Rose: GH and PRL Flashcards
(43 cards)
What is a sommatotropic hormone?
GH
What is a mammotropic hormone?
PRL
What inhibits PRL?
DA
What stimulates GH?
GHRH
What inhibits GH?
GHIH= Somatostatin
DA
What does GHIH act through?
Gi-coupled receptor to decrease cAMP and activate K+ channels
Where are GHRH receptors located? What type of receptor is it?
somatotrophs
transmembrane G protein coupled
GH (somatotropin) is made by…
somatotropes
What is indicative of tissue levels of GH receptor?
Levels of GHBP which binds GH
How does GHBP affect GH?
Acts as a reservoir of growth hormone in plasma and may be a modulator/inhibitor of GH signaling.
What are transmembrane GH receptors on target cells?
Cytokine receptor that activates JAK/STAT secondary messenger signal transduction pathway
Hormone binding causes dimerization and internalization of complex
What are the target cells for GH?
Isoform of GHR is in nearly all cells
Liver produces Insulin-like growth factor-1 (IGF-1=somatomedin)
What are the final hormones mediating the GH axis?
GH
IGF-1
How does GH affect liver IGF-1 gene expression?
GH> stimulates IGF-1 gene expression>
IGF-1 is an EFFECTOR for growth
What happens if IGF-1 > GH?
stimulates chondrogenesis (growth) at epiphyseal growth plates in children
*(Growth promoting effects are antagonized by glucocorticoids - important in children being treated with cortisol.)
How are the diabetogenic properties of GH?
Increase circulating glu:
reduces tissue uptake of glucose
increases liver production of glucose
Decreases circulating glucose:
secondary insulin release
*GH increases the incidence of diabetes mellitus (insulin resistance is often observed in these patients)
GH can affect…
protein metabolism
mineral metabolism
carbohydrate metabolism
fat metabolism
What causes proportional dwarfism?
GH def in children caused by gene mutations in the GH axis
- Laron syndrome
- SHOX loss/point mutations
What is laron syndrome? What is the mechanism?
A cause of dwarfism
autosomal recessive GH receptor variant with insensitivity to GH
*Underlying mechanism for short stature is at the RECEPTOR level
What is the SHOX gene? What happens if you lose a copy?
short stature homeobox gene located on the X
Loss of SHOX copy: e.g., short stature with Turner’s syndrome(45, XO or Turner mosaicism ) is a chromosomal condition altering development in FEMALES. It is associated with loss of a single copy of the SHOX.
What is observed in GH def in adults?
generalized obesity
reduced muscle mass
asthenia (reduced energy, weakness)
reduced cardiac output
Why are random serum samples NOT useful in assessing GH def?
pulsatile pattern
How is the insulin tolerance test used to dx GH def?
Insulin>
hypoglycemia>
stimulates adrenal glands to secrete cortisol and pituitary to secrete GH
**failure to respond to insulin suggests need for GH replacement
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What is hte glucagon test?
glucagon>
transient hyperglycemia>
hypoglycemia>
stimulates GH
- safer than an insulin test
- Failure to respond to insulin may suggest the need for glucocorticoid and growth hormone replacement
