5. Pituitary gland Flashcards
synthesizes ACTH
pars intermedia (adenohypophysis)
antidiuretic hormone (ADH, vasopressin) and oxytocin
synthesized in the hypothalamus but are released into the bloodstream in the pars nervosa
neurohypophyseal hormones
hyperadrenocorticism caused by an ACTH- secreting tumor of the pituitary gland
Pituitary-dependent hyperadrenocorticism (Cushing disease)
a highly sensitive test to differentiate healthy dogs from those with hyperadrenocorticism, but it is not highly specific
urine cortisol to creatinine ratio (UCCR)
screening test of choice for canine hyperadrenocorticism
tests the integrity of negative feedback
low-dose dexamenthasone suppresion test
cheaper dexamenthasone; distinguishes between PDH & ADH
low-dose dexamenthasone suppresion test
Disadvantages:
• 3 blood draws for dogs and 5 for cats
• More false positives due to stress
• 40-50% of dogs with non-adrenal disease had inadequate suppression at 4 and 6 hours
• No baseline for therapeutic monitoring
• Not a good test for identifying iatrogenic HAC
• cannot detect hypoadrenocorticism
• Phenobarbital will cause false positive
low-dose dexamenthasone suppresion test
works on the principle that autonomous ACTH hypersecretion by the pituitary can be suppressed by supraphysiologic concentrations of steroid
High-dose dexamethasone suppression test
Dogs with autonomous cortisol-producing adrenal tumors have maximally suppressed ACTH production via the normal feedback mechanism
therefore, administration of dexamethasone, no matter how high the dose, cannot suppress serum cortisol concentrations
High-dose dexamethasone suppression test
able to suppress ACTH & cortisol secretion in dogs with PDH
High-dose dexamethasone suppression test
Dogs with ____ do not suppress ACTH on the HDDS test
Pituitary macroadenomas
can characterize multple adrenal nodules
High-dose dexamethasone suppression test
much easier sample handling than Endogenous ACTH
High-dose dexamethasone suppression test
Disadvantages:
• Doesn’t always distinguish between ADH and severe PDH
• Takes all day – have to plan ahead
• Have to take 5 samples from a cat
High-dose dexamethasone suppression test
used to diagnose various adrenopathic disorders
1. endogenous or iatrogenic hyperadrenocorticism
2. spontaneous hyperadrenocorticism
a screening test for the diagnosis of naturally occurring hyperadrenocorticism
ACTH stimulation test
has a higher specificity than LDDS test
ACTH stimulation test
less affected by glucocortcoid therapy than LDD
fewer false positives due to stress than LDD
ACTH stimulation test
cannot distinguish bet. PDH & ADH
ACTH stimulation test
a good screening test
Positive (increased) result tells you the dog is sick
UCCR
a lack of secretion of pituitary trophic hormones and diminished target organ function (eg, adrenal cortex)
dysfunction of the CNS
affected animals are often
- depressed
- incoordinated
- weak
- may collapse with exercise
Nonfunctional Pituitary Tumors
invariably associated with pituitary pars intermedia dysfunction (PPID)
excessive hair growth
acquired hypertrichosis
Nonfunctional tumors of the pituitary gland may lead to this as the growth of a neoplastic (but nonsecretory) cell type displaces other pituitary cells
rare disorders in dogs and cats
adult-onset panhypopituitarism
Clinical signs are usually associated with
- local tissue compression
- edema associated with large tumors that act as space-occupying lesions
Adult-onset Panhypopituitarism
Panhypopituitarism in young dogs that usually results from failure of the pars distalis of the pituitary to develop during gestation
This leads to a deficiency of all the pituitary trophic hormones
Juvenile-onset Panhypopituitarism (Dogs)
