Human Growth Hormone (hGH)Growth hormone (GH) is a peptide hormone. It stimulates growth and cell reproduction in humans and other animals. It is a 191-amino acid, single chain polypeptide hormone which is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland. Somatotrophin refers to the growth hormone produced natively in animals, the term somatropin refers to growth hormone produced by recombinant DNA technology, and is abbreviated "rhGH" in humans. This hormone is used clinically to treat children's growth disorders and adult growth hormone deficiency. In recent years, replacement therapies with human growth hormones (HGH) have become popular in the battle against aging. Reported effects include decreased body fat, increased muscle mass, increased bone density, increased energy levels, improved skin tone and texture, and improved immune system function. At this time HGH is still considered a very complex hormone and many of its functions are still unknown. In its role as an anabolic agent, HGH has been used by competitors in sports since the 1970s, and it has been banned by the IOC and NCAA. Traditional urine analysis could not detect doping with HGH, so the ban was unenforceable until the early 2000s, when blood tests that could distinguish between natural and artificial HGH were developed. Blood tests conducted by WADA at the 2004 Olympic Games in Athens, Greece primarily targeted HGH. Effects of growth hormone on the tissues of the body can generally be described as anabolic (building up). Like most other protein hormones GH acts by interacting with a specific receptor on the surface of cells. Stimulating the increase in height in childhood is the most widely known effect of GH, and appears to be stimulated by at least two mechanisms. - Because polypeptide hormones are not fat soluble, they cannot penetrate sarcolemma. Thus GH exerts some of its effects by binding to receptors on target cells, where it activates a secondary messenger. Through this mechanism GH directly stimulates division and multiplication of chondrocytes of cartilage.
- GH also stimulates production of insulin-like growth factor 1 (IGF-1, formerly known as somatomedin C), a hormone homologous to proinsulin. The liver is a major target organ of GH for this process, and is the principal site of IGF-1 production. IGF-1 has growth-stimulating effects on a wide variety of tissues. Additional IGF-1 is generated within target tissues, making it apparently both an endocrine and an autocrine/paracrine hormone. IGF-1 also has stimulatory effects on osteoblast and chondrocyte activity to promote bone growth.
In addition to increasing height in children and adolescents, growth hormone has many other effects on the body: - Increases calcium retention, and strengthens and increases the mineralization of bone
- Increases muscle mass through sarcomere hyperplasia
- Promotes lipolysis
- Increases protein synthesis
- Stimulating the growth of all internal organs excluding the brain
- Plays a role in fuel homeostasis
- Reduces liver uptake of glucose
- Promotes gluconeogenesis in the liver[13]
- It contributes to the maintenance and function of pancreatic islets
- It stimulates the immune system
Claims for GH as an anti-aging treatment date back to 1990 when the New England Journal of Medicine published a study where GH was used to treat 12 men over 60. At the conclusion of the study all the men showed statistically significant increases in lean body mass and bone mineral, while the control group did not. The authors of the study noted that these improvements were the opposite of the changes that would normally occur over a 10 to 20 year aging period. Despite the fact the authors at no time claimed that GH had reversed the aging process itself, their results were misinterpreted as indicating GH was an effective anti-aging agent. A Stanford University School of Medicine survey of clinical studies on the subject published in early 2007 showed that the application of GH on healthy elderly patients increased muscle by about 2 kg and decreased body fat by the same amount. However, these were the only positive effects from taking GH. No other critical factors were affected, such as bone density, cholesterol levels, lipid measurements, maximal oxygen consumption, or any other factor that would indicate increased fitness. Researchers also didn't discover any gain in muscle strength, which led them to believe that GH merely let the body store more water in the muscles rather than increase muscle growth. This would explain the increase in lean body mass.
|
