VBMS 325 growth endocrinology

IGF-1

• primary regulator of growth and lactation in ruminants

• synthesized by most tissues

• recptors on most cell types

• anabolic and mitogenic in muscle, bone, mammary

GHRH control of GH

hypothalamus→ +GnRH^{→ ANT PIT←}stomach + grehlin

stomatostatin control of GH

inhibits GH secretion

GH

• synthesized stored and secreted from ant pit

• receptors located on liver, adipose, bone, muscle, gonads

more pulsatile

= more potency

Grehlin

• growth hormone releasing peptide

• produced by enteroendocrine cells of stomach

• major role in energy homestasis

• receptor located in hypothalamus and ant pit

IGF II

• synthesized by most body tissue

• recptors on most cell types

• important in prenatal growth

direct actions of GH

• metabolc effects in adipose tissue

• anti-lipogenic/lipolytic activities

• stimulation of IGF-I secretion

• antagonizes insulin

indirect actions of GH

mediated by IGF-I

• cell proliferation

• promotes bone growth

• promotes protein synthesis and accretion

effect of nutrtition on GH/IGF-I

• GH secretion (increased secretion with undernutrition)

• GH receptors on the liver (reduced # of GH receptors with under nutrition)

• IGF-I secretion from liver (reduced secretion with undernutrition)

• IGF-I binding proteins (IGFBP1 holds IGF-1 and wont let into blood)

effect of male sex on GH/GHF-I

• testosterone stims plasma GH under good nutrition

• Increases GH pulsatilty which results in more efficient GH receptor recycling, more potent in stims IGF-I, higher blood IGF-I

effect of females on GH/IGF-I

• estrogen also stims GH seceretion and gh receptor # but less potency than tesosterone (less lean growth)

effect of stress

• increase cortisol release

• reduces liver GH receptors and IGF synthesis

• increase synthesis of IGFBP

• lower IGF-I

effect of infection

• increase inflammatory cytokine release

• reduce liver IGF-I sythesis

• reduce appetite

steroid implants

• increased mature body size

• testosterone derivitive (increased GH)

effects of weaning

• increase corisol

• decrease feed intake (down IGF-I)

• Increase illness/infection

leptin

• obese gene

• hyperphagic

• hypo-active

• low metabolic activity

• produced and secreted almost exclusively in adipocytes

leptin; general actions

• suppresses appetite

• increases energy use

• permissive role in reproductive cycling

• increases immune cell activity

plasma leptin

• positively correlated with adiposity

• positively correlate with energy balance

role of leptin in cattle

• secretion increase with increase of fat mass

• decrease secretion with decrease in energy balance and vice versa

• metabolic response to increased leptin secretion in finishing steer

T Allele mutation in cattle leptin

Cys at position 4, has sulfur to create disulfide bridge (sticks 2 porteins together)

C allele mutation in cattle leptin

Arg at position4, still have leptin but its missing disulfide bind and leptin is less potent

myostatin and muscle hypertrophy

• 5 mutations in myostatin gene

• myostatin inhbits muscle development

• myostatin receptor blocker could control muscle growth