Renal conservation of carnitine by infants and adults: no evidence of developmental regulation.
To determine the efficiency of renal conservation of carnitine in infants, urinary carnitine excretion was measured at intervals in 10 infants while plasma carnitine concentration was manipulated by supplementing carnitine-free formula with 0 microM, 140 microM and 280 microM L-carnitine. As carnitine supplementation increased from 0 microM to 280 microM, fractional excretion of free carnitine increased tenfold from 0.6% to 6.0%; fractional excretion of acylcarnitine esters increased to a lesser degree (10.5-15.6%). At all supplementation levels fractional excretion of acylcarnitine esters was significantly greater than fractional excretion of free carnitine. We conclude that free and esterified carnitine are handled differently in the infant kidney. Results in infants were compared to previously reported data for adults. Mean fractional excretions of total, free and esterified carnitine by infants (7.2%, 5.4% and 12.7%, respectively) were similar to those by adults (6.5%, 5.0% and 15.0%). Thus, renal losses of carnitine apparently do not account for the low plasma carnitine concentrations observed in infants fed carnitine-free formulas.
Olson
A L
AL
Department of Pediatrics, University of Iowa, Iowa City 52242.
Rebouche
C J
CJ
D000328:Adult; D002331:Carnitine / Q000378:metabolism*; D004032:Diet; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate
D002331:Carnitine