Introduction

Ageing in humans is associated with a progressive loss of function, which leads to a decreased capacity to maintain homeostasis, initially in the face of stress, and subsequently under baseline conditions. Certain aspects of the ageing process are similar to states of hormone deficiency or excess. Thus, for example, decreased muscle and bone mass, increased body fat, and reduced rates of protein synthesis and tissue healing occur in normal ageing as well as in pathological growth hormone (GH) deficiency. Recent studies suggest that administration of recombinant GH to non-elderly GH-deficient adults leads to improvements in body composition, metabolic variables, muscle strength, cardiac endurance and psychosocial outcomes. Because normal ageing is associated with a decline in GH secretion and serum levels of insulin-like growth factor-I (IGF-I) (Kelijman, 1991; Corpas et al., 1993c), it has been suggested that some of the above noted alterations in body composition and function in older persons may be due to decrements in the GH–IGFI axis. To validate this hypothesis several investigative groups are examining the effects of different hormone replacement paradigms in healthy or frail elderly populations. A major goal of this research effort is to assess whether trophic factors such as GH, GH releasing hormone (GHRH), or other GH-releasing peptides can be used effectively, safely, ethically and economically to prolong physical and functional independence, to compress morbidity and to reduce frailty in the elderly.

Physiological changes in the somatostatin–GHRH–GH–IGF-I axis with ageing

Age related changes of spontaneous and stimulated GH release

GH is an important anabolic hormone which exerts stimulatory effects on protein synthesis and on lipolysis.