EFFECTS OF REPEATED STRESS ON PLASMA ARGININE LEVELS IN YOUNG AND OLDRATS

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 plasm a concentrations of ARG under baseline conditions, during a 30-min imm obilization 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 a nimals, ARG levels decrease significantly after 30 min of stress and r emain suppressed during the entire poststress period (3.5 h). After a 1 day rest period, these young rats may have exhibited adaptation to s tress on day 3. Old animals showed little or no reduction in plasma AR G concentrations during and after immobilization stress exposure on al l three occasions. Baseline levels of old animals were lower in compar ison to young animals and their stress responses were smaller. Thus, i t is possible that significant changes in plasma ARG levels (as the ni tric oxide precursor) during or after stress could serve as an indicat or of impending pathology such as cardiovascular disease or immunocomp etency.