Activity of pituitary-adrenal axis in rats chronically exposed to different stressors

Changes in plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone (COTR) of adult male rats exposed to two chronic types of psychosocial stress: isolation and crowding, as well as physical stress i.e. forced swimming and combined psychosocial and physical stress i.e. isolation accompanied by forced swimming, both under basal conditions and in response to immobilization and cold as short-term stressors, were studied. Chronic isolation produced a significant elevation of basal plasma ACTH and CORT, but chronic isolation accompanied by forced swimming produced a significant elevation only in basal plasma ACTH, but not CORT, while chronic crowding and forced swimming did not elevate the basal plasma levels of these hormones. Chronically stressed animals exposed to immobilization or cold show a significant elevation of plasma CORT. No significant differences in plasma CORT between the four chronically stressed groups of rats were recorded. Novel acute immobilization and cold stress produce a markedly increased plasma ACTH in chronic crowding, forced swimming and isolation accompanied by forced swimming rats. These data suggest that chronic isolation seems to be a stronger stressor for rats compared to other chronic stressors