The adrenal medulla is the central portion of the gland and is the primary source of the hormones epinephrine and norepinephrine. With the exception of pheochromocytomas associated with an excess of catecholamines, clinical disease associated with isolated adrenal medullary disease is very rare. Even in animals with primary hypoadrenocorticism, adrenal medullary function appears to be normal, likely due to extra-medullary secretion of catecholamines.
The adrenal medulla, although apparently not essential to life, plays an important role in response to stress or hypoglycemia. It secretes epinephrine and norepinephrine, which increase cardiac output, blood pressure, and blood glucose and decrease GI activity.
Pheochromocytomas may develop in domestic animals, most often in cattle and dogs. These secrete epinephrine, norepinephrine, or both. Clinical signs are often absent, and tumors may be incidental findings during evaluation for other conditions or at necropsy.
Other adrenal tumors, such as neuroblastomas and ganglioneuromas, may arise in the chromaffin cells of the sympathetic nervous system.
