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Leucine kinetics after a brief fast and in response to feeding in premature infants
S C Denne1, C A Karn, E A Liechty
1Department of Pediatrics, Indiana University School of Medicine, Indianapolis 46202-5210.
Insights
Feeding preterm infants suppresses protein breakdown, not increases protein synthesis. This study on leucine metabolism in premature newborns reveals how feeding impacts protein turnover during fasting and feeding periods.
Area of Science:
- Neonatal physiology
- Nutritional biochemistry
- Pediatric metabolism
Background:
- Understanding protein metabolism is crucial for preterm infant growth.
- Leucine kinetics provide insights into protein synthesis and breakdown.
- Feeding strategies significantly influence neonatal metabolic responses.
Purpose of the Study:
- To investigate the impact of feeding on leucine and protein metabolism in preterm infants.
- To determine whether feeding increases protein synthesis or decreases protein breakdown.
- To explore correlations between fasting and feeding metabolic rates.
Main Methods:
- Leucine kinetics were measured in nine preterm infants (32 +/- 2 wk gestation).
- Measurements were taken during a brief fasting period and hourly during feedings.
- Rates of leucine oxidation, nonoxidative disposal (synthesis), and endogenous release (breakdown) were analyzed.
Main Results:
- Leucine oxidation rates remained similar between fasting and feeding periods.
- Nonoxidative leucine disposal (protein synthesis) showed no significant change with feeding.
- Feeding significantly reduced leucine release from endogenous protein (protein breakdown) (P = 0.02).
- Fasting protein breakdown rates correlated positively with feeding suppression.
- Fasting protein synthesis rates correlated inversely with feeding response.
Conclusions:
- Preterm infants suppress protein breakdown in response to feeding after fasting.
- Feeding impacts protein metabolism by reducing breakdown rather than stimulating synthesis.
- Fasting metabolic rates influence the response to feeding in premature newborns.
Abstract:
To examine how feeding affects changes in leucine and protein metabolism, leucine kinetics were determined in nine preterm infants (32 +/- 2 wk gestation; mean +/- SD) after a brief fast and again during hourly feedings. Rates of leucine oxidation were similar during the fasting and feeding periods (31 +/- 4 vs 37 +/- 6 mumol.kg-1.h-1; mean +/- SE). The nonoxidative disposal rates of leucine (a reflection of protein synthesis) were also similar during both periods (228 +/- 20 vs 205 +/- 10 mumol.kg-1.h-1; mean +/- SE). In contrast, the rates of leucine release from endogenous protein (an indication of protein breakdown) were significantly reduced by feeding (259 +/- 23 vs 185 +/- 11 mumol.kg-1.h-1; mean +/- SE, P = 0.02). A significant positive correlation was demonstrated between the fasting rate of leucine release from endogenous protein and the degree of suppression produced by feeding (r2 = 0.796, P = 0.001). Conversely, a significant inverse correlation was shown between the nonoxidative disposal rate of leucine during fasting and the increase in response to feeding (r2 = 0.848, P < 0.001). These data suggest that premature infants respond to feeding after a brief fast by suppressing protein breakdown, rather than by increasing protein synthesis, and changes in protein metabolism produced by feeding in premature newborns may be influenced by the prevailing rates of protein breakdown and synthesis during fasting.