RENAL HANDLING OF CARNITINE IN ILL PRETERM AND TERM NEONATES

Objective: To investigate the renal handling of carnitine in preterm a nd term ill neonates. Methods: We studied the fractional tubular reabs orption of carnitine and the proximal renal tubular function of infant s in the first week of life who were receiving very little or no carni tine in their diets. Results: Mean plasma levels were low: total carni tine was 16.4 +/- 7.0 mu mol/L, free carnitine was 9.2 +/- 5.0 mu mol/ L, and acylcarnitine was 7.2 +/- 4.1 mu mol/L. The most premature grou p of neonates (gestation age, 26 to 31 weeks) had a fractional tubular reabsorption rate of free carnitine of 94.3% +/- 3.3%, which was lowe r than in the other two groups (98.1% +/- 2.4% for gestational age 32 to 36 weeks, p = 0.001; and 99.2% +/- 0.6% for gestational age 37 to 4 2 weeks, p = 0.002). In all patients the fractional tubular reabsorpti on of acylcarnitine was lower than that of free carnitine, indicating possible tubular secretion of acylcarnitine. It correlated with the to tal plasma carnitine levels (r = 0.53; p = 0.002). The fractional tubu lar reabsorption of free carnitine also correlated with gestational ag e (r = 0.60; p < 0.001). Conclusions: III neonates have a fractional t ubular reabsorption rate of free carnitine within the normal range. It increases with gestational age, and has the same maturation rate as t he other known indexes of proximal tubular function.