(Hypertension. 2000;36:917.)
© 2000 American Heart Association, Inc.
Colin Johnston - A Celebration |
Action of Angiotensin II on DNA Synthesis by Human Saphenous Vein in Organ Culture
From Clinical Pharmacology, National Heart and Lung Institute, Imperial College School of Medicine, St Mary’s Hospital, London, UK.
Correspondence to Dr J. Ibrahim, Center for Cardiovascular Research, Kornberg Medical Research Building, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642-8679.
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Angiotensin II (Ang II), an effector peptide of the renin-angiotensin system, has been reported to stimulate growth of blood vessels in vivo and smooth muscle cells in culture. In this study, the effect of Ang II on DNA synthesis was examined in deendothelialized human saphenous vein in organ culture. After 7 days’ exposure to medium containing 0.4% fetal calf serum plus Ang II, there was a marked increase in DNA synthesis. The effect of Ang II was comparable to the response to platelet-derived growth factor. Responses to Ang II were partially inhibited by the AT1 receptor antagonist candesartan. An AT2 receptor antagonist, PD123319, had no effect on Ang II–induced DNA synthesis, either alone or in combination with candesartan. The Ang II peptide analogues [Sar1,Ile8]-Ang II (saralasin) and [Sar1,Thr8]-Ang II (sarthran) acted as agonists, increasing DNA synthesis. In the presence of saralasin, responses to Ang II were inhibited. Tyrphostin-23, a tyrosine kinase inhibitor, prevented Ang II–induced DNA synthesis and reduced DNA synthesis in tissues incubated in medium containing only 0.4% fetal calf serum. In conclusion, Ang II stimulates DNA synthesis in human saphenous vein in organ culture. The effect of Ang II was more marked than has been previously reported in isolated cultured saphenous vein smooth muscle cells, and this effect is mediated in part by an angiotensin type 1 receptor. It is possible that an undefined receptor for Ang II may also be involved in the stimulation of DNA synthesis in this preparation.
Key Words: human saphenous vein • muscle, smooth • DNA synthesis • angiotensin II • organ culture • angiotensin I
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Angiotensin II (Ang II) is an important regulator of vascular smooth muscle cell growth: infusion of Ang II stimulates vascular hypertrophy in rats,1 2 3 independently of changes in blood pressure,1 3 and also enhances neointimal formation after vascular injury.4 Inhibition of Ang II formation by angiotensin-converting enzyme inhibitors (ACEI) reverses vascular hypertrophy associated with hypertension5 and inhibits neointimal growth after vascular injury in rats.6 However, such effects may be species dependent, because ACEI has been reported to have little or no effect on the response to vascular injury in rabbits,7 pigs,8 or baboons.9 In addition, an ACEI also failed to reduce the incidence of restenosis in a recent clinical trial.10
Angiotensin type 1 (AT1) receptors are considered to mediate most of the effects of Ang II on vascular growth,11 although angiotensin type 2 (AT2) receptors may also contribute.12 13 14 Rodent vascular injury models have been reported to overexpress AT1 receptors,15 and an AT1 antagonist inhibits neointimal hyperplasia in injured rat carotid arteries.16 In contrast, an AT1 antagonist had no effect on intimal hyperplasia in a porcine vascular injury model.17
Ang II has also been reported to promote the growth of cultured smooth muscle cells. Ang II stimulated 3H-thymidine and 3H-leucine incorporation in smooth muscle cells derived from human aorta and subcutaneous arteries.18 In contrast, in human coronary smooth muscle cells, Ang II stimulated protein synthesis but not DNA synthesis.19 In human saphenous vein–derived smooth muscle cells, Ang II induced some DNA synthesis in one study20 but failed to stimulate proliferation or protein synthesis in another.21 Although these data provide some evidence for trophic effects of Ang II, isolated cells may lack cell-cell and cell-matrix interactions that influence responses to growth factors. We therefore examined the effect of Ang II on DNA synthesis in human saphenous vein segments in an organ culture system in which such interactions are maintained. These studies also examined the involvements of receptor subtypes and the possible role of tyrosine kinase activation in Ang II–induced responses.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Clinical Details
Segments of veins surplus to clinical requirement were obtained from 55 patients (43 men and 12 women, age range 50 to 78 years) who were undergoing coronary artery bypass surgery. Studies were in accordance with local ethics committee guidelines. Patients taking ACEI or AT1 antagonists before surgery were excluded from the study.
Tissue Preparation and Culture
Segments of vein were transferred to the tissue
culture laboratory in cold Hanks’ balanced sale solution buffered with
25 mmol/L HEPES and prepared for culture by a procedure based on
that described by Soyombo et
al.22 Briefly, the
adventitia and extraneous adhering fat were removed, and the vein was
cut open longitudinally. The luminal surface was gently rubbed with a
sterile cotton bud to remove the endothelium, and the
tissue was then cut into 
5-mm segments. Segments were then pinned,
luminal surface uppermost, onto culture dishes precoated with a layer
of silicone elastomer. Culture dishes were filled with medium
consisting of Dulbecco’s modified Eagle medium (DMEM) supplemented
with penicillin (100 U/mL), streptomycin (100 µg/mL), and gentamicin
(25 µg/mL). Veins were cultured in a humidified atmosphere of 5%
(vol/vol) carbon dioxide in air at 37°C for 7 days in DMEM containing
0.4% serum (SFM), 30% serum, or SFM plus drugs.
Antagonists or peptide analogues were incubated with
tissues for at least 10 minutes before the addition of Ang II. Drugs
and peptides were replenished daily throughout the culture
period.
Measurement of DNA Synthesis
DNA synthesis was determined by measuring the
incorporation of 3H-methylthymidine.
3H-methylthymidine (1 µCi/mL) was added to
the culture dishes for 24 hours, and the experiment was then terminated
by washing the vein segments twice with ice-cold PBS. All studies were
performed in triplicate. Tissue wet weight was recorded, and veins
were then lysed by exposure to a tissue solubilizer (NCS-II; Amersham)
for 48 hours. The acid insoluble fraction was then extracted on ice
with 10% (wt/vol) trichloroacetic acid. Radioactivity was determined
by means of a scintillation counter, and the counts per minute (cpm)
were normalized to micrograms of wet tissue weight. Initial experiments
were performed to determine a time course for
3H-thymidine incorporation into human
saphenous vein in organ culture. Veins were incubated in culture medium
containing 0.4%, 1%, or 30% serum for 3 time points: 1 day, 3 days,
and 7 days. At the end of these time points,
3H-thymidine incorporation was maximal in
response to 30% serum after 7 days (10-fold increase), and
therefore this time point was chosen for all subsequent
experiments.
Morphometric Analysis
After culture, vein segments from some treatment
groups were fixed in 10% formalin, embedded in paraffin, and stained
with Miller’s elastic and van Giessen stains. Randomly selected vein
sections were also stained with hematoxylin-eosin or
immunostained with a monoclonal Ki67 (Novacastra) antibody
(counterstained with hematoxylin) to identify the nuclear antigen
(Ki67) associated with cell proliferation. For quantification of Ki67
labeling, total cell number and the number of Ki67-positive cells were
counted in the media of vein sections using a x40 objective. Vein wall
thickness was determined by morphometric analysis of images
generated by a Zeiss Axioscope equipped with a CCD camera and
appropriate software (NIH Image). Intimal/neointimal
thickness was defined by tissue on the luminal side of the internal
elastic lamina (a trace of acellular thickening was present in this
layer of all vein segments before culture). Medial thickness was
defined by tissue enclosed by the internal and external elastic
laminae.
Drugs
Candesartan and EXP3174 were gifts from Takeda Inc
and DuPont,
respectively.
Other sources of drugs were as follows: Ang II (human), Novabiochem;
PD123319, Research Biochemicals; and
[Sar1,Ile8]-Ang
II,
[Sar1,Thr8]-Ang
II, and tyrphostin-23, Sigma. Ang II is rapidly broken down by tissue
proteases and therefore is able to achieve stable levels in culture.
Ang II (1 to 100 nmol/L) was delivered via osmotic minipumps (Charles
River) at an infusion rate of 0.5 µL/h. This method of administration
resulted in concentrations of Ang II in culture medium of
8.5±0.7x10-8 mol/L as measured by
radioimmunoassay on day 7 using Ang II (100 nmol/L). Candesartan stock
was made up in dimethyl sulfoxide (DMSO); the final concentration of
DMSO did not exceed 0.0001%. Other antagonists and
peptides were made up in PBS.
Statistical Analysis
Treatment groups were compared by Student’s paired
and unpaired t test as
appropriate or repeated-measures ANOVA for comparison of 3 or more
groups, followed by Dunnett’s test with Instat 3.02 (GraphPad Software
Inc). Statistical significance was accepted at
P<0.05. All values are
mean±SEM of n observations.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Ang II (1 to 100 nmol/L) caused a marked, concentration-dependent increase in DNA synthesis over 7 days (Figure 1A). Tyrphostin-23, a selective inhibitor of tyrosine kinases, reduced 3H-thymidine incorporation in SFM and also abolished the increase induced by Ang II (10 nmol/L). Responses to Ang II varied between individuals, but overall Ang II (10 nmol/L) significantly increased DNA synthesis compared with veins exposed to SFM (Figure 1B). Responses to Ang II were comparable in magnitude to those to platelet-derived growth factor-AB (PDGF-AB; 1 ng/mL), although less than those to 30% serum (Figure 1B).
|
We examined the role of AT1 receptors in responses to Ang II by incubating veins with Ang II and the nonpeptide AT1 antagonist candesartan. Candesartan (1 nmol/L) had no significant effect on DNA synthesis in SFM or 30% serum (data not shown), but it significantly attenuated responses to Ang II (10 nmol/L) (Figure 2A). Higher concentrations of candesartan had no additional effect, and the active metabolite of the related AT1 receptor antagonist, losartan (EXP3174; 10 µmol/L), caused responses to Ang II to be diminished to a similar extent (Ang II+EXP3174=57±47% of Ang II response; n=3). The selective AT2 receptor antagonist PD123319 (100 nmol/L) had no significant effect on the Ang II response (Figure 2A). The combination of PD123319 (100 nmol/L) and candesartan (10 nmol/L) also did not inhibit responses to Ang II to a greater extent than candesartan alone.
|
In view of the failure of candesartan or losartan to abolish responses to Ang II, the effects of the nonselective peptide antagonists [Sar1,Ile8]-Ang II (saralasin) and [Sar1,Thr8]-Ang II (sarthran) were examined. Both saralasin (1 µmol/L) and sarthran (100 nmol/L) acted as agonists and increased DNA synthesis (Figure 2B). In the presence of saralasin (1 µmol/L), DNA synthesis in response to Ang II was abolished (Figure 2B).
In addition to stimulation of DNA synthesis, Ang II caused a small and statistically insignificant increase in thickness of the vein media by 28±17% (n=7). There was no significant change in intimal thickness. Endothelial cell regeneration did not occur over the course of the study, as indicated by the lack of immunohistochemical staining for the endothelial cell antigen CD31 (data not shown). Ang II caused a significant increase in the percentage of Ki67-positive cells (taken as an index of proliferating cells) in the media of vein sections (SFM=2.2±1%; Ang II=6.2±0.7%; n=3; P<0.01). After hematoxylin-eosin staining of vein sections, medial nuclear density appeared to be increased by 30% serum and Ang II. Ang II and 30% serum did not induce detectable differences in histological appearance after Miller’s elastin or van Giessen staining.
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Organ culture studies may have advantages over those that use isolated cells, because cell-cell and cell-extracellular matrix interactions are preserved, and these may influence growth factor responses.23 In our studies, Ang II caused a marked concentration-dependent increase in DNA synthesis in veins cultured for 7 days in medium containing minimal (0.4%) serum. The responses to Ang II in this model were of comparable magnitude to those of a classic mitogen, PDGF. This finding contrasts with the modest stimulation of 3H-thymidine incorporation seen in an earlier study of isolated smooth muscle cells cultured from human saphenous vein.20 Further studies indicated that exposure to Ang II was also accompanied by
3-fold
increase in proliferating cell nuclear antigen Ki67-positive cells in
vein media, providing further evidence for hyperplasia in response to
Ang II. The failure to observe a significant increase in
neointima in response to Ang II in these preparations is
likely to be due to the removal of the endothelium,
because this has been reported to inhibit spontaneous
neointima formation in this
preparation.22 The extent of
DNA synthesis seen in response to Ang II varied between individuals.
The reasons for this are not known, but it perhaps should not be
unexpected given the diversity of patient ages and conditions.
Interindividual differences in the rate of growth and sensitivity to
growth inhibitors have also been observed in vascular
smooth muscle cells cultured from saphenous vein taken from different
individuals.24 The effect of Ang II on DNA synthesis in our vascular model is in contrast with 2 recent studies in which Ang II did not influence DNA synthesis over 3 days of incubation with rat aorta25 and renal artery26 segments in organ culture. In those studies, protein synthesis25 and medial hypertrophy26 were induced. Aside from interspecies differences, several possibilities may explain the difference between the present and former studies. First, in the previous investigations, daily replenishment of Ang II was used. The biological half-life of Ang II in culture systems is extremely short, because it is broken down by tissue proteases.27 It is possible that the continuous exposure achieved in the present study with osmotic minipump infusions may better stimulate DNA synthesis. Second, the longer duration of stimulation with Ang II in the present study (7 days versus 3 days) may also be a contributory factor. Although Ang II can stimulate phospholipase C and generation of diacylglycerol and inositol 1,4,5-trisphosphate within seconds or minutes, tissue exposure to Ang II for >48 hours can activate a delayed stimulation of DNA synthesis through the autocrine or paracrine production of secondary growth factors.28
Activation of tyrosine kinases is believed to participate in multiple steps of signal transduction initiated by a variety of growth factors, including PDGF and, more recently, Ang II.29 The effect of Ang II may involve direct effects on tyrosine kinases29 or transactivation of growth factor receptors.30 In the present study, Ang II–induced DNA synthesis was totally abolished by the tyrosine kinase inhibitor tyrphostin-23, implying a role for tyrosine kinases in the response to Ang II. Interestingly, 3H-methylthymidine incorporation in 0.4% serum was also inhibited by tyrphostin-23, which suggests that some DNA synthesis may occur even in the absence of any growth factor, possibly as a result of injury during vein preparation.22 31
We are unaware of any previous reports concerning the
identity of the angiotensin receptor subtype involved in
Ang II–mediated growth in intact human vascular tissue in organ
culture, although the trophic actions of Ang II on isolated smooth
muscle cells derived from human and animal tissue are mediated by the
AT1 receptor
subtype.11 15 16 32 33
In our studies, the AT1 receptor
antagonists candesartan and EXP3174 only partially
inhibited Ang II–induced DNA synthesis. The concentration of
candesartan was chosen on the basis of previous functional studies
showing that the estimated affinity
(KB) of
candesartan for the AT1 receptor in human
arteries was 10 pmol/L.34
In previous studies, similar (and lower) concentrations of these
antagonists have been shown to completely inhibit DNA
synthesis in rat aortic32
and human aortic vascular smooth muscle cells in
culture.33 The inability of
candesartan and losartan to completely inhibit responses to Ang
II implies involvement of another receptor subtype. However, the
AT2 receptor antagonist PD123319,
either alone or in combination with candesartan, had no effect on
responses to Ang II. It is possible, therefore, that the effect of Ang
II was mediated in part by a
non-AT1/non-AT2 receptor.
Consequently, we examined the effects of the nonselective Ang II
peptide antagonists saralasin and sarthran. In many
preparations, these agents act as antagonists of
angiotensin
receptors35 36
and the receptor for angiotensin
1-7.37 In our study, both
saralasin and sarthran acted as agonists and increased DNA synthesis to
levels comparable to Ang II itself. In the presence of saralasin, Ang
II–induced DNA synthesis was abolished, which indicates that Ang II
and the peptide antagonists act at common receptors. This
effect of the peptide antagonists could involve the
internalization or desensitization of receptors for Ang
II.38 39 These
observations appear consistent with an AT receptor of undefined
subtype contributing to DNA synthesis in response to Ang II; however,
additional studies, such as ligand binding studies with radiolabeled
Ang II and AT1 antagonists, would be
valuable in confirming this possibility.
Non-AT1/non-AT2 receptors have previously been described in tissues of avian species,40 41 42 43 and a unique Ang II binding site in human endometrium has also been described.44 Interestingly, saralasin has been reported to be a partial agonist at the atypical AT receptor found in the nasal salt gland of Anas platyrhynchos.40 A role for non-AT1/non-AT2 receptors in cellular growth in humans has also been proposed. Recently, non-AT1/non-AT2 receptors have been reported to mediate Ang II–induced growth in human cardiac fibroblasts45 and human keratinocytes46 in culture. Degradation products of the octapeptide Ang II (or its precursor molecules) may also exert actions on cells via non-AT1/non-AT2 receptors. Thus, angiotensin (1-7)37 43 and angiotensin IV (3-8)47 48 have been reported to promote or inhibit DNA synthesis in a variety of cell types. It would be important to examine the effects of these analogues and their antagonists in this preparation in future studies.
In summary, the present study demonstrates that Ang II induces marked DNA synthesis in saphenous vein organ culture model via a mechanism that involves activation of tyrosine kinases. Ang II–induced DNA synthesis is mediated in part by AT1 receptors, but it is likely that an atypical receptor (for which sarthran and sarile are agonists) may also contribute. Enhanced vascular smooth muscle cell growth is considered to have an important role in various pathophysiological processes, and consequently, defining the angiotensin receptor subtypes involved in this response may have important clinical implications.
|
Acknowledgments |
|---|
We gratefully acknowledge financial support from Takeda Chemical Industries (Osaka, Japan) for this study. We would also like to thank the surgeons and theater staff at St. Mary’s Hospital for the vascular tissue and Dr James Morton (Department of Medicine, University of Glasgow) for radioimmunoassay measurements of Ang II in samples of culture medium.
Received July 18, 2000; first decision August 29, 2000; accepted September 13, 2000.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Griffin SA, Brown WCB, MacPherson F, McGrath JC, Wilson VG, Korsgaard N, Mulvany MJ, Lever AF. Angiotensin II causes vascular hypertrophy in part by a non-pressor mechanism. Hypertension. 1991;17:626–635.
2. Ibrahim J, Schachter M, Hughes AD, Sever PS. Role of polyamines in hypertension induced by angiotensin II. Cardiovasc Res. 1995;29:50–56.[Medline] [Order article via Infotrieve]
3.
Su EJ, Lombardi DM,
Siegal J, Schwartz SM. Angiotensin II induces vascular
smooth muscle cell replication independent of blood pressure.
Hypertension. 1998;31:1331–1337.
4.
Daemen MJAP,
Lombardi DM, Bosman FT, Schwartz SM. Angiotensin II induces
smooth muscle cell proliferation in normal and injured rat
arterial wall. Circ
Res. 1991;68:450–456.
5.
Levy BI, Michel JB,
Salzmann JL, Azizi M, Poitevin P, Safar M, Camilleri JP. Effects of
chronic inhibition of converting enzyme on mechanical and structural
properties of arteries in rat renovascular hypertension.
Circ Res. 1988;63:227–239.
6.
Powel JS, Clozel
JP, Muller RKM, Kuhn H, Hefti F, Hosang M, Baumgartner HR.
Inhibitors of angiotensin-converting enzyme
prevent myointimal proliferation after vascular injury.
Science. 1989;245:186–188.
7. Clozel JP, Hess P, Michael C, Schietinger K, Baumgartner HR. Inhibition of converting enzyme and neointima formation after vascular injury in rabbits and guinea pigs. Hypertension. 1991;18(suppl):II-55–II-59.
8. Huber KC, Schwartz RS, Edwards WD, Camrud AR, Bailey KR, Jorgenson MA, Holmes DR Jr. Effects of angiotensin converting enzyme inhibition on neointimal proliferation in a porcine coronary injury model. Am Heart J. 1993;125:695–701.[Medline] [Order article via Infotrieve]
9. Hanson SR, Powell JS, Dodson T, Lumsden A, Kelly AB, Anderson JS, Clowes AW, Harker LA. Effects of angiotensin converting enzyme inhibition with cilazapril on intimal hyperplasia in injured arteries and vascular grafts in the baboon. Hypertension. 1991;18(suppl):II-70–II-76.
10. Faxon DP, the Multicentre American Research Trial With Cilazapril After Angioplasty to Prevent Transluminal Coronary Obstruction and Restenosis (MARCATOR) Study Group. Effect of high dose angiotensin-converting enzyme inhibition on restenosis: final results of the MARCATOR study, a multicenter, double-blind, placebo-controlled trial of cilazapril. J Am Coll Cardiol. 1995;25:362–369.[Abstract]
11. Helin K, Stoll M, Meffert S, Stroth U, Unger T. The role of angiotensin receptors in cardiovascular disease. Ann Med. 1997;29:23–29.[Medline] [Order article via Infotrieve]
12.
Janiak P, Pillon
A, Prost JF, Vilaine JP. Role of angiotensin subtype-2
receptor in neointima formation after vascular injury.
Hypertension. 1992;20:737–745.
13. Levy BI, Benessiano J, Henrion D, Caputo L, Heymes C, Duriez M, Poitevin P, Samuel JL. Chronic blockade of AT2-subtype receptors prevents the effect of angiotensin II on the rat vascular structure. J Clin Invest. 1996;98:418–425.[Medline] [Order article via Infotrieve]
14.
Horiuchi M,
Akishita M, Dzau VJ. Recent progress in angiotensin II type
2 receptor research in the cardiovascular system.
Hypertension. 1999;33:613–621.
15.
Deblois D,
Viswanathan M, Su JE, Clowes AW, Saavedra JM, Schwartz SM. Smooth
muscle DNA replication in response to angiotensin II is
regulated differently in the neointima and media at
different times after balloon injury in the rat carotid artery: role of
AT1 receptor expression. Arterioscler
Thromb Vasc Biol. 1996;16:1130–1137.
16. Osterrieder W, Muller RK, Powell JS, Clozel JP, Hefti F, Baumgartner HR. Role of angiotensin II in injury-induced neointima in rats. Hypertension. 1991;18:60–64.
17.
Huckle WR, Drag
MD, Acker WR, Powers M, McFall RC, Holder DJ, Fujita T, Stabilito II,
Kim D, Ondeyka DL, Mantlo NB, Chang RSL, Reilly CF, Schwartz RS,
Greenlee WJ, Johnson RG. Effects of subtype-selective and balanced
angiotensin II receptor antagonists in a
porcine coronary artery model of vascular restenosis.
Circulation. 1996;93:1009–1019.
18. Touyz RM, Deng LY, He G, Wu XH, Schiffrin EL. Angiotensin II stimulates DNA and protein synthesis in vascular smooth muscle cells from human arteries: role of extracellular signal-regulated kinases. J Hypertens. 1999;17:907–916.[Medline] [Order article via Infotrieve]
19. Hafizi S, Chester AH, Allen SP, Morgan K, Yacoub MH. Growth response of human coronary smooth muscle cells to angiotensin II and influence of angiotensin AT1 receptor blockade. Coron Artery Dis. 1998;9:167–175.[Medline] [Order article via Infotrieve]
20. Patel MK, Betteridge LJ, Hughes AD, Clunn GF, Schachter M, Shaw RJ, Sever PS. Effect of angiotensin II on the expression of the early growth-response gene c-fos and DNA synthesis in human vascular smooth-muscle cells. J Hypertens. 1996;14:341–347.[Medline] [Order article via Infotrieve]
21. Mii S, Ware JA, Mallette SA, Kent KC. Effect of angiotensin II on human vascular smooth muscle cell growth. J Surg Res. 1994;57:174–178.[Medline] [Order article via Infotrieve]
22. Soyombo AA, Thurston VJ, Newby AC. Endothelial control of vascular smooth muscle proliferation in an organ culture of human saphenous vein. Eur Heart J. 1993;14:201–206.
23. Sudhir K, Wilson E, Chatterjee K, Ives HE. Mechanical strain and collagen potentiate mitogenic activity of angiotensin II in rat vascular smooth muscle cells. J Clin Invest. 1993;92:3003–3007.
24. Munro E, Chan P, Patel M, Betteridge L, Gallagher K, Schachter M, Sever P, Wolfe J. Consistent responses of the human vascular smooth muscle cell in culture: implications for restenosis. J Vasc Surg. 1994;20:482–487.[Medline] [Order article via Infotrieve]
25. Holycross BJ, Peach MJ, Owens GK. Angiotensin II stimulates increased protein-synthesis, not increased DNA synthesis in intact rat aortic segments in vitro. J Vasc Res. 1993;30:80–86.[Medline] [Order article via Infotrieve]
26.
Schiffers PMH,
Gregario FE, Schenau DVI, De Mey JGR. Effects of candidate autocrine
and paracrine mediators on growth responses in isolated rat arteries.
Arterioscler Thromb. 1994;14:420–426.
27.
Bunkenburg B, Van
Amelsvoort T, Rogg H, Wood JM. Receptor-mediated effects of
angiotensin II on growth of vascular smooth muscle cells
from spontaneously hypertensive rats.
Hypertension. 1992;20:746–754.
28. Weber H, Taylor DS, Molloy CJ. Angiotensin II induces delayed mitogenesis and cellular proliferation in rat aortic smooth muscle cells. J Clin Invest. 1994;93:788–798.
29.
Berk BC, Corson
MA. Angiotensin II signal transduction in vascular smooth
muscle: role of tyrosine kinases. Circ
Res. 1997;80:607–616.
30. Li X, Lee JW, Graves LM, Earp HS. Angiotensin II stimulates ERK via two pathways in epithelial cells: protein kinase C suppresses a G-protein coupled receptor-EGF receptor transactivation pathway. EMBO J. 1998;17:2574–2583.[Medline] [Order article via Infotrieve]
31. Barker JE, Anderson J, Treasure T, Piper PJ. Influence of endothelium and surgical preparation on responses of human saphenous vein and internal thoracic artery to angiotensin II. Br J Clin Pharmacol. 1994;38:57–62.[Medline] [Order article via Infotrieve]
32. Sachinidis A, El Haschimi K, Ko Y, Seul C, Dusing R, Vetter H. CV-11974, the active metabolite of TCV-116 (candesartan), inhibits the synergistic or additive effect of different growth factors on angiotensin II induced proliferation of vascular smooth muscle cells. Biochem Pharmacol. 1996;52:123–126.[Medline] [Order article via Infotrieve]
33. Makita S, Nakamura M, Yoshida H, Hiramori K. Effect of angiotensin II receptor blocker on angiotensin II stimulated DNA synthesis of cultured human aortic smooth muscle cells. Life Sci. 1995;56:383–388.
34. Garcha RS, Sever PS, Hughes AD. Action of AT1 receptor antagonists on angiotensin II-induced tone in human isolated subcutaneous resistance arteries. Br J Pharmacol. 1999;127:1876–1882.[Medline] [Order article via Infotrieve]
35. Liu YJ, Shankley NP, Welsh NJ, Black JW. Evidence that the apparent complexity of receptor antagonism by angiotensin II analogues is due to a reversible and syntopic action. Br J Pharmacol. 1992;106:233–241.[Medline] [Order article via Infotrieve]
36. Brechler V, Jones PW, Levens NR, de Gasparo M, Bottari SP. Agonistic and antagonistic properties of angiotensin analogues at the AT2 receptor in PC12W cells. Regul Pept. 1993;44:207–213.[Medline] [Order article via Infotrieve]
37.
Freeman EJ,
Chisolm GM, Ferrario CM, Tallant EA. Angiotensin 1-7
inhibits vascular smooth muscle cell growth.
Hypertension. 1996;28:104–108.
38. Conchon S, Monnot C, Teutsch B, Corvol P, Clauser E. Internalization of the rat AT1a and AT1b receptors: pharmacological and functional requirements. FEBS Lett. 1994;349:365–370.[Medline] [Order article via Infotrieve]
39.
Thomas WG,
Motel TJ, Kule CE, Karoor V, Baker KM. Phosphorylation
of the angiotensin II (AT1A) receptor carboxyl terminus: a
role in receptor endocytosis. Mol
Endocrinol. 1998;12:1513–1524.
40. Butler DG, Zandevakili R, Oudit GY. Effects of ANG II and III and angiotensin receptor blockers on nasal salt gland secretion and arterial blood pressure in conscious Pekin ducks (Anas platyrhynchos). J Comp Physiol [B]. 1998;168:213–224.[Medline] [Order article via Infotrieve]
41. Nishimura H, Walker OE, Patton CM, Madison AB, Chiu AT, Keiser J. Novel angiotensin receptor subtypes in fowl. Am J Physiol. 1994;36:R1174–R1181.
42. Murphy TJ, Nakamura Y, Takeuchi K, Alexander RW. A cloned angiotensin receptor isoform from the turkey adrenal gland is pharmacologically distinct from mammalian angiotensin receptors. Mol Pharmacol. 1993;44:1–7.[Abstract]
43. Kempf H, le Moullec JM, Corvol P, Gasc JM. Molecular cloning, expression and tissue distribution of a chicken angiotensin II receptor. FEBS Lett. 1996;399:198–202.[Medline] [Order article via Infotrieve]
44. Ahmed A, Li XF, Shams M, Gregory J, Rollason T, Barnes NM, Newton JR. Localization of angiotensin II and its receptor subtype expression in human endometrium and identification of a novel high-affinity angiotensin II binding site. J Clin Invest. 1995;96:848–857.
45. Neuss M, Regitz-Zagrosek V, Hildebrandt A, Fleck E. Isolation and characterisation of human cardiac fibroblasts from explanted adult hearts. Cell Tissue Res. 1996;286:145–153.[Medline] [Order article via Infotrieve]
46. Steckelings UM, Artuc M, Paul M, Stoll M, Henz BM. Angiotensin II stimulates proliferation of primary human keratinocytes via a non-AT1, non-AT2 angiotensin receptor. Biochem Biophys Res Commun. 1996;229:329–333.[Medline] [Order article via Infotrieve]
47. Hall KL, Ventkateswaran S, Hanesworth JM, Schelling ME, Harding JW. Characterisation of a functional angiotensin IV receptor on coronary microvascular endothelial cells. Regul Pept. 1995;58:107–115.[Medline] [Order article via Infotrieve]
48. Yang QL, Hanesworth JM, Harding JW, Slinker BK. The AT (4) receptor agonist [Nle(1)]-angiotensin IV reduces mechanically induced immediate early gene expression in the isolated rabbit heart. Regul Pept. 1997;71:175–183.[Medline] [Order article via Infotrieve]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||