PLASMA LIPOPROTEIN METABOLISM IN PERFUSED RAT LIVERS. I. PROTEIN SYNTHESIS AND ENTRY INTO THE PLASMA*

Abstract

The incorporation of C14-lysine into ultracentrifugally separated low density (D< 1.063) and high density (D < 1.063-1.21) lipoprotein fractions was studied. The specific activity of the low density lipoprotein was four times that of the high density lipoproteins, while the albumin had lower specific activity than either lipoprotein fraction. Marked alteration of cholesterol synthesis induced by whole body irradiation or by prefeeding the liver donor with a 5% cholesterol containing diet did not influence lipoprotein synthesis. Perfusion of normal livers with blood from cholesterol-fed rats significantly increased the incorporation of labeled amino acids into the low density lipoprotein fraction. When the low density lipoproteins were further separated at density 1.019, it was found that the D<1.019 fraction had a much higher specific activity than the D < 1.019-1.063 or the D < 1.063-1.21 lipoprotein fractions.