growth hormone (GH), a single-chain peptide secreted by the anterior pituitary gland in response to GH-releasing hormone. Its secretion is controlled in part by the hypothalamus. GH promotes protein synthesis in all cells, increases fat mobilization and use of fatty acids for energy, and decreases use of carbohydrate. Growth effects depend on the presence of thyroid hormone, insulin, and carbohydrate. Somatomedins, proteins produced chiefly in the liver, play a vital role in GH-induced skeletal growth. GH cannot cause elongation of long bones after the epiphyses close, however, so stature does not increase after puberty. GH accelerates the transport of specific amino acids into cells, stimulates the synthesis of messenger ribonucleic acid (RNA) and ribosomal RNA, influences the activity of several enzymes, increases the storage of phosphorus and potassium, and promotes a moderate retention of sodium. GH secretion, controlled almost exclusively by the central nervous system, occurs in bursts, with more than half of the total daily amount released during early sleep. Somatostatin, an anterior pituitary regulating hormone produced in the hypothalamus, inhibits GH secretion as well as secretion of insulin and gastrin. A deficiency of GH causes dwarfism; an excess results in gigantism in children or acromegaly in adults. Also called somatotropic hormone, somatotropin. See also acromegaly, dwarfism, gigantism, somatostatin.
