Chemical Pathology - Pituitary

Question 1

does pituitary failure cause hypotension?

Answer 1

NO
it is the loss of aldosterone that causes hypotension
if pituitary gland fails, can still produce aldosterone as adrenal glands are intact

Question 2

what are the 6 anterior pituitary hormones and their hypothalamic triggers?

Answer 2

GHRH --> GH
TRH --> TSH, prolactin
Dopamine --> -ve to prolactin release
LHRH/GnRH --> LH/FSH
CRH --> ACTH

Question 3

what is the relationship between TRH and prolactin release?

Answer 3

TRH stimulates prolactin release

primary hypothyroid –> hyperprolactinaemia

Question 4

how do patients with pituitary failure present?

Answer 4

• galactorrhoea
• amenorrhoea
• bitemporal hemianopia

Question 5

what level of prolactin would signal a prolactinoma?

Answer 5

> 6000

only cause of such high prolactin

Question 6

what is the CPFT (Combined Pituitary Function Test) “Triple Test”?

Answer 6

GnRH/LHRH + TRH + insulin (hypoglycaemic stress)

Question 7

what does insulin hypoglycaemic stress cause?

Answer 7

• increase CRF = inc ACTH = inc cortisol and glucose

- increase GHRH = inc GH = inc glucose

Question 8

what happens when you give TRH?

Answer 8

increases TSH and increases prolactin

Question 9

what do you need to ensure when carrying out the CPFT?

Answer 9

• check glucose regularly
• ensure adequate hypoglycaemia (<2.2mM)
• if severe hypoglycaemia occurs, rescue pt with 50mL of 20% dextrose

Question 10

what is the method of carrying out the CPFT?

Answer 10

1. fast pt overnight
2. ensure good IV access
3. weigh pt and calculate dose of insulin required
4. mix and inject insulin, TRH and LHRH/GnRH
5. take bloods at 0,30,60 minutes (glucose, cortisol, GH, LH, FSH, TSH, prolactin, T4)
6. take bloods at 90 and 120 minutes (glucose, cortisol, GH)

Question 11

what are the contraindications to hypoglycaemia?

Answer 11

• cardiac risk factors (ECG normal, no angina)

- history of epilepsy

Question 12

what is the process of hypoglycaemia?

Answer 12

1. sympathetic activation occurs = aggression

2. when v low, neuroglycopaenia may occur (confusion/ LOC)

Question 13

what is the normal response to stress testing?

Answer 13

• glucose drops and then recovers
• GH increases
• cortisol increases
• glucose drop raises TRH stressor, this in turn stimulates prolactin

Question 14

what is abnormal response to stress testin?

Answer 14

reduced production of all hormones

Question 15

what is the treatment of hypopituitarism?

Answer 15

urgent: hydrocortisone replacement 
total therapy:
- hydrocortisone replacement
- thyroxine replacement 
- oestrogen replacement 
- GH replacement

Question 16

what can you also give if prolactinoma is the cause of the failure?

Answer 16

cabergoline or bromocriptine
dopamine agonists
shrink the tumour

Question 17

how will a non-functioning pituitary adenoma present?

Answer 17

bitemporal hemianopia

prolactin high but MUCH lower than prolactinoma

Question 18

why does a non-functioning pituitary adenoma produce a high prolactin?

Answer 18

• adenoma presses on pituitary stalk
• dopamine prevented from reaching anterior pituitary
• no -ve inhibition on prolactin release
• hyperprolactinaemia

Question 19

treatment of a non-functioning pituitary adenoma

Answer 19

• HC replacement
• thyroxine replacement
• oestrogen replacement
• GH replacement
• cabergoline or bromocriptine (brings down prolactin, allows women to ovulate and men to be fertile)

Question 20

why could prednisolone be better than hydrocortisone?

Answer 20

• prednisolone is more potent with longer half life
• more resistant to degradation
• prednisolone can be given OD
• matches circadian rhythm better

Question 21

how does acromegaly present?

Answer 21

• pituitary adenoma
• bitemporal hemianopia
• high persistent GH

Question 22

what are the tests for acromegaly?

Answer 22

• IGF1 (produced by liver in response to GH, promotes tissue and bone growth)
• OGTT (75g glucose and measure in 2 hours)

Question 23

what should happen in OGTT/ what happens in acromegaly?

Answer 23

• GH should drop with glucose

- acromegaly: paradoxical rise in GH with glucose

Question 24

treatment of acromegaly?

Answer 24

• pituitary surgery
• pituitary radiotherapy
• cabergoline
• octreotide (somatostatin analogue –> reduce size of tumour)