Psychosocial conflict in the tree shrew: effects on sympathoadrenal activity and blood pressure

We investigated the influence of psychosocial conflict (PSC) on systolic blood pressure (BP) and on sympathoadrenal activity in male tree shrews. BP was recorded and urinary epinephrine and norepinephrine were determined daily during a 10-day control period and a subsequent 10-day period of PSC. At the end of the experiments, levels of adrenal tyrosine hydroxylase (TH), phenylethanolamine-N-methyl transferase (PNMT), epinephrine, and norepinephrine were determined. The reactivity of the sympathoadrenal system and of BP depended on the social position achieved. In subordinates, urinary norepinephrine excretion was constantly elevated while epinephrine excretion was elevated only transiently. Adrenal norepinephrine, epinephrine, and TH were increased whereas PNMT remained unaffected. Despite the sympathoadrenal arousal, the increase in BP was only temporary. In dominant animals, PSC had no effects on BP, adrenal parameters or urinary norepinephrine. These results reinforce the concept of distinctive neuroendocrine and hemodynamic response patterns to psychosocial stimuli depending on the type and degree of control which an individual can exert over the challenge.