Search

Components of the Renin Angiotensin System (RAS) have been detected in ocular tissues and fluids. The source of the ocular RAS proteins is unknown but possibilities include diffusion or leakage from the systemic circulation, specific uptake from the blood, or local synthesis. We have used RT-PCR and in situ hybridization (ISH) to show that renin mRNA is present in ocular tissues from 3 strains of rats. By RT-PCR, we found 10 of 15 ciliary body samples, 13 of 16 iris samples, and 1 of 3 retina samples were positive for renin mRNA. Also, 6 of 6 brain and 7 of 8 kidney samples were positive. Using ISH, we found renin mRNA in the ciliary muscle adjacent to the sclera extending into the choroid. Tissue near the outflow channels of the anterior chamber angle also labeled. Retinal labeling was weak but present in the nerve fiber layer. Clusters of grains, possibly representing blood vessels, were also seen in the ciliary body, iris, and retina using ISH. These results suggest the presence of a local ocular RAS.

Prorenin (PR) was localized by electron microscopic (EM) immunostaining of cryo-ultramicrotomy sections of human ciliary body and correlated with light microscopic immunostaining. Both layers of the ciliary epithelium contained the prohormone. However, density was much higher in the adjacent extracellular spaces, particularly in the vitreous cortex. This observation adds further evidence to a role of the ciliary epithelium in the transfer, storage or synthesis of components of a putative ocular renin angiotensin system.

The circulating renin-angiotensin system (RAS) is an important determinant in maintaining adequate systemic blood pressure, and it also may modify organ-specific blood flow. All recognized RAS components have been identified in the eye. In this study, angiotensinogen (ANG) was localized using an affinity-purified antibody and paraffin sections of seven human eyes. An antibody for human serum albumin was used for comparison. The ANG was present selectively in the cytoplasm of the nonpigmented ciliary epithelium (NPCE), more prominently in the pars plana than in the pars plicata. Both ANG and albumin were present in the blood vessel lumina of the uvea and retina. Both antibodies also stained perivascular tissue in the uvea, but not in the retina, reflecting the relative tightness of blood-tissue barriers. The detection of ANG in the NPCE may be significant in view of previous descriptions localizing prorenin and angiotensin-converting enzyme in the same cell layer.

After an eye-wall resection for a choroidal melanoma, a 32-year-old woman had subsequent retinal detachment with proliferative vitreoretinopathy (PVR), and an unsuccessful attempt at repair with retinal tacks. Gross and light-microscopic examination of the globe revealed a total retinal detachment with extensive preretinal and subretinal membranes. The membranes surrounded the tack heads and extended in taut bands to form a tractional detachment of the pars plana. The membranes contained glial and nonglial cells. The glial cells immunolabeled for glial fibrillary acidic protein (GFAP), carbonic anhydrase-C (CA-C), vimentin, and glutamine synthetase (GS), thus suggesting that they were Müller's cells. While the tacks did not seem to cause PVR, in this case they may have provided an anchoring point from which membranes were able to exert traction on the retina and pars plana.

The frequency and extent of immunostaining for actin, fibronectin (FN), and glial fibrillary acidic protein (GFAP) were determined in 37 preretinal membranes (PRMs) obtained at vitrectomy from 35 patients with proliferative diabetic retinopathy (PDR) (n = 16), proliferative vitreoretinopathy (PVR) (n = 18), or idiopathic macular pucker (MP) (n = 3). All three proteins were detected in the vast majority of specimens (actin, 86%; FN, 95%; GFAP, 96%), although the extent of staining varied for each. Actin-FN co-localization was observed in all diagnostic groups on comparison of adjacent sections and in double-labeled sections. The extent of actin staining did not correlate with clinical grading of PRM contraction. In PDR membranes, FN staining was low overall, but proportional to the vascular content of the PRM. Fibronectin staining of PVR membranes was greater, and extensive even in avascular specimens. In MP membranes, most cells were GFAP-positive, whereas in PDR and PVR specimens, GFAP staining was variable. The lack of correlation of clinical contractility and membrane composition, as studied in this article by immunostaining, indicates that other factors must play significant roles in determining membrane behavior.

Angiotensin II (A2) is a vasoconstrictor generated by the renin-angiotensin system. A2 appears to act also as an angiogenic factor. Recent evidence suggests that renin is synthesized at many tissue sites and may generate A2 locally. Local A2 may have important functions in the normal and diseased eye. We examined eight human eyes by immunostaining with an antibody to prorenin, the biosynthetic precursor of renin. In all eyes, prorenin staining was extensive in the pars plicata of the ciliary body suggesting that the ciliary body synthesizes renin and this renin may be part of an ocular A2 generating system.

Previous studies of fibronectin (FN) distribution in eye tissue have relied on immunofluorescence (IF) techniques on frozen sections, and have not included the rat. Using rat eyes, a technique was developed for immunoperoxidase (IP) staining of formalin fixed paraffin embedded material, and the results were compared to those obtained by IF. IP was technically more difficult, and required pepsinization of tissue after formalin fixation to obtain consistent results. The optimum pepsin time varied for different structures in the eye. IP offers better tissue preservation and stain resolution. Results with IF were consistent with those observed with the newly applied IP. The distribution of FN in rat eyes was similar though not identical to that reported in other species. Prominent stain was observed in the conjunctiva, basement membrane of the corneal epithelium, corneal stroma, anterior aspect of Descemet's membrane, trabecular meshwork, perivascular stroma of the ciliary body, choroid and retinal blood vessels. Lens structures, vitreous, and internal limiting membrane of the retina were negative.