Abstract
Abstract: :
Purpose: Angiotensin II (ANG II), the effector peptide of the RAS, influences blood flow regulation and cell growth. In the retina, ANG II has been implicated in angiogenesis, as previous studies report RAS blockade attenuating endothelial cell proliferation in retinopathy of prematurity and diabetes. To date, little is known about the role of the RAS in developing retina. We aimed to characterize the cellular location and activity of RAS components in the developing retina of two rat strains, the SD and the transgenic (mRen–2)27 which overexpresses the RAS in the eye. Methods: Retinae from SD and Ren–2 rats were studied on postnatal (P) days 1,7,14,21 and 90 (N=8/group). Immunohistochemistry for RAS components was performed. Retinal prorenin and active renin content was measured by an enzyme kinetic method. Quantitative in vitro autoradiography was used to determine binding densities of angiotensin converting enzyme (ACE) and the angiotensin receptors (AT1 and AT2). To evaluate the effects of RAS blockade on retinal vascular development, a separate group of SD and Ren–2 rats were administered either the ACE inhibitor lisinopril (10mg/kg/day i.p.) or the AT1 antagonist losartan (10 mg/kg/day i.p.) from P1–P7 Results: In both SD and Ren–2 rats from P1–P90, angiotensinogen, prorenin and ANG II were localised to cells in the inner retina (inner limiting membrane (ILM), ganglion cell layer (GCL) and blood vessels. Immunolabelling for AT1 and AT2 was present in the GCL and blood vessels of inner retina. Autoradiographic binding studies revealed AT2 to be more abundant than AT1 from P1–P21. For both Ren–2 and SD rats, ACE binding was lowest at P1 and progressively increased to P90. Retinal renin content was highest in Ren–2 rats, predominately active and increased after P14. Ren–2 rats displayed longer vascular edge advancement and a denser vascular network compared to SD rats. Lisinopril reduced vascular density in the peripheral retina of Ren–2 rats. AT1 blockade had no other effect on retinal vessel length or density in either rat strain. Conclusions: RAS components are localised to the inner retina and hyaloid endothelium of developing rat retina. Overexpression of the retinal RAS in the Ren–2 rat is associated with increased vascular length and density highlighting the pro–angiogenic properties of the RAS. The predominance of AT2 in early postnatal retinal development together with the finding that ACE inhibition but not AT1 antagonism attenuates vascular growth is consistent with the view that AT2 may modulate cell growth/differentiation during organ development.
Keywords: retinal development • blood supply • microscopy: light/fluorescence/immunohistochemistry