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H. A. Reitsamer, B. Tockner, B. Bogner, C. Runge, C. Strohmaier, C. Nischler, G. Grabner; Neuronal Nitric Oxide Synthase Inhibition Does Not Block Parasympathetic Vasodilation in the Choroid. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4143. doi: https://doi.org/.
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To investigate the effect of the neuronal nitric oxide synthase inhibitor (N-omega-propyl-L-arginin) on choroidal blood flow during facial nerve stimulation
Mean arterial pressure (MAP), intraocular pressure (IOP) and choroidal blood flow (ChorBF) were measured in anesthetized new Zealand white rabbits (n = 6). MAP and IOP were measured invasively with canulas in the central ear artery and the vitreous cavity respectively. Laser Doppler Flowmetry was used to measure choroidal blood flow. The facial nerve, which carries parasympathetic fibers to the ciliary ganglion, was exposed in the middle ear cavity using an approach through the tympanic membrane. A platinum electrode was advanced centrally along the canal of the facial nerve. Pulse trains between 2 and 15 Hz with pulse durations of 200µs and 4 mA Amplitude and a total duration between 2 sec and 60 sec were used to stimulate the nerve. Since all variables were measured continuously, effects of the nerve stimulation could be observed immediately, assuring a good position of the electrode.
Stimulation of the nerve caused a significant increase in IOP (+7.6 ± 2.6%) and ChorBF (+13.3 ± 2.7). Perfusion pressure (-14.3 ± 3.7), Choroidal vascular resistance (-28.1 ± 6.8) and heart rate (-3.6 ± 0.8) were decreased. All effects were statistically significant. N-omega-propyl-L-arginin given intravenously as a bolus injection (1.5 mg/kg) did not block the effects mentioned above.
In a previous study we showed that the neuronal nitric oxide synthase inhibitor TRIM (1, 2-trifluoromethylphenyl imidazole) had no effect on choroidal blood flow parameters at baseline and during manipulations of perfusion pressure. The present study also fails to show significant effects of the neuronal nitric oxide synthase inhibitor N-omega-propyl-L-arginin at 1.5mg/kg.
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