Studies of factors influencing alveolar lining layer formation in lung homogenate: further isolation and identification of interfering materials.

Materials which inhibit the formation of stable alveolar lining layer by lung surfactant were investigated with the pig lung homogenate. The inhibitory activity was assessed by the bubble stability test on the bubbles formed by mechanical agitation of a mixture of surface active fraction from lung homogenate and inhibitory materials. The most active inhibitory material was identified as free cholesterol. Free fatty acids had a remarkable inhibitory activity. By modified Wilhelmy balance, it was demonstrated that the addition of free cholesterol to the surface active fraction delayed the formation of the stable surface membrane and at a larger dosage it inhibited the lowering the surface tension at the minimum surface area. The significance of this phenomenon in pathological lungs was briefly discussed.