Growth hormone and IGF

Question 1

Where is growth hormone produced?

Answer 1

In the anterior pituitary gland by the somatotrope cells

Question 2

What are the long term and short term affects of HG and IGF-1?

Answer 2

Long term= promotes growth

Short term= starvation response

Question 3

Describe the starvation response

Answer 3

Increases lipolysis and insulin resistance

• It is a stimulus for GH release
• Decreases blood glucose
• Decreases FFAs
• Decreases protein

Question 4

What is the growth response?

Answer 4

Promotion of protein synthesis

• increased nuclear transcription
• Increased translation
• Increased Aa transport through cell membrane
• DECREASED catabolism of proteins and Aa

Question 5

What is the growth response mainly mediated by?

Answer 5

IGR-1

Question 6

How does GH contribute energy during the starvation response?

Answer 6

-BY using catabolic action to cause hyperglycaemia

Question 7

Describe the effect of insulin like growth factors

Answer 7

• Mimic effects of insulin on growth (building/ storing)
• It is stimulated by IGF
• Produced by different tissues mainly LIVER
• Local effects
• Bound to carrier proteins (increases half life)

Question 8

Discuss IGF-1

Answer 8

• AKA somatomedin C)
• LIVER= main source
• Increases chondrogenesis and growth

Question 9

What are the mechanisms of IGF-1?

Answer 9

• Builds bone growth by stimulating conversion of chondrocytes to osteoblasts
• Promotes bone growth by increasing chondrocytes and osteogenic cell protein deposition

Question 10

Describe the signalment of pituitary dwarfism

Answer 10

• Spontaneous mutation in mini pinschers, Weimaraners and cats
• Hereditary in GSDs
• Autosomal recessive condition

Question 11

What causes pituitary dwarfism?

Answer 11

-Mutation of a gene that regulated pituitary stem cell differentiation
BUT the issue occurs after corticotrope differentiation SO ACTH ISN’T AFFECTED
-Causes decrease in GH, TSH, prolactin, Gonadotrophin
-Can have a cyst but not necessarily

Question 12

What are the clinical features of pituitary dwarfism?

Answer 12

• PROPORTIONATE growth retardation ( different to other forms of dwarfism)
• Sot woolly coat- lack primary hairs and retains secondary hairs
• Soft coat easily damaged= alopecia

Question 13

When is pituitary dwarfism first detected?

Answer 13

2-3 months of age

Question 14

What are the impacts of pituitary dwarfism on the reproductive function?

Answer 14

• Males= cryptochorchidism

- Females= persistent oestrus (no LH so no luteolysis) and don’t ovulate

Question 15

How do you diagnose pituitary dwarfism?

Answer 15

• Decrease GH- requires species specific immunoassay

- Preferred test= IGF-1, will be decrease, longer half life, no pulsatile secretion

Question 16

What impact does excessive concentrations of GH have?

Answer 16

• Gigantism: occurs in young patients before growth plates close
• Acromegaly: develops in adults after close of growth plates

Question 17

In acromegaly which structures continue to grow?

Answer 17

• The growth plates have shut so long bone don’t
• Membranous bones e.g. nose, mandible, vertebrae and paws do
• The soft tissues of the face e.g. tongue (macroglossia)
• Increased interdental spaces
• Internal organomegaly (heart/ liver/ kidneys)

Question 18

Discuss feline acromegaly

Answer 18

• More common in middle ages- old cats
• Mainly in males (90%)
• Caused by pituitary tumours secreting excess GH
• Often diabetic when presented (high GH causes IR)

Question 19

Discuss canine acromegaly

Answer 19

Middle ages-old dogs

• ONLY FEMALE
• Excess endogenous progesterone or excess exogenous progestogens
• Caused by induction of GH gene in mammary glands-> P4 stimulates mammary gland growth, some P4 leaks out in entire bitches, this leakage of GH causes acromegaly

Question 20

How do you diagnose acromegaly

Answer 20

• IGF-1 concentration
• GH concentration
• In dogs look for history of exogenous progesterone
• In cats= CT or MRI scans