Amino acid efflux from rabbit ileal enterocytes.

1. A method is described for converting tissue concentrations of amino acid, determined autoradiographically using sections of rabbit distal ileum, into measurements of total uptake. 2. Using this method the quantity of amino acid recovered from the villus core following short-term incubation with tritiated amino acid was shown to be directly related to the intra-enterocyte concentration of amino acid determined at a site immediately adjacent to the basal membrane. No evidence was obtained for saturation of efflux across the basal membrane of the enterocyte. 3. Amino acid efflux from the mucosa to the villus core, calculated for a constant intra-enterocyte concentration of substrate, was found to be greater for methionine and leucine than for alanine, serine, lysine or arginine. 4. The distribution of amino acids within the core of the villus following efflux from the enterocyte could not be explained by diffusion alone. 5. It is suggested that quantitative autoradiography can be used as an alternative method to study mechanisms responsible for amino acid movement across the basal membranes of enterocytes. Advantages and limitations of the technique are discussed.