Stress adaptation and adrenal activity in isolated and crowded rats.

Socially reared male control rats (Co) were compared with crowded reared rats (Cr) and isolated reared rats (I). We assayed the adaptation to moderate stress (activity and defecation rate in open-field test) and to intensive stress sensitivity to restraint ulcer), so as the basal adrenal activity measuring basal values of corticosterone (R.I.A.) and fresh weight of adrenal and thymus glands. Results show a great lack of adaptation to moderate and intensive stress in Cr and I reared rats which leads to a decrease of activity variables, an increase of defecation rates and a high sensitivity to restraint ulcers. The effect of crowding conditions show higher values than isolation. We also found, in isolated and crowded reared rats, an increase in the adrenal function with great values for the basal secretion of corticosterone and atrophy of the thymus gland, besides which, crowded reared animals showed adrenal hypertrophy.