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DA Velasquez, AK Palkama, Z Si, HW Thompson, RW Beuerman; Effect of Brimonidine on Facility of Outflow and Pore Size in the Bovine Eye In Vitro . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3279.
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Purpose: To evaluate the effect of the α2-agonist UK 14,304 (brimonidine, Sigma) on aqueous outflow and pore sizes in the bovine eye using a perfusion chamber. Method: The posterior 1/3 of the globe, the vitreous, the aqueous humor, and the lens were removed, and 4 peripheral iridotomies were performed. The resulting specimens included all anterior structures and the sclera posterior to the equator, with vortex veins. The specimens were attached to the perfusion chamber and infused with Dulbecco's solution with (n=9) or without (controls, n=20) 2x10-5 M brimonidine at a constant perfusion pressure of 11 mmHg. Facility of outflow and perfusion pressure were electronically recorded continuously for 18 hr. At 18 hr, fluorescent microbeads (0.31, 0.9, 2.03, 2.6, 3.4, 4.2, or 5.1 µm in diameter) were added to the perfusion solution and infusion was continued for an additional 3 hr. At the end of the 3-hr bead perfusion, the diameters of the beads in the perfusate collected outside the eye were determined by fluorescence microscopy. Results: The facility of outflow was 1.78 ± 0.05 µl/min/mmHg in the brimonidine-treated eyes and 0.69 ± 0.06 µl/min/mmHg [M ± SEM] in the control eyes (p<0.001, 2-way ANOVA). In the control eyes, the largest beads that passed through the pores were 2.03 µm in diameter. In the brimonidine-treated eyes, beads as large as 3.4 µm were found in the perfusate outside the eye but not in the ciliary muscle (uveoscleral pathway). Conclusion: Treatment with bromonidine increased total facility of outflow by 158%, compared with untreated specimens. This increase, as well as the presence of larger beads (3.4 µm) in the perfusate and their absence in the ciliary muscle, suggests that brimonidine both increases outflow and affects pore diameter, which evidently are not static.
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