Effect of repeated stress on plasma catecholamines and taurine in young and old rats.

The effect of age and multiple stress responses on plasma norepinephrine (NE), epinephrine (EPI), and taurine (TAU) levels were determined in 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 rats were not the same for the three neurochemicals measured but were relatively unique for the specific biochemicals. In old animals baseline 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 additional stress exposures. Initial stress responses were similar for all three 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 first day disappeared during the second stress period but were again seen during the third stress exposure suggesting subtle indicators of repeated stress subject to adaptation. TAU values for young but not old rats correlated positively with EPI concentrations during the first stress exposure and negatively after the immobilization was terminated indicating a regulatory interaction between EPI and TAU present in young but lost in old animals.(ABSTRACT TRUNCATED AT 250 WORDS)