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Takashi Okuno, Hidehiro Oku, Tetsuya Sugiyama, Ying Yang, Tsunehiko Ikeda; Evidence that Nitric Oxide Is Involved in Autoregulation in Optic Nerve Head of Rabbits. Invest. Ophthalmol. Vis. Sci. 2002;43(3):784-789.
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purpose. To determine the role played by nitric oxide (NO) in the autoregulation
of circulation in the optic nerve head (ONH).
methods. The intraocular pressure (IOP) was increased and maintained at 50 mm Hg
by the infusion of balanced saline solution (BSS) into the anterior
chamber of albino rabbits. Experiments were performed with or without
an intravenous injection of 10, 20, or 50 mg/kg N G-nitro-l-arginine methyl ester
(l-NAME), a nitric oxide synthase (NOS) inhibitor. The
blood flow in the ONH was evaluated by the hydrogen clearance method,
and NO metabolites (nitrite and nitrate) were measured in the ONH under
the same experimental conditions in other rabbits. Visual evoked
potentials (VEPs) were recorded before the IOP elevation and every 15
minutes during the 60 minutes of elevation. The effect of elevated IOP
on the VEPs and the hemodynamics and NO levels in the ONH were
determined. The effect of pretreatment with a NOS inhibitor on the
IOP-induced changes was also investigated.
results. The implicit time of the VEP was prolonged after l-NAME in
a dose-dependent manner, whereas the implicit time in the control group
(saline) was less affected. Blood flow in the ONH was not reduced by an
elevation of the IOP (50 mm Hg) but was significantly reduced by l-NAME (20 mg/kg). The NO metabolites, which were elevated
in the ONH during IOP elevation in the control, were also depressed by l-NAME pretreatment.
conclusions. These results indicate that NO may play a role in the autoregulation of
circulation in the ONH during elevated IOP. This would mean that NO
provides some neuroprotection during an acute phase of ischemia in the
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