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CRON4healthyfuture
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 Posted: Tue May 09, 2006 12:06 am Post subject: Growth Hormone knockout mice cannot live longer on CR |
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I happen to agree strongly with the conclusions of this study, although I do not necessarily agree that they have "proven" that CR is simply a shift in hormones. In other words, more work needs to be done to strengthen the case even further from where it stands today.
But, suffice it to say, there is a preponderance of evidence implicating GH, IGF-1, and Insulin in aging.
In this study, Bartke, Masternak, and some of the other endocrine heroes found that disabling the gene for GH abolished all benefits to reducing food intake. Furthermore, they found that disabling the gene for GH made mice live longer "automatically".
At the most basic level of logic, you could then argue that because these two phenomena are "superimposable", they are essentially equivalent. I agree that most of CR is probably being mediated by hormonal actions, and so I don't have a problem with that, but I am sure there are lots of insulin skeptics that will want to see more evidence.
In any case, a very interesting study.
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| "In the present study, mice with targeted disruption of the growth hormone (GH) receptor [GH receptor/GH-binding protein knockout (GHRKO) mice] and their normal siblings were fed ad libitum (AL) or subjected to 30% CR starting at 2 months of age. In normal females and males, CR produced the expected increases in overall, average, median, and maximal life span. Longevity of normal mice subjected to CR resembles that of GHRKO animals fed AL. In sharp contrast to its effects in normal mice, CR failed to increase overall, median, or average life span in GHRKO mice and increased maximal life span only in females. In a separate group of animals, CR for 1 year improved insulin sensitivity in normal mice but failed to further enhance the remarkable insulin sensitivity in GHRKO mutants. These data imply that somatotropic signaling is critically important not only in the control of aging and longevity under conditions of unlimited food supply but also in mediating the effects of CR on life span. The present findings also support the notion that enhanced sensitivity to insulin plays a prominent role in the actions of CR and GH resistance on longevity. - Proceedings of the National Academy of Sciences " |
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