Growth Hormone, Body Composition, and Aging

Abstract

For many years, it has been known that the composition of the human body changes with advancing age. In healthy youth, about 10% of the body weight is bone, 30% is muscle, and 20% is adipose tissue. After about age 50, these ratios change progressively. At age 75, a typical composition is 8% bone, 15% muscle, and 40% adipose tissue. The loss of bone mass predisposes to fractures of the spine and extremities. Loss of muscle mass reduces strength and endurance. Simultaneously, the functional capacities of most organ systems decline.We do now know the cause for these age-related, undesirable changes in body composition and in physiologic functions. Recently, a new aspect of the geriatric endocrine system was discovered that may provide both a partial explanation and a treatment. After about age 50, the secretion of growth hormone (GH) gradually declines and ultimately stops in many individuals. About half of our citizens over age 65, therefore, are partially or totally deficient in GH.Growth hormone has powerful effects on body composition and on the functions of most organs except the nervous system. Many of these somatotropic effects are opposite in direction to the geriatric declines in structure and function. Thus, GH causes enlargement of muscles, liver, kidneys, bones, and lymphoid organs; shrinkage of adipose mass; and increases in renal blood flow and glomerular filtration rate. The hypothesis arises, therefore, that several of the geriatric changes in structure and function result at least in part from G H deficiency, and could be reversed by continuing treatment with human GH (hGH) at physiologic or replacement doses.

Effects of growth hormone secretagogues on the release of adenohypophyseal hormones in young and old healthy dogs

“…Both basal and stimulated GH secretion and circulating insulin-like growth factor-I (IGF-1) concentrations decline with age in several mammalian species (Corpas et al, 1992;Finkelstein et al, 1972;Muller et al, 2002;Rudman, 1985;Wilshire et al, 1995;Zadik et al, 1985). In dogs too the GH responsiveness to GH stimuli, such as GHRH and hexarelin, decreases with ageing (Cella et al, 1989(Cella et al, , 1995.…”

Greater than predicted decrease in resting energy expenditure with age: cross-sectional and longitudinal evidence

“…Since REE represents the largest fraction of total daily energy expenditure (EE) and since fat-free mass (FFM) is the main contributor to REE (Ravussin et al, 1986), it is not surprising to observe changes in EE in aging individuals (Poehlman and Horton, 1990;Vaughan et al, 1991;Poehlman, 1993;Roberts et al, 1995;Horber et al, 1997). Indeed, aging is accompanied by a decrease in FFM (Rudman 1985;Shimokata et al, 1989;Zamboni et al, 1992) more commonly known as sarcopenia (Evans and Campbell, 1993). However, changes in body composition cannot entirely explain the age-related decrease in REE (Poehlman et al, 1992;Piers et al, 1998;Hunter et al, 2001).…”

The aging brain: is function dependent on growth hormone/insulin-like growth factor-1 signaling?

“…learning and memory Abbreviations GH growth hormone IGF-1 insulin-like growth factor-1 GHRKO GH receptor knockout PRL prolactin TSH thyroid stimulating hormone Growth hormone (GH) levels vary with age from high prepubertal expression to a gradual decline from adulthood to death. This age-related reduction in GH is believed to result in a loss of muscle mass, bone density and energy levels, and an increase in adiposity (Rudman 1985;Meites 1988). Indeed, several reports indicate that GH replacement can reverse many of these conditions as well as improve an individual's Bquality of life ( Rudman et al 1990;Degerblad et al 1990;Jorgensen et al 1991;Almkvist et al 1986;McGauley et al 1990;Binnerts et al 1992).…”