|
Zhong-Sheng
Zhu, Jin-Ming Wang, Department of Cardiovascular Medicine,
People’s Hospital of Wuhan University, Wuhan 430060, Hubei
Province, China
Shao-Liang Chen, Department of Cardiovascular Medicine, Third
Affiliated Hospital of Nanjing Medical University, Nanjing 210006,
Jiangsu Province, China
Supported by the Natural Science Foundation of Education
Office of Hubei Province, No. 2000B03023/3011400802
Correspondence to: Dr. Zhong-Sheng Zhu, Department of
Cardiovascular Medicine, Third Affiliated Hospital of Nanjing
Medical University, Nanjing 210006, Jiangsu Province,
China. zhuzhongsheng6966@hotmail.com
Telephone: +86-13016973706
Received: 2003-10-24
Accepted: 2003-12-08
Abstract
AIM: To investigate the remodeling of mesenteric artery and the
expression of TGF-b1,
c-Jun in mesenteric artery and effects of imidapril and irbesartan
on the remodeling in spontaneously hypertensive rats (SHR).
METHODS:
Thirty SHR (male/female, 21/9), aged 13 wk, were randomly divided
into 3 groups (7 male rats and 3 female rats each group): SHR group,
imidapril group (imidapril 3 mg/kg.d was given in drinking water for
14 wk), and irbesartan group (irbesartan 50 mg/kg.d was given in
drinking water foe 14 wk). Ten homogenous Wistar Kyoto rats, 5 males
and 5 females, weighing 206±49
g, were selected as normal control group (WKY group). Systolic
pressure was measured on d 1, 2, 4, 6, 8, 10, 12 and 14 during the
experiment and the rats were killed at the end of the experiment.
Angiotensin II (Ang II) level in plasma and mesenteric arteries was
measured by radioimmunoassay. The morphology of the secondary
branches of mesenteric artery were examined by light microscopy and
electron microscopy. Reverse transcription polymerase chain reaction
(RT-PCR) was used to detect the expression of transforming growth
factor TGF-b1
and c-Jun mRNA.
RESULTS:
Compared with imidapril group and irbesartan group, the blood
pressure was remarkably increased in SHR group. Ang II level in
plasma and mesenteric arteries in SHR group was the same or lower
than that in WKY group, and was higher in irbesartan group and lower
in imidapril group. The remodeling of mesenteric arteries in SHR
group was mostly obvious among the 4 groups. The ratio of TGF-b1
absorbed light value to GAPDH absorbed light value in the SHR group
was 0.887±0.019, which was significantly higher than that in WKY group,
imidapril group, and irbesartan group with the ratios of 0.780±0.018,
0.803±0.005,
and 0.847±0.017,
respectively (P<0.01). Ang II level in plasma and
mesenteric arteries in imidapril group was significantly lower than
that in irbesartan group (P<0.05). The c-Jun absorbed
light value/GAPDH absorbed light value of mesenteric arteries in the
SHR group was 0.850±0.015, which was significantly higher than that in the WKY,
imidapril, and irbesartan groups (0.582±0.013, 0.743±0.012, and 0.789±0.013, respectively, P<0.01), and was significantly
lower in imidapril group than in irbesartan group (P<0.05).
CONCLUSION:
Imidapril and irbesartan can not only control blood pressure but
also inhibit mesenteric arteries remodeling and mRNA expression of
TGF-b1,
c-Jun in SHR. Imidapril is more effective than irbesartan.
Zhu ZS, Wang JM, Chen
SL. Mesenteric artery remodeling and effects of imidapril and
irbesartan on it in spontaneously hypertensive rats. World J
Gastroenterol 2004;
10(10): 1471-1475
http://www.wjgnet.com/1007-9327/10/1471.asp
INTRODUCTION
It has been reported[1-3] that angiotensin-converting
enzyme inhibitor (ACEI) and angiotensin II type 1 (AT1) receptor
antagonist can inhibit resistance blood vessel remodeling, but their
action mechanism is still unknown. We selected irbesartan and
imidapril to interfere mesenteric artery remodeling in spontaneously
hypertensive rats (SHR) to investigate the expression of c-Jun and
TGF-b1
mRNA in resistance blood vessel of each group rats with reverse
transcription polymerase chain reaction (RT-PCR) and to illustrate
the mechanism of resistance blood vessel remodeling in hypertension
and possible mechanism of these two drugs inhibiting mesenteric
artery remodeling and possible effect on the inhibition of
mesenteric artery remodeling.
MATERIALS AND METHODS
Materials
Thirty
13-wk old SHR (male/female, 21/9, provided by Fuwai Hospital in
Beijing) with an average
body mass of 228±39
g were randomly divided into 3 groups: SHR positive control group,
imidapril treatment group (3 mg/kg.d), irbesartan treatment group
(50 mg/kg.d). Ten homogenous Wistar-Kyoto rats [provided by Fuwai
Hospital in Beijing, in which female rats were 5, male rats were 5,
their average body mass was 206±49
g.] were selected as normal control group. During the 14-wk trial,
all rats were in the breeding conditions: temperature 18-25 °C, humidity 40-60%, protein feed concentration 22-25%.
Methods
Irbesartan
(presented by Hengrui Pharmacy Factory of Jiangsu Province) 50
mg/kg.d[4] and imidapril (presented by Tianbian Pharmacy
Factory of Tianjin) 3 mg/kg.d[5] were dissolved in
drinking water for 14 successive wk, respectively. Index observed
included tail artery systolic blood pressure, angiotensin II (Ang
II), histology of mesenteric artery. Fourteen weeks after irbesartan
and imidapril interfering, all rats were killed and the second grade
embranchment of mesenteric artery (about 2 mm) was taken and put
into 25/L of glutaral for fixing, then transmission electron
microscope (H-600, Hitachi in Japan) was used. About 1 mm of the
artery was put into 100 g/L of neutral formaldehyde and stained with
HE, then observed by light microscope. Morphology of mesenteric
artery was by a computer-assisted image analysis system. RT-PCR
analysis was performed for TGF-b1[6]
and c-Jun[7] mRNA level in mesenteric artery.
SPSS 10.0 statistically analyzed the data and results were
expressed as mean±SD.
RESULTS
Blood pressure from 4 groups was recorded in Table 1
Concentration of Ang II in plasma is shown in Table 2
Morphology of mesenteric artery (Figure 1)
Intima, vessel media, vessel wall were not increased in WKY
group. Vessel lumen was relatively wider (A). Intima, vessel media
and vessel wall were increased. Vessel lumen was relatively narrow
in SHR (B), imidapril (C) and irbesartan (D) groups. The ratios of
intima-media thickness / lumen radius, media / lumen area, lumen /
vessel radius in 4 groups are shown in Table 3.
Microstructure of mesenteric arteries (transmission electron
microscope, Figure 2)
As shown in A for WKY group, endothelial cells of intima
were abundant and normal, media had more smooth muscle cells. As
shown in B for SHR group, endothelial cells of intima had vacuoles
and fibrous tissues with adventitial hyperplasia, the thickness of
adventitia was increased, media was severely fibrous and the fibrous
tissue extended to smooth muscle layer and invaded internal elastic
lamina, internal elastic lamina was tortuous and atrophic, some of
smooth muscle cells were replaced by fibrous tissue. As shown in C
for irbesartan group, endothelial cells of intima had vacuoles and
marrow type corpses, internal elastic lamina was tortuous and
atrophic and infiltrated by collagen fibers, but fibrosis in whole
blood vessel wall relieved as compared with SHR group. The number of
smooth muscle cells in media was slightly more than that in SHR
group. As shown in D for imidapril group, endothelial cells of
intima had marrow type corpses but no vacuole, the number of smooth
muscle cells in media was more than that in irbesartan group,
internal elastic lamina had a close-to-normal distribution, local
internal elastic lamina was narrowed, fibrosis did not occur on
blood vessel walls.
RT-PCR analysis of TGF-b1
and c-Jun mRNA level in mesenteric artery (Figure 3)
mRNA
expression levels of TGF-b1
and c-Jun were analyzed by RT-PCR. Agarose gel electrophoresis of
the PCR products was carried out to measure the relative intensity
of the expression (A and B, Table 4).
Figure 1
Morphology of mesenteric artery, A:
Intima, media of vessel wall are not increased in WKY group and
vessel lumen is relatively wider (HE, ×100). B:
Intima, media of vessel wall are increased in SHR group and vessel
lumen is relatively narrow (HE, ×400). C:
Intima, media of vessel wall are increased in imidapril group and
lumen of vessel is relatively narrow (HE, ×400). D:
Intima, media of vessel wall are increased in irbesartan group and
lumen of vessel is relatively narrow (HE, ×400).
Figure
2 Microstructure of
mesenteric arteries (transmission electron microscope), A:
WKY group, endothelial cells of intima were abundant and normal,
Media has more smooth muscle cells, internal elastic lamina is
normal (×2 000). B:
SHR group, endothelial cells of intima had vacuole and fibrous
tissue with adventitial hyperplasia; thickness of the adventitia was
increased; media was severely fibrous and the fibrous tissue
extended to smooth muscle layer and invaded internal elastic lamina;
internal elastic lamina was tortuous and atrophic; some of smooth
muscle cells were replaced by fibrous tissue (×2
500). C:
Irbesartan group, endothelial cells of intima have vacuole and
marrow type corpses, internal elastic lamina was tortuous and
atrophic and infiltrated by collagen fibers (×2
500). D: Imidapril
group, endothelial cells of intima have marrow type corpses but no
vacuole, numbers of smooth muscle cells in media were more than
those in irbesartan group; internal elastic lamina got a
close-to-normal distribution; local internal elastic lamina got
narrow, fibrosis did not occur on blood vessel wall (×2
000).
Figure
3(PDF) Agarose gel
electrophoresis of TGF-b1
and c-Jun mRNA RT-PCR product of mesenteric arteries, A: Agarose gel
(2%) electrophoresis of TGF-b1
mRNA RT-PCR product of mesenteric arteries of 4 groups. 1: WKY group
GAPDH, 2: SHR group GAPDH, 3: irbesartan group, 4: imidapril group,
5: SHR group, 6: WKY group, 7: irbesartan group GAPDH, 8:
pGEM-7Zf(+)/Hae III markers (from top to bottom: 102, 142, 174, 267,
289, 328, 434, 657 bp), 9: imidapril group GAPDH. B: Agarose gel
(2%) electrophoresis of c-Jun mRNA RT-PCR product of mesenteric
arteries of 4 groups. 1: SHR group GAPDH, 2: WKY group GAPDH, 3:
irbesartan group, 4: imidapril group, 5: SHR group, 6: WKY group, 7:
irbesartan group GAPDH, 8: pGEM-3Zf(+)/Hae III markers (from top to
bottom: 18, 80, 102, 174, 267, 314, 434, 587 bp), 9: imidapril group
GAPDH.
Table
1 Blood
pressure measured in WKY, SHR, imidapril and irbesartan groups
(mean±SD, n=10)
| Group |
Blood
pressure
(mmHg) |
|
13-wk-old |
14-wk-old |
15-wk-old |
17-wk-old |
19-wk-old |
21-wk-old |
24-wk-old |
26-wk-old |
| WKY |
105.90±
16.10d |
115.70±
9.19 |
112.00±
7.53 |
90.00±
9.13 |
125.50±
7.62 |
116.00±
6.99 |
116.00±
11.25 |
121.50±
4.74 |
| SHR |
134.40±
7.72 |
140.00±
17.48 |
151.00±
24.59b |
160.00±
14.90f |
177.00±
16.19f |
177.50±
14.39f |
190.00±
19.00f |
198.10±
14.04f |
| Imidapril |
131.50±
6.68 |
124.30±
7.02 |
127.50±
8.58 |
125.00±
7.45 |
130.80±
15.16 |
138.00±
12.52 |
127.00±
11.10 |
142.00±
6.32 |
| Irbesartan |
140.10±
5.90 |
132.50±
15.14 |
124.00±
18.83 |
122.50±
20.17 |
128.00±
12.06 |
138.00±
6.32 |
126.00±
6.15 |
141.00±
14.87 |
bP<0.01
vs WKY, imidapril, irbesartan groups; dP<0.01
vs
SHR, imidapril, irbesartan groups; fP<0.01
vs WKY, imidapril, irbesartan groups.
Table
2 Concentration of
Ang II in plasma (mean±SD, n=7)
| Group |
Plasma
(pg/mL) |
Mesenteric
artery (pg/100 mg) |
| WKY |
303.15±16.99 |
2 218.63±242.37 |
| SHR |
318.77±16.83 |
2 138.48±110.56a |
| Imidapril |
307.43±25.20 |
1
888.92±147.46ce |
| Irbesartan |
571.38±57.89b |
3
509.18±168.44hfg |
aP<0.05
vs WKY, bP<0.01 vs WKY, SHR, imidapril group, cP<0.05
vs WKY; eP<0.05 vs SHR; fP<0.01
vs SHR; hP<0.01 vs WKY; gP<0.05
vs imidapril.
Table 3 Comparisons
of ratios of intima-media thickness / lumen radius, media / lumen
area, lumen / vessel radius in four groups
(mean±SD, n=7)
| Group |
Media
thickness (mm)/lumen radius
(mm) |
Media
area(mm2)/lumen area
(mm2) |
Lumen
radius(mm)/vessel radius
(mm) |
| WKY |
0.75±0.09 |
0.35±0.04 |
0.65±0.01 |
| SHR |
2.67±0.20a |
1.21±0.14a |
0.46±0.01a |
| Imidapril |
1.67±0.13ec |
0.71±0.05ec |
0.51±0.01ec |
| Irbesartan |
1.47±0.27ge |
0.65±0.14ge |
0.53±0.01ge |
aP<0.05
vs WKY; cP<0.05 vs SHR; eP<0.05
vs WKY; eP<0.05 vs SHR; gP<0.05
vs WKY.
Table 4 Absorbance
of c-Jun/absorbance of GAPDH, absorbance of TGF-b/absorbance
of GAPDH (mean±SD, n=5)
| Group |
Absorbance
of c-Jun/absorbance of GAPDH |
Absorbance
of TGF-b1/absorbance
of GAPDH |
| WKY
group |
0.582±0.013 |
0.780±0.018 |
| SHR
group |
0.850±0.015b |
0.887±0.019d |
| Imidapril
group |
0.743±0.012a |
0.803±0.005c |
| Irbesartan
group |
0.789±0.013 |
0.847±0.017 |
F=1
340 in the ratio of absorbance of c-Jun/absorbance of GAPDH. aP<0.05
vs irbesartan group, bP<0.01 vs WKY, imidapril,
irbesartan group. F=198 in the ratio of Absorbance of TGF-b1/absorbance
of GAPDH. cP<0.05 vs irbesartan group, dP<0.01
vs WKY, imidapril, irbesartan group.
DISCUSSION
It is known that elevated blood pressure in essential
hypertension patients and spontaneously hypertensive rats (SHR)
related to the renin-angiotensin system (RAS)[8-10]. The
main effector peptide of RAS was Ang II[11], which played
an essential role in the pathogenesis of hypertension through the
regulation of cell growth, inflammation, and fibrosis[12].
The main biological effects of Ang II has been found to be the
enhancement of smooth muscle contraction, aldosterone release[13],
arginine vasopressin release, cell proliferation, adjustment of body
fluid balance. It had a close relation to blood vessel remodeling[14].
There were 2 main angiotensin II receptors, AT1 and AT2[15,16].
The AT1 receptor was responsible for most of the pathophysi-
ologic actions of angiotensin II [17], including cell
proliferation, production of growth factors and cytokines, and
fibrosis. AT2 could cause antiproliferation and counteract the cell
growth induced by AT1 activation[18]. In addition,
pressure-lowering agent also had actions on blood vessel remodeling[19].
Both ACEI and AT1 acceptor antagonists have been shown to act
selectively on different cycles and they not only had satisfactory
decompression effect, but also might inhibit blood vessel remodeling[20,21].
These results suggest that imidapril and irbesartan have
ideal decompression effects and inhibiting action upon angiotensin-converting
enzymes and AT1 acceptors. Blood pressure gradually rose and arrived
to 200 mmHg in 26 wk-old SHR, but blood pressure in imidapril and
irbesartan groups fluctuated within normal ranges and no obvious
difference was observed between the 2 groups. Ang II level in plasma
gradually increased in SHR group and slowly decreased in imidapril
group compared with that in WKY group performed with
radioimmunoassay, but there was no statistical significance between
them. Ang II level in plasma increased in irbesartan group and it
had a significant difference when compared with that in WKY group.
Ang II level decreased in mesenteric artery in SHR group and it was
obvious in imidapril group. Ang II level increased in mesenteric
artery in irbesartan group and it had a significant difference.
Campbell et al.[22] made clear with experiment
that Ang II levels in SHR plasma, lung, kidney, heart, adrenal,
aorta, brown adipose tissue were lower than the levels in Donryu
rats. In this experiment, Ang II levels in plasma of SHR group and
WKY group and mesenteric artery were consistent with Duncan’s
experiment. Moreover, imidapril decreased Ang II levels and
irbesartan increased Ang II levels[23] in SHR plasma and
mesenteric artery in this experiment.
Light
microscopy and electron microscopy displayed that imidapril and
irbesartan might inhibit structure alterations especially
interstitial fibrosis. Furthermore, the effect of imidapril was
better than that of irbesartan. It should be pointed out that
electron microscopy of mesenteric artery displayed that the
pathology of mesenteric artery remodeling in SHR possibly involved
in fibrous tissue hyperplasia in adventitia, fibrosis in media,
structure and function damage in endothelial cells. Castro et al[24].
believed that extracellular matrix (ECM) accumulation in blood
vessel walls could be attributable to constriction of artery lumen
in hypertension. The pathological changes of resistance vessels
could relate to the synthesis and excretion reduction of
proteoglycan in blood vessel smooth muscle cells.
Several
experiments have shown that Ang II could induce vascular smooth
muscle cell proliferation in vivo. Griffin suggested that Ang II
infusion in rats increased mesenteric vascular media width, media
cross-sectional area and media/lumen ratio, and these changes were
not inhibited by hydralazine despite normalization of blood
pressure. Kim et al.[25] also revealed that aortic
ERK and JNK activities were significantly increased with the
development of hypertension, and in particular, these activities
were gradually and chronically enhanced in the development of
hypertension and associated with an increase in aortic weight. In
vitro experiments have also shown that Ang II stimulated protein
synthesis and induced cellular hypertrophy in cultured vascular
smooth muscle cells via AT1 receptors. More and more evidences have
shown that AT1 receptors couple to a heterotrimeric G protein Gq.
The activation of AT1 receptors could not only lead to the
activation of PLC-b
and increases of diacylgcerol and Ca2+ in cells but also
activate intracellular signal transduction in cultured vascular
smooth muscle cells. Schmitz et al.[26] reported
that Ang II could also activate JNK of vascular smooth muscle cells.
JNK is well known to increase c-Jun transactivation by
phosphorylating c-Jun on 2 critical N-terminal serine residues and
inducing c-fos gene expression. Therefore, it has been well known
that JNK is involved in the activation of transcription factor, AP-1[27].
AP-1 is bound to TPA response component (TRE) of nucleus DNA to
accelerate transcription and to increase proliferation and protein
synthesis of vascular smooth muscle cells. In vascular smooth muscle
cells, activation of ERK and AP-1 could increase expression of TGF-b1
mRNA[28]. Both vascular endothelial cells and vascular
smooth muscle cells could synthesis TGF-b1[29].
TGF-b1
has been found to be one kind of multi-function proteins[30]
and to adjust hypertrophy and polyploidy of many kinds of cells and
to stimulate and inhibit hyperplasia. In a word, it relates to
vessel remodeling. TGF-b1
is bound to specific receptors in cell surface to initiate the
intracellular p53-dependent signaling cascade, resulting in down
regulation or inhibition of cyclin-dependent kinases 2 and 4, and
inducing cell cycle arrest in G1. Ang II can mediate intracellular
signal transduction of vascular smooth muscle cells. Remodeling of
mesenteric artery in SHR would be inhibited if the expression of
c-Jun and/or TGF-b1
could be inhibited. Therefore, this experiment used AT1 receptor
antagonist irbesartan and ACE inhibitor imidapril to interfere
mesenteric artery remodeling in SHR in order to investigate the
expression difference of c-Jun and TGF-b1
mRNA in mesenteric artery with RT-PCR and to illustrate the
intervention action and effect difference of these two kinds of
drugs on inhibiting mesenteric artery remodeling.
Compared
with WKY group, the mRNA level of TGF-b1
and c-Jun in mesenteric arteries of SHR group was obviously
increased. Imidapril and irbesartan might inhibit the expression of
c-Jun and TGF-b1
mRNA in mesenteric artery of SHR. Imidapril was better than
irbesartan in preventing mesenteric arteries from structure
modulation especially fibrosis and expression of TGF-b1,
-Jun mRNA. Ohta et al proved that aortic TGF-b1,
fibronectin, and collagen type IV WmRNA levels were higher in SHR
than in WKY, and all of these elevated mRNAs in the aorta of SHR
were significantly reduced by an ACE inhibitor, alacepril (50 mg/kg.d),
or an AT1 receptor antagonist, SC-52458 (50 mg/kg.d). Kim et al.[31]
also showed that treatment with AT1 receptor antagonist (E4177, 20
mg/kg.d) significantly inhibited the activation of JNK and ERK in
injured arteries. These experiments illuminate that the results in
our investigation are acceptable. Further study should be done for
the combined action of imidapril and irbesartan.
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Edited
by Wang
XL and Xu FM
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