The duodenal progenitor population. I. Age related increase in the duration of the cryptal progenitor cycle

The duodenal progenitor population has been investigated in four age groups of male Swiss albino mice, utilizing tritiated thymidine and autoradiography following sequential sacrifice of the experimental animals. Parameters evaluated in the different age groups included: (1) duration of the progenitor cycle and its component phases; (2) DNA‐synthetic index; and (3) mitotic index. Analysis of the kinetics of metaphase labeling revealed that the mean duration of the entire cycle lengthens with age, whereas the mean duration of the DNA‐synthetic phase is constant (ca. 7.4 hours) irrespective of age. Estimates of the cycle duration based upon calculations from the DNA‐synthetic index also demonstrate an increase with age, although the absolute values derived in this manner do not agree with those based on metaphase labeling. Determination of the cryptal DNA‐synthetic and mitotic indices disclosed a decrease in the percentage of labeled and/or mitotic cells with increasing age. Thus, the prolongation with age in mean progenitor cycle duration involves an increase in the average time which a duodenal progenitor cell spends in the interphase (G 1 ) portion of the cycle.