Turnover Rates of Fatty Acids of Plasma Triglyceride, Cholesterol Ester and Phospholipid in the Postabsorptive Dog

Abstract

The half-life times of plasma phospholipid and nonphospholipid fatty acids were determined in postabsorptive dogs using C14-carboxyl-labeled palmitic acid. Labeled plasma lipids were introduced into the blood of a recipient dog by cross-circulation with a donor dog that had been fed the radioactive palmitic acid 24 hours previously. Blood samples were taken at various time intervals after the cross-circulation was completed. When the specific activity of the nonphospholipid fatty acids was plotted against time, a semilogarithmic curve was obtained that was resolved into two exponential components with mean half-life times of 22.3 ± 21.9 (S.D.) and 905 ± 182 (S.D.) minutes. A half-life time of 327 ± 81 (S.D.) minutes was found for the phospholipid fatty acids. In one experiment the nonphospholipid fat was further fractionated chromatographically into triglycerides and cholesterol esters. The half-life times of the fatty acids of these two fractions were comparable to the values obtained for the fast and slow components, respectively, found in the preceding experiments. The turnover rate of the triglyceride fatty acids was 1502 ± 505 (S.D.) mg/hr. The rate of appearance of the cholesterol ester fatty acids into the plasma was 29.0 ± 32.7 (S.D.) mg/hr.; the rate of disappearance, 63.4 ± 38.0 (S.D.) mg/hr. A turnover rate of 125.2 ± 49.2 (S.D.) mg/hr. was found for the phospholipid fatty acids in the earlier experiments. The large turnover rate of the plasma triglyceride fatty acids strongly suggests that this fraction is important in the transport of fatty acids in the postabsorptive dog.