Pressure Clamping During Ocular Perfusions Drives Nitric Oxide-Mediated Washout

• Published in: Investigative ophthalmology & visual science 2023-06, Vol.64 (7), p.36-36
• Main Authors: Kelly, Ruth A, McDonnell, Fiona S, De Ieso, Michael L, Overby, Darryl R, Stamer, W Daniel
• Format: Article
• Language: English
• Subjects: Animals; Aqueous Humor; Constriction; Intraocular Pressure; NG-Nitroarginine Methyl Ester - pharmacology; Nitric Oxide; Perfusion; Physiology and Pharmacology; Swine; Trabecular Meshwork
• ISSN: 1552-5783; 0146-0404; 1552-5783
• DOI: 10.1167/iovs.64.7.36

The aim of this study was to test the hypothesis that nitric oxide (NO) mediates a pressure-dependent, negative feedback loop that maintains conventional outflow homeostasis and thus IOP. If true, holding pressure during ocular perfusions will result in uncontrolled production of NO, hyper-relaxation of the trabecular meshwork, and washout. Paired porcine eyes were perfused at constant pressure of 15 mm Hg. After 1 hour acclimatization, one eye was exchanged with N5-[imino(nitroamino)methyl]-L-ornithine, methyl ester, monohydrochloride (L-NAME) (50 µm) and the contralateral eye with DBG, and perfused for 3 hours. In a separate group, one eye was exchanged with DETA-NO (100 nM) and the other with DBG and perfused for 30 minutes. Changes in conventional outflow tissue function and morphology were monitored. Control eyes exhibited a washout rate of 15% (P = 0.0026), whereas eyes perfused with L-NAME showed a 10% decrease in outflow facility from baseline over 3 hours (P < 0.01); with nitrite levels in effluent positively correlating with time and facility. Compared with L-NAME-treated eyes, significant morphological changes in control eyes included increased distal vessel size, number of giant vacuoles, and juxtacanalicular tissue separation from the angular aqueous plexi (P < 0.05). For 30-minute perfusions, control eyes showed a washout rate of 11% (P = 0.075), whereas DETA-NO-treated eyes showed an increased washout rate of 33% from baseline (P < 0.005). Compared with control eyes, significant morphological changes in DETA-NO-treated eyes also included increased distal vessel size, number of giant vacuoles and juxtacanalicular tissue separation (P < 0.05). Uncontrolled NO production is responsible for washout during perfusions of nonhuman eyes where pressure is clamped.