Plasma carnitine concentration and lipid metabolism in infants receiving parenteral nutrition

The relationships among plasma total carnitine concentration, postnatal age, and fatty acid metabolism were evaluated in 57 infants receiving parenteral nutrition. Concentrations of plasma carnitine, triglycerides, free fatty acids, acetoacetate, and beta-hydroxybutyrate were determined before and at 2 and 4 hours from the beginning of a standardized 2-hour lipid infusion. Plasma carnitine concentrations declined with increasing postnatal age. There were no significant differences in gestational age or triglyceride concentrations between infants less than or equal to 4 weeks of age and those greater than 4 weeks of age, whereas free fatty acid concentrations were lower and acetoacetate and beta-hydroxybutyrate concentrations were higher in the younger infants. Infants less than or equal to 4 weeks of age were further grouped according to plasma carnitine concentration greater than 13 nmol/ml (group 1) and less than or equal to 13 nmol/ml (group 2) and were then compared with infants greater than 4 weeks of age (group 3). There were no significant differences in triglyceride concentrations among the three groups; free fatty acids, acetoacetate, and beta-hydroxybutyrate concentrations for group 2 patients were similar to those of group 1 patients or fell between values for group 1 and group 3 patients. These results demonstrate decreasing plasma carnitine concentrations and possibly for more than 4 weeks.