Jacobs H, Jobe A, Ikegami M, Jones S
J Biol Chem. 1982 Feb 25;257(4):1805-10.
We have measured turnover times for alveolar surfactant phosphatidylcholine in rabbits at 3 and 10 days of age and in adult rabbits. To generate accurate estimates of the turnover time of surfactant phosphatidylcholine from lamellar bodies into the alveolar space, large numbers of rabbits at each age were injected with radiolabeled choline, palmitic acid, and phosphate. Phosphatidylcholine was isolated from lamellar body and surfactant fractions from each rabbit. Curves of specific activity versus time were analyzed using the Zilversmit equations for a two compartment precursor-product model. The curves for each labeled precursor at each age were consistent with the lamellar bodies being the sole precursors of surfactant phosphatidylcholine. The same equations were used to calculate turnover times for surfactant phosphatidylcholine; these were 8-10 h in 3- and 10-day-old rabbits but only 3 h in adult rabbits. From estimates of surfactant phosphatidylcholine pool sizes and turnover times, the flux of surfactant phosphatidylcholine was estimated to be 3.4 mumol/h in adult and 0.48 mumol/h in 3-day-old rabbits; however, the flux expressed/kg of body weight is 2.4 times larger in 3-day-old than in adult rabbits. Finally, the conservation of the radiolabeled precursors in phosphatidylcholine implies reutilization of phosphatidylcholine after synthesis and secretion.
我们已测定了3日龄、10日龄家兔以及成年家兔肺泡表面活性物质磷脂酰胆碱的转换时间。为了准确估计表面活性物质磷脂酰胆碱从板层小体进入肺泡腔的转换时间，每个年龄段的大量家兔被注射了放射性标记的胆碱、棕榈酸和磷酸盐。从每只家兔的板层小体和表面活性物质组分中分离出磷脂酰胆碱。使用两室前体 - 产物模型的齐尔弗斯米特方程分析比活性随时间的曲线。每个年龄段每种标记前体的曲线都与板层小体是表面活性物质磷脂酰胆碱的唯一前体一致。使用相同的方程计算表面活性物质磷脂酰胆碱的转换时间；在3日龄和10日龄家兔中为8 - 10小时，而在成年家兔中仅为3小时。根据表面活性物质磷脂酰胆碱池大小和转换时间的估计，表面活性物质磷脂酰胆碱的通量在成年家兔中估计为3.4 μmol/h，在3日龄家兔中为0.48 μmol/h；然而，以每千克体重表示的通量在3日龄家兔中比成年家兔大2.4倍。最后，磷脂酰胆碱中放射性标记前体的守恒意味着合成和分泌后磷脂酰胆碱的再利用。
