Transport of alpha aminoisobutyric acid into ocular fluids and lens.

The rates of accumulation of C-14-labeled alpha aminoisobutyric acid (a-AIB) in the aqueous and vitreous humors and lenses of rabbit eyes following parenteral administration have been determined. The distribution ratios of a-AIB in the aqueous humor of the posterior and anterior chambers, the vitreous humor, and the lens 24 hours after parenteral administration were found to be 0.75, 0.98, 0.1, and 2.5, respectively. The rate of accumulation and the steady-state distribution of the C-14-labeled a-AIB compound in the aqueous humor and the lens was reduced by the administration of nonlabeled a-AIB 15 minutes prior to administration of the labeled compound. A similar inhibitory effect on the rate of accumulation of the labeled amino acid could be produced by several naturally occurring amino acids. Parenterally administered Diamox increased the rate of accumulation of a-AIB in the posterior and anterior chambers as well as the approximate steady-state ratios in these chambers. The significance of these observations is discussed with respect to the mechanism of transport of a-AIB into the intraocular fluids and lens. It is concluded that a-AIB is actively transported across the ciliary epithelial cells, the lens capsule, and, possibly, the anterior surface of the iris.