Activities of enzymes of phospholipid and fatty acid synthesis in fetal and adult rat type II pneumocytes

Although differentiated fetal and adult type II pneumocytes are ultrastructurally similar, it is not known whether there are metabolic differences between them. We measured the activities of selected enzymes of phospholipid and fatty acid synthesis in fetal and adult rat type II cells, in late gestation fetal rat lung expiants and in intact lung from rat fetuses of comparable gestational age. The activity of 1-acylglycerophosphocholine acyltransferase was significantly greater in adult type II cells than in fetal type II cells, fetal expiants or intact fetal lung. The activity of CDPdiacylglycerol glycerol 3 phosphate 3 phosphatidyltransferase was similar in fetal and adult type II cells, but significantly lower in expiants and intact fetal lung. There was a significant positive correlation between the percentage of alveolar epithelial cells in the cultures and tissue studied and CDPdiacylglycerol glycerol 3 phosphate 3 phosphatidyltransferase activity. This suggests that the previously reported correlation between phosphatidylglycerol synthesis and the percentage of alveolar epithelial cells in various lung culture systems may be related to the activity of this enzyme. Phosphatidylglycerol synthesis and CDP diacylglycerol glycerol 3 phosphate 3 phosphatidyltransferase activity may be metabolic markers of type II cells, whereas the acyltransferase activity may be an indicator of type II cell maturation.