Introduction Figure 1. The pituitary gland is often called the body's "master gland": beyond ACTH, it releases hormones that regulate growth, the thyroid, reproduction, water balance, and more. Cushing's disease arises when just one of these signals — ACTH, aimed at the adrenal cortex — becomes chronically overactive, while the gland's many other roles continue as normal (Merck Veterinary Manual). As our cherished pets enter their senior years, it is common to attribute chang