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Why are slow and fast muscles differentially affected during prenatal undernutrition?
1Department of Veterinary Basic Sciences, Royal Veterinary College, London, England.
Insights
Maternal dietary restriction in guinea pigs reduced biceps muscle fiber number but not soleus. Soleus fiber deficits were corrected by extended growth, unlike biceps, suggesting primary fiber development is key.
Area of Science:
- Muscle Biology
- Developmental Biology
- Nutritional Science
Background:
- Prenatal undernutrition can impact fetal development.
- Muscle development involves complex processes of fiber hyperplasia and differentiation.
- Fast-twitch (biceps brachii) and slow-twitch (soleus) muscles exhibit distinct developmental patterns.
Purpose of the Study:
- To investigate the effects of maternal dietary restriction on fetal muscle development.
- To compare the impact of undernutrition on fast-twitch and slow-twitch muscle fiber formation.
- To identify developmental mechanisms underlying muscle fiber number differences in response to in utero undernutrition.
Main Methods:
- Guinea pig fetuses from mothers with restricted diets (60% ad lib intake) were compared to controls.
- Biceps brachii and soleus muscles were analyzed for fiber number and fiber type ratios.
- Muscle development was examined at various gestational ages.
Main Results:
- Biceps brachii muscle fiber number decreased by 26% at birth due to undernutrition.
- Soleus muscle fiber number was initially reduced but later corrected through extended secondary fiber hyperplasia.
- Reductions in fiber number correlated with decreased secondary/primary fiber ratios, except where soleus deficits were corrected.
Conclusions:
- Prenatal undernutrition differentially affects fast-twitch and slow-twitch muscle development.
- The resilience of the soleus muscle may be linked to its primary fiber composition and prolonged hyperplasia.
- Primary fiber development appears unaffected by in utero undernutrition, influencing muscle's capacity for recovery.
Abstract:
The biceps brachii and soleus muscles (fast and slow twitch muscles, respectively) were taken from guinea-pig fetuses, undernourished via maternal dietary intake to 60% of ad lib, and examined for differences from their controls. At birth, muscle fiber number was found to be reduced by 26% in the biceps brachii but was unaltered in the soleus muscle. An examination of the muscles at ages through gestation revealed that any reduction in fiber number was associated with a reduction in the secondary/primary fiber ratio. There was a stage in soleus myogenesis at which fiber number was significantly lower than the control. The deficit was corrected by the continuation of secondary fiber hyperplasia beyond the time of usual cessation. A similar delay was found in the biceps brachii but it did not enable recovery to a full complement of fibers. The difference between the 2 muscles was thought to be related to the relative proportions of primary fibers in the muscles, primary fiber development being apparently unaffected by undernutrition in utero.