Cushing's disease, common in dog, rare in cat, complex in horse.
Increased secretion of glucocorticoids.
Can be pituitary dependant, adrenal dependant, iatrogenic
CNS feels stress, tells hypothalamus to release corticotropin releasing hormone, which tells anterior pituitary to release ACTH, which tells adrenal cortex to release cortisol, whose presence in blood tells anterior pituitary to stop releasing ACTH
pituitary dependant hyperadrenocorticism.
80% of dogs have this form. 90% of those are microadenoma (tiny, benign, active tumor). Macroadenoma causes seizures
secretes ACTH all the time, regardless of Cortisol levels
Adrenals get bigger.
adrenal tumor on one gland. That gland produces cortisol constantly, ACTH never released due to cortisol levels in blood, other adrenal shrinks in disuse atrophy.
More common in large-breed dogs
Can be removed with surgery, give and taper steriods to wake up atrophied gland
Glucocorticoid administration leads to constant cortisol in blood, ACTH never released, adrenals never make cortisol, disuse atrophy, get very small.
Clinical signs of hyperadrenocorticism
PU/PD (cortisol increases GFR and inhibits ADH release)
pendulous abdomen (weak belly muscles from protein breakdown)