Re-adaptation of the colonic mucosa following protracted stress in rats

Background We previously found that DNA synthesis of the colonic mucosa rises under protracted physical stress. At 8 stress weeks DNA values regained those of untreated animals, and was regarded as DNA adaptation to stress. Aims To assess whether the 8 weeks' DNA adaptation to stress could be maintained following stress-free intervals, ending with a stress stimulus. Methods Sixty rats were transported to the stress laboratory. Thirty were water plunged and 30 sham handled once a day, 5 days a week, for 8 weeks. After 8 stress weeks, groups of five animals were allowed to rest for 1, 2, 3 and 4 weeks, ending with single water plunging or sham handling. Five additional rats were untreated. All 65 animals received an i.p. injection of 3H-thymidine before sacrifice. The ratio radioactive DNA/total DNA reflected the DNA synthesis of the colonic mucosa. Results Following DNA adaptation at 8 stress weeks, DNA replication in the right colon of the stressed rats significantly increased at 9, 10 and 11 weeks (P < 0.05), but at 12 weeks it had decreased to 8-week values. Conclusions DNA replication in the right colon of the stressed rats did not prevail: it increased considerably in the following weeks, but at 12 weeks (only 4 weeks later), re-adaptation to DNA synthesis had occurred. The review of the literature indicates that this is the first report in which, following adaptation to protracted stress, a re-adaptation phase to DNA replication is demonstrated in the colonic mucosa of experimental animals.