Elements in the pathophysiology of diminished growth hormone (GH) secretion in aging humans

Remarkable decreases in growth hormone (GH) secretion accompany healthy aging. The pathophysiology of this hyposomatotropism is confounded by concurrent changes in body composition (with increased visceral fat), physiological declines in estrogen and androgen concentrations, differences in gender responses to aging, and alterations not only in the quantity of GH secreted, but also (as more recently evident) in the orderliness or regularity of the GH release process (e.g., as assessed by approximate entropy). In addition, physical fitness or aerobic capacity also positively modulates GH secretion. Lastly, confounding variables such as altered sleep patterns and nutritional state may contribute to overall regulation of the GH axis in aging. Despite confounding variables, available human experiments suggest partial growth hormone-releasing hormone (GHRH) deficiency in healthy older individuals, presumptively combined with somatostatin excess, and disruption of the moment-to-moment pattern of coordinated and orderly GH release. Here, the authors review these selected facets of recent experimental evaluation of the human GH insulin-like growth factor-I (GH-IGF-I) feedback axis in aging humans.