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Frank W Rozsa, William Kern, Wonsuk Kim, Natalie Lopes, Leah Linenfelser, Sarah Skender, Julia E Richards, Alan Argento; Changing properties of bovine aqueous humor with age. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5726.
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© ARVO (1962-2015); The Authors (2016-present)
To identify physical properties of bovine aqueous humor that correlate with age.
Fresh bovine aqueous humor (bAqH) was collected from 67 globes via paracentesis through the center of the cornea using 27-gauge needle attached to a 1 ml tuberculin syringe. Dynamic viscosity was measured over a range of temperatures, including bovine body temperature (38.5oC) from at least three samples per globe using a RheoSense m-VROC small sample viscometer. Aliquots of bAqH were stored at -80oC. A SpeedVac was used to concentrate some bAqH samples to directly compare viscosities. Protein concentration in bAqH was determined by Bio-Rad Bradford protein assay with bovine serum albumin standard. bAqH samples were run on 7.5% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) followed by immunoblotting using anti-myocilin and anti-transferrin peptide antibodies. Comparison of means between different age groups were made using the Student's t-test with α = 0.05.
Data were stratified into three age groups; <2 years (n=35), 2-3 years (n=23) and >3 years (n=9). In all cases, bovine aqueous humor behaved as a Newtonian fluid and the viscosity was dependent on testing temperature (-0.0154 cPs/oC in range: 35.6oC - 41.6oC). Overall, there was a modest correlation between protein concentration and viscosity in bAqH. Direct comparison on the effect of concentrating a bAqH sample showed that the viscosity increased from 0.756 cPs at 294 μg/ml to 0.785 cPs at 533 μg/ml for pre- and post- concentrated samples, respectively. Age stratified data suggested that older cows have higher protein content in bAqH. However, viscosity did not appear to vary significantly across any of three age groups. We did not observe appreciable differences in myocilin content across the 67 bAqH samples.
This study addressed relationships between myocilin, protein concentration, and viscosity in aqueous humor, and how these variables correlate with age. Viscosity is a fluid’s property that describes its tendency to resist free flow. At a given level of motive force, a higher viscosity fluid will flow more slowly than a lower-viscosity fluid. It might be expected that aqueous humor properties and composition would affect the outflow facility and attendant intraocular pressure. These results suggest that protein concentration of bAqH may vary with age and that there may be a modest correlation between protein concentration and viscosity of bAqH.
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