Background: Previous study showed that under the influence of protracted physical stress, the DNA synthesis (DS) of the gastroduodenal mucosa rises, the highest peak being reached at 4 weeks. At 8 stress weeks, the DS decreases to values similar to those recorded at the beginning of the experiment. The possibility that this DS adaptation (DSA) could be maintained beyond 8 weeks in animals allowed to subsequent resting (stress-free) weeks, was now explored.
Methods: Sixty-five rats were investigated. 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 5 animals were allowed to rest for one, two, three and four weeks, ending with single water plunging or sham handling. All 65 animals received ip injection of 3H-thymidine before they were sacrificed. The ratio radioactive DNA/total DNA reflected the DS of the stomach and duodenum.
Results: DSA was achieved at 8 stress weeks (stomach). The DS in the stomach of stressed rats had significantly increased at 10 weeks (P < 0.05), but at 12 weeks it had decreased to 8 weeks values. The DS in the duodenum of stressed rats had significantly increased at 9, 10 and 11 weeks (P < 0.05), but at 12 weeks DS values had decreased to those of 8 weeks.
Conclusions: The DSA at 8 stress weeks had not prevailed because the DS increased considerably in the following weeks. At 9-11 weeks, DS values had significantly increased (P < 0.05) in stressed rats, but at 12 weeks a DS re-adaptation (DSRA) had occurred. Thus, it took 8 weeks to achieve DSA (stomach), but only 4 weeks to accomplish DSRA. Animals experienced sham handling as an stressor (milder) as it also induced DS re-adjustments in the gastroduodenal mucosa. Autoradiography showed that the labelling in DNA synthesizing cells was limited almost exclusively to the mucosal layer. The model described may prove of value to studies aimed at abating the disparate fluctuations of DNA synthesis in the gastroduodenal mucosa during the various phases of protracted stress.