Equine Cushing's disease.

In the horse, adenomata of the pairs intermedia of the pituitary gland have been associated with the distinct clinical entity of Cushing's disease which arises largely as a result of excessive secretion of adrenocorticotropin (ACTH) or other proopiomelanocortin (POMC) peptides. Pars intermedia peptide secretion is under dopaminergic control and compounds such as pergolide or bromocriptine, which are dopamine agonists, can palliate the clinical signs. A variety of endocrinological abnormalities, relevant to both pathogenesis and diagnosis, may be demonstrated in equine Cushing's disease, including hyperadrenocorticism, peripheral insulin resistance and excessive POMC-peptide secretion from the pituitary gland. Preliminary studies on carbohydrate metabolism suggest that quantification of insulin activity may be a useful prognostic index in cases of equine Cushing's disease, and that insulin therapy of secondary diabetes mellitus may be indicated in some cases.