Peptide Hormones: GH
Growth hormone (also known as Somatotropin) is a large peptide consisting of 191 amino acids1. It is similar in structure to prolactin and is secreted from the pituitary in a pulsatile pattern as a result of stimulation by growth hormone releasing hormone (GHRH). Somatostatin is a hormone that acts to suppress the release of growth hormone from the pituitary and opposes the action of GHRH1. GH secretion peaks during puberty and steadily declines in maturity. This increase in GH is largely responsible for the accelerated growth rate experienced during adolescence. The secretion of GH peaks during the night in the early stages of sleep. Exercise, stress, high levels of plasma amino acids and hypoglycemia all increase the secretion of growth hormone. Hyperglycemia following a meal elevated free fatty acids, obesity, hypo and hyperthyroidism and dopamine agonists decrease the secretion of GH1.
While GHh has effects of its own, it also exerts many effects through IGF1 and IGF22. GH alone enhances lypolysis and increases protein synthesis. Given to calorically restricted men for 1 to 3 weeks, GH significantly increases nitrogen retention, but these effects diminish after three weeks3. GH has anti-insulin effects resulting in elevated blood glucose levels. Excess amounts of GH can result in a condition known as acromegaly. This condition is characterized by local overgrowth of bone especially the skull and jaw bones. Diabetes is also present in acromegaly, as is enlargement of cartilage in the ears, nose, ribs and joints. Carpal tunnel syndrome is a common complaint of those with excess growth hormone production. Internal organs, especially the heart and spleen as well as enlargement of the hands and feet are also the result of excess GH stimulation. GH causes the secretion of IGF-1, which feeds back to reduce growth hormone secretion which may be one of the mechanisms of reduced efficacy with growth hormone over time.
GH use has become pretty widespread with everyone from bodybuilders to athletes to actors and life extensionists using it for one purpose or another. GH alone is considered as not very effective for increasing lean muscle mass, but is used largely for reducing body fat. More importantly, GH is legal, therefore some are choosing to use GH and insulin over AAS because GH and insulin are legal and easy to obtain while AAS are cheaper, more effective and generally safer to use.
The effects of GH are countered by the effects of another hormone known as somatostatin. Somatostatin does not inhibit the effects of GH but rather has an effect on the secretion of GH from the pituitary. Of course, when GH is administered exogenously, somatostatin will only inhibit the release of endogenous GH. Somatostatin does have other effects, however. As GH levels increase through exogenous administration, somatostatin is released resulting in decreased endogenous production. In addition, somatostatin also decreases the secretion of insulin from the pancreas. Another major action of somatostatin is the inhibition of thyrotropin release1. Thyrotropin stimulates the thyroid gland to produce thyroid hormones. With exogenous administration of GH, the user experiences both decreased insulin response and decreased thyroid hormone production. This has prompted some users to combine GH with insulin and thyroid hormone to correct these deficits.
Though it was once common for users to inject 15 IU or more of GH per day, it seems that 4 to 6 IU per day is more common of late. It seems that higher doses produced more side effects with rapidly diminished results due to loss of efficacy. There have been recent attempts to schedule GH as a controlled substance but as yet this has not happened. In any case, the illicit use of GH is not as legally benign as some users think as a provision regarding distribution and intent to distribute for illicit purposes was included in the steroid control act of 1990 was a 5 year felony.
1. Wilson, Jean D., and Foster, Daniel W., eds. Williams Textbook of Endocrinology. 9th ed. Philadelphia: Saunders, 1997.
2. Fryburg DA. Insulin-like growth factor I exerts growth hormone- and insulin-like actions on human muscle protein metabolism. Am J Physiol. Aug;267(2 Pt 1):E331-6, 1994
3. Lundeberg S, Belfrage M, Wernerman J, von der Decken A, Thunell S, Vinnars E. Growth hormone improves muscle protein metabolism and whole body nitrogen economy in man during a hyponitrogenous diet. Metabolism. 40(3):315-22, 1991