[Differences in the reaction of old and young rats to immobilization stress].

Studies have been made on the reaction of 55 male old and young Wistar rats to acute 1-hour immobilization. Corticosterone was determined in the blood serum using radioimmune assay. Similar phasic changes in the level of corticosterone in the blood serum were revealed in young and old rats, although in the latter these changes occurred 1 day later. The decrease in the body weight and in the mass of the adrenals was also observed which was more significant in old animals.