"From the finding that removal of the sympathetic nerves did not affect blood pressure much, Cannon inferred that the sympathetic nervous system did not contribute to blood pressure in intact, undisturbed organism. In the 1980s, however, several reports showed that sympathectomy compensatorily activates other effectors, such as the renin-angiotensin-aldosterone system, the vasopressin system, and the adrenal medulla, and compensatory activation of these effectors maintains blood pressure at approximately normal levels. In the setting of sympathectomy, interference with any of the effectors evokes immediate, precipitous declines in blood pressure. Because Cannon was so firmly convinced of the functional unity of the sympathoadrenal system, which would be activated only in emergencies, he never considered adequately the possibility that the sympathetic nervous system might indeed contribute to levels of blood pressure and other monitored variables under resting conditions."
Adrenaline and the Inner World: An Introduction to Scientific Integrative Medicine
