Influence of maturation on ulcer-development and immunodeficiency induced by activity-stress in rats

Young adult rats housed in the activity-wheel cages and fed only 1 hr daily, have ulcers in the glandular stomach and reveal immunodeficiency. The present study was attempted to investigate how to separate the ulceration and immunodeficiency in order to utilize the activity-stress (A-S) model as an animal model of the human stress ulcer. Six and 10 weeks old rats were used as subjects in this study. They were stressed for 3, 5, or 7 days. In the younger rats, the longer stress exposure caused to deteriorate more both the ulcer and immunodeficiency. The ulceration was found in all of the three stress periods, while the immunodeficiency was recognized in the 5- and 7-day stressed rats. In the elder rats, the ulceration was found in the 5- and 7-day stressed rats, whereas the immunodeficiency was seen only in the 7-day stressed rats. In the free-feeding control rats, relative weights of the thymus and spleen in the elder rats were smaller than those of the younger rats. In the adrenal weight, there was no difference between two age rats. The thymus and spleen of rats exposed to the stress revealed atrophy in both ages. These results suggest that immature rats are more susceptible for the stress than young mature rats, and application of mature rats to the A-S experiment appears to be available in the case of utilizing A-S rats as the stress ulcer model.