Autoradiographic localisation of 3H-biotin in chick tissues

In an autoradiographic study with a 243 days' exposure time of the autoradiographs, the tissue distribution of 3H-labelled biotin was investigated. Label being always related to cytoplasma, no label was found in the nucleus in cells suitable for such an observation. High labelling was found in differentiated cells, e.g. in hepatocytes, proximal tubular cells of kidney, villous epithelia of small intestine, fat cells, epithelial cells of proventriculus, and uropygial gland and in ependymal cells of the plexus chorioideus. Undifferentiated and rapidly proliferating tissue compartments were only weakly labelled as for example undifferentiated kidney cortex, bone marrow, lymphatic tissue. Organs engaged in fat synthesis showed intensive labelling. In these organs as well as in liver and kidney the accumulation of label is in agreement with the known biochemical function. The accumulation of label, e.g. in osteoblasts or in the ependymal cells of the plexus chorioideus, gives evidence that biotin is an essential vitamin not only for the liver and the kidney.