DISTRIBUTION OF LYMPHOID NODULES, ABERRANT CRYPT FOCI AND TUMORS IN THE COLON OF CARCINOGEN-TREATED RATS

Sprague-Dawley rats were given eight weekly subcutaneous injections of 1,2-dimethylhydrazine (DMH) or of vehicle then were sacrificed at 1, 5 or 24 weeks after the last injection of DMH. The locations of pre-ex isting aggregates of lymphoid nodules (ALNs), the location and multipl icity (size) of aberrant crypt foci (ACF), and the locations of tumour s in the colon were determined. A trimodal distribution of pre-existin g ALNs along the length of the colon was significantly correlated with the timodal distribution of DMH-induced adenocarcinomas (ACs). A unim odal peak in ACF of all sizes occurred between the sites of two distal ALNs. Thus, the distribution of ACF at 1 or 5 weeks did not correlate with the distribution of AC found at 24 weeks. Of the 2640 ACF observ ed at 1 or at 5 weeks, none were found in the proximal 25% of the colo n where ACs eventually occurred. It was concluded that: (1) ALNs play a promotional role in AC formation; (2) the ACs which form in the prox imal quarter of the colon seldom if ever form via an ACF precursor; an d (3) the location, the number and the size of ACF observed early afte r DMH exposure did not correlate with the location or predict the inci dence of ACs which eventually formed in the colon.