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Abstract
Autophagy is a universal, highly regulated mechanism responsible for the degradation
of long-lived proteins, cytomembranes and organelles during fasting and may be the
cell repair mechanism that mediates the anti-ageing effects of calorie restriction
(Bergamini and Gori, 1995). The function of autophagy was studied in vivo on male
Sprague Dawley rats fed ad libitum or 40% food restricted. Autophagy was induced in
overnight fasted rats by the injection of an anti-lipolytic agent and was investigated
by electron microscopy. Changes in regulatory plasma nutrients and hormones were assessed
and rate of proteolysis was calculated from the release of 14C(6)-valine from pre-labelled
resident proteins. Results in rats fed ad libitum showed that autophagic-proteolytic
response to antilypolitic agents was paramount in one month-old rats; was high but
delayed in 2 month-old rats, decreased remarkably in 6 month-old rats and almost negligible
at older age. Parallel ageing-related changes were observed in the effects of treatment
lowering glucose and insulin plasma levels. Calorie restriction prevented all changes.
In view of the known suppressive effects of insulin, it may be concluded that the
age-changes of autophagy are secondary to the ageing-related alteration in glucose
metabolism and hormone levels, whose appearance is delayed by calorie restriction.
Data may support the hypothesis that ad libitum feeding accelerates the rate of ageing
by raising insulin plasma levels and suppressing autophagy and membrane maintenance,
and that calorie restriction may break this vicious circle.