Chem: Section 11.2- Endocrine Lab Assessment and Disorders

What are stimulation and suppression tests used to determine?

stimulation tests determine hormone insufficiencies

suppression tests determine hormone hyperfunction

What is the dexamethasone suppression test used to differentiate?

differentiates between adrenal hypercortisolism and pituitary hypercortisolism

What is the ACTH stimulation test used to differentiate?

differentiates between primary (Addison's) and secondary hypocortisolism

What is the metyrapone stimulation test used to evaluate?

used to evaluate pituitary's ability to produce ACTH in response to low cortisol or the hypothalamus' ability to produce CRH in response to low ACTH

can also diagnose 11-beta-hydroxylase deficiency (precursor to cortisol)

What factors can affect hormone levels?

diurnal or pulsatile nature of hormones, tumors, posture, sodium levels, diuretics, stress

What method is most commonly used to measure hormones?

immunoassay

What is cortisol's relationship to insulin?

cortisol suppresses insulin (so it can't stop glucose)

so increased cortisol = increased glucose

How is angiotensinogen produced by the liver converted into aldosterone?

angiotensinogen >

angiotensin I (via renin from kidneys) >

angiotensin II >

aldosterone

**renin is secreted by kidneys in hypovolemic states (decreased blood volume)

Which amino acid are catecholamines synthesized from, and by which enzymes?

synthesized from tyrosine by catechol-o-methyl transferase (COMT) and monoamine oxidase (MAO)

What are the two receptors for catecholamines? Which catecholamines are associated with each?

alpha- and beta-adrenergic receptors

norepinephrine= alpha only

epinephrine= alpha and beta

How is epinephrine broken down?

Epinephrine → metanephrine → vanillylmandelic acid (VMA)

How is norepinephrine broken down?

Norepinephrine → normetanephrine → vanillylmandelic acid (VMA)

How is dopamine broken down?

Dopamine → homovanillic acid (HVA)

Which is more sensitive for measurement-- total catecholamines or the end products?

end products, because catecholamines break down very quickly

What age are pheochromocytomas most common in?

adults

What age are neuroblastomas most common in?

children

What tissue do pheochromocytomas arise from?

most arise from the adrenal medulla

What tissue do neuroblastomas arise from?

can arise anywhere along the sympathetic nervous system chain, but most commonly arise from the adrenal medulla

What are the S/S of pheochromocytomas?

weight loss, sweating, headache, palpitations, hypertension, anxiety

What are the testing options for pheochromocytomas?

24 hour urine

clonidine suppression test

Why are 24 hour urines preferred to plasma testing for hormones?

most hormone are pulsatile or diurnal, so the time the plasma is drawn will affect testing. In a 24 hour urine, the pulsatile or diurnal nature of the hormone does not matter.

What is the clonidine suppression test used to differentiate?

used to determine if the cause of high BP is due to a pheochromocytoma tumor or something else (clonidine should shut down hormones, if they are not shut down=tumor)

What are the S/S of neuroblastomas?

rapid heartbeat, diarrhea, hypertension (children should not have high BP!)

How are neuroblastomas diagnosed?

tissue biopsy, presence of cancer cells in bone marrow, imaging, and increased blood or urine levels of catecholamines

Pheochromocytoma and neuroblastomas produced (excess/minimal) catecholamines

excess

What things besides tumors can elevate catecholamine levels?

stress, upright posture, exercise, hypoglycemia, cold, mental states of anger and anxiety