Growth hormone, GH, is a peptide produced by the pituitary which enters circulation and works in multiple tissues of the body via the GH receptor. The activated GH receptor provides some effects directly and other effects indirectly by stimulating production of IGF-1. Some increase in GH may be achieved naturally by means of exercise; larger increases can be achieved by injection.Injectable GH is typically provided as lyophilized powder in vials.
Any injectable GH product should be identical with natural GH, which has 191 amino acids. Some products however are a cheaper analog with 192 amino acids. These products can cause adverse immune response and should not be used.
What does growth hormone itself do at higher doses, exclusive of what may happen from released IGF-1?
In skeletal muscle, GH at supraphysiological doses interferes with insulin signaling, decreases glucose uptake, increases fatty acid uptake, and increases basal rate of lipid oxidation (fat burning).
Overall, the effects promote anabolism and a metabolic shift towards fat-burning over glucose-burning.
At supraphysiological doses, GH also increases lipid storage within muscle cells, which is an adverse effect, yielding to some extent lipotoxicity. (Only adipose cells are capable of storing substantial amounts of lipids without self-harm and metabolic impairment.) At normal GH levels, the story in muscle is largely the same as above, except that normal GH levels actually support normal insulin signaling, rather than impair it, and do not cause abnormal lipid storage.
In adipose tissue, GH increases lipolysis, decreases lipogenesis, decreases glucose uptake, and decreases local activity of corticosteroids by downregulating 11βHSD1. Some of the increase in lipolysis appears to be from upregulating adipose β2 and β3 receptors.
All this helps in fat loss or to help in partitioning nutrients towards muscle gain. Additionally, the increase in serum free fatty acids produced from increased lipolysis appears to be GH’s mechanism for increasing muscle anabolism. When this increase in free fatty acids is blocked, GH no longer increases muscle anabolism.
In the liver, GH stimulates conversion of glycogen to glucose, impairs insulin sensitivity and thereby reduces glucose uptake, increases uptake of triglycerides, increases storage of triglycerides, and increases production of VLDL (“bad cholesterol.”)
In both muscle tissue and the liver, GH also stimulates production of IGF-1. IGF-1 produced by the liver provides systemic effect; the effect of IGF-1 produced in muscle is thought to be mostly local.
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A 191-amino acid polypeptide hormone secreted by the human adenohypophysis (PITUITARY GLAND, ANTERIOR), also known as GH or somatotropin. Synthetic growth hormone, termed somatropin, has replaced the natural form in therapeutic usage such as treatment of dwarfism in children with growth hormone deficiency.