Pituitary-adrenal stress response in the absence of brain-pituitary connections.

To examine whether an acute pituitary-adrenal response to stress may occur in vivo in the absence of hypothalamic-pituitary connections, we measured plasma beta-endorphin (beta-EP) and corticosterone (C) in rats after acute thermal injury. beta-EP rose significantly after thermal injury in normal rats and rats bearing pituitary-to-kidney autotransplants but not in animals with pituitary aspiration without reimplantation. Corticosterone responses paralleled beta-EP but were significant only in normal controls. Propranolol pretreatment did not reduce postburn beta-EP and C rises in autotransplanted animals. Therefore, since circulating factors contribute in vivo to pituitary-adrenal responses, the widespread practice of using "stress hormone" responses to quantitate perioperative stress or pain may in some circumstances be flawed.