Acetylcarnitine and free carnitine in body fluids before and after birth.

The acetylcarnitine concentration in amniotic fluid fell significantly between 33 and 37 and 40 weeks of gestation. It was significantly higher in samples that had a low lecithin to sphingomyelin ratio. The acetylcarnitine content of tracheal fluid was higher in samples obtained from premature newborns. The major excretory form of carnitine is the acetate ester and only in adults does the urine contain significant amounts of free carnitine. The level of acetylcarnitine in plasma significantly increases after the first day of life; there was no difference in the plasma levels of carnitine between full-term and premature newborns. Plasma-free carnitine and acetylcarnitine levels were significantly lower in infants who were receiving a soybean-based formula. A positive correlation was found between the plasma level of ketone bodies and that of acetylcarnitine.