Anatomy: lies in the sella turcica at the base of the brain. It is connected to the hypothalamus by the pituitary stalk.

The gland is divisible into 2 distinct parts:

I. Anterior lobe (pars distalis, intermedia and tuberalis)

II. Posterior lobe ( pars nervosa, infundibular stalk)

Pituitary Gland

Pituitary Gland Function in horses

Physiology:

• Glucocorticoids from the adrenal cortex essential for regulation of carbohydrate and lipid metabolism.
• Secretion of glucocorticoids controlled by ACTH from the anterior pituitary.
• Release of ACTH mediated by exercise, stress, temperature, light and hypoglycemia*
• ACTH primarily formed in corticotropes of pars distalis from proopiomelanocortin (POMC).
• POMC is also a precursor of B-endorphin and A-melantropin.
• Pars intermedia composed of melanotropes and also contains POMC.

Anterior Lobe Dysfunction

Definition and Etiology:

• Functional adenomas of the pars intermedia have been recognized for years in older horses.
• "Equine Cushing's Disease" clinical similarities with human condition. [pituitary pars intermedia
• Dysfunction =PPID. Pars intermedia pituitary adenoma = PIPA.]
• Characterized by hypercorticism secondary to ACTH hypersecretion from a pituitary tumor
• Hyperplasia of pars intermedia associated with increased secretion of B-END, A-MSH and ACTH (to a lesser degree).
• Clinical signs due to excess glucocorticoids, destruction of pars nervosa, increased concentrations of POMC.
• Differences between Cushing's in horses and humans:

- anatomic location

- POMC post-translational processing.

Clinical Signs: result from complex metabolic aberrations.....

• average age = 19years
• no sex or breed predilection (Ponies ???)
• hirsutism and failure to shed seasonally
• lethargy
• muscle wasting
• PU/PD
• recurrent infections
• chronic laminitis

Clinical Pathology:

• normal to reduced white cell count with neutrophilia (stress), lymphopenia and eosinopenia
• mild anemia +/-
• hyperglycemia*
• Hyperlipemia