Effect of dietary polyunsaturated phospholipid on the chemical composition of serum lipoproteins in rat.

The effect of soybean phospholipid (SP), given at the rate of 100/g/kg diet for 2-3 weeks, on the chemical composition of serum lipoprotein in rats was examined. Soybean oil (SO) containing almost comparable amounts of linoleic acid was used as a control diet. SP significantly decreased the concentration of serum cholesterol and apolipoprotein A-I (apo A-I) and increased apolipoprotein B (apo B). There was no significant change in the concentration of serum apolipoprotein E (apo E) and the other lipids. The reduction of cholesterol levels in all the lipoprotein fractions was observed. The reduction of the serum apo A-I was brought about by the addition of SP at the level of 1% while that of the cholesterol at the level of 4%. The subunit composition of apo A-I, but not apolipoprotein C, in high density lipoprotein (HDL) was also altered by SP. The high molecular weight of apo B was responsible for the increment of apoproteins in the low density lipoprotein (LDL). The triglyceride, but not the cholesterol ester, also increased in LDL. there was no significant difference between the groups in the fatty acid compositions of serum triglyceride and phospholipid. In the liver, SP significantly increased the concentration of cholesterol ester and decreased triglyceride. These results are discussed in the context of the role of the lipoprotein and apoprotein in the regulation of serum cholesterol concentration.