PPID diagostic testing Flashcards
What is PPID
- a disease of older/aged horses and ponies which results from a loss of ability to regulate hormonal output from the pars intermedia of the pituitary gland
- as a result hormones from the pars intermedia are secreted excessively
- currently the most appropriate tests are resting ACTH and TRH stimulation
What is EMS
- a condition defined by the presence of obesity, insulin resistance and predisposition to laminitis
- when IR develops the cells are less sensitive on action of insulin and result is increased insulin secretion and hyperglycemia
- current tests look at how body can respond to glucose administration
what are the melanotrophes in the pars intermedia producing
- POMC
- alpha MSH
- CLIP
- beta endorphins
- beta MSH
- beta LPH
- ACTH
what does ACTH do
increase corticosteroids release via adrenal gland stimulation
what does MSH do
regulation of appetite, sexual behaviour and melanin production
what does CLIP do
modulation of pancreatic exocrine function
what do beta endorphins do
behaviour (docility/sedative?)
what do beta lipoproteins do
melanin production, steroidogenesis and lipolysis
explain the pathology of PPID
- pars intermedia adenoma
- leads to excessive production of POMCs derived peptides
- leads to hyperadrenocorticism
describe pathogenesis of PPID
- lack of inhibitory control on pars intermedia cell function that permits development of adenomas
- inhibition is mediated by hypothalamic dopamine
- neurodegeneration of periventricular neurons (oxidative stress) impairs negative feedback to pars intermedia
what is the process of taking and interpreting basal plasma ACTH in suspected PPID horses
- single chilled EDTA blood sample is adequate
- seasonal ref ranges published to allow testing at any time of year
- horses with PPID have HIGH plasma ACTH
- 87% sensitivity, 97% specificity
describe the process of taking and interpreting TRH stim test in PPID suspected horses
- measures ACTH (not cortisol as in ACTH stim)
- get baseline ACTH
- inject TRH iv
- collect 2nd ACTH 10-30 mins later
- PPID horses have a HIGH baseline ACTH and/or post stimulation plasma ACTH value >100pg/ml
- no seasonal ref ranges so cant perform august-october
- highly sensitive and specific!
explain the pathophysiology of EMS
equine metabolic syndrome
- adiposity leads to insulin resistance and laminitis (unknown if obesity develops because or IR or vice versa)
- IR caused by downregulation of insulin signalling by adipokines and accumulation of intracellular lipids
- other factos include inflammation, oxidative stress, altered adipocyte function, altered endothelial function, pro-thrombotic state etc
what are the 3 stages of insulin resistance
- compensated IR: normal glucose concentrations maintained by increased insulin output
- uncompensated IR: glucose concentrations increasing and increased insulin concentration
- type 2 DM: end stage, persistent hyperglycaemia because of inadequate insulin output
how is EMS diagnosed
aims are to confirm insulin resistance status and rule out PPID
- resting insulin and glucose measurement
- proxies of insulin sensitivity
- dynamic testing (CGIT and in feed glucose challenge)
- blood pressure measurement
- adipokine measurement
