Aging, GH and the brain
Research studies clearly indicate that age-related changes in cellular and tissue function are linked to decreases in the anabolic hormones, as e.g. GH and IGF-1. Although there has been extensive research on the effects of these hormones on bone and muscle mass, their effect on brain ageing has received little attention. In response to moderate CR (that increases mean and maximal lifespan by 30-40%, see above), age-related decreases in GH secretion are ameliorated (despite a decline in plasma levels of IGF-1) suggesting that some of the effects of CR are mediated by modifying the regulation of the GH/IGF-1 axis. Small blood vessel (microvascular) density on the surface of the brain decreases with age and these vascular changes are ameliorated by moderate CR. Administration of GH increases microvascular density in aged animals and further analysis indicates that the cerebral vasculature is an important producer of local IGF-1 for the brain. Antagonism of IGF-1 action in the brains of young animals impaired both learning and reference memory. Investigation of the mechanisms of action of IGF-1 suggests that it regulates age-related alterations in some essential brain receptors. The beneficial role of GH, and IGF-1 in ameliorating vascular and brain aging are counterbalanced by their well-recognized roles in age-related pathogenesis. Although research in this area is still evolving, results suggest that decreases in GH and IGF-1 with age have both beneficial and deleterious effects. Furthermore, part of the actions of moderate CR on tissue function and lifespan may be mediated through alterations in the GH/IGF-1 axis [10].
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