- mediates indirect growth and fat metabolism effects of GH - protein binding increases half-life in circulation - fairly steady conctn throughout the day (good marker of GH status)

LECTURE - Prolactin & GH Testing Flashcards by Richen Basig

target tissue of prolactin

mammary glands

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major stimulus for PRL pathway

suckling

- also estrogen and stress (severe illness and traumatic experience)

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_______ is inhibitory to the release of prolactin

dopamine (brake that is always ON; unless there is a strong positive stimulus)
= if prolactin is released = brake is released

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made by lactotroph cells in the anterior pituitary

prolactin

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several forms of prolactin in circulation

little = monomer (23 kDa)
big = dimeric
big-big (macro) = polymeric and/or attach immunoglobulin

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functions of prolactin

pregnancy and lactation (breast milk production and secretion)
uterine smooth muscle contraction
reproduction (Sex hormone synthesis and fertility)

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diagnosis of hyperprolactinemia

increased prolactin conctn detected in serum: immunoassay methods
screen hyperprolactinemic samples for macroprolactin
magnetic resonance imaging (MRI) scan for tumors

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prolactin is a _________ hormone

peptide

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T or F. Prolactin is under negative regulation by the hypothalamus!

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this can be a source of falsely elevated serum prolactin

macroprolactin (clumped molecules)

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target tissue of growth hormones

entire body

from somatotroph

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these are produced and secreted by somatotrophic cells of the anterior pituitary gland

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major functions of GH

tissue and bone growth
response to stress
modulates fat/carbohydrate/protein metabolism and body composition

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made primarily by liver in response to GH

insulin-like growth factor (IGF-1)

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IGF-1

mediates indirect growth and fat metabolism effects of GH
protein binding increases half-life in circulation
fairly steady conctn throughout the day (good marker of GH status)

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lactotrophs

in anterior pituitary = PRL

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hyperprolactinemia causes

physiological = pregnancy, breast feeding, stress, etc.
pituitary tumour = increase PRL is a marker for adenoma
damage to hypothalamic pituitary dopamine path (brake not working)
primary hypothyroidism (increased TRH) = spillage; pituitary works overtime and thus PRL increases as well
macroprolactin
medications, renal failure, liver disease

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T or F. macroprolactin is not related to a clinical condition

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clinical presentation of hyperprolactinemia

galactorrhea
hypogonadism + infertility
low sex drive
headaches and visual probs
females = menstrual dysfunction, vaginal dryness
males = ED, decreased body hair and muscle mass, delayed puberty

what is macroprolactin?

multimeric PRL complex
delayed clearance = increased levels = more likely to clump
less/minimal biological activity than monomeric PRL
detected variably by many PRL immunoassays
seen in 10-45% of hyperprolactinemia cases
may lead to delayed diagnosis or misdiagnosis

how to identify macroprolactin

gel filtration (size exclusion) chromatography
polyethylene glycol (PEG) precipitation **
obtain results from more than 1 immunoassay

PEG clears most of macroprl - re-run test - see if PRL still elevated = then true elevation

what effects do dopamine-receptor antagonists have on the H-P axis?

increase proalctin secretion

GH distribution

found as monomer, homodimer, heterodimer, or multimer form
distribution = 50% free and 50% bound to Gh-binding poteins
short half-life in circulation (about 20 mins)

lipogenesis and lipolysis, AA uptake, glucose protein synthesis effects on GH

lipogenesis = negative stimulus on GH

lipolysis, AA uptake, glucose protein synthesis = positive stimulus

how is GH measured in the lab?

immunoassays

expcted final outcomes of GH

raises glucose and FFA aconcentrations

the actions of GH are mediated directly through these and indirectly through these

directly = GH receptors on many tissues indirectly = hpatic insulin growth factor release (IGF-1)

normal pattern of GH secretion from pituitary

- pulsatile release, with most release at night (very low during the day) - circadian rhythm - influenced by age, gender, and body composition

when should blood samples be collected if a physician wants to know if a patient is making enough GH?

repetitive sampling under standardized conditions

these stimuli stimulates release of GHRH from the hypothalamus

- exercise - stress - sleep - alpha 2 adrenergic activity - fasting (hypoglycemia) - increased amino acids - hormones - neurotransmitters

what inhibits GHRH ?

- cortisol - beta-adrenergic acitivty - hyperglycemia - obesity - FFA - hypothyroidism - aging - IGF-1

T or F. IGF-1 inhibits more release of GH by shutting down production at hypothalamus and pituitary

SRIF (somatostatin)

inhibitory to GH | - IGF-1 also stimulates this to stop release of GH

how is IGF-1 measured in the lab?

immunoassay

GH excess causes

pituitary tumors (adenoma) hypothalamic lesions GHRH-producing tumors

result of GH excess

soft tissue and bone overgrowth - gigantism in children - acromegaly in adults

characteristic physical features in kids with GH excess

- very tall | - large long-bones

characteristic physical features in adults with GH excess

- large/coarse facial features - large organs - skin changes - osteoarthritis - hypertension - insulin resistance

what is seen often in patients with GH excess?

DM, myopathy, CVD risk

testing for GH excess dynamic testing

- dynamic = induce hyperglycemia - see how the system will respond > should be an inhibitory response (hyperglycemia) = should shut off somatostatin - if GH excess in the pituitary = hormone release remains sustained = overproduction not responsive to regular inhibition; inhibiting factors not working = typically due to tumor

testing for GH excess (3)

- measure serum IGF-1 (screen) - glucose supppresssion test > give oral glucose load > meausre serum GH 2 hrs psot-load - normally this would make GH undetectable - magnetic resonance imaging = see if it's a tumor

causes of GH defiicency or resistance

- pituitary or hypothalamic abnormalities (def) | - GH insensitivity (resistance)

characteristic features in children with GH deficiency or resistance

- low growth rate - short stature - central adiposity - susceptible to hypoglycemia

characteristic features in adults with GH deficiency or resistance

- decreased bone density - abnormal body composition - impared serum lipids - premature mortality

things that might contribute to the inability to produce GH

- GHRH receptor mutation - pituitary damage - GH gene mutation - GH antibodies - GH receptor mutation - target organ resistance - IGF-1 deficiency

testing for GH deficiency

- IGF-1 levels; a screen - exercise stimulation test = 20 mins of exercise should cause GH elevation - insulin tolerance test = give IV insulin; measure GH = DANGEROUS

treatment for patients with GH deficiency

- GH supplements like recombinant hGH (22kDa monomer) | - athletes misuse to increase lipolysis, lean muscle mass, VO2 max