Age‐related changes in stress‐induced cardiovascular and lumbar sympathetic nerve activity responses

Abstract

Central angiotensin II (AngII) signaling plays an important role in stress‐induced cardiovascular and sympathetic responses. However, the effects of age and high salt (HS) diet on central AngII‐mediated mechanisms are not known. We compared restraint stress‐induced BP, HR and lumbar sympathetic nerve activity (LSNA) responses in young and old rats under control conditions, after central infusion of losartan (15 μg/μL/hour), an AngII type‐1 receptor inhibitor, and after feeding rats with 8% HS diet for 10 days. BP, HR and LSNA were measured in young (5 mo) and old (27 mo) Fischer 344 x Brown Norway rats using radiotelemetry. Restraint stress was induced by placing animals in acrylic cylinder restrainers. Old rats had significantly higher resting BP and lower HR compared with young. Restraint stress induced rapid BP, HR and LSNA increases in both young and old; however, changes were significantly reduced in the old rats. Losartan significantly inhibited stress‐induced BP increases in young rats, while it had no effect on HR responses. In contrast, in the old rats, both BP and HR responses remained unaffected by losartan. HS diet feeding increased baseline BP both in young and old rats, with a more pronounced effect in old animals; however, it did not significantly alter restraint‐stress‐induced responses. In conclusion, resting BP increases with age, but hypertensive responses to stress diminish with age due to a decline in AngII‐mediated central mechanisms.