Substrate changes during fasting and refeeding contrasted in old and young rats

Area of Science:

• Gerontology
• Metabolic Biochemistry
• Physiology

Background:

• Aging is associated with altered metabolic regulation.
• Understanding age-related changes in carbohydrate and lipid metabolism is crucial for metabolic health.
• Previous studies indicate decreased glucose tolerance with aging.

Purpose of the Study:

• To investigate age-dependent alterations in carbohydrate and lipid metabolism during fasting and refeeding.
• To compare the metabolic responses to fasting and refeeding in young, middle-aged, and aged rats.
• To identify potential mechanisms underlying depressed glycogenesis in aged rats.

Main Methods:

• Fasting and refeeding protocols were applied to rats of three age groups: young (4 months), 1-year-old, and aged (over 24 months).
• Measurements included liver, skeletal muscle, and myocardial glycogen levels, plasma free fatty acid (FFA) concentrations, blood glucose, and plasma glucagon.
• Glycogenesis rates were assessed during the refeeding period.

Main Results:

• Fasting induced similar changes in carbohydrate and lipid substrates across all age groups, including reduced liver and skeletal muscle glycogen, elevated myocardial glycogen, and increased plasma FFA.
• Refeeding led to impaired myocardial and soleus muscle glycogenesis in aged and 1-year-old rats compared to young rats.
• Depressed glycogenesis in aged rats was not linked to altered tissue triglyceride or plasma FFA but was associated with a slightly greater glucagon elevation.

Conclusions:

• Aging significantly affects carbohydrate metabolism, specifically impairing glycogenesis in the heart and skeletal muscle following refeeding.
• The observed decline in glycogenesis with age suggests a broader impact of aging on carbohydrate metabolism than previously recognized.
• Further research is needed to elucidate the precise etiology of age-related deficits in glycogenesis.