Vitamin A supply of the cornea

Results are presented indicating that epithelial cells from the bovine cornea accumulate [³H]retinol from the retinol-binding protein (RBP). The uptake process is saturable with characteristics similar to those of small intestinal cells. It therefore seems likely that vitamin A is delivered to the corneal cells by RBP. Different routes for the passage of RBP to the cornea were investigated. Tear fluid from a monkey did not contain even trace amounts of RBP. Aqueous humor from monkeys contained a significant quantity of prealbumin but only small amounts of RBP. In contrast, both RBP and prealbumin could be demonstrated in considerable amounts within the monkey cornea. Experiments in rabbits with radioactively labeled serum albumin as a model substance suggested that the scleral blood vessels in the limbus region are the likely source for most of the vitamin A required by the cornea.