From: Robert Coyote (coyyote@hotmail.com)
Date: Thu Feb 07 2002 - 06:54:58 MST
With regard to calorically restricted mice, there has been a report1 that
the IGF-1 receptor density increases with age (as compared to no consistent
changes in ad lib-fed animals with age), accompanied by a decrease in IGF-1
levels and an increase in growth-hormone release. IGF-1 levels increase in
ad lib-fed aging mice and in aging humans, while growth-hormone release
decreases with age.
The amplitude of growth-hormone secretory pulses decreases with age in ad
lib-fed animals, and short-term caloric restriction in young animals also
results in a decline in the amplitude of growth hormone. However, in older
caloric-restricted animals, growth-hormone pulses were similar to those in
young ad lib-fed mice, with both the number of pulses of growth hormone and
mean growth hormone concentrations increased substantially compared to older
ad lib-fed mice. Apparently, there is a long-term adjustment that takes
place in the growth hormone and IGF-1 axis in chronically calorically
restricted mice so that, even with 40% less food (called "moderate caloric
restriction" to distinguish it from outright starvation), the animals have
greater protein synthesis, along with greater growth-hormone and lower IGF-1
levels.
Sonntag et al, "Pleiotropic Effects of Growth Hormone and Insulin-like
Growth Factor (IGF-1) on Biological Aging: Inferences from Moderate
Caloric-Restricted Animals," J. Gerontol.: Biological Sciences
54A(12):B521-B538 (1999).
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