Human Ageing and the Growth Hormone/Insulin-Like Growth Factor-I (GH/IGF-I) Axis - The Impact of Growth Factors on Dementia

Abstract

There is clear evidence that human ageing is associated with reduced activity of the growth hormone (GH)/insulin-growth factor-I (IGF-I) axis, the so called "somatopause". Although this condition is likely to contribute to age-related changes in body composition, structure functions and metabolism, we are now in face of the paradox of lifelong GH/IGF-I deficiency or resistance resulting in prolonged life expectancy. This evidence questions whether GH deficiency is or is not a beneficial adaptation to ageing. On the other hand, neuroendocrine studies provided evidence that brain ageing is associated to peculiar age-related alterations in the control of GH/IGF-I axis, mostly including GHRH deficiency and SS hyperactivity, reflecting the age-related cholinergic impairment. This hormonal pattern is present in normal and demented elderly subjects, and a neuroendocrine distinction among these conditions is impossible. This review will focus on the age-related decline in the activity of GH/IGF-I axis as a function of either normal or pathological brain ageing. Particularly, the influence of GH/IGF-I axis on cognitive functions and related disorders will be discussed.