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Z. Lu, P.A. Scott, S. Hofmann, D.R. Overby, T.F. Freddo, H. Gong; The Mechanism of Increasing Outflow Facility by Rho–Kinase Inhibition With Y27632 in Bovine Eyes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1856.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate how Y–27632 (Y27; a selective inhibitor of rho–kinase and cell contractility) affects outflow facility (C), the hydrodynamic patterns of outflow, and the morphology of the inner wall (IW) and juxtacanalicular tissue (JCT) in bovine eyes.
Twelve bovine eyes were perfused at 15 mmHg with Dulbecco’s PBS containing 5.5 mM glucose (DPBS) to establish a stable baseline C. The anterior chamber contents were exchanged for DPBS with 50 µM Y27 in 7 eyes, while 5 eyes received DPBS alone. Eyes were again perfused (0.5 mL), and then exchanged with DPBS containing fluorescent microspheres (0.5µm; 0.002% v/v), followed by more perfusion (0.5 mL) to label the hydrodynamic patterns of outflow. Eyes were then perfusion–fixed with Karnovsky’s fixative. Radial and tangential sections in all quadrants were prepared and confocal images were taken along the IW of the aqueous plexus (AP). The total length (TL) and the tracer–decorated length (L) of IW were measured in >15 images/eye, and the average percent effective filtration length (PEFL=L/TL) in each eye was calculated. The sections with AP were then processed and examined under light microscopy. The TL of IW and the length exhibiting IW and JCT separation (SL) were measured in >16 micrographs/eye, and the average percentage separation length (SL/TL.) was also calculated.
After Y27 treatment, C increased an average 0.83±0.26 µl/min/mmHg (58%) while in control eyes the change in C was 0.04±0.14 µl/min/mmHg (6%) and this difference was significant (p=0.03). Control eyes showed segmental distribution of tracer in the trabecular meshwork (TM), with clustering of microspheres near collector channel ostia. Y–27 treated eyes showed a more uniform pattern, with extensive labeling along the IW. The PEFL in Y27–treated eyes (58.3±6.5%) was 2–fold larger than that in control eyes (22.1±6.1%, p=0.002). Light microscopic examination revealed that the IW and JCT were significantly distended compared to control eyes, with discernable separation between the IW and JCT. The percentage separation length was 2.8–fold larger in Y27 treated eyes (59.3±3.6%) than in control eyes (20.8±2.0%; P<0.001).
Y27 significantly increases C and the PEFL along the IW of the AP in bovine eyes. These changes coincided with greater separation between the IW and JCT, findings previously correlated with increasing C during "washout". Y27 may act through a mechanism that is similar to washout by redistributing aqueous outflow through a larger area of the IW and JCT.
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