Natural growth hormone is secreted by the pituitary gland constitute a family of hormones which biological activity is fundamental for the linear growth of a young organism but also for the maintenance of the integrity at its adult state. The pituitary gland is an important link between the nervous system and the endocrine system. The pituitary gland is known to release many hormones that affect growth, sexual development, metabolism, glucocorticoids and the reproductive system. The pituitary gland has also been shown to release hormones that affect bone growth and regulate activity in other hormone secreting glands. The production of GH is modulated by many factors, including stress, nutrition, sleep and GH itself. However, its primary controllers are two hypothalamic hormones: the growth hormone-releasing factor (GRF or GHRH), a 44 amino acid sequence that stimulates the synthesis and secretion of GH and; somatostatin (SS), which inhibits GH release in response to GRF. Growth hormone (GH) secretion is regulated by two hypothalamic peptides: GH-releasing hormone (GHRH), which exerts stimulatory effect on GH release and somatostatin which exhibits an inhibitory influence. The decrease of growth hormone secretion with the age, demonstrated in humans, favors a metabolic shift towards catabolism which initiates or participates to the ageing of an organism. The loss in muscle mass, the accumulation of adipose tissues, the bone demineralization, the loss of tissue regeneration capacity after an injury, which are observed in elderly, correlate with the decrease in the secretion of GH.
Artificial manipulation of growth hormone levels has been demonstrated to have significant therapeutic utility. Human growth hormone (HGH) supplementation has been shown to be an effective treatment for growth hormone deficiencies and their related disease states in humans. The production of recombinant proteins provides a useful tool for the treatment of many diverse conditions. Recombinant growth hormone (rGH) is now commercially available for both medical and veterinary uses. For example, recombinant GH administration has been used to treat growth hormone deficiencies in short stature children, or as an anabolic agent in burn, sepsis, and as well as in the elderly and AIDS patients. However, the long-term safety of rGH has not yet been determined. Further, several side effects result from the use of rGH in human have been reported, i.e., left ventricular mass index, an increase in serum lipoprotein, and a subtle change in immune parameters. Resistance to GH action has been reported in malnutrition and infection. Long-term studies in patients undergoing HGH therapies have shown no causal correlation between GH or IGF-I therapy and cancer development. Chronic artificial elevation of growth hormone levels in humans usually results in either gigantism or acromegaly. GH, besides affecting skeletal growth, can also influence other organ systems, in particular, the liver and kidney. In the kidney, it has been associated with glomerulosclerosis and nephropathy. In the liver, it has been shown to cause an increase in liver size, as a consequence of both hyperplasia and hepatocyte hypertrophy.
While growth hormone is naturally produced by the pituitary gland, the secretion of growth hormone into the bloodstream is controlled by a second protein, growth hormone releasing factor (GRF). There are two ways to approach the problem of increasing circulating levels of growth hormone: increase the level of human growth hormone in the organism directly or increase the organisms natural tendency to produce growth hormone. The latter strategy may be achieved via supplementation with GRF. While growth hormone is naturally produced by the pituitary gland, the secretion of growth hormone into the bloodstream is controlled by a second protein, growth Hormone releasing factor. Most growth hormone is secreted at night, during deep sleep, but some is secreted in response to exercise and other forms of physical stress. Growth hormone secretion rates are highest in adolescents and lowest in the elderly. In young adults, sleep is associated with marked hormonal changes, including increased release of growth hormone (GH) and elevated levels of peripheral melatonin concentrations. A pulse of growth hormone occurs shortly after sleep onset in association with the first episode of slow-wave sleep (SWS) and often represents 50-100% of the total daily GH output. There is good evidence to indicate that the nocturnal release of GH contributes to the maintenance and quality of sleep. In general, the body's natural growth hormone level is increased by exercise and slow-wave deep sleep. In addition, for optimal HGH production and secretion the adequate protein intake is also important. |
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