HYALURONAN IN THE BOVINE OCULAR ANTERIOR SEGMENT, WITH EMPHASIS ON THE OUTFLOW PATHWAYS

Purpose. It has been postulated that glycosaminoglycans play a role in the regulation of outflow resistance. The purpose of these studies wa s to localize the distribution of hyaluronan (HA) in the anterior segm ents of bovine eyes to understand better the possible role of HA in th e outflow pathway. Methods. Eyes from four 2-week-old calves and four 1-year-old cows were examined using a biotinylated-hyaluronan binding protein to localize HA in tissue sections of the anterior segment of b ovine eyes. Various fixations and microwave irradiation were compared. The vitreous body in each section served as a positive control. Secti ons treated with Streptomyces hyaluronidase were used to confirm speci ficity. Results. No significant difference in distribution of HA was f ound between various fixations and between calves and cows. HA was fou nd in subconjunctival connective tissue and in intercellular spaces of limbal and conjunctival epithelium, but not in corneal epithelium. St aining was sometimes found on the surface of the corneal epithelium an d endothelium, as well as on the conjunctival epithelium. No staining was found within the corneal stroma. There was HA in the iris stroma, but not in the root of the iris or ciliary body stroma. HA was present in the anterior, nonfiltering part of the trabecular meshwork (TM) an d surrounding collector channels and blood vessels in the sclera; to a lesser extent, it was present in the juxtacanalicular region of the T M. HA was detectable neither within trabecular beams nor filling the i ntertrabecular spaces. Strong staining was found, however, in the nerv e bundles in the angle region. Staining for IIA in vitreous was invari ably positive, and in Streptomyces hyaluronidase-treated sections it w as negative. Conclusion. HA was not uniformly distributed in the bovin e TM. The distribution of HA. in the flow pathway of the aqueous outfl ow system indicates that only a small fraction of the HA found in bioc hemical analyses of the bovine meshwork is located in the region where the flow resistance is thought to reside.