An "enhancer" is a type of regulatory element that can increase the efficiency of transcription, regardless of the distance or orientation of the enhancer relative to the start site of transcription. Growth hormone is a hormone, which stimulates growth of all tissues capable of growing. Human growth hormone (HGH) is known to have a number of effects on metabolic processes, e.g., stimulation of protein synthesis and free fatty acid mobilisation and to cause a switch in energy metabolism from carbohydrate to fatty acid metabolism. Deficiency in growth hormone can result in a number of severe medical disorders, e.g., dwarfism. HGH products are thus regarded as a growth enhancer. Growth factors are molecular signals or mediators that enhance cell growth or proliferation, alone or in concert, by binding to specific cell surface receptors. Growth factors are multifunctional and potent cellular regulators. Their biological effects include proliferation, chemotaxis and stimulation of extracellular matrix production.
Growth factors can have both stimulatory and inhibitory effects. Peptide growth factors are elements of a complex biological language, providing the basis for intercellular communication. They permit cells to convey information between each other, mediate interaction between cells and change gene expression. The effect of these multifunctional and pluripotent factors is dependent on the presence or absence of other peptides. Cytokine is a generic term for proteins released by one cell population which act on another cell as intercellular mediators. Examples of such cytokines are lymphokines, monokines, and traditional polypeptide hormones. Included among the cytokines are growth hormone such as human growth hormone, N-methionyl human growth hormone, and bovine growth hormone. Growth hormone, also known as somatotropin, is a peptide hormone containing 191 amino acids and having a molecular weight of about 22 kD. Insulin-like growth factor I (IGF-I) is a polypeptide naturally occurring in human body fluids, for example, blood and human cerebral spinal fluid. Most tissues and especially the liver produce IGF-I together with specific IGF-binding proteins. These molecules are under the control of growth hormone (GH). Growth hormone functions to regulate somatic growth and also maintains muscle mass and strength. It can also act as a counterregulatory hormone opposing the action of insulin on carbohydrate and lipid metabolism. A deficiency in human growth hormone secretion can result in various medical disorders, depending on the age of onset. In children, the syndrome is characterized by short stature, with normal body proportions and reduced growth rate, also known as dwarfism. A deficiency in human growth hormone secretion later in life may be characterized by excessive adiposity, reduced muscle mass, impaired exercise capacity, reduced body water, decreased bone mineral density, and psychological disorders. |
|
