Histology and cell kinetics of rectal mucosa of A/HeJ mice administered syngeneic rectal antigen and its effects on radiation induced rectal cancer, 2

Syngeneic rectal antigen was intramuscularly administered in the thigh of A/HeJ mice, once a week for two weeks and the histology and cell kinetics of the rectal mucosa were examined. One week after immunization, the rectal mucosa of the administered mice showed transient hyperplasia and the number of goblet cells was decreased. By autoradiographic studies, the number of 3H-labelled cells was found to be increased with concomitant spread of the proliferative zone. G2 and M phase in the administered mice became shorter than those of control mice. Thus, it was observed that with shortening of the cell cycle, the frequency of DNA synthesis increased. Two weeks after immunization, the rectal mucosa of the treated animals showed far greater atrophy than that of the control mice. Increase of labelled cells and expansion of the cell proliferative zone were observed by autoradiography. Four weeks after immunization, no difference in histologic findings could be seen between the experimental and control group, but labelling index remained higher in the former. Eight weeks after immunization, no difference in labelling index could be observed between the two groups, but there was cell proliferative zone spread in the experimental group. The control mice showed no remarkable difference in the histological findings and labelling index throughout the experimental period. It was therefore concluded that administration of syngeneic rectal antigen to A/HeJ mice induced transient hyperplasia and subsequent atrophy of the rectal mucosa. Simultaneous cell kinetic studies revealed shortening of the cell cycle and expansion of the cell proliferative zone. It was observed that X-irradiation during the period of active cell proliferation and cell kinetics caused effectively induced cancerous change in the cells. (author)