Thomas Olivecrona

Mechanisms for removal of chyle triglyceride from the circulating blood as studied with [14C]glycerol and [3H]palmitic acid-labeled chyle

Abstract Chyle containing triglyceride labeled both in the glycerol (14C) the fatty acid (3H) moiety was injected into carbohydrate-fed male rats, and tissue-lipid radioactivity studied at several time intervals. The liver at short times contained mainly labeled neutral lipids with a ratio 14C/3H of 0.7–0.8. At later times, this ratio decreased fatty acid label entered into the phospholipids. It is argued that these data are compatible with the view that the liver contained unchanged chyle triglyceride and in addition triglycerides phospholipids formed from fatty acids released upon hydrolysis of the chyle triglyceride. The adipose tissue showed ratios 14C/2H below 0.3, and it is argued that this tissue probably took up mainly fatty acids released on hydrolysis of the chyle triglyceride, probably by lipoprotein lipase in the adipose tissue. The data on the other tissues indicate that the spleen, the lungs, and the small intestine, like-the liver, can remove intact chylomicron triglyceride from the circulating blood. The skeletal muscle the heart, on the other h, take up mainly fatty acids liberated on hydrolysis of the chyle triglyceride, and in this respect resemble the adipose tissue. The kidney gave intermediary data may use both mechanisms.

Radioactivity in blood and liver partial glycerides, and liver phospholipids after intravenous administration to carbohydrate-fed rats of chyle containing double-labeled triglycerides.

Abstract A chromatographic method permitting fast and complete separation of all nonphospholipid fractions in rat blood and liver except for 1,2-diglycerides from cholesterol, and 1- from 2-monoglycerides is described. The level of radioactivity and the ratio 14C/3H were determined in partial glycerides and free fatty acids from blood and liver and in liver phospholipids at short time intervals after the intravenous injection into carbohydrate-fed rats of chyle containing triglycerides labeled with [14C]glycerol and [3H]palmitic acid. The ratios 14C/3H in blood partial glycerides showed that they were not formed by breakdown of chyle triglycerides in the circulating blood, but were probably original constituents of the chyle. The sum of 3H radioactivity in partial glycerides and free fatty acids in the liver never exceeded one tenth of the total 3H radioactivity in this organ. The ratios 14C/3H in the labeled liver partial glycerides indicated that these were mainly formed during the resynthesis of triglycerides and phospholipids. There was a progressive rise of fatty acid radioactivity in the liver phospholipids. Only a small amount of 14C radioactivity was found in these—slightly relatively more in the phosphatidyl ethanolamine than in the phosphatidyl choline fraction.

Metabolism in the rat of chyle obtained after feeding hydrogenated coconut oil labeled with stearic acid.

1. 1. Chyle with a high content of saturated fatty acids, labeled with [3,4-3H2]-stearic acid, was obtained from a thoracic duct cannulated rat fed hydrogenated coconut oil. The chyle was injected intravenously into carbohydrate re-fed rats and the blood and tissue radioactivity studied. 2. 2. The rate of disappearance from the blood and the tissue distribution of the label was quite similar to that obtained in experiments with corn-oil chyle. 3. 3. For a short time most of the label in the liver was in non-phospholipid stearic acid. Then increasing amounts appeared in the phospholipids, and label appeared in oleic acid in both phospholipids and non-phospholipids. 4. 4. By 160 min the relative proportion of labeled oleic to labeled stearic acid was 4 in the liver non-phospholipids and 0.28 in the liver phospholipids. These figures are quite similar to those obtained in experiments with stearic acid administered as free fatty acid. 5. 5. It is concluded that the chyle triglycerides are removed by the liver without immediate breakdown. The trapped chyle is then the substrate for a system that liberates stearic acid in a form rendering its subsequent metabolism involving desaturation and distribution between ester fractions indistinguishable from that of stearic acid injected as the albumin complex.

The metabolism of [3H]oleic acid in the partially hepatectomized rat

Abstract [ 3 H]Oleic acid complexed to rat serum or 5% bovine serum albumin was injected intravenously into partially hepatectomized or laparotomized rats. The fractional turnover rates for the injected label in the two groups was calculated, labeling of liver and carcass lipids 2 min after injection were studied, and the concentrations of liver glycerides, phospholipids, and plasma free fatty acids were measured at this time. 1. 1. The fractional turnover rate of plasma free fatty acids was significantly decreased by partial hepatectomy. In spite of this the flux of plasma free fatty acids per min remained essentially unchanged. 2. 2. Liver glyceride and plasma free fatty acid concentrations were significantly increased by partial hepatectomy while liver phospholipid concentration was unaffected. 3. 3. More label was found in liver lipids in the partially hepatectomized group per g wet tissue, and a much higher proportion of this radioactivity was in the non-phospholipid fraction as compared to the laparotomized group. It is suggested that an increased incorporation of plasma free fatty acids into liver triglycerides is the major factor in the liver fat accumulation after partial hepatectomy.