SERUM-PROTEINS AND AQUEOUS OUTFLOW RESISTANCE IN BOVINE EYES

Purpose. Recent evidence shows that much of the protein in the anterio r chamber aqueous humor enters diffusively through the root of the iri s. The proximity of the protein entry point to the trabecular meshwork suggests that the protein content of the aqueous humor in the trabecu lar meshwork might be much higher than previously suggested. The autho rs were interested in investigating the possible hydrodynamic implicat ions of these proteins. Methods. Bovine eyes were perfused with concen trations of bovine serum in buffer ranging from 0% to 15% to determine the effect on outflow resistance. Immunohistochemical methods were us ed on these eyes and unperfused eyes to determine the distribution of albumin in the anterior segment. Results. Preliminary perfusion studie s suggested that increasing the concentration of serum in buffer from 0% to 15% decreased the rate of ''wash-out'' in bovine eyes, with a 15 % solution essentially eliminating the wash-out phenomenon. Perfusion of a series of bovine eyes with a total of 5 ml of 15% serum in buffer showed a ''wash-out'' rate of 0.0498 +/- 0.0428 ([mul/min/mm Hg]/[ml perfusate]), whereas control eyes perfused with buffer washed-out at a rate of 0.1677 +/- 0.0271 (P < 0.05); a second series of eyes perfuse d with a total of 10 ml of 15% serum washed-out at a rate of 0.0533 +/ - 0.0294, whereas control eyes had a rate of 0.1813 +/- 0.0342 (P < 0. 02). Immunohistochemical investigations showed significant quantities of albumin in the outflow pathway of unperfused eyes, whereas perfusio n with buffer eliminated this protein; perfusion with 10% to 15% serum in buffer maintained the level of albumin in the outflow pathway simi lar to that found in unperfused eyes. Use of cuprolinic blue in a crit ical electrolyte concentration confirmed previous findings that sulfat ed proteoglycans are not eliminated from the trabecular meshwork durin g wash-out. Conclusions. Wash-out in nonhuman species may result from progressive depletion of an anterior segment depot of plasma-derived p roteins entering the trabecular meshwork. Modeling studies confirm tha t plasma-derived proteins in the aqueous humor of the trabecular meshw ork can generate a significant fraction of aqueous outflow resistance. The lack of wash-out in human eyes suggests that this system may main tain flow resistance in a fashion fundamentally different from other s pecies.