PURPOSE. To investigate the role of endothelin-1 (ET-1) in retinal glial cells in regulating retinal blood flow (RBF) during hyperoxia in cats. METHODS. We measured the vessel diameter (D), blood velocity (V), and blood flow (F) simultaneously in first-order retinal arterioles using a laser Doppler velocimetry system. The animals were under general anesthesia during hyperoxia (100% oxygen) for 10 minutes 24 hours after intravitreal injection of L-2-aminoadipic acid (LAA), a gliotoxic compound,

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... r diluted hydrochloric acid (0.01 N) used as the vehicle control. We also measured the changes in the RBF after intravitreal injection of BQ-123, a specific ET type A receptor antagonist, in LAA-treated eyes. To examine if endothelin-converting enzyme-1 (ECE-1), as an ET-1generating enzyme located in retinal glial cells, immunohistochemical examinations with costaining of antiglial fibrillary acidic protein (GFAP) antibody and anti-ECE-1 antibody were performed in whole-mount retinas. RESULTS. During hyperoxia, the decreases in D, V, and F in response to hyperoxia were attenuated significantly (P < 0.01 for all comparisons) in the LAA-treated eyes compared with the vehicle control (LAA, D, À8.5 6 1.5%; V, À13.8 6 1.5%; F, À27.8 6 3.0% versus vehicle control, D, À16.8 6 1.3%; V, À26.3 6 2.0%; F, À48.9 6 2.4%). In LAA-treated eyes, intravitreal injections of BQ-123 did not change the rate of hyperoxia-induced RBF compared to LAA-treated eyes. The anti-ECE-1 antibody was costained with anti-GFAP antibody in the whole-mount retinas. CONCLUSIONS. The current findings suggest that retinal glial ET-1 may play an important role in regulating RBF during hyperoxia in cats.