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S. E. Ohia, M. Kulkarni, Y. Njie-Mbye, D. Jackson, M. Zhao, C. A. Opere; Measurement of Hydrogen Sulfide Concentration in Isolated Bovine Eyes. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3305.
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Evidence from our laboratory shows that hydrogen sulfide (H2S) can elicit pharmacological actions at pre- and postjunctional sites in ocular tissues. Although enzymes involved in the biosynthesis of this gas are present in the eye, it is unclear whether they can generate H2S in situ.
In the present study, we measured basal levels of H2S in the various tissues of bovine eyes and also examined the effect of enzyme inhibitors and H2S donors on endogenous production of this gas in the neural retina.
Endogenous H2S levels were measured in ocular tissues using a well established spectrophotometric method. Ocular tissues comprising of the cornea, iris, ciliary muscle, retina, vitreous humor and choroid were homogenized in a mixture of zinc acetate and borate buffer followed by addition of N, N-dimethyl-p-phenylenediamine and ferric chloride. Samples were incubated at 37°C for different time periods and centrifuged at 5000g. The absorbance of the resulting solution was measured at 670 nm and H2S concentration was calculated against a calibration curve of standard H2S (2.0-750 µM). In studies examining the effects of H2S donor, sodium hydrosulfide, (NaHS) and enzyme inhibitors (cystathionine γ-lyase: proparglyglycine, PAG and cystathionine β-synthase: aminooxyacetic acid, AOA) on retina, tissues were homogenized in the presence of the respective compounds and subjected to the same methodology as mentioned above.
There was time-dependent increase in endogenous H2S production in bovine neural retina reaching a maximum of 700 µM/g wet tissue at 30 mins. With the exception of the vitreous humor, H2S was detected in various bovine ocular tissues including the iris, choroid, ciliary muscle, cornea and retina. The highest amount of endogenous H2S was detected in cornea (7700µM/g wet tissue) and retina (7400 µM/g wet tissue). In the retina, both PAG (1 mM) and AOA (1 mM) attenuated the production of H2S whereas NaHS (1 µM) elicited an increase in H2S production in retina when compared to basal levels.
We conclude that H2S is present in various tissues of the isolated bovine eye. Furthermore, the production of endogenous H2S is enhanced in the presence of an H2S donor and is blocked by inhibitors of enzymes that synthesize this gas in the retina.
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