Composition and Surface Activity of Normal and Phosphatidylglycerol-Deficient Lung Surfactant

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Abstract
The possibility that pulmonary surfactant, characterized by a phosphatidylglycerol deficiency, as in early fetal life, might have inferior surface properties was evaluated. We obtained this specific surfactant from adult rabbits by withholding glucose and giving them an excess of myoinositol by mouth and intravenously. Controls were given a similar quantity of glucose. The myoinositol resulted in a drastic reduction of surfactant phosphatidylglycerol, from 7.2 to 0.3% of phospholipids, and a corresponding increase in phosphatidylinositol from 4.8 to 11.3%. In addition, the myoinositol treatment increased the myoinositol that was disaturated from 18.5 to 27.3% (p < 0.05). The corresponding figures for disaturated phosphatidyl- choline were 56.0 and 60.5%, respectively (NS). The myoinositol treatment for 4 days increased the pool size of alveolar surfactant by 32% (p < 0.01). The surface activity was studied with modified Wilhelmy balance and the pulsating bubble surfactometer. Surfactant containing phosphatidylinositol rather than phosphatidylglycerol was not inferior, as compared to surfactant that contained phosphatidylglycerol (minimum surface tension: 2.0 versus 2.2 mN·m-1; collapse rate at 10 nM·m-1: 1.85 versus 1.95 min-1; rate of adsorption from subphase to surface: 32 versus 35 mN·m-1·30 s-1), nor was there a difference in the ability of the two surfactants to improve lung stability of 27-day-old rabbit fetuses (air retention at 35 cm H2O: 1.8 versus 1.8 ml/30 g; air retention at 0 cm H20: 0.8 versus 0.9 ml/30 g). We conclude that phosphatidylinositol surfactant does not have inferior surface properties. Myoinositol affects not only the acidic surfactant phospholipids but also increases the pool size of surfactant by an as yet unknown mechanism.