Changes in plasma phospholipids in the presence and absence of erythrocytes 31P-NMR time-course studies

Whole human blood and plasma were incubated at 37 degrees C and 31P-NMR spectra were acquired from aliquots of plasma dissolved in sodium cholate. The narrow resonances of phospholipids were well resolved, allowing identification and accurate quantification of the various phospholipid classes. During the course of plasma incubation, the rate of increase in 2-lysphosphatidylcholine (2-LysoPtdCho) corresponded closely to the rate of decrease in phosphatidylcholine. However, little or no change was observed in the sphingomyelin concentrations. The rate of cholesteryl ester formation in plasma was also determined using HPLC and was observed to be similar to the rate of 2-LysoPtdCho increase in plasma; this is consistent with the rate of acyl transfer from phosphatidylcholine to free cholesterol catalysed by lecithin:cholesterol acyltransferase. However, during the course of whole blood incubation, the rate of 2-LysoPtdCho increase in plasma was significantly lower than the rate of 2-LysoPtdCho production during incubation of plasma alone (31 +/- 4 micromol x 1(-1) x h(-1) and 80 +/- 8 micromol x 1(-1) x h(-1), respectively). The difference between the rates can be attributed to the action of enzymes present in blood cells including those in the erythrocytes that catalyse acylation or hydrolysis of 2-LysoPtdCho.