Role of nitric oxide in maintenance of basal anterior choroidal blood flow in rats

PURPOSE: The aim of this study was to use laser Doppler flowmetry to measure anterior choroidal blood flow in the anesthetized rat and to determine the role of nitric oxide (NO) in the maintenance of basal ocular blood flow in vivo. METHODS: By using laser Doppler flowmetry, blood flow from the anterior choroid in pentobarbital-anesthetized rats was measured continuously. Graded single doses (0.03-300 mg/kg) of the nonselective NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) were administered intravenously to establish dose-response relationships. Other groups of animals were tested with L-NAME after the prior administration of L-arginine, with D-NAME, or with the selective neural NO synthase inhibitor 7-nitroindazole. RESULTS: Intravenous administration of L-NAME produced a dose-related depression of anterior choroidal blood flow in the 0.3- to 30-mg/kg range. Maximal depression of approximately 60% occurred at the 30-mg/kg dose, peaked at approximately 30 minutes, and lasted throughout the 60-minute experimental period. At 10 mg/kg, L-NAME reduced ocular blood flow by approximately 50%, an effect that was abolished by pretreatment with intravenous L-arginine (300 mg/kg). Both D-NAME (10 mg/kg, intravenously) and 7-nitroindazole (50 mg/kg, intraperitoneally) were inactive with regard to ocular blood flow depression. CONCLUSIONS: Laser Doppler flowmetry appears to be a useful tool for continuous, online measurement of anterior choroidal blood flow in the rat eye. Results with L-NAME and 7-nitroindazole suggest that local tonic generation of endothelial NO plays an important role in the maintenance of basal anterior choroidal blood flow in this species.