Challenge: Growth and Youth in a Bottle?
After human GH (Growth Hormone) became available through genetic engineering, a new problem for the medical community was to determine under which circumstances synthetic GH treatment is appropriate. Until recently, the FDA had approved treatment only for the following uses:
(1) for children with GH defciency,
(2) for adults with a pituitary tumor or other disease that causes severe GH defciency, and
(3) for patients with AIDS who have severe muscle wasting.
Although not approved by the FDA for this use, GH therapy is also widely used to promote faster healing of skin in patients who have been severely burned. In 2003, amid emotionally charged debates, the FDA approved GH shots for another group, the shortest 1.2% of children who are unusually short for no apparent reason. This therapy involves multiple GH injections per week for a number of years under careful supervision of pediatric endocrinologists for an average gain in height of 1 to 3 inches. Children with GH defciency experience more dramatic gains of about 6 to 8 inches on GH therapy.
Another group who may beneft from replacement GH therapy is the elderly. GH secretion typically peaks during a person’s 20s, then in many people may start to dwindle after age 40. This decline may contribute to some of the characteristic signs of aging:
■ Decreased muscle mass (GH promotes synthesis of proteins, including muscle protein)
■ Increased fat deposition (GH promotes leanness by mobilizing fat stores for use as an energy source)
■ Reduced bone density (GH stimulates bone-forming cells)
■ Thinner, sagging skin (GH promotes proliferation of skin cells)
(However, inactivity is also believed to play a major role in ageassociated reductions in muscle mass, bone density, and strength.)
Several studies in the early 1990s suggested that some of these consequences of aging may be counteracted through the use of synthetic GH in people older than age 60. Elderly men treated with supplemental GH showed increased muscle mass, reduced fatty tissue, and thickened skin. In similar studies in elderly women, supplemental GH therapy did not increase muscle mass signifcantly but did reduce fat mass and protect against bone loss. Even though these early results were exciting, further studies were more discouraging. Despite increased lean body mass, many treated people surprisingly do not have increased muscle strength or exercise capabilities. Also, when GH is supplemented for an extended time or in large doses, harmful side effects include an increased likelihood of diabetes, kidney stones, high blood pressure, headaches, joint pain, and carpal tunnel syndrome (thickening and narrowing of the tunnel in the wrist through which the nerve supply to the hand muscles passes; carpal means “wrist”).
Furthermore, synthetic GH is costly ($15,000 to $20,000 annually) and must be injected regularly. Also, some scientists worry that sustained administration of synthetic GH may raise the risk of developing cancer by promoting uncontrolled
cell proliferation. For these reasons, most investigators no longer view synthetic GH as a potential “fountain of youth.” Instead, they hope it can be used in a more limited way to strengthen muscle and bone suffciently in the many elderly who have GH defcits, to help reduce the incidence of bone-breaking falls that often lead to disability. The National Institute of Aging is currently sponsoring a nationwide series of studies involving GH therapy in the elderly to help sort out potentially legitimate roles of this supplemental hormone.
Source: Physiology, Sherwood