Effects of repeated stress on plasma arginine levels in young and old rats

The effect of age and recurring stress responses on endogenous plasma arginine (ARG) concentrations were determined. Blood from catheterized young (3 months) and old (24 months) were used to ascertain the plasma concentrations of ARG under baseline conditions, during a 30-min immobilization experience and during a 3.5 h poststress period. Rats were again immobilized and blood drawn following a 1 day rest period (day 3) and then after an additional 3 day rest period (day 7). For young animals, ARG levels decrease significantly after 30 min of stress and remain suppressed during the entire poststress period (3.5 h). After a 1 day rest period, these young rats may have exhibited adaptation to stress on day 3. Old animals showed little or no reduction in plasma ARG concentrations during and after immobilization stress exposure on all three occasions. Baseline levels of old animals were lower in comparison to young animals and their stress responses were smaller. Thus, it is possible that significant changes in plasma ARG levels (as the nitric oxide precursor) during or after stress could serve as an indicator of impending pathology such as cardiovascular disease or immunocompetency.