Growth Hormones and Insulin-like Growth Factor 1

Question 1

• How is GH production regulated?

Answer 1

Stimulatory – GHRH, ghrelin

Inhibitory – GHRIH/somatostatin (stimulated by GH & IGF-1), IGF-1 (stimulated by GH)

Question 2

• What are the long and short-term effects of GH and IGF-1?

Answer 2

Long-term – promotes growth, growing animals, protein synthesis
Short-term – starvation response, lipolysis, insulin resistance

Question 3

• What JAK/STAT signalling pathway is involved in the response to GH?

Answer 3

Receptor associated JAK2, activates STAT1 & STAT5

Question 4

• What are the physiological effects of GH?

Answer 4

Hyperglycaemia, increased rate of protein synthesis, increased lipolysis, increased insulin antagonism, increased gluconeogenesis

Question 5

• How does IGF-1 increase bone growth?

Answer 5

Increases chondrocytes and osteogenic cell replication
Increases chondrocytes and osteogenic cell protein deposition to promote bone growth
Convert chondrocytes to osteoblasts and form new bone

Question 6

• What is the most likely cause of pituitary dwarfism?

Answer 6

Most likely caused by a mutation of a gene coding for a transcription factor that regulates pituitary stem cell differentiation (ACTH not affected)

Question 7

• What is a consequence of pituitary dwarfism specific to females?

Answer 7

Failure to ovulate due to decreased LH levels

Question 8

• What bones continue to grow in acromegaly?

Answer 8

Membranous bones e.g. nose, mandible, vertebrae & feet

Question 9

• What is the most likely cause of canine acromegaly?

Answer 9

Induction of GH gene in mammary glands

Question 10

• How can pituitary dwarfism be diagnosed?

Answer 10

Dynamic pituitary stimulation test – no rise in GH in affected dogs

Question 11

• How can acromegaly be diagnosed?

Answer 11

IGF-1 concentration or GH concentration, CT or MRI brain scan (for cats)