What is the expected response to ACTH stimulation in patients with primary Addison's disease?

In patients with primary Addison's disease, the adrenal glands are damaged, leading to insufficient production of cortisol. The disease is characterized by adrenal insufficiency, which means that when adrenocorticotropic hormone (ACTH) is administered, the adrenal glands cannot respond appropriately due to their impaired function.

Thus, the expected response to ACTH stimulation in these individuals is no change in serum cortisol levels. This lack of response occurs because the adrenal cortex, which produces cortisol, is unable to synthesize and secrete this hormone even in the presence of ACTH, which normally stimulates its production in healthy individuals.

The other options involve scenarios where either an increase in cortisol would be expected or normal responses to ACTH stimulation would occur, neither of which is true in the case of Addison's disease. The condition’s hallmark is the inability of the adrenal glands to function properly, thus leading to a lack of cortisol secretion despite adequate stimulation from ACTH.