eNOS, a pressure-dependent regulator of intraocular pressure.
OBJECTIVE
Pathology in the primary drainage pathway for aqueous humor in the eye is responsible for ocular hypertension, the only treatable risk factor in patients with glaucoma. Unfortunately, the mechanisms that regulate pressure-dependent drainage of aqueous humor and thus intraocular pressure (IOP) are unknown. To better understand one possible underlying molecular factor that regulates IOP, nitric oxide (NO), pressure-dependent drainage in transgenic mice overexpressing endothelial NO synthase (eNOS) was studied.


METHODS
IOP was measured by rebound tonometry in mice, and pressure versus flow data were measured by ex vivo perfusion at multiple pressures between 8 and 45 mm Hg, using mock AH ±100 μM L-NAME. A subset of eyes was examined histologically using standard techniques or was assayed for fusion protein expression by Western blot analysis.


RESULTS
IOP was lower (9.6 ± 2.7 vs. 11.4 ± 2.5 mm Hg; mean ± SD; P = 0.04) and pressure-dependent drainage was higher (0.0154 ± 0.006 vs. 0.0066 ± 0.0009 μL/min/mm Hg; P = 0.002) in the transgenic mice than in the wild-type animals; however, pressure-independent drainage was unaffected. The NOS inhibitor L-NAME normalized pressure-dependent drainage in transgenic animals. For IOP >35 mm Hg, the slope of the pressure-flow curve in wild-type mice increased to match that seen in transgenic mice. Shear stress in the pressure-dependent pathway at elevated pressures was calculated to be in a range known to affect eNOS expression and activity in vascular endothelia.


CONCLUSIONS
Endothelial NOS overexpression lowers IOP by increasing pressure-dependent drainage in the mouse eye. Data are consistent with NO's having a mechanoregulatory role in aqueous humor dynamics, with eNOS induction at elevated IOPs leading to increased pressure-dependent outflow.
Department of Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona, USA. dan.stamer@duke.edu
W Daniel
WD
Stamer
Yuan
Y
Lei
Alexandra
A
Boussommier-Calleja
Darryl R
DR
Overby
C Ross
CR
Ethier
D000818:Animals; D001082:Aqueous Humor / Q000502:physiology; D015153:Blotting, Western; D004247:DNA / Q000235:genetics*; D004195:Disease Models, Animal; D004728:Endothelium, Corneal / Q000201:enzymology* / Q000473:pathology; D005786:Gene Expression Regulation; D005838:Genotype; D007429:Intraocular Pressure / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D052250:Nitric Oxide Synthase Type III / Q000096:biosynthesis / Q000235:genetics*; D009798:Ocular Hypertension / Q000201:enzymology / Q000235:genetics* / Q000503:physiopathology; D016133:Polymerase Chain Reaction; D014065:Tonometry, Ocular
D004247:DNA; D052250:Nitric Oxide Synthase Type III