the abdominal aorta (HBF) as
well as renal vascular resistance (RVR), mesenteric vascular resistance (MVR) and hindlimb vascular resistance (HVR) triggered by
the central administration of a selective 5-HT1A receptor agonist - 8-OH-DPAT.
Antagonist
used
Target
element
8-OH-DPAT 5-HT1A
Examined parameters
t
HR
MAP RBF MBF HBF RVR MVR HVR
K
K
K
K
K
K
L
L
L
ZD7155
AT1
Q
Q
Q
Q
Q
Q
Q
Q
Q
kaptopril
ACE
Q
Q
Q
Q
Q
Q
Q
Q
Q
Ant-V1a
V1a
Q
Q
Q
Q
Q
Q
Q
Q
Q
HS014
MC4
Q
Q
L
Q
Q
Q
L
L
L
h- increase, i - decrease, n- no change; t - average survival time; ACE - angiotensin-converting enzyme; Ant-V1a - [b-merkapto-b,
b-cyklopentametylenopropionyl1,O-me-Tyr2,Arg8]AVP; P<0.05.
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Fig. 2. Peripheral blood flow RBF (A), MBF (B) and HBF (C) changes after i.c.v. administration of 5 µg of 8-OH-DPAT (˜) and i.v.
0.5 mg/kg of ZD7155 (¢) or i.v. 30 mg/kg of captopril (p) premedication. In control groups i.v. ZD7155 with i.c.v. 0.9% saline (¤),
i.v. captopril with i.c.v. 0.9% saline (r) or i.v. and i.c.v. 0.9% saline (¯) were used. The moment of i.v. premedication with ZD7155,
captopril or 0.9% saline was marked with the dashed arrow, while the moment of i.c.v. 8-OH-DPAT or 0.9% saline administration was
marked as the solid arrow. The values were calculated as percent of initial values and presented as mean ± standard deviation (S.D.),
n=6, * P<0.05 vs. control group, # P<0.05 vs. 8-OH-DPAT only treated group.
Initial values in controls treated with 0.9% saline: RBF 5.76 ± 0.67 ml/min, MBF 7.48 ± 1.71 ml/min, HBF 8.91 ± 1.58 ml/min.
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Fig. 3. Peripheral resistance RVR (A), MVR (B) and HVR (C) changes after i.c.v. administration of 5 µg of 8-OH-DPAT (˜) and i.v. 0.5
mg/kg of ZD7155 (¢) or i.v. 30 mg/kg of captopril (p) premedication. In control groups i.v. ZD7155 with i.c.v. 0.9% saline (¤), i.v.
captopril with i.c.v. 0.9% saline (r) or i.v. and i.c.v. 0.9% saline (¯) were used. The moment of i.v. premedication with ZD7155, captopril
or 0.9% saline was marked with the dashed arrow, while the moment of i.c.v. 8-OH-DPAT or 0.9% saline administration was marked as
the solid arrow. The values were calculated as percent of initial values and presented as mean ± standard deviation (S.D.), n=6, * P<0.05
vs. control group, # P<0.05 vs. 8-OH-DPAT only treated group.
Initial values in controls treated with 0.9% saline: RVR 14.11 ± 3.98 mmHg/ml/min, MVR 10.41 ± 3.62 mmHg/ml/min, HVR 9.01 ± 1.84
mmHg/ml/min.
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selective antagonist of those receptors, in the dose of
10 µg/kg.
No influence of the selective blocking of the V1a receptor on
the changes in HR (Fig. 4A) and MAP (Fig. 4B) caused by the
central stimulation of the 5-HT1A receptors was found.
The administration of [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP in the control
group did not affect the examined circulatory system parameters
(Fig. 4, Fig. 5 and Fig. 6).
No influence of the premedication with the V1a vasopressin
receptor antagonist on the changes in peripheral vascular flow
RBF (Fig. 5A), MBF (Fig. 5B) and HBF (Fig. 5C), as well as
peripheral resistance RVR (Fig. 6A), MVR (Fig. 6B) and HVR
(Fig. 6C), triggered by the central administration of 8-OHDPAT, was found.
The role of central MC4 melanocortin receptors in hemodynamic
changes triggered by central 8-OH-DPAT administration
The last phase of the experiment was to determine the role
of central MC4 melanocortin receptors in the resuscitative
effect of the central stimulation of 5-HT1A receptors. For this
purpose, 5 minutes prior to the i.c.v. administration of 8-OHDPAT, an i.c.v. injection of a selective MC4 receptor antagonist,
HS014 in the dose of 5 µg was performed.
The selective blocking of central MC4 receptors caused a
partial reduction of the effect of the centrally administered 8-OH-
DPAT on MAP (P<0.05) (Fig. 7B) with a simultaneous lack of
impact on the HR (Fig. 7A) (P³0.05). Furthermore, HS014
considerably delayed the changes in MAP observed after the
administration of 8-OH-DPAT (the increase appeared 10 minutes
later, 15 min. vs. 5 min.) (Fig. 7B). No influence of the central
administration of HS014 on the survival time of the animals was
reported. The administration of HS014 in the control group did
not affect the examined circulatory system parameters. (Fig. 7,
Fig. 8 and Fig. 9).
A slight, but statistically significant decrease in the peripheral
resistance RVR (Fig. 9A), MVR (Fig. 9B) and HVR (Fig. 9C)
triggered by the icv administration of 8-OH-DPAT after i.c.v.
premedication with HS014 (P<0.05) was observed. The changes
in vascular resistance were not accompanied by changes in
peripheral flow RBF (Fig. 8A), MBF (Fig. 8B) and HBF (Fig.
8C), which remained the same in both groups (P³0.05).
DISCUSSION
The role of sympathetic nervous system as a trigger of
resuscitation effects of 5-HT1A stimulation was presented
previously (9, 25). This is why we focused on other systems.
In earlier research it was noted that the renin-angiotensin
system participates in the resuscitative effects of the central
stimulation of the histaminergic system (27). Due to the fact that
in the research of other authors it has been noted that the effect
Fig. 4. Changes in HR (A) and MAP
(B) after icv administration of 8-OHDPAT (5 µg) (˜) and i.v. 10 µg/kg of
[b-mercapto-b, b-cyclopentamethylenepropionyl 1,O-me-Tyr 2,Arg 8 ]AVP
premedication ( ¢ ) and in control
groups in which i.v. [b-mercapto-b, bcyclopentamethylenepropionyl 1 ,Ome-Tyr2,Arg8]AVP with i.c.v. 0.9%
saline (¤) or i.v. and i.c.v. 0.9% saline
were used (¯). The moment of i.v.
premedication with [b-mercapto-b, bcyclopentamethylenepropionyl1, Ome-Tyr2,Arg8]AVP or 0.9% saline was
marked with the dashed arrow, while
the moment of i.c.v. 8-OH-DPAT or
0.9% saline administration was
marked as the solid arrow. The values
were presented as mean ± standard
deviation (S.D.), n=6, * P<0.05 vs.
control group, # P<0.05 vs. 8OHDPAT only treated group.
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Fig. 5. Peripheral blood flow RBF (A), MBF (B) and HBF (C) changes after i.c.v. administration of 5 µg of 8-OH-DPAT (˜) and i.v.
10 µg/kg of [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP premedication (¢) and in control groups in which
i.v. [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP with i.c.v. 0.9% saline (¤) or i.v. and i.c.v 0.9% saline were
used (¯). The moment of i.v. premedication with [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP or 0.9%
saline was marked with the dashed arrow, while the moment of i.c.v. 8-OH-DPAT or 0.9% saline administration was marked as the solid
arrow. The values were calculated as percent of initial values and presented as mean ± standard deviation (S.D.), n=6, * P<0.05 vs.
control group, # P<0.05 vs. 8-OH-DPAT only treated group.
Initial values in controls treated with 0.9% saline: RBF 5.76 ± 0.67 ml/min, MBF 7.48 ± 1.71 ml/min, HBF 8.91 ± 1.58 ml/min.
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Fig. 6. Peripheral resistance RVR (A), MVR (B) and HVR (C) changes after i.c.v. administration of 5 µg of 8-OH-DPAT (˜) and i.v.
10 µg/kg of [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP premedication (¢) and in control groups in which
i.v. [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP with i.c.v. 0.9% saline (¤) or i.v. and i.c.v. 0.9% saline were
used (¯). The moment of i.v. premedication with [b-mercapto-b, b-cyclopentamethylenepropionyl1,O-me-Tyr2,Arg8]AVP or 0.9%
saline was marked with the dashed arrow, while the moment of i.c.v. 8-OH-DPAT or 0.9% saline administration was marked as the solid
arrow. The values were calculated as percent of initial values and presented as mean ± standard deviation (S.D.), n=6, * P<0.05 vs.
control group, # P<0.05 vs. 8-OH-DPAT only treated group.
Initial values in controls treated with 0.9% saline: RVR 14.11 ± 3.98 mmHg/ml/min, MVR 10.41 ± 3.62 mmHg/ml/min, HVR 9.01 ±
1.84 mmHg/ml/min.
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of angiotensin in haemorrhagic shock is dependent exclusively
on the AT1 receptors (11, 28), an antagonist of those receptors ZD7155 was used in the current research. Unlike in the
histaminergic system, we found no influence of selective
blocking of the AT1 receptors on the effects triggered by the
stimulation of the central 5-HT1A receptors. Similarly, in all the
examined parameters, no impact of the earlier administration of
captopril on the effects triggered by the administration of 8-OHDPAT into the lateral ventricle was registered. Data obtained
from our study reveals that central activation of 5-HT1A
receptors does not influence the renin-angiotensin system. The
above results are consistent with the reports of Van de Kar et al.
(29), who concluded that serotonin, through the 5-HT2
receptors, increased the plasma renin activity. However,
stimulation of 5-HT1A receptors did not produce such a result.
The selection of the blocked receptor was made upon the
basis of the existing reports in the available literature. In the
research of Jochem (5) it was noted that V1a receptors participate
in the resuscitative effect connected with the activation of the
histaminergic system, while the V1b and V2 receptors take no part
in this effect. In our study no influence of blocking the V1a
vasopressin receptors on the effects of the stimulation of central
5-HT1A was found. Those results are similar to those reported
by Jorgensen et al., that although the central administration of
serotonin has increased mRNA expression for vasopressin, this
effect was dependent on the stimulation of 5-HT2 receptors.
Central administration of the selective 5-HT1A agonist (8-OHDPAT) did not induce such effects (30).
Stimulation of the MC4 receptors triggers potent
resuscitative effects in haemorrhagic shock (23, 31). Intravenous
administration of a non-selective agonist of melanocortin MC1,
MC3, MC4 and MC5 receptors NDP- MSH or selective MC4
receptor agonists RO27-3225 and PG-931 has caused an
increase in the HR, MAP and the survival time of rats in critical
hypovolaemia. The intraperitoneal administration of a selective
MC4 receptor antagonist HS024 has inhibited the resuscitative
effect of the NDP-aMSH administered in the same manner (32).
The administration of a selective MC4 receptor antagonist
HS014 into the lateral brain ventricle has completely blocked the
anti-shock effects of the intravenously administered
adrenocorticotropic hormone (ACTH) (23).
In this study, i.c.v. premedication with HS014 prior to the i.c.v.
administration of 8-OH-DPAT caused a statistically significant
decrease in MAP, with no effects on the HR. What is more, the
peripheral resistances were considerably lower. Peripheral blood
flow was without substantial changes, most probably due to the
extremely low blood volume. These results suggest the role of
POMC derivatives and the MC4 receptor in the resuscitative
effects of the central stimulation of 5-HT1A receptors. Our
findings remain consistent with the reports of other authors. In the
research of Jorgensen et al. (33) it was noticed that the peripheral
administration of serotonin receptor agonists increases secretion
Fig. 7. Changes in HR (A) and MAP (B)
after i.c.v. administration of 8-OH-DPAT
(5 µg) (˜) and i.c.v. 5 µg of HS014
premedication (¢) and in control groups
in which i.c.v. HS014 with i.c.v. 0.9%
saline (¤) or i.c.v. 0.9% saline in 0 min
and 5 min time points were used (¯). The
moment of i.c.v. premedication with
HS014 or 0.9% saline was marked with
the dashed arrow, while the moment of
i.c.v. 8-OH-DPAT or 0.9% saline
administration was marked as the solid
arrow. The values were presented as mean
± standard deviation (S.D.), n=6,
* P<0.05 vs. control group, # P<0.05 vs.
8-OHDPAT only treated group.
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Fig. 8. Peripheral blood flow RBF (A), MBF (B) and HBF (C) changes after i.c.v. administration of 5 µg of 8-OH-DPAT (˜) and i.c.v.
5 µg of HS014 premedication (¢) and in control groups in which i.c.v. HS014 with i.c.v. 0.9% saline (¤) or i.c.v. 0.9% saline in 0 min
and 5 min time points were used (¯). The moment of i.c.v. premedication with HS014 or 0.9% saline was marked with the dashed
arrow, while the moment of i.c.v. 8-OH-DPAT or 0.9% saline administration was marked as the solid arrow. The values were calculated
as percent of initial values and presented as mean ± standard deviation (SD), n=6, * P<0.05 vs. control group, # P<0.05 vs. 8-OHDPAT only treated group.
Initial values in controls treated with 0.9% saline: RBF 5.76 ± 0.67 ml/min, MBF 7.48 ± 1.71 ml/min, HBF 8.91 ± 1.58 ml/min.
669
Fig. 9. Peripheral resistance RVR (A), MVR (B) and HVR (C) changes after i.c.v. administration of 5 µg of 8-OH-DPAT (˜) and i.c.v.
5 µg of HS014 premedication (¢) and in control groups in which i.c.v. HS014 with i.c.v. 0.9% saline (¤) or i.c.v. 0.9% saline in 0 min
and 5 min time points were used (¯). The moment of i.c.v. premedication with HS014 or 0.9% saline was marked with the dashed
arrow, while the moment of i.c.v. 8-OH-DPAT or 0.9% saline administration was marked as the solid arrow. The values were calculated
as percent of initial values and presented as mean ± standard deviation (S.D.), n=6, * P<0.05 vs. control group, # P<0.05 vs. 8-OHDPAT only treated group.
Initial values in controls treated with 0.9% saline: RVR 14.11 ± 3.98 mmHg/ml/min, MVR 10.41 ± 3.62 mmHg/ml/min, HVR 9.01 ± 1.84
mmHg/ml/min.
670
of ACTH. Moreover, the i.c.v. administration of 8-OH-DPAT
caused a significant increase in the mRNA expression for
corticotropin-releasing hormone and mRNA for POMC, as well as
a 5-fold increase in the ACTH plasma concentration (34).
Therefore, the present results show that the central
melanocortin MC4 receptor partially participates in the
resuscitative effect of central 5-HT1A activation. However, the
angiotensin and vasopressin systems do not participate in this
activity (Table 1).
On the other hand, it would be interesting to study the
influence of serotonin in other extreme conditions, like antidiuretic phenomenon during spaceflights, for which the antidiuretic hormone system activation seems to play an important
role (35).
Of course, the measured parameters used in our study (HR,
MAP, blood flow and vascular resistance) do not fully examine the
resuscitative effects. Perhaps other parameters like cardiac output
or renal perfusion still need to be examined for a deeper
understanding of the phenomenon. Also, it has to be mentioned
that the study was still an experimental one and the clinical
implications may, needless to say, differ from ours. Like for
example the hypotensive effect of some antidepressants (36).
However, the results of this study contribute new data on effectory
mechanisms through which serotonin acts in haemorrhagic shock.
In conclusion, the central stimulation of the 5-HT1A
receptors triggers a resuscitative effect linked with an increase in
the HR and MAP, as well as the regulation of peripheral blood
flows and vascular resistance. The POMC derivatives and the
central MC4 receptor are partial effectory mechanisms of this
action. The renin-angiotensin system and vasopressin do not
participate in the resuscitative effect evoked by the central
stimulation of 5-HT1A receptors.
Acknowledgements: The authors would like to thank
Professor Jerzy Jochem for his invaluable assistance during the
planning of the experiment as well as his indispensable input he
contributed in extensive discussion with the authors.
Conflict of interests: None declared.
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R e c e i v e d : March 18, 2014
A c c e p t e d : July 22, 2014
Author's address: Dr. Pawel Sowa, ENT Department, 10
Curie-Sklodowskiej Street, 41-800 Zabrze, Poland
E-mail: [email protected]