Fibronectin turnover in the premature neonate measured with [15N]glycine.

Fibronectin is a large-molecular-weight glycoprotein present on most cell surfaces and in plasma. Plasma fibronectin concentrations in neonates are lower than those in adults and a direct relationship exists between plasma concentration and gestational age. We determined the half-life and fractional synthetic rate (FSR) of plasma fibronectin in the premature infant. Infants and adults received a loading dose of [15N]glycine followed by a constant infusion [15N]glycine incorporation into plasma fibronectin and urine hippurate was determined by gas chromatography-mass spectrometry. The plasma fibronectin FSR in the preterm neonates was 15.5 +/- 9.9%/d(means +/- SD) and the half-life was 5.55 +/- 2.25 d. Birth weight correlated inversely with plasma fibronectin half-life. In the adults the plasma fibronectin FSR ranged from 20 to 87%/d and half-life ranged between 0.79 and 3.47 d. These data suggest that decreased plasma fibronectin levels in preterm infants are due to reduced FSRs rather than to greater turnover of a relatively small plasma pool.