Phosphatidylcholine- Lysophosphatidylcholine Cycle Pathway Enzymes in Rabbit Lung. II. Marked Differences in the Effect of Gestational Age on Activity Compared to the CDP-Choline Pathway

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Abstract
Summary: Lysophosphatidylcholine (lysoPC), a breakdown product of phosphatidylcholine (PC), might be important in pulmonary PC synthesis through fatty acid exchange reactions. This study defines the levels of three of the enzymes of the PC-lysoPC cycle pathway (lysophospholipase (LPL) (EC. 3.1.1.5), lysophosphatidylcholine-lysophosphatidylcholine acyltransferase (LAT), and acyl-CoA lysophosphalidylcholine acyltransferase (acryl-CoA LAT) (EC. 2.3.1.23)) in developing fetal rabbit lung and compares them with the enzymes of the CDP-choline synthetic pathway (choline kinase (CK) (EC. 2.7.1.32), phosphorylcholine cytidyl transferase (CyT) (EC. 2.7.7.15), and phosphorylcholine glyceride transferase (PCGT) (EC. 2.7.8.2)). Lung homogenates of fetal rabbits of known gestation, newborn, and adult rabbits were used for the enzyme, protein, and phospholipid analyses. Total lung phospholipid, PC, and protein increased with gestational age. Thirty days' gestation, newborn, and maternal lung activities of CK, CyT, and PCGT had decreased to only 50% of their activities at 22–26 days' gestation. In contrast, LPL and LAT activities increased 4–5− fold from 22–26 days to 30 days' gestation, and increased further in the newborn lung, finally to a level matching maternal lung (about 8–10-fold higher than the 22–26 days' gestation activities). The microsomal acyl-CoA LAT also snowed a similar increasing activity with gestational age. In fetal rabbit lung, enzymic activities for the apparent major PC synthetic pathway decreased. In contrast, the marked increases in LPL, LAT, and acyl-CoA LAT activities with increasing gestational age and at birth suggests importance of the PC- lysoPC cycle pathway in regulating synthesis and turnover with maturation. Speculation: There are marked increases in lung lysoPC cycle pathway enzymes with gestational and postnatal ages. This finding suggests that this cycle pathway is very important in pulmonary maturation and in the formation of surface-active dipalmitoyl- PC.

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