Influence of human low density and high density lipoprotein cholesterol on the in vitro prostaglandin I2 synthetase activity.

We investigated in vitro the influence of low density lipoprotein (LDL) cholesterol and high density lioprotein (HDL) cholesterol separated from human serum on prostaglandin I2 synthetase activity studied by the conversion of prostaglandin H2 to prostaglandin I2 by the microsomal fraction of pig aorta. 6-Oxo-prostaglandin F1 alpha was analyzed by gas-liquid chromatography using prostaglandin F1 alpha as internal standard. We found a linear negative correlation (P less than 0.001) between the amount of LDL cholesterol in the incubation solution and prostaglandin I2 synthetase activity, whereas there was a positive correlation (P less than 0.01) between HDL cholesterol and prostaglandin I2 synthesis. A very low concentration of LDL cholesterol and a high concentration of HDL cholesterol stimulated prostaglandin I2 synthesis, whereas a high LDL cholesterol concentration inhibited prostaglandin I2 biosynthesis by 64%. The concentration range of LDL and HDL cholesterol was representative of physiologically low, normal or elevated levels of lipoproteins.