(Hypertension. 2000;36:1099.)
© 2000 American Heart Association, Inc.
Colin Johnston - A Celebration |
Retinal Neovascularization Is Prevented by Blockade of the Renin-Angiotensin System
From the Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia (C.J.M., S.L.S., J.L.W.-B.); the Department of Medicine, The University of Melbourne, St Vincents Hospital, Fitzroy, Victoria, Australia (D.J.K., R.E.G.); the Department of Medicine, The University of Melbourne, Austin and Repatriation Medical Centre, Heidelberg West, Victoria, Australia (M.E.C.); the Department of Anatomy, Monash University, Clayton, Victoria, Australia (J.F.B.); and Merck Research Laboratories, Bluebell, Pa (S.S.).
Correspondence to Dr Jennifer L. Wilkinson-Berka, Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia, 3010. E-mail j.berka{at}physiology.unimelb.edu.au
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Abstract |
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Both angiotensin II and vascular endothelial growth factor are angiogenic agents that have recently been implicated in the pathogenesis of proliferative diabetic retinopathy. In this study, retinal neovascularization was examined in a model of retinopathy of prematurity with the use of neonatal transgenic (mRen-2)27 rats, which overexpress renin in tissues, and Sprague-Dawley rats. Blockers of the renin-angiotensin system were administered during the neovascularization period. The ACE inhibitor lisinopril and the angiotensin type 1 receptor antagonist losartan both increased retinal renin levels and prevented inner retinal blood vessel growth. Quantitative in situ hybridization revealed that the expression of vascular endothelial growth factor and its type 2 receptor in the inner retina and proliferating blood vessels were increased in rats with retinopathy of prematurity. Lisinopril reduced both retinal vascular endothelial growth factor and its type 2 receptor mRNA in retinopathy of prematurity rats, whereas losartan had no effect. It is predicted that agents that interrupt the renin-angiotensin system may play an important role as retinoprotective agents in various forms of proliferative retinopathy.
Key Words: renin\b • growth substances\b • angiotensin\b • renin-angiotensin system
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Introduction |
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Angiogenesis is the major feature of several retinal pathologies including proliferative diabetic retinopathy and retinopathy of prematurity (ROP).1 In these conditions, retinal neovascularization has catastrophic effects on vision leading to hemorrhage, edema, and ultimately, blindness.1 The factors that stimulate retinal blood vessel growth have not been fully defined, but circumstantial evidence indicates that this involves not only angiogenic cytokines such as vascular endothelial growth factor (VEGF) but also vasoactive hormones such as angiotensin II (Ang II). Recently, in a multicenter trial, the EURODIAB Controlled Trial of Lisinopril in Insulin-Dependent Diabetes Mellitus (EUCLID) study group reported that ACE inhibition (ACEI) was associated with a reduction in proliferative diabetic retinopathy,2 providing a potential clinical role for suppression of the renin-angiotensin system (RAS) in preventing and treating retinal neovascularization.
The hypothesis that an ocular RAS is involved in the development of proliferative diabetic retinopathy is supported by evidence that all components of the RAS are present in the retina3 4 5 6 7 and that Ang II, the effector molecule of this system, is angiogenic.8 We have localized renin to the macroglial Müller cell,3 making this the likely site for pathophysiological processes involving the retinal RAS. The Müller cell is also the site of synthesis of the potent angiogenic factor VEGF and its tyrosine kinase receptors.9 There is evidence of an association between VEGF, the RAS, and retinal neovascularization because both VEGF and prorenin increase in the vitreous of patients with proliferative diabetic retinopathy10 11 and Ang II increases VEGFR-2 receptor mRNA in retinal endothelial cells.12
This study sought to determine if the retinal renin-angiotensin and VEGF systems influence vessel growth in a rat model of ROP and whether RAS blockade can prevent retinal neovascularization. Comparisons were made with the transgenic (mRen-2)27 rat, which exhibits enhanced renin expression in many tissues including the retina.13 14 15
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Methods |
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Retinopathy of Prematurity (ROP) Model
All experimental procedures adhered to the guidelines of the Australian National Health and Medical Research Council. Newborn Sprague-Dawley (SD) and homozygous transgenic Ren-2 rats and their mothers were housed in an incubator regulated at 80±2% O2 and <2% CO2, with medical grade O2 and industrial grade air. The gas composition of the chamber was monitored every 4 to 8 hours by an ML 205 gas analyzer and chart recorder (MacLab/2E System, AD Instruments Pty Ltd) while an air flow rate of
2.5L/min guarded
against increases in metabolically produced
CO2 and falls in O2
tension. The rats were housed in the incubator for 11 days. Retinal
neovascularization was induced by exposure to room air for 7 days after
the time in oxygen.16 Adult
homozygous Ren-2 rats are usually maintained on ACEI for blood pressure
control. This drug was withdrawn from the hypertensive mothers 3 weeks
before mating. All rats were allowed free access to water and standard
rat chow (GR2, Clark-King & Co) and exposed to 12-hour light/dark
cycles. SD and Ren-2 rats (n=6 rats/group) were subjected to the following protocols: ROP shams (newborn pups housed in room air for 18 days), ROP (newborn pups housed in 80±2% O2 for 11 days and then in room air for 7 days), and ROP rats administered either the ACEI lisinopril (Zeneca Pharmaceuticals, 10 mg/kg body wt IP daily) or the angiotensin type 1 (AT1) receptor blocker losartan (Merck, 10 mg/kg body wt IP daily) from days 11 to 18. At day 18, rats were anesthetized for the collection of tissues (60 mg/kg body wt IP Nembutal, Bohringer Ingelheim).
Retinopathology and Quantification of Blood
Vessels
Eyes were enucleated, fixed for 2 hours in Bouin’s
fixative, dehydrated in alcohol, and then embedded in paraffin for
sectioning at 90° to the optic nerve. Each eye was serially sectioned
at 3 µm (500 sections/eye), and every 10th section was stained
with hematoxylin and eosin to examine retinal morphology. The number of
blood vessel profiles (BVPs) in the inner retina were evaluated in a
double-masked fashion in 3 randomly chosen sections. The inner retina
comprised the inner limiting membrane (ILM), the ganglion cell layer
(GCL), and the inner plexiform layer (IPL). A BVP was defined as an
endothelial cell or a blood vessel with a lumen.
Because it was unclear whether vessels in the vitreous originated from
the inner retina, they were excluded from the BVP index. Each section
was projected onto a screen by means of a closed-circuit camera. A
stereological test grid measuring 150x150 mm and divided into
16-U areas was superimposed onto each image, and an automatic stage was
used to advance across the entire retina by means of an unbiased
counting frame. BVPs within 
500-U areas were counted per
eye.
Renin Assay
Both eyes from each rat were enucleated, and lenses
and vitreous were removed. Active renin was measured in the left eye
and total renin (trypsin activated) in the right eye by means
of an enzyme kinetic
method.3 13
Prorenin was derived as total minus active renin. Plasma was obtained
by cardiac puncture from anesthetized rats before the rats were
killed and assayed for active renin and
prorenin.3 13
VEGF and VEGFR-2 Gene Expression
Riboprobes were synthesized from cDNAs encoding mouse
VEGF and VEGFR-2 (Dr S. Stacker, Ludwig Institute, Melbourne,
Australia). The cDNAs were cloned into pGEM 4Z (Promega) and linearized
with HindIII to produce
antisense probes with SP6 RNA polymerase. Gene expression of VEGF and
VEGFR-2 in retina were evaluated by 2 different techniques as
previously described.9
Briefly, in the first method, densitometry was performed on
autoradiographs of the entire retina (n=6 retina per group). In the
second approach, dark field images were obtained from 3-µm paraffin
sections of retina. The area of the inner retina occupied by
autoradiographic grains was determined in 6 sections from
each rat.
Statistical Analysis
Data were analyzed by ANOVA followed by a
Fisher’s post hoc comparison, with a value of
P<0.05 considered
statistically significant. Because retinal renin levels were not
normally distributed, these data were analyzed after
logarithmic transformation.
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Results |
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Histology
In shams, BVPs in the inner retina were observed in the ILM and IPL (Figure 1A), and none extended into the vitreous. By contrast, in ROP rats, all eyes exhibited BVPs protruding into the vitreous from the ILM (Figure 1B). Numerous BVPs were observed in the IPL that appeared tortuous and branched. Hemorrhage and inflammatory cells were present in the vitreous and inner retina of some eyes. In SD and Ren-2 ROP rats treated with either lisinopril or losartan (Figure 1, C, D, G and H), the inner retina appeared similar to shams, although occasional vessels protruded into the vitreous of lisinopril-treated ROP rats.
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Retinal Blood Vessel Profile Index
There was no significant difference in the number of
BVPs per unit area of inner retina between SD and Ren-2 ROP shams
(Figure 2). In contrast, BVPs were increased in both SD and
Ren-2 ROP groups compared with shams. Furthermore, Ren-2 ROP rats had
significantly more BVPs than did SD ROP rats. Lisinopril
and losartan reduced the number of BVPs in both SD ROP and
Ren-2 ROP rats to the level of ROP shams.
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P<0.01 vs SD ROP; 
P<0.01 vs respective ROP group; §P<0.05 vs SD ROP.
Eye and Plasma Renin
The results are presented in the
Table.
In ROP shams, total renin was 6 times higher in Ren-2 than in SD
rats. ROP increased retinal total renin in both SD and Ren-2 rats and
was further increased with lisinopril and losartan.
In both rat strains, the rise in total renin with RAS blockade was
mainly due to active renin, particularly in SD ROP rats. The plasma of
Ren-2 ROP sham rats contained more total renin than SD ROP shams, but
it was mainly prorenin. Plasma active renin in SD and Ren-2 shams was
not different, and ROP did not alter their levels. ROP increased plasma
prorenin moderately in Ren-2 ROP rats. With lisinopril and
losartan treatment, plasma total renin increased in both SD ROP
and Ren-2 ROP rats, with SD ROP containing mainly active renin and
Ren-2 ROP similar amounts of active renin and
prorenin.
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Quantitative In Situ Hybridization
Microscopy
In shams, VEGF
(Figure 3, A and B) and VEGFR-2 (not shown) expression were
detected in the ILM, GCL, inner nuclear layer (INL), and retinal
pigment epithelium. With ROP, the intensity of both VEGF
(Figure 3, C and D) and VEGFR-2 (not shown) mRNA were
increased, and expression was also observed on vessels protruding into
the vitreous. In ROP rats treated with lisinopril, labeling
for VEGF
(Figure 3, E and F) and VEGFR-2 (not shown) was reduced to
almost undetectable levels. Losartan did not alter the
intensity or distribution of VEGF
(Figure 3, G and H) or VEGFR-2 (not shown) mRNA in ROP
compared with untreated ROP rats. Quantification of optical density in
autoradiographs of VEGF
(Figure 4A) and VEGFR-2
(Figure 4B) and cellular expression of VEGF
(Figure 4C and VEGFR-2
(Figure 4D) in dark-field micrographs confirmed the
qualitative assessment of probe distribution. No differences in the
distribution of VEGF and VEGFR-2 expression were observed between rat
strains.
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Discussion |
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This study implicates the local ocular RAS in the pathogenesis of retinal neovascularization in ROP, as evidenced by increased retinal renin levels and prevention of vascular growth by both ACEI and AT1 receptor blockade. In addition, in the Ren-2 rat, which phenotypically exhibits enhanced retinal active renin levels, the vessel profiles were increased more than for SD rats with induction of the hypoxia-mediated retinal injury. Of particular significance was the ability of the RAS blockers to suppress retinal neovascularization in both Ren-2 and normal SD rats. Together, these findings suggest that endogenous retinal Ang II is involved in the retinal neovascularization process.
Identification of RAS components including angiotensinogen, ACE, and renin expression within the eyes of humans, rats, and other species has provided evidence for a local RAS.3 4 5 6 7 The detection of retinal Ang II receptors by gene expression5 and ligand binding6 further supports the presence of a functioning intraretinal RAS. Local production of Ang II is also suggested by the finding that retinal Ang II levels in bovine eyes are higher than in plasma.4 Previously, we reported that renin protein exists in normal rodent and human retina mainly in the form of active renin, with localization to the Müller cell.3 The present study provides evidence that after ROP and RAS blockade, retinal renin levels are greatly increased, with the predominant form being active renin. This rise in active eye renin is likely to represent an increase in local synthesis because active renin in plasma was not increased by ROP, and plasma would be expected to contribute <1% to ocular renin content, assuming that rat ocular blood volume is only 3.3% of total eye weight.17 Overall, these findings are consistent with rapid tissue processing of renin and suggest, as for the kidney,18 that RAS blockade elicits a local functional feedback on retinal renin synthesis.
The finding that ocular renin content (total renin, active renin, and prorenin) in the neonatal Ren-2 rat is elevated compared with age-matched SD rats is expected on the basis of previous findings that those extrarenal tissues that normally express renin display an amplified RAS in the Ren-2 rat.14 15 The fact that Ren-2 and SD ROP sham rats have similar numbers of BVPs in the inner retina but that Ren-2 ROP shams phenotypically contain elevated ocular active renin could indicate that in the developing eye, renin may be stored and not important for the induction of normal vasculogenesis. Only after ROP in both Ren-2 and SD rats were BVPs increased and accompanied by a substantial rise in ocular active renin. The larger rise in BVPs in Ren-2 ROP rats compared with SD ROP rats may be explained by the release of increased amounts of stored active renin forming Ang II after the hypoxic stimulus. Whether circulating Ang II itself might be elevated and contributes to the retinal neovascularization process associated with ROP remains to be investigated, but this would seem unlikely on the basis of the observation for plasma active renin discussed above. With respect to a role for blood pressure in the stimulation of retinal blood vessel growth in the Ren-2 ROP rat, no association between hypertension and retinal neovascularization has been reported in humans19 or the spontaneously hypertensive rat.20
Many reports have indicated that ACEI retards the cellular and fibrointerstitial damage in conditions such as diabetic nephropathy.13 Similar studies in the eye have been limited, although the recent report by the EUCLID study group2 suggests that ACEI with lisinopril slows the progression of proliferative diabetic retinopathy in patients. Our present findings, together with previous observations on the retinal RAS3 and the demonstration of angiogenic properties of Ang II, provide strong support at the cellular level for anticipating a beneficial action from RAS blockade in retinal conditions displaying neovascularization.
VEGF, a potent vessel permeability and angiogenic factor, is implicated in blood vessel growth.21 VEGF binds to high-affinity tyrosine kinase receptors VEGFR-1 and VEGFR-2, also known as flt-1 and flk-1, respectively.22 These two receptors have different functions, with VEGFR-2 viewed to induce alterations in cell morphology, actin reorganization, chemotaxis, and mitogenesis, whereas VEGFR-1 lacks such effects.22 VEGF expression is induced by hypoxia and is considered to be the stimulus in neovascularizing eye pathologies such as proliferative diabetic retinopathy and ROP.10 21 23 To evaluate the associated roles of the renin-angiotensin and VEGF systems in retinal neovascularization, we chose a rodent model of ROP. It is well established that exposure of neonatal animals to a high oxygen environment results in cessation of vessel growth in the inner retina, whereas subsequent exposure to room air is presumed to cause tissue hypoxia, which leads to upregulation of retinal VEGF and neovascularization.20 Using quantitative in situ hybridization, we found that VEGF and VEGFR-2 mRNA are increased with ROP in the inner retina and in proliferating retinal vessels of both SD and Ren-2 rats. This is consistent with previous findings in ROP models21 23 and has been observed in the eyes of patients with proliferative diabetic retinopathy.10 The appropriateness of this model to other forms of retinal neovascularization, such as occurs in diabetes, requires further evaluation. There is increased VEGF and VEGFR-2 expression in experimental diabetic retinopathy,24 and our previous findings suggest a decrease in retinal VEGF mRNA with ACEI in rodent diabetes.25
The sequence and interaction of growth factor actions in retinal angiogenesis has yet to be fully explored; however, the ability of Ang II to increase VEGF mRNA in human renal glomerular mesangial cells and the finding that losartan inhibits this process26 suggest that an increase in retinal Ang II with tissue hypoxia may be the initiating event in the rat ROP model. To our knowledge, there have been no previous studies evaluating this concept in the eye. Otani and colleagues12 have reported that Ang II enhances VEGFR-2 mRNA and VEGF-induced cell growth in cultured bovine retinal endothelial cells. In the present study, retinal neovascularization was associated with a rise in retinal renin, VEGF, and VEGFR-2 mRNA. These findings, together with the observation that ACEI prevented neovascularization and virtually abolished VEGF and VEGFR-2 mRNA, suggest that Ang II may potentiate or initiate VEGF-induced neovascularization. Unlike Otani et al12 and in contrast to our findings with ACEI, AT1 receptor blockade, although preventing retinal neovascularization in ROP, failed to suppress expression of VEGF and VEGFR-2. This suggests that although Ang II appears to act as the primary effector molecule in retinal neovascularization in ROP, VEGFR-2 expression may not be primarily influenced by the AT1 receptor but may be mediated by other pathways such as the angiotensin type 2 receptor or cytokines. It may also be possible that VEGF is not essential for neovascularization in the ROP model. Indeed, 98% inhibition of VEGF with soluble VEGF receptor chimeric proteins in a murine model of ischemic retinopathy resulted in only a partial reduction (56%) in retinal neovascularization.27 However, a pivotal role for VEGF in the growth factor pathway leading to ROP should not be underestimated; a recent study reported that inhibition of VEGF receptor kinase activity blocked retinal neovascularization in the ROP model.28
Our findings imply that the retinal RAS plays an important role in the pathogenesis of neovascularization in the ROP model. This information provides a rationale for the use of agents that interrupt the RAS in the prevention of proliferative retinopathy related to retinal hypoxia and possibly ischemia.
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Acknowledgments |
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This study was supported by Merck Research Laboratories, the Diabetes Australia Research Trust, the National Health and Medical Research Council of Australia, and Juvenile Diabetes Foundation International. Dr Richard Gilbert is the recipient of a Career Development Award from the Juvenile Diabetes Foundation International. The authors thank Alison Cox for technical assistance.
Received August 23, 2000; first decision August 23, 2000; accepted September 1, 2000.
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J. A. Phipps, J. L. Wilkinson-Berka, and E. L. Fletcher Retinal Dysfunction in Diabetic Ren-2 Rats Is Ameliorated by Treatment with Valsartan but Not Atenolol Invest. Ophthalmol. Vis. Sci., February 1, 2007; 48(2): 927 - 934. [Abstract] [Full Text] [PDF]
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S. Satofuka, A. Ichihara, N. Nagai, T. Koto, H. Shinoda, K. Noda, Y. Ozawa, M. Inoue, K. Tsubota, H. Itoh, et al. Role of Nonproteolytically Activated Prorenin in Pathologic, but Not Physiologic, Retinal Neovascularization Invest. Ophthalmol. Vis. Sci., January 1, 2007; 48(1): 422 - 429. [Abstract] [Full Text] [PDF]
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J. L. Wilkinson-Berka, D. Jones, G. Taylor, K. Jaworski, D. J. Kelly, S. B. Ludbrook, R. N. Willette, S. Kumar, and R. E. Gilbert SB-267268, a Nonpeptidic Antagonist of {alpha}v{beta}3 and {alpha}v{beta}5 Integrins, Reduces Angiogenesis and VEGF Expression in a Mouse Model of Retinopathy of Prematurity. Invest. Ophthalmol. Vis. Sci., April 1, 2006; 47(4): 1600 - 1605. [Abstract] [Full Text] [PDF]
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J.-S. Silvestre and B. I. Levy Molecular Basis of Angiopathy in Diabetes Mellitus Circ. Res., January 6, 2006; 98(1): 4 - 6. [Full Text] [PDF]
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P. B. Bergman, C. J. Moravski, S. R. Edmondson, V. C. Russo, L. A. Bach, J. L. Wilkinson-Berka, and G. A. Werther Expression of the IGF System in Normal and Diabetic Transgenic (mRen-2)27 Rat Eye Invest. Ophthalmol. Vis. Sci., August 1, 2005; 46(8): 2708 - 2715. [Abstract] [Full Text] [PDF]
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N. Nagai, Y. Oike, K. Noda, T. Urano, Y. Kubota, Y. Ozawa, H. Shinoda, T. Koto, K. Shinoda, M. Inoue, et al. Suppression of Ocular Inflammation in Endotoxin-Induced Uveitis by Blocking the Angiotensin II Type 1 Receptor Invest. Ophthalmol. Vis. Sci., August 1, 2005; 46(8): 2925 - 2931. [Abstract] [Full Text] [PDF]
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 H Yokota, F Mori, K Kai, T Nagaoka, N Izumi, A Takahashi, T Hikichi, A Yoshida, F Suzuki, and Y Ishida Serum prorenin levels and diabetic retinopathy in type 2 diabetes: new method to measure serum level of prorenin using antibody activating direct kinetic assay Br J Ophthalmol, July 1, 2005; 89(7): 871 - 873. [Abstract] [Full Text] [PDF]
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 The DIRECT Programme Study Group The DIabetic REtinopathy Candesartan Trials (DIRECT) Programme: baseline characteristics Journal of Renin-Angiotensin-Aldosterone System, March 1, 2005; 6(1): 25 - 32. [Abstract] [PDF]
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S. Sarlos and J. L. Wilkinson-Berka The Renin-Angiotensin System and the Developing Retinal Vasculature Invest. Ophthalmol. Vis. Sci., March 1, 2005; 46(3): 1069 - 1077. [Abstract] [Full Text] [PDF]
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N. Nagai, K. Noda, T. Urano, Y. Kubota, H. Shinoda, T. Koto, K. Shinoda, M. Inoue, T. Shiomi, E. Ikeda, et al. Selective Suppression of Pathologic, but Not Physiologic, Retinal Neovascularization by Blocking the Angiotensin II Type 1 Receptor Invest. Ophthalmol. Vis. Sci., March 1, 2005; 46(3): 1078 - 1084. [Abstract] [Full Text] [PDF]
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 T. G. Ebrahimian, R. Tamarat, M. Clergue, M. Duriez, B. I. Levy, and J.-S. Silvestre Dual Effect of Angiotensin-Converting Enzyme Inhibition on Angiogenesis in Type 1 Diabetic Mice Arterioscler Thromb Vasc Biol, January 1, 2005; 25(1): 65 - 70. [Abstract] [Full Text] [PDF]
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H. Toko, Y. Zou, T. Minamino, M. Sakamoto, M. Sano, M. Harada, T. Nagai, T. Sugaya, F. Terasaki, Y. Kitaura, et al. Angiotensin II Type 1a Receptor Is Involved in Cell Infiltration, Cytokine Production, and Neovascularization in Infarcted Myocardium Arterioscler Thromb Vasc Biol, April 1, 2004; 24(4): 664 - 670. [Abstract] [Full Text] [PDF]
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J. L. Wilkinson-Berka, S. Babic, T. de Gooyer, A. W. Stitt, K. Jaworski, L. G. T. Ong, D. J. Kelly, and R. E. Gilbert Inhibition of Platelet-Derived Growth Factor Promotes Pericyte Loss and Angiogenesis in Ischemic Retinopathy Am. J. Pathol., April 1, 2004; 164(4): 1263 - 1273. [Abstract] [Full Text] [PDF]
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 C. Tikellis, M. E. Cooper, Stephen. M. Twigg, W. C. Burns, and M. Tolcos Connective Tissue Growth Factor Is Up-Regulated in the Diabetic Retina: Amelioration by Angiotensin-Converting Enzyme Inhibition Endocrinology, February 1, 2004; 145(2): 860 - 866. [Abstract] [Full Text] [PDF]
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 X. Zhang, M. Lassila, M. E. Cooper, and Z. Cao Retinal Expression of Vascular Endothelial Growth Factor Is Mediated by Angiotensin Type 1 and Type 2 Receptors Hypertension, February 1, 2004; 43(2): 276 - 281. [Abstract] [Full Text] [PDF]
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 T. A. Ciulla, A. G. Amador, and B. Zinman Diabetic Retinopathy and Diabetic Macular Edema: Pathophysiology, screening, and novel therapies Diabetes Care, September 1, 2003; 26(9): 2653 - 2664. [Abstract] [Full Text] [PDF]
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S. Sarlos, B. Rizkalla, C. J. Moravski, Z. Cao, M. E. Cooper, and J. L. Wilkinson-Berka Retinal Angiogenesis Is Mediated by an Interaction between the Angiotensin Type 2 Receptor, VEGF, and Angiopoietin Am. J. Pathol., September 1, 2003; 163(3): 879 - 887. [Abstract] [Full Text] [PDF]
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 D. J. Kelly, C. Hepper, L. L. Wu, A. J. Cox, and R. E. Gilbert Vascular endothelial growth factor expression and glomerular endothelial cell loss in the remnant kidney model Nephrol. Dial. Transplant., July 1, 2003; 18(7): 1286 - 1292. [Abstract] [Full Text] [PDF]
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J. L. Wilkinson-Berka, N. S. Alousis, D. J. Kelly, and R. E. Gilbert COX-2 Inhibition and Retinal Angiogenesis in a Mouse Model of Retinopathy of Prematurity Invest. Ophthalmol. Vis. Sci., March 1, 2003; 44(3): 974 - 979. [Abstract] [Full Text] [PDF]
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C. J. Moravski, S. L. Skinner, A. J. Stubbs, S. Sarlos, D. J. Kelly, M. E. Cooper, R. E. Gilbert, and J. L. Wilkinson-Berka The Renin-Angiotensin System Influences Ocular Endothelial Cell Proliferation in Diabetes: Transgenic and Interventional Studies Am. J. Pathol., January 1, 2003; 162(1): 151 - 160. [Abstract] [Full Text] [PDF]
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W D. Strain and N. Chaturvedi Review: The renin-angiotensin-aldosterone system and the eye in diabetes Journal of Renin-Angiotensin-Aldosterone System, December 1, 2002; 3(4): 243 - 246. [Abstract] [PDF]
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F Mori, T Hikichi, T Nagaoka, J Takahashi, N Kitaya, and A Yoshida Inhibitory effect of losartan, an AT1 angiotensin II receptor antagonist, on increased leucocyte entrapment in retinal microcirculation of diabetic rats Br J Ophthalmol, October 1, 2002; 86(10): 1172 - 1174. [Abstract] [Full Text] [PDF]
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S. F. Abcouwer, P. L. Marjon, R. K. Loper, and D. L. Vander Jagt Response of VEGF Expression to Amino Acid Deprivation and Inducers of Endoplasmic Reticulum Stress Invest. Ophthalmol. Vis. Sci., August 1, 2002; 43(8): 2791 - 2798. [Abstract] [Full Text] [PDF]
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H Funatsu, H Yamashita, Y Nakanishi, and S Hori Angiotensin II and vascular endothelial growth factor in the vitreous fluid of patients with proliferative diabetic retinopathy Br J Ophthalmol, March 1, 2002; 86(3): 311 - 315. [Abstract] [Full Text] [PDF]
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J. A. Nadal, G. M. Scicli, L. A. Carbini, and A. G. Scicli Angiotensin II stimulates migration of retinal microvascular pericytes: involvement of TGF-beta and PDGF-BB Am J Physiol Heart Circ Physiol, February 1, 2002; 282(2): H739 - H748. [Abstract] [Full Text] [PDF]
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