Abstract
To characterize the participation of vasopressin (AVP) and oxytocin (OT) in hypothalamus-pituitary-adrenal
regulation after adrenalectomy (ADX), we evaluated corticosterone, ACTH, AVP and OT
plasma concentrations and AVP and OT content of the paraventricular nucleus (PVN)
at different periods (3 h, 1, 3, 7 and 14 days) in sham or ADX rats under basal conditions
and after immobilization stress. ADX animals showed undetectable corticosterone levels,
while sham animals showed a marked increase in corticosterone and ACTH 3 h after surgery,
then lowering to basal control levels. ADX rats showed high basal ACTH levels with
a triphasic response without changes after immobilization. After three hours, the
ADX group showed higher OT levels than the sham group. OT was increased after immobilization
stress in sham and ADX groups. AVP plasma levels did not change throughout the basal
or stress studies in either group. There was a decrease in hypothalamic AVP content
1 and 3 days after ADX under basal and stress conditions. Plasma osmolality showed
a significant decrease in the ADX group at 3, 7, and 14 days. In conclusion, there
are different pituitary-adrenal axis set points after removal of the glucocorticoid
negative feedback. The role of vasopressinergic and oxytocinergic neurons in the ACTH
secretion after ADX or immobilization stress appears to differ. Magnocellular AVP
is unlikely to contribute to ACTH secretion in response to ADX or immobilization stress.
On the other hand, OT is elicited by immobilization stress and might contribute to
the ACTH secretion during short-term ADX.
Key words
Hypothalamo-pituitary-adrenal axis · Immobilization stress · Oxytocinergic neurons
· Vasopressinergic neurons · Paraventricular nucleus
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M. de Castro, M. D., Ph. D.
Depto de Clínica Médica, Faculdade de Medicina de Ribeirao Preto · USP ·
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