Energy intake and utilization vary during development in rats.

Area of Science:

• Physiology
• Metabolic studies
• Animal models

Background:

• Understanding energy balance is crucial for metabolic health.
• Age-associated changes in energy metabolism can lead to obesity.
• Wistar rats are a common model for studying metabolic processes.

Purpose of the Study:

• To investigate energy intake, utilization, and partitioning in male Wistar rats during growth and aging.
• To determine the factors contributing to age-associated obesity in rats.
• To assess the role of leptin resistance in weight regulation.

Main Methods:

• Longitudinal measurements of energy intake, expenditure, and body composition in male Wistar rats from 25 to 180 days of age.
• Analysis of serum concentrations of free triiodothyronine, leptin, and free fatty acids.
• Evaluation of energy balance to identify distinct growth and fat storage phases.

Main Results:

• Two distinct periods were identified: rapid growth (25-90 d) with lipid and protein storage, and slowed growth (90-180 d) with fat accumulation.
• Daily energy intake and expenditure decreased with age, particularly before 90 days.
• Protein deposition ceased in the second period, with excess energy stored as fat, leading to obesity.
• Resting metabolism did not decrease; instead, partial leptin resistance contributed to the inability to maintain stable body weight.

Conclusions:

• Age-associated obesity in Wistar rats is characterized by a shift in energy partitioning towards fat storage.
• Reduced energy intake and expenditure, coupled with partial leptin resistance, are key factors in weight gain post-growth.
• Leptin resistance, rather than diminished resting metabolism, underlies the failure to maintain body weight stability in aging rats.