| The greatest secretion of GH occurs in children and young adults; it occurs chiefly during sleep
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| Although GH can exist in variant forms, the major species is a 22 kDa protein. Nearly two-thirds of GH in the circulation
is associated with a 29 kDa binding protein that is identical to the extracellular domain of the GH receptor. This binding protein prolongs the half-life of GH in plasma, about 20 minutes.
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| The normal human pituitary contains approximately 10 mg of GH; less than 5% of this is released each day. GH is released in bursts with a periodicity of 3-4 hours and greatest secretory activity occurs during sleep. At the peak of a secretory burst, the plasma GH concentration may be 100-fold greater than baseline; this means that no meaningful reference interval can be derived for this hormone. Secretory bursts occur most frequently in children and young adults.
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