PPID-Mallicote Flashcards
Pars distalis
Cell type: corticotropes
- > POMC
- > ACTH
Pars intermedia
Cell type: melanotropes
- > POMC
- > ACTH -> makes lots of stuff
Melanotrophs under inhibitory control of
Dopamine, secreted from hypothalamus
-> This under positive control of TRH which stims release of MSH
Seasonal regulation of Pars intermedia
plasma conc of alpha-MSH concentration in normal horses is considerably higher in September
Pathologic hallmark PPID in horses
- hypertrophy
- hyperplasia
- adenoma formation of pars intermedia
* results in 40 fold inc POMC-derived peptides and ACTH
ACTH stimulates
adrenal production of cortisol
Critical path of PPID
hypothalamic neurodegeneration leading to decreased of dopamine
*loss of dopaminergic inhibition on Pars intermedia
PPID in horses is ultimately due to
damage to the hypothalamus
Best indication of PPID
hypertrichosis in an aged horse
Baseline ACTH test
if done in fall can mimic a stim test
Aug-Oct normal < 100pg/L
Nov-July normal < 35
*collect in plastic EDTA tube, keep cool. Separate plasma on day of collection and freeze in plastic. Ship samples via air the next day on ice
TRH stim test
Most useful in mild/subclinical dz
Horses with PPID have increased ACTH and Cortisol after TRH admin, normal horses don’t
Retesting at 4-6 month intervals may be necessary
Dexamethasone suppression test
Should reduce cortisol production in normal horse
Loss of dex suppression may only be a late dz event
Inaccurate tests for PPID eval
- Single blood or salivary cortisol measurement
- Diurnal cortisol rhythm measurements
- Urinary cortisol:creatinine assays
Reasons to treat PPID
- Quality of life and PPID related laminitis
2. temporarily overcome infertility in older broodmares with confirmed PPID
PPID therapy aim
to increase dopaminergic control of pituitary
-using dopamine agonists or serotonin agonists
