Abstract
Obesity of middle-aged mammals is followed at old age by anorexia and cachexia leading to sarcopenia. Complex age- and body composition-related alterations in the regulation of energy homeostasis may be assumed in the background. We aimed to test the possible contribution of age- and body composition-related changes of satiety responses to catabolic brain-gut-axis peptide cholecystokinin (CCK) to these alterations in energy balance during aging. Male Wistar rats (6-8 animals/group) aged 2 months (juvenile), 3 months (young adult), 6 or 12 months (early or late middle-aged), and 24 months (old) were injected intraperitoneally with 5 μg CCK-8 prior to re-feeding after 48-h food-deprivation. CCK suppressed re-feeding in young adult (26.8%), early middle-aged (35.5%), and old (31.4%) animals, but not in juvenile or late middle-aged rats (one-way ANOVA). CCK-resistance of 12 months old rats was prevented by life-long calorie-restriction: CCK suppressed their re-feeding by 46.8%. Conversely, in highfat diet-induced obese 6 months old rats CCK failed to suppress re-feeding. In conclusion, age-related changes in satiety responsiveness to CCK may contribute to the age-related obesity of middle-aged as well as to the anorexia of old animals. CCK-responsiveness is also influenced by body composition: calorie-restriction prevents the resistance to CCK, pre-existing obesity enhances it.
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