Which hormonal levels would suggest secondary hypoadrenocorticism in an older St Bernard?

In the context of diagnosing secondary hypoadrenocorticism, it is important to understand the roles of ACTH (adrenocorticotropic hormone) and cortisol in the feedback loop of the hypothalamic-pituitary-adrenal (HPA) axis. In cases of secondary hypoadrenocorticism, the underlying issue resides at the level of the pituitary gland, where inadequate ACTH production results in insufficient stimulation of the adrenal glands.

When ACTH levels are low, the adrenal glands do not produce enough cortisol, leading to low basal cortisol levels. This pattern (low ACTH and low cortisol) indicates that the adrenal glands are not responding adequately due to lack of stimulation from ACTH, which is a hallmark of secondary adrenal insufficiency. Therefore, when faced with an older St. Bernard exhibiting these hormonal levels, one can suspect secondary hypoadrenocorticism.

High levels of ACTH paired with low cortisol, as seen in primary hypoadrenocorticism, reflect an adrenal issue rather than one related to the pituitary gland. Likewise, high cortisol combined with low ACTH indicates primary hyperadrenocorticism (Cushing's disease), not secondary hypoadrenocorticism. Normal cortisol with high ACT