Variability of cell proliferation in the proximal and distal colon of normal rats and rats with dimethylhydrazine induced carcinogenesis.

Abstract

To investigate the patterns of cell proliferation in proximal and distal colons in normal rats and rats with 1,2-dimethylhydrazine (DMH) induced carcinogenesis using the thymidine analogue bromodeoxyuridine. Colonic crypt cell proliferation was immunohistochemically detected using the anti-bromodeoxyuridine Bu20a monoclonal antibody. Marked regional differences were found in both groups. Total labelling index (LI) and proliferative zone size in both normal (8.65+/-0.34 vs 7.2+/-0.45, 27.74+/-1.07 vs 16.75+/-1.45) and DMH groups (13.13+/-0.46 vs 11.55+/-0.45, 39.60+/-1.32 vs 35.52+/-1.58) were significantly higher in distal than in proximal colon (P<0.05), although the number of cells per proximal crypt was greater (31.45+/-0.20 vs 34.45 +/-0.39, 42.68+/-0.53 vs 49.09+/-0.65, P<0.0001). Crypt length, total LI and proliferative zone size all increased in both proximal and distal regions of DMH rats compared to normal controls (P<0.0001). In DMH-treated rat colon a shift of labelled cells to higher crypt cell positions was demonstrated distally whilst a bi-directional shift was evident proximally (P<0.05). Our results show that changes in cell proliferation patterns, as assessed by bromodeoxyuridine uptake, can act as a reliable intermediate marker of colonic cancer formation. Observed differences between proliferation patterns in distal and proximal colon may be associated with the higher incidence of tumors in the distal colon.