This study was performed to evaluate the effects of nerve growth factor (NGF) upon angiogenesis in the rat cornea, to examine its possible application as an alternative angiogenic inducer and to provide basic data for further studies. Angiogenesis was induced by cornea micropocket assay, as previously described. Eight of thirty two eyes of Sprague-Dawley rats were randomly assigned to one of four groups, namely, a non-NGF group (Group 0), a 0.5 ng of NGF group (Group 0.5), a 1.0 ng of NGF group (Group 1.0) and a 5.0 ng of NGF group (Group 5.0). Pellets made of poly-2-hydroxylethylmethacrylate and sucralfate were implanted into the corneal stroma no closer than 1 mm from the limbus. After the implantation, the number of new vessels, vessel length and circumferential neovascularization were examined daily under the surgical microscope over a period of 7 days. The area of neovascularization was determined using a mathematical formula. Although new vessels in Group 0 and Group 0.5 were first observed at day 5, those of Groups 1.0 and 5.0 were first noted on days 4 and 3, respectively. However, the growth rates of new vessels in Groups 1.0 and 5.0 were higher than those of Groups 0 and 0.5 with the passage of time. The number, length, circumferential neovascularization and areas covered by the vessels in Groups 1.0 and 5.0 were significantly more than in Group 0 and Group 0.5 (p<0.05). This study showed that NGF had a dose-dependent angiogenic effects on the rat cornea and that the minimal effective dose of NGF was 1.0 ng per cornea. Also, it showed that NGF would be useful in angiogenic studies as an alternative angiogenic inducer.
Angiogenesis Inducing Agents/*toxicity ; Animals ; Cornea/blood supply/*drug effects ; Corneal Neovascularization/*chemically induced ; Dose-Response Relationship, Drug ; Female ; Male ; Nerve Growth Factor/*toxicity ; Random Allocation ; Rats ; Rats, Sprague-Dawley

BACKGROUNDCorneal neovascular leakage can lead to edema and secondary scarring. Previous studies have shown that pericytes play a key role in maturation of angiogenesis. The present studies investigate the relationship between vascular permeability and pericyte coverage of endothelial cells in rat corneal neovascular induced by alkali burns.

METHODSCorneal neovascular vessels induced by alkali burns was performed in Sprague-Dawley rats. Corneas were excised on 1, 2, 3, 5, 7 and 10 days after cauterization. The vascular permeability rate was measured by the Evans blue method. The microvessel pericyte coverage index (MPI) was applied to quantify the pericyte coverage through double immunofluorescent staining of frozen sections of corneas with CD31 as the endothelial and alpha-smooth muscle actin (alpha-SMA) as the pericyte markers. The correlation between permeability rate and MPI was analyzed. Pericyte coverage was confirmed ultrastructually using transmission electron microscopy.

RESULTSThe vascular permeability rate was (1.14 +/- 0.17), (0.24 +/- 0.08), (0.29 +/- 0.16), (0.14 +/- 0.10), (0.09 +/- 0.06) and (0.05 +/- 0.04) microg x ml(-1) x mm(-2) respectively on 1, 2, 3, 5, 7 and 10 days after cauterization. The MPI was 0, 16.07%, 11.95%, 43.84%, 73.97% and 86.21% respectively at the above mentioned time points. The correlation coefficient between MPI and the permeability rate was -0.943 (P = 0.005).

CONCLUSIONSPericyte recruitment was significantly correlated with the permeability of corneal neovascularization induced by alkali burns in rats. Therapeutic strategies aiming at anti-leakage should be most effective if they promote pericytes proliferation in the course of corneal neovascularization.

Alkalies ; Animals ; Burns, Chemical ; physiopathology ; Capillary Permeability ; Cell Movement ; Cornea ; blood supply ; ultrastructure ; Corneal Neovascularization ; physiopathology ; Eye Burns ; chemically induced ; physiopathology ; Female ; Fluorescent Antibody Technique ; Pericytes ; physiology ; Rats ; Rats, Sprague-Dawley