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Surfactant- associated protein B (SP- B) is critical to the biophysical fun ction of pulmonary surfactant. No information is available on SP- B synthesis a nd kinetics in humans. We administered a 24- h i.v. infusion of 13C- valine as metabolic precursor of SP- B to six newborn infants (weight 3.5 ± 0.5 kg; ag e 12 d, range 1- 43 d). Three of the study infants also received i.v. 2H- palm itate to label surfactant disaturated phosphatidylcholine (DSPC). SP- B and DSP C were isolated from tracheal aspirates, and their respective 13C and 2H enrichm ents were measured by gas chromatography- mass spectrometry. SPB kinetics was m easured successfully in all six infants. SP- B median (range) fractional synthe sis rate was 30% per day (20- 78% per day), secretion time was 4.5 h (1- 9 h), time to peak was 24 h (12- 36 h), and half- life was 21 h (8- 35 h). The ascending part of the SP- B kinetic curve was similar to the DSPC curve, sugge sting similar secretion pathways. SP- B half- life seemed to be shorter than D SPC half- life. These results agree with existing animal data. We conclude that the measurement of SP- B kinetics is feasible in vivo in humans by stable isot ope technology.
No information is available on SP-B synthesis a nd kinetics in humans. We administered a 24-h iv infusion of 13C-valine as metabolic precursor of SP-B to six newborn infants (weight 3.5 ± 0.5 kg; ag e 12 d, range 1-43 d). Three of the study infants also received iv 2H-palm itate to label surfactant disaturated phosphatidylcholine (DSPC). SP - B and DSP C were isolated from tracheal aspirates, and their respective 13C and 2H enricm ents were measured by gas chromatography- mass spectrometry. SPB kinetics was m easured successfully in all six infants. SP- B median (range) fractional synthe sis rate was 30% per day (20-78% per day), secretion time was 4.5 h (1- 9 h), time to peak was 24 h (12- 36 h), and half-life was 21 h h). The ascending part of the SP- B kinetic curve was similar to the DSPC curve, sugge sting similar secretion pathways. SP- B half- life seeme These results agree with existing animal data. We conclude that the measurement of SP-B kinetics is feasible in vivo in humans by stable isotope technology.