GROWTH HORMONE (GH)  

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Properties
    -    polypeptide (191 amino acids)  
Sources
    - anterior pituitary gland
Secretion and blood levels
    - diurnal rhythm  
    - pulse in early night  
    - GHRH stimulates secretion  
    - exercise stimulates secretion  
    - GH stimulates IGF-I (somatomedin C) by liver  
           - IGF-I causes many GH effects  
           - IGF-I blood levels remain stable  
           - IGF-I inhibits GHRH secretion  
           - somatostatin inhibits GH secretion  
           - somatostatin from hypothalamus and gut  
           - GHRH / somatostatin negative feedback loop  
           - hexapeptides stimulate GH secretion  
           - some GH bound to proteins (GHBPs)  

Physiological Activities  
    - acts on many tissues  
    - muscle, bone, liver, kidney, heart, lymphoid tissues  
    - acts through cell membrane  
    - activates tyrosine phosphorylating enzyme  
    - increases AA uptake and protein synthesis  
    - increases blood glucose  

Changes with Aging  
       - height of nocturnal pulses decline  
       - 80 percent by age 80  
       - due to increased GHRH  
       - causes increased IGF-I levels  
       - liver retains sensitivity to GH  

Effects from GH Supplementation  
       - effects from chronic supplementation are unknown  
       - reported beneficial effects  
           - in GH deficient elders  
                - increases muscle mass, bone mass, skin thickness  
                - decreases body fat  
                - may increase immune function  
                - may increase healing  
               - increases cognitive functions  
       - reported adverse effects  
           - Na+ and H2O retention 
            - hypertension  
           - increases blood glucose  
           - decreases insulin sensitivity  
           - no increase in muscle strength  
            - gynecomastatia  
           - enlarged organs (kidney, spleen, liver)  
           - carpal tunnel syndrome  
           - osteoarthritis  
           - diabetes mellitus  
           - ? increases cancer growth ?

Effects from Indirect GH Supplementation  
       - GHRH  
             - dose must be diurnal  
           - chronic GHRH loses effectiveness  
       - IGF-I  
           - does not reduce insulin sensitivity  
           - increases growth of certain cancers  
           - decreases normal apoptosis (programmed cell death).  
       - hexapeptides  
           - administered by nasal spray, orally, subcutaneous injection  
           - effects still unknown  
       - GH mimics  
           - effects include all GH effects (+ and -)  
       - net effects  
           - no conclusive evidence that GH slows aging  
           - does not affect all age changes  
           - may be harmful for individuals with normal GH  
       - indirect GH supplementation  
           - not shown to work well  
           - can lead to the same adverse as GH  
           - exercise provides increased GH levels and benefits but without the drawbacks.  

Caution  
       - questionable benefits  
       - questionable effectiveness over time  
       - serious drawbacks  

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Copyright 2020: Augustine G. DiGiovanna, Ph.D., Salisbury University, Maryland

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