Youth Hormone
Human growth hormone (HGH) is a heterogenous mixture of polypeptides secreted by the anterior pituitary gland. The principal form of HGH is a polypeptide containing 191 amino acids with a molecular weight of 215,000 daltons. This form of HGH is produced by recombinant DNA technology and is marketed for the treatment of short stature in growth hormone (GH)-deficient children and adolescents. Recombinant HGH or somatropin is also used for the treatment of GH deficiency in adults, short stature in association with renal insufficiency, AIDS-related wasting and short stature associated with Turner's Syndrome. In all of these cases, GH must be administered parenterally since it has very poor oral bioavailability.
GH is the primary hormone responsible for growth in humans, as well as other mammals, and it helps regulate such metabolic processes as anabolism and lipolysis. Normal human aging is associated with decreased GH secretion. Mean GH level in those over the age of 60 is about half of that in young adults. The reduction in GH levels with aging is believed to contribute to age-related decreases in muscle mass and strength and decreased lipolysis.
The effects of GH are largely mediated via IGF-1 (insulin-like growth factor 1). IGF-1 is a mitogen and may promote some cancers, including prostate, breast and colorectal cancers. Clearly, long-term safety studies, as well as efficacy studies, are essential to evaluate the role, if any, of GH replacement in the aging population.
The release of GH from somatotroph cells of the anterior pituitary gland is a complex process involving multiple regulators. The hypothalamic peptide GHRH (growth hormone-releasing hormone) acts on the somatotrophs to release GH, while the inhibitory peptide somatostatin blocks GH release. In addition, GH release appears to be influenced by a third, separate mechanism, as well—a growth hormone secretagogue pathway. GH secretagogues, abbreviated GHSs, can be amino acids, such as L-arginine, small peptides and nonpeptides. Further, neurotransmitters, such as acetylcholine, dopamine and norepinephrine, and neuropeptides, such as opioid peptides, are also involved in the control of GH secretion.
Recently, hgh has entered the dietary supplement marketplace, as have IGF-1 (see Insulin-Growth Factor 1) and several so-called GH secretagogues or releasers. The substances being marketed as GH secretagogues or releasers include the amino acids L-arginine, L-glutamine, L-ornithine, glycine, L-dopa, as well as such substances as ornithine alpha-ketoglutarate (see Ornithine Alpha-Ketoglutarate) and the herbs Macuna pruriens and Tribulus terrestris.
Supplemental HGH and secretagogues or releasers have putative anabolic and lipolytic activities, as well as putative "anti-aging" activity.
