6. Growth hormone and IGF Flashcards
how is growth hormone regulate
- hypothalamus sends signal to anterior pituitary
- anterior pituitary releases growth hormone
- growth hormone acts on liver which produces IGF-1`
what are the effects of growth hormone
long term:
- promotes growth
- growing animals
- protein synthesis
short term:
- starvation response
- lipolysis
- insulin resistance
is growth hormone water or lipid soluble
water soluble –> receptor on outside of cell
growth hormone promotes protein synthesis for growth by:
- increasing nuclear transcription
- increasing translation
- increasing amino acid transport through cell membrane
- decrease catabolism of proteins and amino acids
what is the physiological effect of growth hormone for growth response
slower, long lasting hypertrophic actions
- mostly mediated by insulin-like growth factor
- some direct growth hormone action
what are the stimuli for growth hormone to be released in the starvation response
- decreased blood glucose
- decreased free fatty acids
- decreased protein
- trauma, stress and excitements
- exercise
what are the physiological effects of growth hormone in the starvation response
- rapid catabolic actions = hyperglycemia
- increase rate of protein synthesis and use of protein (quick)
- enhances fat use (slow) increasing lipolysis
- promotes hyperglycemia by decreasing glucose transport across cell membranes, increasing insulin antagonism and increases gluconeogenesis
what are the effects of growth hormone
what do insulin like growth factors do/what are they
- mimic effects of insulin on growth
- stimulated by growth hormone
- produced by different tissues but mainly liver
- has paracrine and autocrine effects
- bound to carrier proteins (increase their half life)
what does IGF-1 do
- mainly made in the liver
- increases condrogenesis and growth
what is the mechanism behind IGF-1 and condrogenesis/growth
- increase chondrocytes and osteogenic cell replication
- increase chondrocytes and osteogenic cell proteins deposition to promote bone growth
- convert chondrocytes to osteoblasts and form new bone
what is the signalment for pituitary dwarfism
- spontaneous mutation (congenital)
- more common in min pins, weimaraners and cats
- hereditary in german sheps
- autosomal recessive condition
what is pituitary dwarfism
- dwarfism is most likely caused by mutation of a gene coding for a transcription factor that regulates pituitary stem cell differentiation
- defect occurs after corticotrope differentiation (ACTH not affected)
- decreases GH, TSH, prolactin, gonadotropins but ACTH preserved
- dwarfism can be accompanied by a cyst
what are the clinical features of pituitary dwarfism
- proportionate growth retardation
- soft woolly hair coat (lack of guard hairs, retention of secondary hairs and easily epilated)
- initially bright and alert
- first detected at 2-3 months of age
- become lethargic, have a decreased appetite and appear systemically ill (runt, can have secondary hypothyroidism)
- can live until 5 years of age if treated
- owner may opt for euth
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discuss the reproductive function of pituitary dwarfism
males: uni/bilateral cryptorchidism
females: persistent oestrus, failure to ovulate (low progesterone)
how do you diagnose pituitary dwarfism
- decreased GH (but pulsatile and needs specific radio-immunoassay)
- decreased IGF-1:preferred
growth hormone excess causes
- overgrowth of bone, connective tissue and viscera leading to acromegaly
what is acromegaly
- pituiatry disorder that develops AFTER closure of epiphyses
- long bones can no longer grow
- membranous bones continue to grow
- increased facial soft tissues
- internal organomegaly
discuss acromegaly in cats
- middle aged to old cats
- mostly males
- most often caused by pituitary tumour secreting excess GH
- usually diabetic at presentation (most common cause of insulin resistance in cats)
discuss canine acromegaly
- middle aged to old dogs
- always females!
- due to excess endogenous/exogenous progesterone
- caused by induction of GH gene in mammary glands
- mammary GH idential to pituitary GH
how is acromegaly diagnosed
- IGF-1 concentration
- GH concentration (special handling, not practical)
- supportive vlinical signs and lab work with normal thyroid/adrenal testing
- history of natural or exogenous progesterone exposure (in dogs)
- CT or MRI brain scan for cats
what are the clinical signs of acromegaly
- broad coarsened facial features
- prognathism and icnreased soft tissue over eyes
- macroglossia (big tongue)
