EFFECT OF ACIDOSIS ON BILIRUBIN-LIPID EXTRACT SURFACTANT INTERACTION

The risk of bilirubin toxicity in newborn infants with respiratory dis tress syndrome and hyperbilirubinemia may depend on many factors inclu ding pH of the system. Biophysical activity and inhibition characteris tics were studied in vitro for lipid extract surfactant (Curosurf, 0.2 5 mg/ml phospholipids), bilirubin (1.0 mg/ml dissolved in NaOH) and mi xed solutions at different pH ranging from 5.0 to 7.4. It was found th at unconjugated bilirubin modifies surface tension behavior of lipid e xtract surfactant films. Maximum and minimum surface tension levels we re significantly higher in mixed solutions compared to experiments usi ng pure Curosurf independently from pH. Film area compression for pure Curosurf was not influenced by pH and varied between 22 +/- 4% at pH 5.0 and 23 +/- 9% at pH 7.4. Adding bilirubin to lipid extract surfact ant, area compression to achieve minimum surface tension increased sig nificantly to 83 +/- 4% at pH 5.0 and 85 +/- 4% at pH 7.4 (p < 0.01). Bilirubin alone showed negligible surface activity independently from pH (83 +/- 7% at pH 5.0 and 78 +/- 9% at pH 7.4) (p > 0.5). We conclud e that bilirubin has a detrimental effect on the surface tension prope rties of lipid extract surfactant in vitro and that this interaction i s independent from pH. These data suggest no influence of acidosis on alveolar surfactant system in babies with respiratory distress syndrom e and hyperbilirubinemia.