The role of soluble proteins in generating aqueous outflow resistance in the bovine and human eye

Previous research has shown that wash-out in bovine and primate eyes can be greatly reduced by perfusing with buffer containing 5-15% serum. It was suggested that protein diffusion from the iris root might raise the in vivo protein concentration in the trabecular meshwork to a level much higher than in the anterior chamber. In this study, we investigated the protein concentration in effluent from the outflow pathways in bovine and human eyes, its possible relationship to wash-out, and whether the reduction of wash-out was caused by a bulk protein effect. Bovine and human eyes were placed under silicone oil and perfused with buffer. Outflow facility was continuously determined while effluent was periodically collected from the surface of the eye, and the soluble protein concentration in the effluent was determined. Separate studies were conducted perfusing either albumin or γ-globulin through bovine eyes. Theoretical models were developed to study the transport of protein into the perfusion fluid. In the bovine eyes, the initial protein concentration in the collected effluent was approximately 1% that of serum, much lower than the 10-15% buffer in serum required to prevent wash-out. Furthermore, the rate of change of outflow facility showed a different dependence on perfused volume than did the protein concentration. Human eyes showed a much higher level of protein in the perfusate, that decayed over a much longer time period. A statistically significant correlation existed between outflow resistance and soluble protein concentration in both bovine and human eyes. However, modelling studies suggested that this correlation might be due to flow resistance setting the flowrate which then determines the protein concentration of the effluent. Separate experiments indicated that the decreased rate of wash-out caused by perfusion of 10-15% serum in buffer was not due to either albumin or 7-globulin alone. These results suggest that the reduction of wash-out observed in previous studies when serum proteins were perfused through bovine and monkey eyes was not due to the general level of serum proteins but may instead be due to interactions of a particular protein(s).