EFFECT OF REPEATED STRESS ON PLASMA-CATECHOLAMINES AND TAURINE IN YOUNG AND OLD RATS

The effect of age and multiple stress responses on plasma norepinephri ne (NE), epinephrine (EPI), and taurine (TAU) levels were determined i n F344 rats. Blood samples obtained from catheterized young (3 months) and old (24 months) animals were used to examine plasma levels of NE, EPI, and TAU under baseline conditions and in the same animals after a 30-min immobilization stress. Rats were again immobilized and blood drawn (Day 3) following a 1-day rest period and, after an additional 4 -day rest period (Day 7). Age differences seen between young and old r ats were not the same for the three neurochemicals measured but were r elatively unique for the specific biochemicals. In old animals baselin e values of NE but not EPI and TAU were higher then young animals and all three values did not change for the baseline during the two additi onal stress exposures. Initial stress responses were similar for all t hree biochemicals in both age groups. Although no signs of adaptation were evident in the old animals, adaptation to immobilization was seen for EPI and TAU but not NE on the third occasion in the young animals . Correlations seen between NE and EPI in young and old rats on the fi rst day disappeared during the second stress period but were again see n during the third stress exposure suggesting subtle indicators of rep eated stress subject to adaptation. TAU values for young but not old r ats correlated positively with EPI concentrations during the first str ess exposure and negatively after the immobilization was terminated in dicating a regulatory interaction between EPI and TAU present in young but lost in old animals. Thus, changes in levels and interrelationshi ps of specific biochemicals during repeated stress experiences in rats may provide a good model of the aging process.