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Abstract
Brain corticotropin-releasing hormone (CRH) concentration and pituitary adreno-cortical
responses were examined in chronically stressed rats: body restraint stress (6 h/day)
for 4 or 5 weeks. Stressed rats showed a reduction in weight gain. CRH concentration
in the median eminence and the rest of the hypothalamus were not different between
control and chronically immobilized rats. The anterior pituitary adenocorticotropic
hormone (ACTH) concentration was elevated in chronically stressed rats, whereas plasma
ACTH and corticosterone levels did not differ from the control values. The median
eminence CRH concentration was reduced to the same extent at 5 min after onset of
ether exposure (1 min) in chronically immobilized rats and controls. However, plasma
ACTH and corticosterone showed greater responses to ether stress in chronically immobilized
rats than in control rats. Plasma ACTH and corticosterone responses to exogenous CRH
were not different between control and chronically immobilized rats, while the response
to arginine vasopressin (AVP) was significantly greater in chronically immobilized
rats. These results suggest that chronic stress caused an increase in the ACTH-secreting
mechanism and that pituitary hypersensitivity to vasopressin might at least be partly
responsible for this.