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 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
- muscle wasting
- recurrent infections
- chronic laminitis
- normal to reduced white cell count with neutrophilia (stress), lymphopenia and eosinopenia
- mild anemia +/-