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Growth hormone is secreted from the anterior part of pituitary gland and stimulates mainly liver to produce IGF-1, the polypeptide growth factor of 70 amino acids. The effects of IGF-1 include the synthesis of new proteins in the body and the stimulation of binding sulfate to cartilage, eventually the promotion of the physical growth of animal body.
Since most actions of growth hormone are mediated by IGF-1 and it is impossible to measure serum growth hormone concentration accurately, blood IGF-1 level is indirect assay of human growth hormone secreted.
Mechanism
of Action
- Alter target cell activity
(i.e., increase or decrease rates of normal processes)
- Response is dictated by target cell type
- Typical changes produced by hormones:
- change plasma membrane permeability and/or membrane potential by open/close ION CHANNELS
- Synthesis of proteins (viz., enzymes = regulatory proteins)
- Activate/deactivate enzymes
- Induce secretary activity
- Stimulate mitosis
Physiological
Function of Growth Hormone
- Metabolic effects of growth hormone
- Promoting protein deposit
- Enhance a.a transport through cell membranes
- Enhance RNA translation
- Increase nuclear transcription of DNA
- Decrease catabolism of protein and a.a.
- Enhancing fat utilization for energy
- Enhancing fat acid covert to acety-CoA
- Ketosis
Funtion of IGF-1
- IGF-1 stimulates - myoblast L6 cell growth (increase cell mass)
Suppression of protein degradation
Accelerate a.a uptake
Enhance cell proliferation
Stimulate differentiation to form postmitotic myotubes
Increase creatine kinase (regenerate ATP in muscle)
Glucose uptake increase
Stimulate myoblast differentiation
Mitogenic effect (cell proliferation)
FGF - mitogenic effects (myoblast proliferation),
inhibit differentiation
TGF-β not mitogenic effects
inhibit differentiation
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