Protein Composition of Synthetic Surfactant Affects Gas Exchange in Surfactant-Deficient Rats. † 1619

Synthetic surfactant peptides offer an opportunity to standardize the protein composition of surfactant. We tested the effect of a standard phospholipid mixture (PL), PL + 3% full length SP-B_1-78 (B), PL + 3% SP-B_1-78 & 1% palmitoylated SP-C_1-35 (BC), PL + 3% of SP-B_1-78 with serine substituted for the cationic residues lysine and arginine in the native sequence (B_ser), PL + 3% KL₄(KL₄), and PL + 3% SP-B_1-78 & 1% KL₄ (BKL₄) on oxygenation and lung function in a surfactant-deficient rat model. Sixty-four adult rats (200-225 g) were intubated and ventilated with 100% oxygen, a tidal volume of 7.5 ml/kg, and a rate of 60/min. Their lungs were lavaged with saline until the PaO₂ dropped below 80 torr, at which time 100 mg/kg of surfactant was instilled. After 60 min of ventilation, pressure-volume curves were performed in situ. All surfactant preparations had minimum surface tensions <10 mN/m, hystereses of 19-26 cm² (except for PL), and a reproducibility of 51-77% (except for KL₄) on a modified Langmuir/Wilhelmy balance. Instillation of PL, B_ser, and BKL₄ increased mean arterial/Alveolar PO₂ ratios by 50-100% over post-lavage values. KL₄ increased mean arterial/Alveolar PO₂ ratios by 118%, B by 191%, and BC by 225%. Lung volumes at 30 cm H₂O pressure were highest after treatment with BC, intermediate after treatment with B, KL₄, and PL, and lowest after treatment with BKL₄ and B_ser. These data suggest that a combination of synthetic surfactant peptides B and C surpasses KL₄ in improving oxygenation and lung compliance in surfactant-deficient rats.