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J.J. Kang Derwent, K. Lorentz, S. Tummala; Changes in Retinal Blood Velocity in Response to Modulation of the Intraretinal Nitric Oxide Level . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1792.
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The present study was undertaken to determine the effect of modulating intraretinal nitric oxide (NO) levels on retinal blood velocity using a Scanning Laser Ophthalmoscope (SLO).
Retinal blood velocity was determined by tracking 1 µm yellow–green fluorescent microspheres (505 nm maximum absorption and 515 nm maximum emission) in anesthetized pigmented adult rats. Using the SLO, retinal blood velocities were obtained in arteries, veins, and small vessels by recording several 2–min digital movies at each time point. Directional flow of fluorescent microspheres and vessel characterization were determined based on examination of infrared reflectance and fluorescein angiogram images. The NO levels were modulated by one 3 µl intravitreal injections of either nitric oxide synthase (NOS) inhibitors, NG–nitro–L– arginine methyl ester (L–NAME, 2.5 mM vit. conc, eNOS inhibitor) and 1–(2–trifluoromethylphenyl) imidazole (TRIM, 2 mM vit. conc, nNOS inhibitor) or a NO donor, S–nitroso–N–acetylpenicilliamin (SNAP, 2 mM vit. conc). Intraocular pressure (IOP) was measured before and after the injection. Post–treatment velocity measurements were obtained every 15 minutes for ∼2 hours after the injection.
Neither changes in image quality nor changes in IOP were observed with the intravitreal injections. No change in heart rate was observed after the injection. After L–NAME treatment, overall blood velocity decreased compared to the control values. Arterial velocity decreased by ∼15%, venous velocity decreased by ∼36% and small vessel velocity decreased by ∼26%. TRIM treatment increased arterial velocity by ∼15%, venous velocity by ∼20% and small vessel velocity by ∼5%. SNAP treatment also increased arterial velocity by ∼28% and venous velocity by ∼13%.
These findings suggest that intravitreal administration of the pharmacological agents had selective local effects on the retina. Changes in blood velocity due to the neuronal NOS inhibitor suggest that neuronal NOS may also be involved in controlling blood flow in the retina.
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