Serotonin immunohistochemistry reveals immature EC cells.

Radioautographic studies of rat duodenal mucosa were carried out after single injections of 3H-thymidine, and the labelling indices of enterochromaffin (EC) cells identified by serotonin immunohistochemistry and by the diazo reaction were compared. The labelling index of EC cells by serotonin immunohistochemistry was 2.3% (mean percentage of 2 rats), while no labelled cells were found in diazo-positive EC cells. This finding indicates that serotonin immunohistochemistry reveals a less mature population of EC cells than conventional techniques such as the diazo reaction.