Plasma and urine carnitine levels during development.

Plasma and urine free carnitine concentration during human development was evaluated. A positive correlation was found between plasma level and body weight in premature neonates weighing between 1.15 and 1.80 kg. In full terms newborns, tbe free carnitine concentration (mean ± S.E., 31.2 ± 2.5. nmoles/ml) is similar to that of premature babies with 33 to 36 wk of gestational age (37.5 ±3.1 nmoles/ml) but significantly lower than that of premature babies aged 30 to 33 wk of gestation (43.0 ± 5.6 nmoles/ml). In the first 2 wk of life, free carnitine level showed a good correlation with age in the full-term newborns. Adult levels are reached by the end of the first 6 months. No sex related difference was observed in any of the different groups during growth. Urinary excretion of free carnitine per day is significantly lower in infants 0 to 3 years old (mean ± S.E., 15.5 ± 1.8 µmoles/24 hr) and in children 3 to 10 years old (115.3 ± 11.4 µmoles/24 hr) than in subjects ranging in age from 22 to 70 years (216.9 ± 20.6 µmoles/24 hr). We found no difference between day- and nighttime urinary excretion in newborns and infants. Speculation: The present observations suggest that fetal free carnitine storage mainly occurs during the 30th to 33rd wk of life. Because the fatty acids are the main energy fuel in the postnatal period and their β-oxidation is carnitine dependent, an exogenous source of this substance seems useful to maintain plasma levels similar to those found in the fetus. The lower free carnitine excretion observed in our children group compared to adult may be related to a smaller muscle mass, different kidney excretion, or reduced endogenous synthesis. © 1980 International Pediatric Research Foundation, Inc.