Chemical Pathology - Pituitary Flashcards
does pituitary failure cause hypotension?
NO
it is the loss of aldosterone that causes hypotension
if pituitary gland fails, can still produce aldosterone as adrenal glands are intact
what are the 6 anterior pituitary hormones and their hypothalamic triggers?
GHRH --> GH TRH --> TSH, prolactin Dopamine --> -ve to prolactin release LHRH/GnRH --> LH/FSH CRH --> ACTH
what is the relationship between TRH and prolactin release?
TRH stimulates prolactin release
primary hypothyroid –> hyperprolactinaemia
how do patients with pituitary failure present?
- galactorrhoea
- amenorrhoea
- bitemporal hemianopia
what level of prolactin would signal a prolactinoma?
> 6000
only cause of such high prolactin
what is the CPFT (Combined Pituitary Function Test) “Triple Test”?
GnRH/LHRH + TRH + insulin (hypoglycaemic stress)
what does insulin hypoglycaemic stress cause?
- increase CRF = inc ACTH = inc cortisol and glucose
- increase GHRH = inc GH = inc glucose
what happens when you give TRH?
increases TSH and increases prolactin
what do you need to ensure when carrying out the CPFT?
- check glucose regularly
- ensure adequate hypoglycaemia (<2.2mM)
- if severe hypoglycaemia occurs, rescue pt with 50mL of 20% dextrose
what is the method of carrying out the CPFT?
- fast pt overnight
- ensure good IV access
- weigh pt and calculate dose of insulin required
- mix and inject insulin, TRH and LHRH/GnRH
- take bloods at 0,30,60 minutes (glucose, cortisol, GH, LH, FSH, TSH, prolactin, T4)
- take bloods at 90 and 120 minutes (glucose, cortisol, GH)
what are the contraindications to hypoglycaemia?
- cardiac risk factors (ECG normal, no angina)
- history of epilepsy
what is the process of hypoglycaemia?
- sympathetic activation occurs = aggression
2. when v low, neuroglycopaenia may occur (confusion/ LOC)
what is the normal response to stress testing?
- glucose drops and then recovers
- GH increases
- cortisol increases
- glucose drop raises TRH stressor, this in turn stimulates prolactin
what is abnormal response to stress testin?
reduced production of all hormones
what is the treatment of hypopituitarism?
urgent: hydrocortisone replacement total therapy: - hydrocortisone replacement - thyroxine replacement - oestrogen replacement - GH replacement
what can you also give if prolactinoma is the cause of the failure?
cabergoline or bromocriptine
dopamine agonists
shrink the tumour
how will a non-functioning pituitary adenoma present?
bitemporal hemianopia
prolactin high but MUCH lower than prolactinoma
why does a non-functioning pituitary adenoma produce a high prolactin?
- adenoma presses on pituitary stalk
- dopamine prevented from reaching anterior pituitary
- no -ve inhibition on prolactin release
- hyperprolactinaemia
treatment of a non-functioning pituitary adenoma
- HC replacement
- thyroxine replacement
- oestrogen replacement
- GH replacement
- cabergoline or bromocriptine (brings down prolactin, allows women to ovulate and men to be fertile)
why could prednisolone be better than hydrocortisone?
- prednisolone is more potent with longer half life
- more resistant to degradation
- prednisolone can be given OD
- matches circadian rhythm better
how does acromegaly present?
- pituitary adenoma
- bitemporal hemianopia
- high persistent GH
what are the tests for acromegaly?
- IGF1 (produced by liver in response to GH, promotes tissue and bone growth)
- OGTT (75g glucose and measure in 2 hours)
what should happen in OGTT/ what happens in acromegaly?
- GH should drop with glucose
- acromegaly: paradoxical rise in GH with glucose
treatment of acromegaly?
- pituitary surgery
- pituitary radiotherapy
- cabergoline
- octreotide (somatostatin analogue –> reduce size of tumour)
