A comparison of in vivo cell proliferation measurements in the intestine of mouse and man.

Using tritiated thymidine (3HTdR) labelling in vivo in the mouse we have determined the labelling index (LI%) at each cell position along the sides of sections of crypts in the small and large bowel. We have compared LI versus cell position frequency plots obtained in this way with those obtained using bromodeoxyuridine (BrdUrd) in vivo in the small intestine. Both thymidine analogues give identical patterns and similar levels of labelling: for example, the overall LI is 29.1% after 3HTdR and 34.7% after BrdUrd in the mouse ileum. Similar data have been obtained following in vivo labelling in humans with BrdUrd prior to gastrointestinal surgery for cancer and in mouse colon following 3HTdR labelling. Comparisons between the mouse and human data show that the spatial distribution of label within the crypts occurs at the same relative positions in the two species. However, the intestinal crypts are between 2-fold and 4-fold larger, particularly in their length, in the human: for example, 250 and 450 cells per crypt for ileum and 590 and 2000 cells per crypt for the colon in mouse and human respectively. The absolute value of the maximum LI in the mouse small intestine (56.5%) is higher than it is in the human (26.3%). However, the patterns of proliferation are similar in the two species under steady-state conditions.