Cardiovascular, sympathetic and adrenal cortical responsiveness of aged fischer-344 rats to stress.

While resting, Fischer-344 rats underwent a decrease in heart rate and an increase in diastolic blood pressure and plasma norepinephrine with increasing age. The blood pressure of adult rats increased significantly during a 3 minute immobilization. The blood pressure of old rats failed to increase during stress, decreased to below control level immediately following the termination of stress and they died within 24 hours. Three minutes of stress failed to increase the heart rate of old rats while 30 min of stress produced a small increase in the heart rate, approximately sol1 3 to sol1 2 of the increase seen in younger rats. The old rats showed no decrease in the maximal adrenergic medullary or cortical responses to stress, but they had a prominent 3 min delay in the maximal peak of norepinephrine release. The 30 minute stress caused a greater increase in plasma epinephrine in old rats than in adult rats while it initiated a decrease in beta-adrenergic responses such as heart rate and plasma glucose. The present results indicate that old rats lose their ability to cope with acute stress due to decreased adrenergic responsiveness and increased "shock" reaction.