Final answer:
In secondary adrenal insufficiency, ACTH levels are low, leading to reduced cortisol production. Aldosterone levels might be less affected due to different regulatory mechanisms. The cosyntropin stimulation test in these patients typically shows a blunted cortisol response.
Step-by-step explanation:
In secondary adrenal insufficiency, the production of ACTH by the pituitary is impaired, which leads to decreased stimulation of the adrenal cortex and thus reduced secretion of cortisol. Aldosterone levels may be less affected in secondary adrenal insufficiency compared to primary because aldosterone secretion is largely regulated by the renin-angiotensin system, although some patients could experience a decline in its levels.
During a cosyntropin stimulation test, synthetic ACTH (cosyntropin) is administered to gauge the adrenal glands' ability to produce cortisol. In a patient with secondary adrenal insufficiency, this test will result in blunted increase in cortisol levels or no change, due to the prior insufficient ACTH stimulation leading to atrophy or diminished responsiveness of the adrenal cortex. In secondary adrenal insufficiency, there is a lack of ACTH, which should stimulate cortisol production; hence the response to cosyntropin will be diminished, indicating adrenal insufficiency.