PP28 Hormonal Regulation of Growth 1

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PP28Hormonal Regulation of Growth 1

• Chapter 10 pg 179-198
• ANS 3043
• University of Florida
• Dr. Michael J. Fields

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Hormones Influencing Growth Growth Hormone

• Protein Hormone
• Mode of Action
• Direct Actions mediated through tissue
  receptors
• Reduces glucose transport in to cells and its
  metabolism
• Binds to liver and other cells to stimulate IGF
  release
• Binds to muscle to enhance protein synthesis
• Binds to fat cells to enhance lipolysis

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Hormones Influencing Growth GH

• Indirect Actions modulated through release of
  other hormones or growth factors
• Promotion of growth and actions of other
  endocrine factors (insulin, thyroid hormone,
  catecholamines)
• Most growth effects are mediated through IGF I
  and II released from liver
• IGF actions can be autocrine, paracrine,
  endocrine
• IGF acts on muscle, bone, fat and other tissues
• Localized actions on adipose tissue to increase
  lipolysis to provide energy

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Hormones Influencing Growth GH

• Specific Actions
• Bone
• Direct Actions
• Stimulates production of IGF I in proliferation
  zone
• Indirect Actions
• Increases chondrocyte proliferation and
  osteoblast activity
• Increases long bone growth prior to closure of
  epiphyseal plate
• Increases periosteal growth, which increases bone
  mass

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Hormones Influencing Growth GH

• Muscle
• Direct Actions
• Increased muscle protein synthesis and decreased
  protein degradation
• Increased amino acid transfer and incorporation
  into muscle
• Increased fibroblasts differentiation
• Indirect Actions
• Mediated by IGF I secreted by liver into
  circulation
• Either myogenic cells or other cells in close
  proximity produce IGF-I, which act via paracrine
  or autocrine actions to increase protein
  accretion
• Increases uptake of glucose and amino acids into
  muscle

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Hormones Influencing Growth GH

• Muscle
• IGF Binding Proteins bind IGF
• Increases half-life of IGFs in circulation
• Modulates interaction of IGF I with its cell
  receptor
• Modulates binding of IGF IGFBP with tissues

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IGF-I and GH concentrations in miniature and
normal Brahman cattle (7 months old)
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Association Between Growth and IGF-I Receptors in
Muscle
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Hormones Influencing Growth GH

• Adipose
• Direct Actions
• Increases lipolysis by stimulating mobilization
  of fatty acids from adipose
• Indirect Actions
• Decreases insulin stimulation of glucose
  metabolism
• Increases catecholamine-stimulated lipolysis

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Hormones Influencing Growth GH

• Metabolism Effects
• Administered frequently and systemically as an
  injection
• Swine
• Increases body weight, improved feed conversion,
  decreased feed intake
• Carcasses have more muscle and less fat

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Hormones Influencing Growth Growth Hormone
Releasing Hormone

• Administration
• Administered very frequently since it is a
  peptide
• Results in similar composition differences
  compared with exogenous GH

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Hormones Influencing Growth Somatostatin

• Immunization against Somatostatin
• Increases growth hormone secretion by release of
  suppressive effects of somatostatin
• Therefore increases growth

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Hormones Influencing Growth GH

• Transgenic Animals
• Insertion of a growth hormone gene that can be
  turned off and on
• Over expression of growth hormone resulting in
  increased growth

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Hormones Influencing Growth GH

• GH Abnormalities
• Dwarfs GH deficient
• Respond to exogenous GH
• Laron type dwarfs excessive GH
• Lack of functional hepatic GH receptor
• Pygmies normal GH
• Post GH receptor defect
• Gigantism excess GH
• Excess GH before epiphyseal plate closure
• Acromegaly excess GH
• Excess GH after epiphyseal plate closure results
  in extensive flat bone growth

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12 yr
Little women of Loja with early fetal death in
males
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Hormones Influencing Growth GH

• Summary
• Major hormone coordinating body metabolism
• Along with insulin and glucagon
• Controls the distribution of nutrients among
  various tissues
• By inducing IGF I secretion, it serves as the
  major mediator of growth
• When adequate nutrient intake is available
• Nutrient limited
• GH increases significantly and is lipolytic
• Decreased animal growth because IGF I becomes
  uncoupled from GH and secretion of IGF I
  decreases
• Facilitates transfer of nutrient from adipose to
  vital functions and lean tissues