Radioimmunochemical Determination of Cellular Retinoic Acid-binding Proteins in Cytosols

Radioimmunoassays have been developed for cellular retinol-binding protein and cellular retinoic acidbinding protein, postulated mediators of vitamin A action in nonvisual functions. These assays are considerably more sensitive for detection and quantitation of these proteins than previous methods. The higher sensitivity has permitted the detection of cellular retinoic acid-binding protein in adult rat tissues previously considered negative. These include kidney, lung, and spleen. The only tissues negative for both binding proteins were adrenals, skeletal muscle, ileal mucosa, and serum. Assay of tissue levels of cellular retinol-binding protein and cellular retinoic acid-binding protein reveals them to be widely distributed throughout most organs of the rat. No tissue or sex differences in these proteins were detected in these studies.