Triacylglycerol and very low density lipoprotein secretion into plasma of squirrel monkeys

The plasma level of triacylglycerols in horses fed high-fat diets containing either soybean oil or palm oil

The influence of dietary soybean oil versus palm oil on the plasma level of triacylglycerols was determined in a crossover experiment with four horses. Based on published data for humans and laboratory animals it was expected that a diet rich in unsaturated fatty acids in the form of soybean oil compared to saturated fatty acids in the form of palm oil would lower the plasma triacylglycerol level. The feeding of soybean oil versus palm oil for a period of four weeks did not change the level of plasma triacylglycerols in horses. Mean levels of triacylglycerol, free fatty acids and 3-hydroxybutyrate were 0.17 (SE, 0.04), 0.44 (SE, 0.063) and 0.16 (SE, 0.008) mmol/l, respectively. The fatty acid composition of the plasma triacylglycerols reflected the fatty acid composition of the diets. The activity of lipoprotein lipase was not different between the treatments. It is concluded that, under the present experimental conditions, the feeding of soybean oil to horses does not affect triacylglycerol secretion into plasma and thus does not influence the concentration of plasma triacylgycerols, when compared to the feeding of palm oil.

Use of a nonionic detergent (Triton WR 1339) in healthy cats to assess hepatic secretion of triglyceride

OBJECTIVE

To determine whether a nonionic detergent (Triton WR 1339) can be used in cats to assess hepatic secretion of triglyceride.

ANIMALS

28 healthy cats.

PROCEDURE

Triton WR 1339 was administered IV according to the following schedule: 5, 50, 150, and 250 mg/kg of body weight. Control cats did not receive an injection or received 0.9% NaCl or PBS solutions at the same osmolarity and volume as the 250 mg/kg group. Blood samples were collected throughout the 48-hour period after administration for determination of triglyceride and cholesterol concentrations and for RBC morphology and osmotic fragility studies.

RESULTS

Administration of Triton WR 1339 at 150 and 250 mg/kg caused profound hypertriglyceridemia. Triglyceride concentrations increased in a curvilinear fashion for the first 2 hours and remained increased for approximately 24 hours. Area under the time-concentration curve for triglyceride at 5 hours differed significantly among groups. At 12 and 24 hours, cholesterol was significantly higher in cats receiving 250 mg/kg. The most dramatic changes in osmotic fragility and RBC morphology were in cats receiving 250 mg/kg; 1 of these cats developed severe icterus and died 5 days later. Feeding rice and casein before administering Triton WR 1339 at 150 mg/kg did not appear to affect the hypertriglyceridemia response.

CONCLUSIONS AND CLINICAL RELEVANCE

Triton WR 1339 can be administered IV to cats at a rate of 150 mg/kg to assess hepatic triglyceride secretion, although some cats may have increased RBC osmotic fragility. Higher dosages caused substantial adverse effects, whereas lower dosages did not alter plasma triglyceride concentration.

Effects of Triton WR 1339 and orotic acid on lipid metabolism in rats

In order to investigate the effect of hepatic cholesterol flux on biliary bile acids, Triton WR 1339 and orotic acid were administered to rats, and the biliary cholesterol, phospholipids and bile acids were analyzed together with serum lipoproteins and hepatic lipids. Triton, which raised serum very low density lipoprotein and lipid levels and decreased serum high density lipoprotein liver lipid levels, increase the biliary cholic acid group/chenodeoxycholic acid group ratio (CA/CDCA) in the bile without affecting the total amount of bile acids and the other biliary lipids. Orotic acid, which decreased serum lipid and lipoprotein concentrations and increased liver lipid levels, increased the biliary excretion of cholesterol and phospholipids, but produced no significant change in the total amount of bile acids and in the CA/CDCA ratio in bile.

In vitro and in vivo interactions of Triton 1339 with plasma lipoproteins of normolipidemic rhesus monkeys. Preferential effects on high density lipoproteins

Triton WR-1339 was incubated in vitro in various proportions with plasma from normolipidemic rhesus monkeys or with ultracentrifugally purified lipoproteins, and the products were examined by isopycnic density gradient ultracentrifugation, agarose column chromatography, electrophoretic and immunochemical techniques, and electron microscopy. Some experiments used apo A-I, apo A-II, or Triton labeled with either 125I or 131I. At concentrations of less than 10 mg/ml plasma, Triton interacted preferentially with HDL, changing lipoprotein size and density; Triton was progressively incorporated into the HDL particles, displacing apo E, apo A-I, and apo A-II. At concentrations above 10 mg/ml plasma, Triton displaced all apo A-I from the particle, and much lipid was dissolved into the Triton micelles. When Triton-treated HDL particles were used as a substrate for the enzyme LCAT, enzyme activity decreased in parallel to the displacement of apo A-I. There was no displacement of apo B from LDL nor any loss of lipids; but the particles became deformed and formed rouleaux. A single intravenous dose of Triton WR-1339 administered to a normolipidemic monkey (N) and to a hypercholesterolemic monkey (H) resulted in concentration-dependent HDL changes similar to those observed in vitro. LDL was less affected by Triton, with changes occurring only at high doses. After these structural changes, intravenously injected 131I apo A-I disappeared rapidly from the circulation; 125I apo A-II disappeared less rapidly. These increased clearances were accompanied by a drop in apo A-I plasma levels and the disappearance of HDL particles from plasma. The lipoprotein and apolipoprotein patterns returned to normal 14 days after Triton. We conclude that Triton WR-1339, when exposed to rhesus plasma in vitro or in vivo, interacts preferentially with HDL in a dose-dependent manner. At low concentrations, Triton acts on surface components of the HDL particle; at higher concentrations, Triton penetrates the particle, causing structural disruption. Because of its high affinity for HDL, Triton WR-1339 is a useful reagent for study of HDL structure-function relationships.

Composition of plasma and nascent very low density lipoprotein from perfused livers of hypercholesterolemic squirrel monkeys

The composition of circulating very low density lipoprotein (VLDL) was compared with the composition and secretion of nascent VLDL from perfused livers of squirrel monkeys that were fed unsaturated or saturated fat diets to elicit different degrees of plasma hypercholesterolemia. All squirrel monkeys studied had cholesteryl ester-rich plasma VLDL, although greater enrichment occurred in hypercholesterolemic animals fed saturated fat. Livers from hypercholesterolemic animals were capable of secreting VLDL particles enriched in cholesteryl ester, suggesting hepatic origin for a portion of this circulating lipid moiety. Total VLDL lipid, but not protein output by perfused livers of hypercholesterolemic monkeys, was greater than that by livers from hypocholesterolemic animals. These results indicate that saturated fat-induced hypercholesterolemia is associated with changes in the composition of hepatic VLDL in the squirrel monkey.