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Carnitine status and blood ammonium levels in low birth weight infants
T Nakamura1, S Nakamura, Y Kondo
1Department of Pediatrics, Kumamoto University Medical School, Japan.
Insights
Carnitine levels decrease in low birth weight infants with elevated blood ammonium. Impaired renal carnitine reabsorption and acylcarnitine accumulation contribute to this deficiency, suggesting carnitine may regulate ammonium levels.
Area of Science:
- Neonatal physiology
- Nutritional biochemistry
Background:
- Low birth weight infants often exhibit altered metabolic profiles.
- Carnitine plays a crucial role in fatty acid metabolism and ammonia detoxification.
Purpose of the Study:
- To investigate the relationship between carnitine status and blood ammonium levels in low birth weight infants.
- To explore the mechanisms underlying carnitine deficiency in this population.
Main Methods:
- Monitoring of 43 appropriate for gestational age low birth weight infants.
- Grouping infants based on blood ammonium levels on postnatal day 7.
- Analysis of plasma free carnitine, short chain acylcarnitine, renal reabsorption of free carnitine (RRFC), and acylcarnitine/free carnitine clearance ratio (RAFCC).
Main Results:
- Plasma free carnitine decreased in all infants compared to normal controls.
- Plasma short chain acylcarnitine increased in infants with the highest ammonium levels.
- Blood ammonium positively correlated with short chain acylcarnitine and negatively with free carnitine.
- Decreased RRFC and RAFCC were observed in infants with higher ammonium levels.
Conclusions:
- Accumulation of short chain acyl moieties and reduced renal reabsorption of free carnitine are potential causes of low plasma free carnitine in infants with elevated blood ammonium.
- Carnitine status may play a regulatory role in blood ammonium levels in low birth weight infants, warranting further research.
Abstract:
Forty-three low birth weight infants appropriate for gestational age (AGA) were monitored to evaluate carnitine status in relation to blood ammonium levels. The infants were grouped into three depending on blood ammonium level on postnatal day 7: 62.9 +/- 3.8 mumol/L in group 1 (N = 13), 38.9 +/- 8.4 mumol/L in group 2 (N = 23), and 24.5 +/- 2.9 mumol/L in group 3 (N = 9). Plasma free carnitine levels decreased in all three groups (p less than 0.001) and plasma short chain acylcarnitine increased only in group 1 (p less than 0.002), compared to findings in normal infants. The blood ammonium level positively and negatively correlated to plasma short chain acylcarnitine (p less than 0.002) and plasma free carnitine levels (p less than 0.002), respectively. The reabsorption rate of free carnitine in renal tubules (RRFC) was decreased at rates of 37.5, 27.5, and 25% of infants in groups 1, 2, and 3, respectively. The acylcarnitine/free carnitine clearance ratio (RAFCC) was decreased in groups 1 (p less than 0.01) and 2 (p less than 0.05) compared with group 3. Thus, an accumulation of short chain acyl moieties and insufficiency in renal absorption of free carnitine are putative causes of lowered plasma free carnitine in infants with higher blood levels of ammonium. The possibility that the carnitine status regulates blood ammonium levels in low birth weight infants warrants continued investigation.