Adaptive vasodilatory response after octreotide treatment
Ying-Ying
Yang1,
Han-Chieh
Lin1,
Yi-Tsau
Huang2,
Tzung-Yan
Lee2,
Wui-Chiang
Lee1,
Ming-Chih
Hou1,
Fa-Yauh
Lee1,
Full-Young
Chang1, and
Shou-Dong
Lee1
1 Division of Gastroenterology, Department of Medicine,
Taipei Veterans General Hospital and National Yang-Ming University
School of Medicine and 2 Institute of Traditional Medicine,
National Yang-Ming University School of Medicine; Taipei 11217, Taiwan
 |
ABSTRACT |
Despite the suppression of glucagon release, an adaptive
response aimed at maintaining vasodilatation after octreotide
treatment may exist in portal hypertension. The present study was
undertaken to evaluate the possible interaction between endothelium and
non-endothelium-derived vasodilators after 1-wk octreotide
administration in cirrhotic rats. Rats were allocated to receive either
vehicle or octreotide (30 or 100 µg/kg every 12 h
subcutaneously). Hemodynamic values, plasma glucagon levels,
endothelium-related vasodilatory activities, and aortic endothelial
nitric oxide synthase (eNOS) expression were determined after
treatment. Octreotide administration decreased plasma glucagon and
increased serum 6-keto-PGF1
and NOx levels without
affecting the hemodynamic values. In cirrhotic rats receiving octreotide, there was a blunt response to either L-NAME or
indomethacin administration alone, but this blunt pressor response
disappeared after simultaneous administration of the two drugs.
Additionally, an increased aortic eNOS expression was observed in
cirrhotic rats receiving 1-wk octreotide. It is concluded that 1-wk
octreotide treatment did not correct the hemodynamic derangement in
cirrhotic rats. The enhanced endothelium-related vasodilatory activity
was noted after octreotide treatment that overcame the
octreotide-induced hemodynamic effects in portal hypertension.
glucagon; nitric oxide; prostacyclin; portal hypertension; somatostatin
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INTRODUCTION |
IT HAS BEEN SHOWN
that peripheral arterial vasodilatation is an initial phenomenon of the
hemodynamic derangements after the development of portal hypertension
(7, 30, 35). The increased endothelium- (both nitric oxide
and prostacyclin) and non-endothelium- (glucagon, etc.) derived
vasodilators are responsible for the pathogenesis of peripheral
arterial vasodilatation in portal hypertension (4, 13, 29,
34). For many years, the present pharmacological treatment can
only partially correct the above hemodynamic derangement of portal
hypertension. Recently, it had been reported that inhibition of both
nitric oxide and prostacyclin by long-term anti-tumor necrosis factor
(TNF)-
administration in portal vein stenosed (PVL) rats was
accompanied by a compensatory release of glucagon (25).
Similarly, chronic inhibition of cyclooxygenase by indomethacin led to
an enhanced nitric oxide synthase activity and consequently to
sustained hyperemia in both systemic and splanchnic circulation (8). Taken together, it is possible that an adaptive
response aimed at maintaining vasodilatation after pharmacological
treatment may exist in portal hypertension (8, 25).
Octreotide is a synthetic octopeptide analog of somatostatin that had a
much longer biological half-life (3). In cirrhotic patients, short-term administration of octreotide decreased hepatic and
azygous blood flow with minimal portal hypotensive effect (17,
22). In addition, a number of studies in patients with cirrhosis
and portal hypertension showed minimal or transient systemic
hemodynamic effects after octreotide treatment (17, 21,
22). In PVL rats, both acute and chronic administration of
octreotide effectively decreased portal pressure, but its influence on
systemic hemodynamics was inconsistent (1, 2, 5, 19). Moreover, the effects of octreotide on hemodynamics of cirrhotic rats
were controversial (6, 9). Previous studies have
demonstrated that chronic octreotide administration exhibited its
hemodynamic effects by reducing plasma glucagon levels and increasing
vascular reactivity in portal hypertensive animals (11, 19,
31). However, the influence of octreotide administration on
endothelium-derived vasodilatory system (both nitric oxide and
prostacyclin) has not yet been established. The present study is
undertaken to evaluate the hemodynamic effects of 1-wk octreotide
treatment in cirrhotic rats produced by chronic bile duct ligation. To
evaluate the interaction between 1-wk octreotide treatment and the
endothelium-derived vasodilatory activity, the vascular responses
to N
-nitro-L-arginine methyl
ester (L-NAME) and indomethacin, serum levels of glucagon,
6-keto-PGF1
, nitrate and nitrite (NOx), and aortic
nitric oxide synthase (eNOS) protein expression were examined in
cirrhotic rats receiving 1-wk octreotide.
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MATERIALS AND METHODS |
Animals.
Adult male Sprague-Dawley rats weighing between 250 and 350 g were
used in all experiments. Cirrhosis with portal hypertension was
produced by common bile duct ligation (CBL), as previously described
(15). In brief, under ether anesthesia, the common bile
duct was ligated with 3-0 silk and sectioned between the ligatures. The
midline abdominal incision was closed with catgut. Sham-operated rats
had their bile duct exposed but not ligated or sectioned. All rats were
caged at 24°C with a 12:12-h light-dark cycle and were allowed free
access to food and water. Animal studies were approved by the Animal
Experiment Committee of the National Yang-Ming University and were
conducted humanely.
Experiment 1: Hemodynamic studies.
Three weeks after CBL, three groups of bile duct-ligated rats
(nine rats in each group) received vehicle, or 30 µg/kg or 100 µg/kg of octreotide every 12 h subcutaneously (Novartis
Pharmaceutical, Basel, Switzerland) for 7 consecutive days. Another
group of 4-wk sham-operated rats was included for comparison.
Hemodynamic studies were performed at the eighth day after drug
administration. The two doses of octreotide chosen in the present study
were followed as in our previous studies (10-12, 18,
19).
All rats were fasted 18 h before the hemodynamic studies and
had free access to water. Under ketamine anesthesia (100 mg/kg im), a
tracheostomy was performed to keep the airway patent. A catheter was
inserted into the left ventricle through the right carotid artery for
radioactive microsphere injection. Correct positioning of the catheter
was confirmed by blood pressure tracing. A femoral artery catheter was
also inserted to monitor the arterial pressure and heart rate and to
withdraw the reference blood sample. The abdomen was then opened by a
midline incision, and the portal vein was cannulated via a small ileal
vein for measurement of portal pressure. The tip of the catheter was
placed in the distal part of the superior mesenteric vein. The rectal
temperature was maintained at 37°C by use of a heating lamp. All
pressures were measured and recorded with a multichannel recorder
(model RS 3400, Gould, Cupertino, CA). After the hemodynamic values had
stabilized, cardiac output and regional organ blood flows were measured
by the radioactive microsphere technique with the reference sample method as previously described (19). In brief, the
reference sample was withdrawn from the femoral artery into a syringe
for 75 s at a rate of 0.8 ml/min, by use of a Harvard pump
(Harvard Apparatus, Millis, MA). Ten seconds after the withdrawal of
the reference sample, ~60,000 57Co-labeled microspheres
of 15-µm diameter (New England Nuclear, Boston, MA) were injected and
flushed with 0.4 ml saline into the left ventricle through the right
carotid artery catheter over a period of 20 s. After hemodynamic
measurement, the animals were killed with a bolus of saturated
KCl, and the individual organs were dissected. The
radioactivity of each organ and the reference blood sample were counted
in a
-scintillation counter (Auto Gamma 5000, Packard, Downers
Grove, IL). Adequate mixing of microspheres was assumed when the
difference of radioactivity between the left and right kidney was below
10%.
Cardiac output (CO) (ml/min) was calculated as
Cardiac index (CI) was derived from the formula
Regional organ blood flows were calculated according to the
following formula
Portal territory blood flow (PTBF, expressed in
ml · min
1 · 100 g body
wt
1) was taken as the sum of spleen, stomach, small
bowel, colon, and mesentery with pancreas blood flows. Systemic
vascular resistance (SVR) was calculated according to the following
formula
where MAP is mean arterial pressure. Portal territory vascular
resistance (PTVR) was calculated as follows
Vascular resistances were expressed as
dyn · s · cm
5 × 103/100
g body wt.
Experiment 2: Plasma glucagon, NOx, and
6-keto-PGF1
determinations.
To avoid the confounding factors induced by saline injection during
hemodynamic measurement or anesthesia, another set of octreotide and
vehicle-treated CBL rats and a group of sham-operated rats as described
in experiment 1 were used for measuring plasma NOx,
6-keto-PGF1
, and glucagon concentrations. The study protocol was exactly the same as in previous experiments. All rats were
fasted 18 h before measurement. Thereafter, blood samples were
obtained by decapitation and collected in prechilled tubes containing
EDTA. The samples were centrifuged for 15 min at 4°C and stored at
70°C until assays. Plasma glucagon levels were determined by RIA
(Daiichi Radioisotope Laboratories, Tokyo, Japan) with cross-reactivity
100% to glucagon, <0.1% to oxytomodulin, 0% to human insulin, human
proinsulin, human C-peptide, somatostatin, and pancreatic polypeptide.
Serum levels of NOx, an index of nitric oxide generation
(13), were measured by a colorimetric method based on the
Griess reaction (Cayman Chemical, Ann Arbor, MI). Levels of
6-keto-PGF1
, the stable metabolite of prostacyclin, were
also determined by means of ELISA (Cayman Chemical, Ann Arbor, MI) with
intra- and interassay coefficient of variation
10%.
Experiment 3: Dose response of indomethacin or
L-NAME on systemic hemodynamics.
Two sets of octreotide or vehicle-treated CBL rats and
sham-operated rats as described in experiment 1 were used in
this experiment for evaluation of the dose response of indomethacin or
L-NAME on systemic hemodynamics. The study protocol was
exactly the same as in previous experiments. Under ketamine anesthesia,
the right femoral artery and the right femoral vein were cannulated
with PE-50 tubing to monitor MAP and to infuse drugs. CO was measured by thermodilution, as previously described (6). Briefly, a thermistor was placed in the aortic arch just distal to the aortic valve, and the thermal indicator (100 µl of 5% normal saline) was
injected into the right atrium through a PE-50 catheter. The aortic
thermistor was connected to a cardiac output computer
(cardiotherm-500-AC-R, Columbus Instruments International, OH). Five
thermodilution curves were obtained for each CO measurement. The final
cardiac output value was obtained from the arithmetic mean of the
computer results. CI and SVR were calculated as described above.
After an initial stable period of 30 min, the basal values were
obtained. Then the sequential doses of indomethacin (5, 10, and 20 mg/kg, Sigma Chemical, St. Louis, MO) or L-NAME (3, 6, 12, and 24 mg/kg, Sigma Chemical) were administered intravenously in each
set of cirrhotic and sham-operated rats, respectively. All the
hemodynamic parameters were recorded continuously. CO was measured at
the point of maximal change of MAP after the injection of each dose of
indomethacin or L-NAME in each animal. CI and SVR were
calculated as described above. Above doses of indomethacin or
L-NAME were chosen by previous report and preliminary
study. These dosages induced a typical dose-dependent change in
systemic hemodynamics in vehicle-treated CBL rats. The total duration
of the experiment was up to 90 min.
Experiment 4: Influence of the combination of indomethacin and
L-NAME on systemic hemodynamics.
Another set of octreotide or vehicle-treated CBL and sham-operated rats
as described in experiment 1 was used in this experiment to
assess of the effects of the combination of indomethacin and L-NAME on systemic hemodynamics. The study protocol was
exactly the same as in previous experiments. In a preliminary study,
the CBL rats could not tolerate the combined administration of higher doses of indomethacin and L-NAME. We therefore chose the
combined administration of L-NAME (6 mg/kg) and
indomethacin (5 mg/kg) to assess the vascular response in octreotide or
vehicle-treated CBL and sham-operated rats. The procedure was similar
to experiment 3; after basal values were obtained, the
combined doses of 6 mg/kg of L-NAME and 5 mg/kg of
indomethacin were infused through bilateral femoral veins in each set
of cirrhotic and sham-operated rats. The total duration of the
experiment was up to 40 min.
Experiment 5: Western blotting for aortic eNOS
expression in cirrhotic rats.
Aortic eNOS protein expressions were examined in cirrhotic rats
receiving vehicle and those receiving 1-wk octreotide (30 and 100 µg/kg every 12 h). To assess the acute effect of octreotide on
eNOS protein expression, another two groups of CBL rats receiving octreotide, 30 or 100 µg/kg every 12 h for 1 day, were also
included. There were 15 rats in each group. Under ether anesthesia, a
laparotomy was performed. The thoracic aorta was rapidly excised from
the aortic valve to the diaphragm and then rinsed in cold
phosphate-buffered nitrogen. Tissue samples were stored at
70°C
until analysis. The Western blots were performed as previously
described (24). After pulverization, frozen arteries were
glass homogenized in a lysis buffer (50 mM
-glycerophosphate, 100 µM Na3VO4, 2 mM MgCl2, 1 mM EGTA,
0.5% Triton X-100, 1 mM dithiothreitol) containing proteases
inhibitors (20 µM pepstatin, 20 µM leupeptin, 1,000 U/ml aprotinin,
and 1 mM phenylmethylsulfonyl fluoride). Protein concentration was
determined for each sample by use of the Bradford method (Bio-Rad). The
proteins were separated on denaturing SDS-7.5% polyacrylamide gels by
electrophoresis. Proteins were then transferred to a polyvinylidene
difluoride membrane (Millipore, Bedford, MA) by wet electroblotting for
10 h at 4°C. Blots were blocked for 90 min with 5% nonfat dry
milk in TBS-T, pH 7.5 (20 mM Tris base-137 mM NaCl-0.1% Tween 20).
Prestained proteins markers (Sigma Chemical) were used for molecular
weight determinations. For quantification of eNOS expression, 20 µg
of protein extract from aortas were chosen as previously suggested.
Equal protein loading was confirmed by india ink staining of protein in
each lane of the same blot. Blots were incubated with the first
antibody [anti-eNOS monoclonal antibodies (Transduction
Laboratories, Lexington, KY)] (1:250) for 90 min at room temperature
and washed. Then the blots were incubated again for another 45 min with
a 1:1,500 dilution of horseradish peroxidase-conjugated mouse antibody
(Dako, Glostrup, Denmark) and washed. Subsequent detection of the
specific proteins (140 kDa for eNOS) was performed by enhanced
chemiluminescence (ECL Western blotting analysis system; Amersham
International), according to the manufacturer's
instruction. The signal intensity (integral volume) of the appropriate bands on the autoradiogram was analyzed by use of the Image Quant software package (Biosoft, Indianapolis, IN).
Statistics.
Results are expressed as means ± SE. One-way ANOVA and unpaired
Student's t-test were used for statistical analysis
when appropriate. Significance was determined at P < 0.05. Correlation between serum levels of glucagon, NOx, and
6-keto-PGF1
were determined by hatched regression.
 |
RESULTS |
Experiment 1: Systemic and splanchnic hemodynamics.
Four weeks after bile duct ligation, CBL rats receiving vehicle had
significantly lower MAP and SVR associated with higher CI than
sham-operated rats (P < 0.01). After 1-wk octreotide
administration, lower CI and higher SVR (P < 0.05)
were noted in CBL rats treated with 30 µg/kg octreotide per 12 h
than in vehicle-treated CBL rats. The values of systemic
hemodynamics in CBL rats treated with 100 µg/kg octreotide per
12 h were not significantly different from those in
vehicle-treated CBL rats (Table 1).
Similar changes of CI and SVR were also observed in experiments
3 and 4. The portal pressure, portal territory blood
flow, and portal territory vascular resistance were the same among the
three groups of cirrhotic rats.
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Table 1.
Systemic and splanchnic hemodynamic values in sham-operated rats
and in cirrhotic rats receiving vehicle and octreotide
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|
Experiment 2: Plasma glucagon,
6-keto-PGF1
, and NOx after
octreotide treatment.
Higher plasma glucagon, 6-keto-PGF1
, and NOx levels were noted in
all CBL rats than in sham-operated rats. In CBL rats receiving two
different doses of octreotide, plasma glucagon level was remarkably decreased in a dose-dependent manner (P < 0.01) in all
CBL rats (Fig. 1A).
Conversely, serum 6-keto-PGF1
and NOx levels were dose-dependently increased (P < 0.01) after treatment
(Fig. 1, B and C). In CBL rats, plasma glucagon
levels were negatively correlated to both 6-keto-PGF1
(r =
0.86, P < 0.05) and NOx
(r =
0.78, P < 0.05) (Fig.
2, A and B).

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Fig. 1.
Serum levels of glucagon (A), 6-keto-PGF1
(B), and nitrate and nitrite (NOx) (C) in common
bile duct ligated (CBL) rats treated with 30 (hatched bars) and 100 µg/kg (cross-hatched bars) octreotide per 12 h and with vehicle
(solid bars) were higher than in sham-operated rats (open bars). Lower
glucagon levels associated with higher 6-keto-PGF1 and
NOx were noted in CBL rats treated with 30 and 100 µg/kg octreotide
per 12 h than in vehicle-treated CBL rats. Moreover, plasma
glucagon was significantly (*P < 0.01) suppressed by
octreotide in a dose-dependent manner; conversely, serum levels of
6-keto-PGF1 and NOx were dose-dependently elevated after
octreotide administration (#P < 0.01).
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Fig. 2.
Correlation between plasma glucagon to 6-keto-PGF1
(X = 732 0.353Y, r = 0. 86, P < 0.05) (A) and NOx
(X = 859 22.1Y, r = 0.78, P < 0.05) (B) of CBL rats.
|
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Experiment 3: Dose response changes of SVR to
indomethacin or L-NAME infusion.
At each dose of indomethacin administration, the percent change of SVR
from baseline values was significantly elevated in all experimental
groups, but dose-dependent elevation was noted only in CBL rats
receiving vehicle and 30 µg/kg per 12 h octreotide (Fig.
3A). Similar to indomethacin
administration, the dose-dependent increment of the percent change of
SVR from baseline by incremental doses of L-NAME was also
noted in CBL rats treated with vehicle and with 30 µg/kg octreotide
per 12 h (Fig. 3B). Moreover, a blunt response to
L-NAME administration expressed as smaller percent change
of SVR from baseline was noted in CBL rats treated with 100 µg/kg
octreotide per 12 h by incremental doses of L-NAME
infusion (Fig. 3B). Basically, the percent change of SVR
from baseline after L-NAME or indomethacin administration
in cirrhotic rats receiving octreotide was lower than in those
receiving vehicle (Fig. 3, A and B).

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Fig. 3.
A: percent changes in systemic vascular resistance (SVR)
in CBL rats treated with 30 (hatched bars) or 100 µg/kg
(cross-hatched bars) octreotide per 12 h or with vehicle (solid
bars) and in sham-operated rats (open bars); SVR was increased by
incremental dose of indomethacin (5, 10, and 20 mg/kg). Dose-dependent
increment of SVR was noted only in vehicle- (**P < 0.01) and 30 µg/kg per 12 h (*P < 0.05)
octreotide-treated CBL rats. B: percent changes in SVR
by infusion of N -nitro-L-arginine
methyl ester (L-NAME) in another 4 experimental groups;
significant elevations (**P < 0.01; *P < 0.05) of SVR from baseline values in different groups with
incremental doses of L-NAME (3, 6, 12, and 24 mg/kg) were
similar to indomethacin administration.
|
|
Experiment 4: Influence of the combination of indomethacin and
L-NAME on systemic hemodynamics.
After the combination of indomethacin and L-NAME
administration, the percent change of SVR from baseline in cirrhotic
rats receiving octreotide was higher than in those receiving vehicle (Fig. 4). But the percent change in SVR
was not different between cirrhotic rats receiving 30 and 100 µg/kg
per 12 h octreotide.

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Fig. 4.
Percent changes in SVR in CBL rats treated with 30 (hatched bars) or 100 µg/kg octreotide per 12 h or with vehicle
(solid bars) and in sham-operated rats (open bars). Percent change in
SVR from baseline by combination of indomethacin (5 mg/kg) and
L-NAME (6 mg/kg) was significantly (*P < 0.05) higher in CBL rats treated with 30 and 100 µg/kg octreotide per
12 h than in vehicle-treated CBL rats. The percent changes were
not different between CBL rats treated with 30 or with 100 µg/kg
octreotide per 12 h.
|
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Experiment 5: Western blotting for aortic eNOS
protein expression in cirrhotic rats.
Western blot analysis for the aortic eNOS protein expressions in CBL
rats after 1-day or 1-wk octreotide and vehicle administration was
shown in Fig. 5. The expression of eNOS
protein was significantly higher in CBL rats receiving 1-wk octreotide
than in those treated with vehicle. Meanwhile, the expression of eNOS
protein was not different between CBL rats receiving vehicle and those
receiving 1-day octreotide.

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Fig. 5.
Western blot analysis of endothelial nitric oxide
synthase (eNOS) protein (molecular mass 140 kDa) expression from
thoracic aorta in cirrhotic rats receiving vehicle, 1-wk octreotide,
and 1-day octreotide; 20 µg of protein was loaded per lane.
A: CBL rats receiving octreotide 30 µg/kg per 12 h
for 7 days. B: CBL rats treated with vehicle. C:
CBL rats receiving octreotide 100 µg/kg per 12 h for 7 days.
D: CBL rats treated with 1 day octreotide 30 µg/kg per
12 h. E: CBL rats treated with 1 day octreotide 100 µg/kg per 12 h. BSA, bovine serum albumin (molecular mass 96 kDa). An upregulation of eNOS protein expression was noted after 1 wk
of octreotide administration especially in rats receiving 100 µg/kg
per 12 h compared with those receiving vehicle. In contrast, eNOS
protein expression was similar between cirrhotic rats receiving 1 day
of octreotide and those receiving vehicle.
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|
 |
DISCUSSION |
In the present study, we found a modest increase in SVR and
decrease in CI of cirrhotic rats receiving 30 µg/kg per 12 h
octreotide. In contrast, all the systemic effects in cirrhotic rats
receiving 100 µg/kg per 12 h octreotide were not different from
cirrhotic rats receiving vehicle. Our results suggested the absence of
the dose-dependent effects of octreotide on systemic hemodynamics in
cirrhotic rats with portal hypertension. Please note that the hemodynamics in this study was measured under ketamine anesthesia. Sikuler et al. (33) have demonstrated that hemodynamics
studies in portal hypertensive animals were preferably performed under ketamine anesthesia. It is conceivable that the influence of anesthesia in this study should have been minimized to the least extent. However,
in this study, we found that plasma glucagon levels were significantly
higher in cirrhotic than in sham-operated rats. This is in line with
previous observations showing the presence of hyperglucagonemia in
portal hypertension (4, 19). As expected, plasma glucagon
levels were decreased in CBL rats receiving chronic octreotide,
indicating that both dosages used in the present study were effective.
In addition, we found that plasma glucagon levels were lower in CBL
rats receiving 100 µg/kg per 12 h octreotide than in rats
receiving 30 µg/kg per 12 h octreotide, suggesting a
dose-dependent effect in suppression of glucagon release after octreotide treatment. It has been shown that octreotide does not exert
a direct effect on the vascular smooth muscle cell (32), and the suppression of glucagon and/or other peptide vasodilators (i.e., substance P, etc.) release may represent the main mechanism of
action of octreotide on hemodynamics in portal hypertension (28). Glucagon is a potent vasodilator and is involved in
the vasodilatation in portal hypertension (4). In addition
to nitric oxide (16), hyperglucagonism also contributes,
in part, to the pathogenesis of decreased vascular reactivity in portal
hypertension (23, 27). Moreover, chronic octreotide
treatment increased vascular reactivity in portal hypertensive animals
(11, 31). Increased circulating vasodilators (i.e.,
glucagon, etc.), decreased vascular responsiveness to vasoconstrictors
and increased activity of nitric oxide and prostacyclin are the major
factors involved in the pathogenesis of vasodilatation in portal
hypertension (4, 14, 16, 26, 29, 34). However, most of the
studies in cirrhotic patients have demonstrated a minimal or transient
systemic effect after octreotide treatment whereas the systemic
hemodynamics could only be partially corrected in portal hypertensive
animals receiving octreotide (1, 2, 5, 17, 19, 21, 22). Taken together, it would be of interest to know whether there is an
interaction between chronic octreotide administration and the activity
of nitric oxide and prostacyclin.
Fernández et al. (8) have reported that, in portal
hypertensive rats, long-term inhibition of cyclooxygenase activity by
indomethacin led to an enhanced activity of nitric oxide synthase that
maintained splanchnic hyperemia. Munoz et al. (25) have shown that suppression of nitric oxide and prostacyclin release by
anti-TNF-
administration did not correct splanchnic vasodilatation in portal vein-stenosed rats. This effect may have resulted from a
compensatory release of glucagon after long-term anti-TNF-
administration (25). Together, these results indicated the
presence of an adaptive response between vasodilators aimed at
maintaining vasodilatation in portal hypertension. In the present
studies, the serum levels of NOx and 6-keto-PGF1
were
dose-dependently increased in cirrhotic rats receiving octreotide
compared with those receiving vehicle, and the changes in plasma levels
of the NOx and 6-Keto-PGF1
were negatively correlated
with plasma glucagon levels. We also observed that the magnitude of
changes in systemic hemodynamics to L-NAME or indomethacin
was lower in cirrhotic rats receiving octreotide than in those
receiving vehicle. This finding was in contrast to the expected
enhanced vascular responses to L-NAME or indomethacin
infusion in the presence of increased nitric oxide or prostacyclin
release. Because the serum levels of NOx and 6-keto-PGF1
were "simultaneously" elevated in rats receiving octreotide, the
expected increased in vascular response to L-NAME may be
masked by the overproduction of prostacyclin. A similar condition also
existed when the cyclooxygenase activity was inhibited by indomethacin.
In contrast, in cirrhotic rats receiving octreotide, the blunt vascular
response after administration of either indomethacin or
L-NAME alone can be totally corrected by the combined
administration of indomethacin and L-NAME. Taken together, the present study suggested that, after the suppression of
glucagon release by octreotide, an enhanced endothelial related vasodilatory effect might exist in cirrhotic rats. Our hypothesis is
further confirmed by the Western blot analysis of aortic eNOS protein
expressions. We found that the aortic eNOS protein expression was
enhanced in cirrhotic rats receiving 1-wk octreotide compared with
those receiving vehicle. By contrast, the aortic eNOS protein expression was similar between rats receiving 1 day of octreotide and
those receiving vehicle. Therefore, the enhancement in endothelial related vasodilatory activity was mainly attributed to the chronic octreotide treatment rather than to the acute effect of the drug.
In this study, we found that portal pressure and splanchnic hyperemia
were not decreased in cirrhotic rats receiving both lower and higher
doses of octreotide. This finding is different from a number of
previous studies in portal vein-stenosed rats (a model of portal
hypertension without the presence of cirrhosis), showing that chronic
octreotide administration decreased portal pressure and corrected in
part the splanchnic hyperemia (12, 19, 31). However, the
present results are in line with the study reported by Fort et al.
(9) showing that in cirrhotic rats produced by bile duct
ligation, portal pressure and mean arterial pressure remained unchanged
after chronic octreotide treatment. The discrepant findings regarding
the effects of octreotide between the two different models cannot be
explained by our present study. However, in addition to the possible
interaction between plasma glucagon, nitric oxide, and prostacyclin
that contributes to maintaining splanchnic hyperemia, different models
of portal hypertension may also play a role for the different
pharmacological responses observed between cirrhotic and portal vein
stenosed rats (20). Although Cerini et al.
(5) reported a reduction of portal pressure after acute
intravenous infusion of octreotide in cirrhotic rats, the different
route of administration (intravenous vs. subcutaneous) may probably be
one reason for the discrepant responses between acute and chronic
octreotide administration in cirrhotic rats.
In conclusion, the present study showed that, despite the suppression
of plasma glucagon levels, 1-wk octreotide treatment did not
correct the systemic hemodynamics and splanchnic hyperemia in cirrhotic
rats produced by chronic bile duct ligation. Increased nitric oxide and
prostacyclin biosynthesis were noted after long-term octreotide
treatment, indicating an enhancement of the endothelium-related vasodilatory activities that may probably overcome the
octreotide-induced hemodynamic effects in portal hypertension.
 |
ACKNOWLEDGEMENTS |
This work was supported by Grant NSC89-2314-B-075-068 from the
National Science Council and Grant VGH89-62 from the Taipei Veterans
General Hospital, Taipei, Taiwan.
 |
FOOTNOTES |
Address for reprint requests and other correspondence: H.-C.
Lin, Division of Gastroenterology, Dept. of Medicine, Taipei Veterans
General Hospital, No. 201, Sec. 2, Shih-Pai Road, Taipei 11217, Taiwan
(E-mail: hclin{at}vghtpe.gov.tw).
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 2 August 2000; accepted in final form 31 January 2001.
 |
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