Growth Endocrinology

What is the primary regulator of growth and lactation (in ruminants)

Growth Hormone (GH) / IGF-1 axis

What does GH primarily do

• Direct metabolic effects

• stimulates IGF-1 production

What does IGH-1 do

• cell proliferation (mitogenic)

• bone growth

• protein synthesis

what stimulates GH release

GNRH

What inhibits GH release

somatostatin

how is GH secreted

Pulsatile (episodic bursts)

Where is ghrelin produced

stomach

what are ghrelin’s functions

• stimulates appetite

• stimulates GH secretion

When is ghrelin highest

during fasting

How does GH affect fat metabolism

• decrease (fat storage)

• increase lipolysis (fat breakdown)

how does GH interact with insulin

antagonizes insulin (anti-insulin effect)

How does GH interact with epinephrine

potentiates epinephrine (enhances fat breakdown)

What are GH indirect effects mediated by?

IGF-1

What does IGF-1 promote

• muscle growth

• bone growth

• protein synthesis

What happens to GH during undernutrition

GH increases

What happens to IGF-1 during undernutrition

IGF-1 decreases

What does IGF-1 decrease

• fewer GH receptors in liver

• Reduced protein synthesis

What is “uncoupling” of GH/IGF axis

high GH but low IGF-1 due to poor nutrition

What do IGF binding proteins do

regulate IGF availability

What does IGFBP-3 do

Protects IGF and acts as reservoir

How does testosterone affect growth

• ↑ GH pulsatility

• ↑ IGF-1

• ↑ lean growth

how does estrogen compare

also increases GH but less potent → less lean growth

how does stress affect growth

• ↑ cortisol

• ↓ GH receptors

• ↓ IGF-1

How does infection affect growth

• ↓ IGF-1

• ↓ appetite

what does leptin signal

• body fat levels

• energy status

what does leptin do to appetite

suppresses appetite

what does leptin do to metabolism

• ↑ Energy use

• ↑ Lipolysis

• ↓ protein synthesis

what happens to leptin with more fat

increases

what happens with negative energy balance

decrease

what is the effect of high leptin in cattle

• ↓ feed intake

• ↓ growth rate

Myostatin function

inhibitor of muscle growth

what happens if myostatin is mutated

increased muscle mass (“double muscling”)

Why is myostatin important in livestock

• genetic selection for muscle growth

• potential therapeutic target

how do GH, IGF-1, leptin and myostatin interact

• GH → drives metabolism & IGF-1 production

• IGF-1 → drives growth

• Leptin → regulates energy availability

• Myostatin → limits muscle growth