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Jason Chang, Catherine Marando, C Ethier, W Daniel Stamer, Darryl Overby; Effects of Nitric Oxide Donor on Outflow Facility in Mice. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2002.
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Overexpression of endothelial nitric oxide synthase (eNOS) has been shown to increase conventional outflow facility and lower intraocular pressure (IOP) in transgenic mice (Stamer et al. IOVS 2011 52:9438). To better understand how nitric oxide (NO) contributes to the regulation of IOP in non-transgenic animals, we examined the effects of a NO-donor on conventional outflow facility in wild-type mice.
Enucleated eyes from C57BL/6 mice (6-8 week old females) were perfused at pressures of 8, 15, 20 and 25 mmHg using a computerized system. Eyes were perfused at 35°C in a bath of isotonic saline with Dulbecco’s phosphate buffered saline + 5.5mM glucose (DBG) supplemented with either a light-activated NO-donor (100µM S-nitroso-N-acetylpencillamine, SNAP; N = 4) or inactive donor (100µM N-acetylpencillamine, NAP; N = 4). Eyes were perfused either immediately after enucleation or after 4 hours storage at 4°C, with the treatments assigned randomly. The conventional outflow facility was defined as the slope of the linear regression through the flow rate-pressure data. NO release from SNAP and NAP was characterized using an NO-sensitive probe (WPI; ISO-NO II) that was calibrated following the manufacturer’s protocol. Light exposure levels were measured using a luminometer (Mastech).
SNAP was highly light sensitive: a brief initial light exposure (10 min; 680-800 lumens/m2) followed by darkness caused a burst of NO release, however continued light exposure led to an initial increase followed by a rapid NO depletion. Under conditions of initial light exposure followed by darkness, NO release from 100 µM SNAP (10 mL) increased over 1 hr to reach a peak of 140 ± 20 nM (mean ± SD), while NO release from 100 µM NAP was negligible (0 ± 4 nM). Conventional outflow facility in SNAP-treated eyes following brief light exposure was 64% greater than in NAP-treated eyes (0.0570±0.0147 vs. 0.0348±0.0085 µL/min/mmHg; p < 0.05).
A NO-donor increased conventional outflow facility by 64% in wild-type mice, similar to the 2-fold increase previously reported in transgenic mice that over-express eNOS. These data further support the role of NO in the regulation of IOP by modulation of conventional outflow facility.
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