Published online by Cambridge University Press: 08 January 2010
Growth hormone (GH) is a potent metabolic hormone of importance for body composition, bone mass, serum lipids, physical fitness and mental capacity. Accumulated experience has shown that although the majority of GH-deficient patients benefit from replacement therapy with GH, the response to GH differs between individuals. The basis of this variation in sensitivity is not fully understood. This review will focus on the impact of gender and age on several outcome measures.
GH secretion in healthy individuals – effects of age and gender
The secretion of GH peaks during puberty and declines thereafter with advancing age. Studies of the 24-hour GH serum concentration have shown a reduction, ranging from 32 to 45%, in elderly subjects (aged 55–85) compared with younger to middle-aged individuals (aged 18–45) (Ho et al., 1987; Vermeulen, 1987; Corpas et al., 1992). In healthy men aged 21–71 a 14% decrease in GH secretion, and a 6% decrease in GH half-life has been calculated for every advancing decade (Iranmanesh et al., 1991). In addition, the somatotroph responsiveness to GH releasing hormone (GHRH) (Pavlov et al., 1986; Iovino, Monteleone & Steardo, 1989), and to insulin-induced hypoglycaemia is impaired in the elderly (Kalk et al., 1973), but stimulation with combinations of arginine and GHRH seems less dependent on age (Ghigo et al., 1990). At present the mechanisms underlying the reduced GH secretion in ageing are not fully understood. The restoration of the somatotroph responsiveness after repeat stimulation (Corpas et al., 1992) indicates a functional and reversable state.
Obese subjects are characterized by reduced serum GH concentrations (Weltman et al., 1994) and blunted response to stimuli of GH secretion (Williams et al., 1984).