TISSUE DISTRIBUTION OF THE RECEPTOR FOR PLASMA RETINOL-BINDING PROTEIN

The tissue distribution of the retinol-binding-protein receptor has be en studied by using a cell-free binding assay. High binding activity w as found in placenta, retina pigment epithelial cells, bone marrow and kidneys. Specific binding activity was also found in the small intest ines, spleen and liver, and to a lesser extent in lung. Scatchard anal ysis revealed that the difference in binding activity was due to varia tions in receptor level and not affinity changes. When the kidneys wer e separated into cortex and medulla we found that almost all the speci fic binding activity present in kidneys was recovered in the cortex. T he choroid plexus, an important site in the delivery of nutrients to t he cerebrospinal fluid, expressed Very high binding activity. The pine al gland, which has been shown to store vitamin A, also showed high bi nding activity. Testes from immature animals showed higher binding act ivity than testes from mature rabbits. Cultured undifferentiated kidne y keratinocytes showed about 40 times higher binding activity than dif ferentiated cells. Skin fibroblasts demonstrated no binding activity. In conclusion, the data presented in this report show that the level o f the retinol-binding-protein receptor varies considerably between cel l types. The observed tissue distribution of the receptor agrees well with the present knowledge on retinol function and metabolism by vario us cells.