Aart J. van der Lely, M.D. PhD Erasmus University Medical Centre Rottersdam (EMCR)
Regulation of GH secretion in aging
Although an age-related decline in plasma growth hormone (GH) levels is well documented, the possible role of GH in the control of aging is controversial. GH is produced by the pituitary gland. The hypothalamus is a part of the brain that is located just above the pituitary gland, where it acts as a controller of pituitary function.
GH in circulation acts on many tissues and organs. One of the main tasks of GH is to increase the production of a substance by the liver, called Insulin-like Growth Factor-I (IGF-I). Circulating IGF-I levels undergo important age-related variations increasing at puberty and decreasing, thereafter, to low levels in the elderly. Low IGF-I levels in the elderly mainly reflect impaired GH secretion but the decline in gonadal sex steroid levels, and malnutrition may also play a role in the age-related decrease in IGF-I activity. This, in turn, partially accounts for age-related changes in bones, muscles, cardiovascular system, central nervous system and the immune system. However, it is currently unclear whether treatment with exogenous GH, or IGF-I can retard or reverse age-related changes in body structure and function [1;2]. There is much evidence that some aspects of aging are similar to those observed in selective hormone deficiencies during adulthood. Replacement therapy in GH deficiency in adulthood is very successful in reversing the related clinical symptomatology. However, preliminary studies of GH treatment in the normal elderly have been largely disappointing: an increase in muscle mass is only accompanied by improved muscle strength if exercise is also increased during this period. No real benefit of GH therapy, additional to that of exercise, has been reported. Epidemiological studies indicate a relationship between high-normal IGF-I levels and cancer development. Therefore, no definitive answers can presently be given regarding the safety of long-term GH therapy in otherwise healthy individuals during the somatopause [3;4].
