growth hormone or somatotropin (sōmăt´ətrō´pən), glycoprotein hormone released by the anterior pituitary gland that is necessary for normal skeletal growth in humans (see protein). Evidence suggests that the secretion of human growth hormone (HGH) is regulated by the release of certain peptides by the hypothalamus of the brain. One such substance, called somatostatin, has been shown to inhibit the secretion of HGH. HGH is known to act upon many aspects of cellular metabolism, but its most obvious effect is the stimulation of the growth of cartilage and bone in children.
See also auxins (plant growth hormones).
Role in Dwarfism and Gigantism
A deficiency of growth hormone secretion before puberty (by the end of which the synthesis of new bone tissue is complete) results in pituitary dwarfism. Pituitary dwarfs, who can be as little as 3 to 4 ft (91–122 cm) tall, are generally well proportioned except for the head, which may be relatively large when compared to the body (this relationship of head to body is similar to that of normal children). Unlike cretins, whose dwarfism is caused by a deficiency of thyroxine, pituitary dwarfs are not mentally retarded; they are often sexually immature. They can be treated by injections of synthetic growth hormone, either somatrem or somatropin, which are produced by genetically engineered bacteria.
An excess of growth hormone in children results in gigantism; these children grow to be over 7 ft (213 cm) in height and have disproportionately long limbs. Excess growth hormone produced after puberty has little effect on the growth of the skeleton, but it results in a disease affecting terminal skeletal structures known as acromegaly.
Other Medical Uses
HGH has been used with some success to combat the weight loss and general wasting characteristic of AIDS and cancer. It is used illegally by bodybuilders and athletes to increase muscle mass. Controversy surrounds its use in normal children who simply want to be taller. In addition, a 1990 medical study that reported the reversal of many of the physiological effects of aging with regular injections of HGH has created a lucrative black market for it and has prompted funding of further trials. There has been no conclusive evidence, however, to support the use of HGH as an anti-aging treatment, and it can cause serious side effects, including diabetes, in older adults.