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A developmental switch affecting growth of fatty rats
G E Truett1, J A Walker, R B Harris
1Pennington Biomedical Research Center, Baton Rouge, Louisiana 70808, USA. truettge@pbrc.edu
Insights
Fatty (fa/fa) rats show a developmental switch around 22 days of age. This triggers hyperphagia and rapid growth, leading to obesity.
Area of Science:
- Genetics
- Developmental Biology
- Physiology
Background:
- Fatty (fa/fa) rats accumulate adipose tissue early but appear obese later.
- Understanding the onset of obesity in these rats is crucial for metabolic research.
Purpose of the Study:
- To analyze the effects of the fa genotype on pup growth and physiological changes through 4 weeks of age.
- To identify the developmental timing of significant growth and metabolic alterations in fatty rats.
Main Methods:
- Studied fatty (fa/fa) rat pups housed with dams up to 4 weeks.
- Analyzed daily gain, stomach contents, liver weight, and plasma insulin.
- Investigated effects of litter size reduction on growth patterns.
Main Results:
- Fa genotype effects on daily gain were not significant until 23 days of age.
- A significant genotype by age interaction was observed for growth and physiological markers starting at 23 days.
- Litter size reduction did not alter the timing of these genotype effects.
Conclusions:
- A developmental switch around 22 days of age triggers hyperphagia and accelerated growth in fatty rats.
- This switch occurs independently of environmental changes like pup separation.
- The findings highlight a critical developmental window for the onset of obesity in fa/fa rats.
Abstract:
Fatty (fa/fa) rats accumulate more adipose mass than their littermates soon after birth, but they first appear obese during the fourth week of life. We analyzed the effects of fa genotype on growth of pups housed with their dams through 4 wk of age. The fa genotype effects on daily gain were undetectable from 7 to 22 days of age but became highly significant (P = 10(-18)) at 23 days of age. When litters were reduced to 4 pups, fa genotype effects on daily gain also became detectable at 23 days of age. The fa genotype effects on daily gain, stomach contents weight, liver weight, and plasma insulin of rats killed from 20 to 24 days of age displayed a marked genotype by age interaction, becoming highly significant at 23 days of age. These changes occur without the environmental changes induced by separating pups from their dams. These observations suggest that a developmental switch triggers hyperphagia and rapidly increases growth rate of fatty rats after 22 days of age.