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Evaluation of Nitric Oxide Synthesis in the Optic Nerve Head in vivo Using Microdialysis and High-Performance Liquid Chromatography and Its Interaction with Endothelin-1

Purpose: To investigate the relationship between nitric oxide synthesis and endothelin-1 (ET-1) in the optic nerve head in vivo. Methods: A concentric microdialysis probe was inserted into the optic nerve head of a rabbit and was perfused with Ringer’s solution at a constant flow rate of 2 µl/min. The perfused dialysates were collected every 10 min, and levels of nitrite and nitrate in the 10-min dialysate samples were measured after intravitreal injection of ET-1 (100 pmol) using high-performance liquid chromatography based on the Griess method. Results: Basal levels of nitrite and nitrate in the 10-min dialysate were 0.08 ± 0.01 and 3.95 ± 0.50 µM, respectively. We confirmed that these levels were reduced by intravenous L-NAME and restored by L-arginine. Intravitreal ET-1 significantly elevated the levels of nitrate to 189% of baseline 10 min after ET-1 application, which was inhibited by pretreatment of intravenous L-NAME (50 mg/kg). Conclusion: These results indicate that production of nitric oxide is closely connected with the ET-1 signaling pathway.