Pituitary gland function in horses (Proceedings)


Pituitary gland function in horses (Proceedings)

Apr 01, 2008

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


  • 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