Radioautographic study of uptake and storage of indoleamines in the rabbit enterochromaffin cells

After in vitro intra-arterial injection of tritium-labeled 5-hydroxytryptamine or -hydroxytrytophan (³H]5-HT or ³H]5-HTP) (5·10^?7 M) in the presence of cold noradrenaline (5·10^?6 m) into rabbit colon, a clear-cut labelling pattern was observed by radioautography. Labelled cells were observed within the mucosa. The labeling was less important after ³H]5-HTP than after ³H]5-HT injection. Ultrastructural study indicates that labeling is confined to the cytoplasm and coincides with polymorphic secretory granules.Hence these labeled cells display not only APUD cells characteristics but also true neuronal properties.