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 -hydroxytryptophan ([3H]5-HT or [3H]5-HTP) (5 x 10(-7) M) in the presence of cold noradrenaline (5 x 10(-6) M) into rabbit colon, a clear-cut labeling 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.