Cell proliferation in human colorectal mucosa in organ culture: the early adaptive changes

In organ culture tissues undergo adaptive changes which complicate the assessment of proliferative indices. In the present study, a technique devised to preserve collagen metabolism and mesenchymal stroma in tissues of mixed origin was employed to investigate the kinetic behaviour of human colorectal mucosa over the first 24 hours in culture. During this period the structural preservation of tissue is good. The mitotic index in mucosa is profoundly depressed throughout the explants during the first 2-6 hours in culture. During this same period, however, heavy uptake of tritiated thymidine, indicating DNA synthesis, is observed within 150 micron of the cut edge of the samples but not centrally. This phenomenon has been described previously and assumed to be the result of inadequate diffusion of oxygen into the tissue. The 'edge labelling' phenomenon is followed by a wave of mitosis in the tissue edge at 8-18 hours in culture. This delay between tritiated thymidine uptake and the appearance of mitoses in the tissue edge may simply represent the duration of the S + G2 phase of the cell cycle, but is more likely to be due to cells in G1 moving into the S phase followed by cells hitherto blocked in G2 being stimulated into the M phase. After 18 hours the mitotic and labelling indices become more uniform throughout the samples suggesting that 'edge labelling' is partly due to local stimulation of cell proliferation by trauma rather than central inhibition due to diffusion problems. These results suggest that in this organ culture system, assessment of proliferative indices should be carried out after these adaptive changes have settled.