Tests of anterior pituitary function

Question 1

Testing for GH release

Answer 1

Insulin hypoglycemia test

Administer insulin induces hypoglycemia, below 2.2 mM hypoglycemia should induce GHRH release and release of ACTH, GH, and PRL.

Don’t do it in elderly, chronic heart disease, hypertensive, or epileptic.

Question 2

Testing for PRL release

Answer 2

Metoclopramide

A Dopamine receptor antagonist

Should Increase proline release

Contraindicated in pheochromocytoma, because it can increase their release of glucocorticoids.

Question 3

Test for TSH release

Answer 3

Use TRH

but be aware that it is rare but possible that this will cause blood vessel constriction and hemorrhage in patients with pituitary tumors

Question 4

Testing for ACTH release

Answer 4

The ACTH test (also called the cosyntropin, tetracosactide, or Synacthen test)

These are all synthetic ACTH anaolgs

Should induce cortisol release, and if it does then this excludes Addison’s disease (primary adrenal insufficiency)

If it fails to induce cortisol, then it is a primary adrenal insufficiency

Question 5

What tests are used to diagnose cushing syndrome vs cushing disease?

Answer 5

Overnight dexamethasone suppresion test.

ACTH levels are measure first, then dexamethasone is given, then cortisol levels are measured in the morning.

Outcomes:

Low ACTH, and no suppression of cortisol, there is a primary adenoma of the adrenal cortex

Increased ACTH, and no suppression at either dose, then there is an ectopic ACTH producing tumor. SCC of the lung.

Increased ACTH, and only high dose suppression, then it is an ACTH pituitary adenoma = Cushing’s Disease

Question 6

What test is used to check GnRH release?

Answer 6

Clomiphene binds and causes internalization of estrogen receptors on the hypothalamus, which should relieve inhibition on endogenous GnRH release.

Should elevated FSH and LH.

GnRH administration test, administered on multiple consecutive days, to mimic the pulsative secretion of GnRH. shoudl induce FSH and LH.

Question 7

How do pituitary tumors, aka sellar masses, present?

Answer 7

Neurological sypmtoms:

• headache
• Diplopia - double vision
• Bilateral Temporal Hemanopia
• Pituitary apoplexia, sudden bleeding into the adenoma
  
  • rapidly developing headache and visual impariments, due to swelling and optic nerve compression.
• CSF rhinorrhea, due to penetration of the sinuses.

Hormonal disturbances,

• hyperfunction of one and hypofunction of the rest
• hypofunction of all
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