No abstract

No abstract

Argentaffin and other "endocrine" cells of the gastrointestinal tract were investigated in the mouse jejunum by electron microscopic radioautography after administration of 3H-thymidine either in a single injection or by continuous infusion.One hour after a single injection or after a 24-hour infusion of 3H-thymidine, no labeling is seen in the three main types of "endocrine" cells : Type EC (true argentaffin) or biconcave granule cells, Type L or large spherical granule cells, and Type S or small spherical granule cells. Furthermore, no mitosis of these cells may be observed. Hence, they are not capable of division.However, when continuous infusion is prolonged for one and one-half days, examination of the lower half of the crypts shows labeling in some cells of the three types. The number of granules in these cells is small.By three days, labeled cells of the three types appear in villi, while the number of their granules increases. With time, the percentage of labeled cells rises gradually to reach over 60% after four days and over 80% after six to eight days of continuous infusion.After the infusion is stopped, the number of labeled cells decreases. Thus, eight days after the end of a four-day infusion less than 10% cells are labeled.It is concluded that the three main types of "endocrine" cells observed in the mouse jejunum arise from unidentified precursors in the lower half of the crypts. They migrate from crypts to villi and are probably extruded from villus tips. Even though the three cell types seem to evolve independently, their turnover time is the same, that is, about four days.