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Ioannis K. Petropoulos, Anne-Laure Martin, Georgios Mangioris, Efstratios Mendrinos, Peter C. Rimensberger, Constantin J. Pournaras; Effect of Nitric Oxide Inhalation on Retinal Arteriolar Diameter in Minipigs. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6826.
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L-arginine retinal juxta-arteriolar microinjection exerts a vasodilatory effect on retinal arterioles in minipigs, probably by stimulation of nitric oxide (NO) production. The purpose of the present study was to investigate the effect of inhaled NO on the retinal arteriolar diameter in minipigs.
Five minipigs were anesthetized, intubated and mechanically ventilated, and a Swan-Ganz catheter was inserted for measuring cardiac output by the thermodilution technique. Ocular fundus image (one eye per animal) was monitored and recorded in a digital videotape under stable hemodynamic and ventilatory conditions. After baseline recordings, inhaled NO at a concentration of 80 ppm was added to the breathing circuit for 30 minutes and was then weaned off. Retinal arteriolar diameter was assessed in arbitrary units (AU) at baseline, 30 minutes after the initiation of inhaled NO, and again 30 minutes after interruption of the inhaled NO, using a Retinal Vessel Analyzer (Imedos GmbH, Jena, Germany). At the same time points, body temperature, arterial blood gases, heart rate, arterial blood pressure, central venous pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output were measured, and systemic and pulmonary vascular resistances were calculated.
Mean baseline retinal arteriolar diameter was 161.4 ± 18.4 AU. Thirty minutes after the initiation of NO inhalation, mean retinal arteriolar diameter had increased by 8.9 ± 5.3 % compared to baseline (p<0.05), measuring 175.2 ± 15.5 AU. Thirty minutes after the interruption of NO inhalation, mean retinal arteriolar diameter had decreased to 171.1 ± 21.0 AU, but was still bigger than at baseline by 5.5 ± 2.6 % (p<0.05). None of the hemodynamic parameters recorded was altered significantly. In particular, cardiac output, arterial blood pressure and systemic vascular resistance were not modified.
Inhalation of 80 ppm NO induces vasodilation of the retinal arterioles in minipigs, which is partially sustained over 30 minutes after weaning the inhaled NO. Further studies are needed to evaluate a potential clinical application of this treatment modality in vascular diseases of the retina.
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