Different Effects of Novel Stressors on Sympathoadrenal System Activation in Rats Exposed to Long-Term Immobilization.

Activation of the sympathoadrenal system, evaluated by plasmalevels of epinephrine (E) and norepinephrine (NE) after exposure of rats to variousstressors, is well documented. However, response of rats exposed longtermto a homotypic stressor and then exposed once to a heterotypic novelstressor is poorly understood. In the present study, we examined changes inplasma levels of catecholamines (CA) and corticosterone (COR) of rats after asingle (2-h) or long-term repeated immobilization (41 times, 2 h daily) and inrats adapted to long-term immobilization exposed once to the novel stress ofcold exposure or insulin or 2-deoxy-D-glucose (2DG) administration. Longtermimmobilization produced a significant elevation of basal plasma COR butnot NE and E levels. Long-term immobilized rats exposed to insulin or 2DGshowed significant elevation of plasma CA and COR levels in comparison to theadministration to control rats. Exposure of long-term immobilized and controlrats to cold stress increased plasma NE and COR, whereas plasma E was notsignificantly changed. The exposure of long-term immobilized rats to a furthersingle immobilization (2 h) increased plasma CA levels, but, in naive controlrats, the single immobilization produced more pronounced increases. Thesedata suggest that rats exposed to homotypic long-term immobilization are ableto respond to heterotypic stressors by higher activation of the sympathoadrenalsystem as compared with the control, previously unstressed rats. Reduced plasmaCA levels in long-term immobilized rats exposed to homotypic stressor aremost probably due to an adaptation at the level of brain regulatory centers. [ABSTRACT FROM AUTHOR]