title: Re-adaptation of the colonic mucosa following protracted stress in rats.
abstract: 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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Gastrointestinal and Liver Pathology Research Laboratory, Karolinska Institute and Hospital, Stockholm, Sweden. Carlos.Rubio@onkpat.ki.se
authors.forename: C A
authors.initials: CA
authors.lastname: Rubio
authors.forename: P
authors.initials: P
authors.lastname: Hellström
authors.forename: M
authors.initials: M
authors.lastname: Sveander
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D001345:Autoradiography / Q000379:methods; D004261:DNA Replication / Q000502:physiology*; D005753:Gastric Mucosa / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013312:Stress, Physiological / Q000503:physiopathology*