Iris Blood Vessels Research Articles

Region-related and layer-specific permeability of the iris vasculature with morphological mechanism: A novel understanding of blood-aqueous barrier

The permeability of iris blood vessels has an important role in maintaining aqueous humor (AH) homeostasis, contributing to variation in iris volume and probably the pathogenesis of angle closure glaucoma. This study investigates the permeability of the iris microvasculature to plasma-derived protein and correspond it with the morphologic characteristics of vascular mural cells (MCs).Twenty-two enucleated porcine eyes were used in this study. 12 eyes were micro-perfused with vehicle alone as control or with FITC-albumin as a marker of protein leakage and histological sections subsequently made to examine for FITC-albumin presence. The other 10 eyes were immunolabeled via micro-perfusion for αSMA and VE-cadherin to investigate their topographic distribution in the porcine iris vasculature, and to cross correspond with the locations of FITC-albumin deposits.Distribution of FITC-signals exhibited a site-dependent pattern and time-dependent change in the iris. Fluorescence was initially detected around capillaries in the superficial and deep layer of the iris microvascular network. The pupillary region and the iris root retained more fluorescent signal than the iridal ciliary region. At low magnification, αSMA labelling displayed a regional variation which was inversely correlated with vascular permeability. At the cellular level, αSMA labeling corresponded with vascular MCs distribution in the iris vascular network.The correspondence between iris microvascular permeability to FITC-albumin and the pattern of αSMA distribution and MCs coverage adds to the understanding of the elements comprising the blood-aqueous barrier with implications for the bio-mechanics of iris volume change.

High-Resolution Imaging of the Ocular Vasculature of Conjunctivitis in Mice Using Highly Bright Polymer Dots.

Ocular diseases are mainly caused by vascular aberrations in the eye, and accurate imaging and analysis of the ocular vascular structure is crucial. In this study, poly(9,9-dioctylfluorene-alt-benzothiadiazole) (PFBT) polymer dots (Pdots), with the advantages of easy synthesis, high brightness, and low toxicity, are used as nanoprobes to perform high-resolution imaging of the vasculature of the eyeball and optic nerve. Moreover, rapid imaging of the choroidal microvessels is carried out by stereoscopic fluorescence microscopy with a resolution of up to 1.6µm. The comprehensive 3D vascular information of retinal aorta and optic nerve microvessels is obtained by combining tissue clearing and multiphoton microscopy. In addition, the vascular density of Schlemm's canal and iris blood vessels is compared between the conjunctivitis mice and the normal mice. These results suggest that PFBT Pdots have great application potential in the fast and accurate imaging of ocular diseases.

Quantitative changes in iris vasculature and blood flow in patients with different refractive errors.

To evaluate the association between microvascular changes in the iris and refractive errors. A cross-sectional case study. Seventy eyes from 70 patients with refractive errors were enrolled. Iris microvasculature was analyzed using optical coherence tomography angiography (OCTA). We divided the iris images into three regions and calculated the vessel area density (VAD) and vessel skeleton density (VSD) of the inner one-third, inner two-thirds, and the entirety of the iris. The VADs and VSDs of the different regions were significantly different. The VAD and VSD of the inner one-third of the iris were higher than those of the other regions. The iris blood vessels were denser near the pupil margin, and blood vessels from the iris root to the pupil edge were radially distributed. The VAD and VSD of patients with mild hyperopia and emmetropia were higher than those of patients with moderate and high myopia. As the spherical equivalent increased, the VAD and VSD of the iris increased. Neither age nor sex contributed to significant differences in VAD and VSD. Quantitative changes in iris microvasculature may indicate the development of myopia.

A novel in vivo model of puncture‐induced iris neovascularization

PurposeTo assess iris neovascularization by uveal puncture of the mouse eye and determine the role of angiogenic factors during iris neovascularization.MethodsUveal punctures were performed on BalbC mouse eyes to induce iris angiogenesis. VEGF‐blockage was used as an anti‐angiogenic treatment, while normoxia‐ and hypoxia‐conditioned media from retinal pigment epithelium (RPE) cells was used as an angiogenic‐inducer in this model. Iris vasculature was determined in vivo by noninvasive methods. Iris blood vessels were stained for platelet endothelial cell adhesion molecule‐1 and vascular sprouts were counted as markers of angiogenesis. Expression of angiogenic and inflammatory factors in the puncture‐induced model were determined by qPCR and western blot.ResultsPunctures led to increased neovascularization and sprouting of the iris. qPCR and protein analysis showed an increase of angiogenic factors, particularly in the plasminogen‐activating receptor and inflammatory systems. VEGF‐blockage partly reduced iris neovascularization, and treatment with hypoxia‐conditioned RPE medium led to a statistically significant increase in iris neovascularization.ConclusionsThis study presents the first evidence of a puncture‐induced iris angiogenesis model in the mouse. In a broader context, this novel in vivo model of neovascularization has the potential for noninvasive evaluation of angiogenesis modulating substances.

A novel in vivo model of puncture-induced iris neovascularization.

PurposeTo assess iris neovascularization by uveal puncture of the mouse eye and determine the role of angiogenic factors during iris neovascularization.MethodsUveal punctures were performed on BalbC mouse eyes to induce iris angiogenesis. VEGF-blockage was used as an anti-angiogenic treatment, while normoxia- and hypoxia-conditioned media from retinal pigment epithelium (RPE) cells was used as an angiogenic-inducer in this model. Iris vasculature was determined in vivo by noninvasive methods. Iris blood vessels were stained for platelet endothelial cell adhesion molecule-1 and vascular sprouts were counted as markers of angiogenesis. Expression of angiogenic and inflammatory factors in the puncture-induced model were determined by qPCR and western blot.ResultsPunctures led to increased neovascularization and sprouting of the iris. qPCR and protein analysis showed an increase of angiogenic factors, particularly in the plasminogen-activating receptor and inflammatory systems. VEGF-blockage partly reduced iris neovascularization, and treatment with hypoxia-conditioned RPE medium led to a statistically significant increase in iris neovascularization.ConclusionsThis study presents the first evidence of a puncture-induced iris angiogenesis model in the mouse. In a broader context, this novel in vivo model of neovascularization has the potential for noninvasive evaluation of angiogenesis modulating substances.

Lymphocyte infiltration and activation in iris-ciliary body and anterior chamber of mice in corneal allograft rejection.

To investigate the infiltration and activation of lymphocyte in iris-ciliary body and anterior chamber after allogenic penetrating keratoplasty (PK), for further revealing the role of iris-ciliary body in corneal allograft immune rejection. In the mice models of PK, BALB/C mice received orthotopic isografts (n =35) or C57BL/6 donor allografts (n =25). Grafts were examined daily for 3 weeks by slit-lamp microscopy and scored for opacity. The infiltration of CD4(+) T lymphocyte in iris-ciliary body and anterior chamber was examined by immunohistology and the mRNA of CD80 and CD86 in both cornea graft and iris-ciliary body by RT-PCR was analyzed in allograft recipient at days 3, 6, 10 and the day when graft rejection occurred. Isograft recipients were examined as control at the corresponding time points. Transmission electron microscope was used to study the ultrastructure, especially cell infiltration, of iris-cilary body and corneal graft at day 3, 7 and the day when rejection occurred after allogenic PK. Rejection was observed in all the allograft recipients followed more than 10 days, at a median time of 15 days (range 12-18 days), but not in any of isografts. CD4(+) T cells were first detected at day 6 after transplantation in limbus and Ciliary body, and then in the stroma of recipient, iris, anterior chamber and corneal allograft with an increased number until graft rejection occurred. CD80 and CD86 mRNA were detected under RT-PCR examination in both graft and iris-ciliary body of allograft recipient, but not in any of isograft recipient. Three days after operation, lymphocytes and monocytes macrophages were visible in iris blood vessels and the anterior chamber, and vascular endothelial cell proliferation and activation were significant under transmission electron microscopy examination. At day 7, corneal endothelial cells became thinner. Lymphocytes and mononuclear macrophages were found with great number in the anterior chamber and adhered to the corneal endothelium. Blood vessels in iris increased and were filled with lymphocytes. And lymphocytes were detected to migrate through endothelial cell gap out of vessels. When allograft rejection occurred, macrophages attached to endothelial cells with large number of lymphocytes and macrophages infiltrating in iris. Lymphocyte infiltration and activation occurred in iris-ciliary body after allogenic PK, and the lymphocytes could migrate from iris blood vessel to the anterior chamber, which might play an important role in corneal allograft immune rejection.

Mapping of the Neonatal Fc Receptor in the Rodent Eye

The neonatal Fc receptor (FcRn) has been known to modulate IgG transport and protect against IgG catabolism, resulting in extension of the serum half-life of IgG. The goal of this study was to localize FcRn receptor expression in the rat's eye. The cornea, retina, conjunctiva, ciliary body and iris, retinal pigment epithelium and choroid, and lens were dissected from each rat's eye, and total RNA was purified. The first-strand cDNAs were synthesized and subjected to PCR reaction. For control samples, reverse transcriptase was omitted. A monoclonal antibody against the FcRn heavy chain was used to localize the distribution of the FcRn receptor in ocular tissues. Lymphatic vessels and blood vessels were stained with a rabbit anti-mouse lymphatic vessel endothelial receptor-1 polyclonal antibody and a rabbit anti-human von Willebrand factor polyclonal antibody, respectively. RT-PCR demonstrated expression of FcRn RNA in cornea, retina, conjunctiva, ciliary body and iris, and lens but absence of expression in the retinal pigment epithelium and choroid. Immunohistochemistry and double staining confirmed the expression of FcRn receptor to the conjunctival lymphatic vessels but not in the conjunctival blood vessels. In the ciliary body, the FcRn receptor was found to be expressed in both the nonpigmented ciliary epithelium and the ciliary blood vessels. The expression of FcRn receptor was confirmed in the retinal blood vessels, iris blood vessels, optic nerve vascular structures, corneal epithelium and endothelium, and lens epithelium. The FcRn receptor is expressed in multiple ocular tissues. The blood-ocular barrier showed FcRn receptor expression, indicating that IgG transport from ocular tissues to the blood system may use this receptor. The role of the FcRn receptor in the anterior segment and the conjunctiva remains unclear.

Proliferation of the vascular endothelium of the iris following total debridement of the corneal epithelium and limbal excision of rabbits

Damage to the corneal epithelium causes not only a reaction for its repair but also affects other parts of the cornea as well as different components of the anterior segment of the eye. The purpose of this investigation was to analyze the consequences, following epithelial and limbal damage, to the iris of rabbits (Oryctolagus cuniculus). The corneal epithelium was thoroughly scraped followed by surgical excision of the limbus. Next, (3)H-thymidine ((3)H-TdR) was injected intravitreally both into the right (experimental) and left (control) eyes which had their anterior segments processed for autoradiography at intervals of 2, 7 and 21 days after surgery (three rabbits per interval). The irises were also examined with scanning-electron and confocal microscopy after Evans blue injection. There was a high frequency of labeling in the cells of the iris blood vessels in the experimental eye, particularly the endothelial ones. The ratio of labeled cells between experimental and control irises was 40:1, with a population of nuclei increasing by 25% and remaining labeled up to 21 days. There was also an increase in the volume of the iris vasculature as shown by confocal microscopy. The high labeling frequencies of the vascular cells were observed throughout the iris from the ciliary to the pupillary regions. The lesions on the corneal epithelium elicit proliferation of the iris vascular cells, mainly its endothelium, as well as an early breakdown of the blood-aqueous barrier. The daughter cells resulting from the damage to the eye surface were detected up to 21 days after a single injection of (3)H-TdR, most likely due to their slow turnover. As a consequence of this proliferation, the vasculature of the iris increased in volume.

Caveolin-1 is up-regulated in transdifferentiated lens epithelial cells but minimal in normal human and murine lenses

Caveolae are flask-shaped invaginations of the plasma membrane found in many cell types. Caveolae play a role in lipid transport, endocytosis, signal transduction, and cell transformation. Expression of caveolin-1, the principal component of caveolae and a regulator of caveolae-dependent signaling and endocytosis, was investigated in lens epithelial cells and lens fiber cells in wild-type (wt) and SPARC-null mice and normal human donors in vivo and in vitro. RT-PCR, immunofluorescence and immunoblot analyses of human and murine ocular tissues revealed that caveolin-1 was expressed in the corneal epithelium, corneal endothelial cells, and blood vessels of iris, ciliary body and retina, but minimal in the normal lens epithelia or fiber cells of murine and human lens. In contrast, caveolin-1 was significantly up-regulated in mesenchymal-transdifferentiated lens epithelia in SPARC-null cataract lenses. In addition, lens epithelial cells from primary culture or from cultures of immortalized lens epithelial cell lines expressed significant amounts of caveolin-1. The lens epithelial cells expressed epidermal growth factor (EGF) receptor and were responsive to EGF-mediated cell proliferation, but they did not show EGF-dependent caveolin-1 tyrosine phosphorylation. Caveolin-1 might have a role in the process of epithelial-mesenchymal transdifferentiation (EMT) in the lens, the most common cause of vision loss in human secondary cataracts.

Co-localization of Junction-associated Proteins of the Human Blood–Aqueous Barrier: Occludin, ZO-1 and F-actin

Recent studies in mouse and rabbit eyes have begun to identify the molecular constituents of tight and adherens junctions that represent the structural equivalent of the blood–aqueous barrier (BAB). These species are commonly used as experimental models to examine the pathobiology of anterior uveitis, an inflammatory condition in which the junctions of the BAB are compromised. Because it was unclear whether major molecular elements of the junctions in these species were the same as those in humans, the goal of this study was to determine if the junction related proteins ZO-1 and occludin are present in normal human ciliary epithelium and iridial vascular endothelium. To determine their presence, sections of human anterior uvea were probed in 14 normal, human, eyebank eyes immunolabelled with antibodies to ZO-1, and occludin, and confocal microscopy was used to examine them. Phalloidin staining for F-actin was also assessed. ZO-1 and occludin were both localized along the apico-lateral surfaces of the non-pigmented ciliary epithelium and the interendothelial clefts of iris blood vessels. In both locations, the distribution of occludin was more focal than seen for ZO-1. ZO-1 was also found along the apical surfaces between the pigmented and non-pigmented ciliary epithelial cell layers. The distribution of these proteins supports the notion that occludin is more specifically associated with tight junctions than is ZO-1 in the normal human BAB. No change in this distribution was found with increasing age. These data are consistent with findings reported previously in rabbit ciliary epithelium and iridial vascular endothelium, indicating the relevance of experimental induced uveitis studies in rabbit, as a model of BAB breakdown in human uveitis.

Exfoliation syndrome and exfoliation glaucoma.

Exfoliation syndrome abnormal deposition in the anterior segment of the eye of an unknown substance thought to be related to elastic fibres and basement membrane components is associated with accelerated cataract progression. increased frequency of intraoperative and postoperative complications and increased risk for glaucoma and. therefore, is a clinically important finding. A clear association has been shown with age. The syndrome occurs worldwide but its prevalence seems to vary from country to country. The best-known sign of exfoliation syndrome is deposits of greyish-white material on the anterior lens surface. Sometimes exfoliation material can also be seen at the pupillary border, on the anterior iris surface, corneal endothelium, and on the anterior vitreous face. When clinically detected, exfoliation syndrome is somewhat more often unilateral than bilateral. According to recent investigations clinically unilateral exfoliation syndrome is probably never truly unilateral but rather asymmetric, because exfoliation material has been detected ultrastructurally and immunohistochemically around iris blood vessels of the nonexfoliative fellow eyes. Indeed, electron microscopy identifies in various organs of patients with exfoliation syndrome fibrils similar to those seen in intraocular exfoliation deposits. Other clinical signs associated with exfoliation syndrome are pigment dispersion, transillumination defects of the iris and reduced response to mydriatics. In unilateral exfoliation syndrome, intraocular pressure (IOP) of the exfoliative eye is approximately 2 mmHg higher than IOP of the nonexfoliative fellow eye. Whether elevated IOP, vascular changes or exfoliation syndrome itself is the main factor causing optic nerve head damage and conversion of an exfoliative eye to glaucomatous, is not known. Glaucoma in the exfoliation syndrome has been shown to have a more serious clinical course than in primary open-angle glaucoma (POAG). At the time of diagnosis, IOP and its diurnal variation are generally higher and visual field defects tend to be greater in exfoliation glaucoma than in POAG. Because the decrease in lOP variation and lowering of the mean IOP level has been shown to improve visual field prognosis more in exfoliation glaucoma than in POAG, the glaucomatous process is considered to be more pressure-related in exfoliation glaucoma. Furthermore, progression of optic disc damage has been shown to be similar in exfoliation glaucoma and POAG when lOPs are lowered to a comparable level by the treatment. However, vascular disturbances in the posterior segment of the eye might after all be of equal importance in these two types of glaucoma; optic disc haemorrhages and venous occlusions have been reported to be as frequent in exfoliation glaucoma as in POAG. Perhaps in exfoliation glaucoma circullatory disturbances combined with high IOP lead to a particularly relentlessly progressing form of the disease.

Expression of vascular endothelial growth factor (VEGF) and its receptors is regulated in eyes with intra-ocular tumours.

The immunolocalization and gene expression of vascular endothelial growth factor (VEGF) and its cognate tyrosine kinase receptors, Flt-1 and KDR, has been studied in ocular melanomas and retinoblastomas using in situ hybridization and immunohistochemistry. Tumour-related alterations in VEGF/VEGF-receptor expression have also been examined in separate and uninvolved iris, retina and choroid of the same eyes. Although VEGF immunoreactivity in the normal retina was virtually absent, low-level VEGF expression was evident in the ganglion cell-bodies, Müller cells and in a distinct population of amacrine cells. VEGF gene expression was absent in the iris and choroid of normal eyes. In tumour-bearing eyes, high levels of VEGF protein and gene expression were observed within the vascularized regions of the tumours, while the adjacent retina and choroid showed increased VEGF levels when compared with normals. Flt-1 and KDR gene expression and immunolocalization occurred in VEGF-expressing ganglion, Müller and amacrine cells in normal eyes. Within the intra-ocular tumours, VEGF-receptor gene expression and protein was evident in the endothelial cells and also in cells close to the vessels, while in the adjacent retina, Flt-1 and KDR levels were elevated over normal, especially in the blood vessels. Flt-1 and KDR were both observed at elevated levels in the choroid and iris blood vessels. This study suggests that VEGF, Flt-1 and KDR are expressed by neural, glial and vascular elements within normal human retina. Intra-ocular tumours demonstrate a high level of VEGF and VEGF-receptor expression; within uninvolved, spatially separate retina, choroid and iris in the same eyes, expression is also elevated, especially within the vasculature. Retinal vascular endothelia may respond to high intra-ocular levels of VEGF by increasing expression of their VEGF receptors, a phenomenon which could have relevance to neoplasm-related ocular neovascularization.

Early changes in iris blood vessels in exfoliation syndrome

PURPOSE. To look for possible changes in iris blood vessels that might precede the formation of true exfoliation material, and to correlate these changes, if present, to aging of the iris. METHODS. Iris blood vessels of 10 clinically normal irises from 10 eyes (ages: 1 day–80 years), 4 irises with exfoliation (ages: 64–80 years) and 3 irises from primary open-angle glaucoma (POAG) (ages: 27–65 years) were examined with an electron microscope. RESULTS. Pronounced multilayering of the basal lamina around the vessels, abnormal excessive formation of microfibrils, presence of atrophic invaginations in the outer cell membranes of endothelial cells containing interlacing basal lamina, and an apparent decrease in the perivascular collagen fibers were evident in exfoliative iris vessels devoid of true exfoliation material. Similar, but much milder, changes were evident in normal aged and POAG irises. CONCLUSIONS. Abnormal elastic tissue and/or basal lamina production plays a role early in the formation of exfoliation material around iris blood vessels.

Galactose-containing glycoconjugates of the iris, the aqueous outflow passages and the cornea in capsular glaucoma

The aim of the study was to compare galactose-containing glycoconjugates of the iris, the aqueous outflow passages and the cornea with exfoliation material in capsular glaucoma. Six formalin-fixed, paraffin-embedded human eyes with capsular glaucoma and six control eyes were studied by using a panel of 11 biotinylated lectins to galactose- and N-acetylgalactosamine-containing glycoconjugates. The Gal (beta 1-->3) GalNAc-reactive lectins peanut agglutinin (PNA) and Bauhinia purpurea alba agglutinin (BPA) and the Gal (beta 1-->4)GlcNAc-reactive lectins Ricinus communis agglutinin (RCA-I) and Phaseolus vulgaris erythroagglutinin (PHA-E) gave the strongest label with exfoliation material. Lectin binding to the iris was variable. The binding of PNA, BPA, RCA-I, Erythrina cristagalli agglutinin (ECA), PHA-E and Glycine max agglutinin (SBA) to the subendothelial region of iris blood vessels closely resembled their binding to exfoliation material. RCA-I and PHA-E bound moderately to the aqueous outflow passages. The surface of the corneal epithelium showed positive reaction with most lectins studied, but the keratocytes reacted with RCA-I and PHA-E only. Neuraminidase pretreatment generally increased the reaction intensity. The findings suggest that the glycoconjugate composition of exfoliation material in the classical locations along the anterior and posterior chamber closely resembles that in the subendothelial region of iris blood vessels.

Histopathology of Argon Laser Peripheral Iridoplasty

ABSTRACT We report the light and electron microscopic findings from two eyes treated with argon laser peripheral iridoplasty (ALPI) for bilateral angle-closure glaucoma. The patient, a 45-year-old man, died from complications of acquired immunodeficiency syndrome 16 days following ALPI. Ocular pathologic findings included contraction furrow formation and proliferation of fibroblast-like cells, accompanied by collagen deposition on the iris surface, denaturation of stromal collagen, and coagulative necrosis of blood vessels within the anterior two thirds of the iris stroma. These findings suggest that heat shrinkage of collagen may be responsible for the short-term response to ALPI, and that contraction of the fibroblastic membrane may be responsible for its long-term effects. Additionally, the presence of coagulative necrosis of iris blood vessels suggests that overttreatment may result in iris necrosis. To our knowledge this is the first report of the histopathology of ALPI.

Vascular Anastomoses Between the Iris and Persistent Hyperplastic Primary Vitreous

Prominent radial iris blood vessels created small but definite pupillary notches in five children with persistent hyperplastic primary vitreous and persistence of the tunica vasculosa lentis. Detection of these abnormal iris vessels suggested the presence of persistent hyperplastic primary vitreous and related syndromes even when the diagnosis was obscured by the presence of an opaque lens. These vessels represented early developmental arrest and may have been associated with abnormal development of the macula and optic nerve. Surgical and amblyopia therapy, therefore, may not provide useful vision, and should be undertaken with caution.

An electron microscopic study of the permeability of intraocular blood vessels using lanthanum as a tracer in vivo

In the present work lanthanum has been used as an electron microscopic tracer to study intraocular blood vessel permeability in vivo. Aqueous solutions of lanthanum were injected intravenously in rabbits. The eyes were enucleated 30 or 60 min later. Lanthanum was detected as irregular electron-dense deposits in the vascular lumen of intraocular blood vessels. In normal eyes, the tracer did not permeate the endothelium of blood vessels in iris, ciliary processes, choroid, or retina. Conjunctival application of prostaglandin E 1 (25 μg) 15 min before lanthanum injection, induced leakage of the tracer from blood vessels in the anterior parts of the ciliary processes and their iridial extensions. Leakage occurred through gaps between endothelial cells. Blood vessels showing increased permeability to lanthanum were readily detected, as heavy deposits of tracer material had accumulated in their walls. In the present work, lanthanum has been found to be a suitable tracer to study intraocular blood vessel permeability in the experimental animal. The technique is direct and simple, and the tracer is easily visualized in the electron microscope.

Reinnervation, myelination and organization of iris tissue implanted into the rat midbrain — an ultrastructural study

The ultrastructure of autologous irides implanted into the midbrain of mature Sprague-Dawley rats was studied over a time period of 4–14 days. Most features of the normal iris still persisted throughout this time, including typical iris blood vessels and amelanotic melanocytes. At 5-4 days after implantation, the normal innervation of the implanted iris had degenerated, except for the presence of intact Schwann cells and some myeiin debris. Reinnervation, beginning about the seventh day, proceeded rapidly. By the fourteenth day, extensive reinnervation of the implant was evidenced by the presence of numerous small (0.1–0.6 μm) and large (2–4 μm) non-myelinated axons ensheathed in Schwann cell cytoplasm. Axonal varicosities, filled either with dense core or clear core vesicles, formed junctions with axons. These jun characterized by an accentuation of areas of the axonal membrane and pre- or post-junctional thickenings; however, we did not observe typical synaptic complexes. Some large axons within the myelinated iris developed thick myelin sheaths of the peripheral nervous system (PNS) type; we believe this is the first reported instance in which myelination of central axons by Schwann cells within the brain parenchyma has been produced by the implantation of PNS elements.

Neovascularization induced by intraocular xenografts of normal, preneoplastic, and neoplastic mouse mammary tissues.

The capacity to induce neovascularization was compared in normal, preneoplastic, and neoplastic mouse mammary tumors from strains with a high incidence of tumors (C3H, C3H-Avy, C3H-AvyfB) by implantation of small biopsy fragments on the iris surface in New Zealand White rabbits. Proliferation of iris blood vessels was studied by: 1) direct, in vivo slit-lamp stereomicroscopy and fluorescein angiography; 2) filling of the microvasculature with colloidal carbon; and 3) histologic examination. Ninety percent of mammary tumor implants elicited iris neovascularization after 48-72 hours, regardless of their histologic classification or the presence or absence of mammary tumor virus. Corticosteroid treatment reduced immediate postoperative inflammation (12-36 hr) but did not abolish subsequent growth of new vessels. Necrotic tumor fragments failed to elicit any neovascular response. In contrast, only 6% of normal tissues from resting mammary glands caused any vasoproliferation. Hormone-stimulated mammary tissues from pregnant and lactating mice exhibited a transient neovascular capacity that was lost during postweaning involution. Of the implants from premalignant hyperplastic alveolar nodules (HAN's), 30% produced a pattern of vessel growth similar to that of tumor implants. D-1 line (HAN outgrowth) tissues, which have a predicted low incidence of tumors, induced significantly fewer neovascular responses (P less than 0.002) than morphologically and biochemically similar D-2 line tissues, which have a predicted high incidence of tumors. These data suggest that the capacity to induce neovascularization is acquired during malignant progression of mouse mammary tissues; therefore, demonstration of this property may be useful in the identification of those intermediate populations most at risk for neoplastic transformation.

THE ACTION OF ANGIOTENSIN ON INTRAOCULAR PRESSURE.

<h3>Introduction</h3> Current findings strongly suggest that intraocular pressure (IOP) of the cat eye is dependent upon venous pressure^2-5,7-10which in turn can be regulated by changes in resistance of the iris artery and its radial branches.⁶ Acetazolamide has been demonstrated to lower intraocular pressure, at least in part, by its ability to produce a fall in venous pressure^2,3through its constrictive effect of the iris blood vessels.⁶Many other agents, even though of diverse origin and activity, which have been shown capable of producing a lowering of IOP in patients with glaucoma, have all been found to have the common effect of producing an increase in resistance in the iris artery.⁹ Recently dilutions of serum were also shown capable of producing increases in resistance of the iris artery. Almost all of this serum vasoconstrictor activity could be ascribed to a substance which had many of