Effect of essential fatty acid deficiency on the size and distribution of rat plasma HDL

The effect of high-fibre diet on plasma lipoproteins and hormones in genetically obese Zucker rats

The effects of prolonged substitution of readily digested carbohydrates (wheat starch) for poorly digested carbohydrates (mixture of various fibres and crude potato starch) on plasma lipids, lipoproteins and hormones were investigated in Zucker, genetically obese rats. Lean rats were also studied in parallel. Usually, plasma lipid and insulin levels and insulin/glucose ratio were higher in obese rats vs. their lean littermates. High-fibre diet intake led to weight loss in both obese and lean rats. With a high-fibre diet, plasma lipid, insulin and glucose postprandial levels in both groups were reduced when compared with their respective control animals. Dietary fibre modified the lipoprotein profile. Triglycerides and cholesterol were reduced in all studied lipoprotein fractions. The study of high density lipoprotein (HDL) fraction in rats fed a high-fibre diet demonstrated a decrease in the HDL1 subpopulation and in the apolipoprotein (apo)E proportion. The findings show that a high-fibre diet modulates plasma lipid, insulin and glucose levels and modifies the plasma lipoprotein distribution and composition in normolipaemic, lean rats as well as in hyperlipaemic, genetically obese rats.

Adaptive regulation of lipoprotein lipase and salt-resistant lipase activities in essential fatty acid deficiency: an experimental study in the rat

Lipoprotein lipase (LPL) activities of postheparin plasma, heart, lungs, and adipose tissue, and salt-resistant lipase (hepatic lipase, SRL) activities of postheparin plasma, liver, and adrenals were examined in essential fatty acid deficient (EFAD) rats and in age-matched controls. The LPL activity of heart was higher in the deficient than in the control rats, but did not differ in the other tissues. The SRL activity of postheparin plasma was twofold higher, and that of liver and adrenals approximately 50% higher in the group with EFA deficiency. It is suggested that SRL exhibits an adaptive up-regulation in EFA deficiency. This up-regulation may be linked to a role for the enzyme in the transport of polyenoic fatty acids.

Determination of size and molecular weight distributions of lipoproteins using automatic image analysis and density gradient ultracentrifugation

A Leitz-Tas automatic image analysis system has been used to investigate the size distributions of human lipoprotein particles isolated by density gradient ultracentrifugation. Computerized image analysis enabled us to obtain more precise determinations of modal diameter and overall range in diameter for each lipoprotein subspecies than those determined by classical methods. In addition, lipoprotein molecular weight distributions were calculated from measurements of flotation density and particle size distributions. This method offers certain advantages over other procedures used to characterize mean molecular weight with regard to the ability to define lipoprotein polydispersity. The method and its limitations are discussed and illustrated with results obtained with human lipoproteins.

Increased liver lipase activity in rats with essential fatty acid deficiency

Liver lipase activity was measured in EFA-deficient rats (long-term) and in control rats and rats fed an EFA-deficient diet for two weeks (short-term). Liver lipase activity was significantly enhanced by EFA deficiency, both in long-term and short-term experiments. The enhanced liver lipase activity could be normalized by feeding these rats normal laboratory chow for 14 days. Since during EFA deficiency prostaglandin synthesis is impaired, the possible involvement of prostaglandins in the observed changes in liver lipase activity during EFA deficiency was studied. Administration of the prostaglandin synthesis inhibitor indomethacin (5 mg/kg body weight, i.p.) to normally fed rats for two days led to an increase of liver lipase activity. Prostaglandin E2 was found to inhibit the secretion of liver lipase activity by freshly isolated parenchymal liver cells in vitro. These results indicate that the increase in liver lipase activity during EFA deficiency may be due to an impairment of the prostaglandin synthesis.

Increased plasma triglyceride secretion in EFA-deficient rats fed diets with or without saturated fat

Metabolic responses to essential fatty acid-deficiency in rats include an increased rate of triglyceride secretion into the plasma, a large reduction in the HDL1 plasma lipoprotein concentration, and increased concentrations of liver triacylglycerols and cholesteryl esters. Because of differences in the types of EFA-deficient diets used, it is not clear whether these responses were solely due to the absence of EFA from the diet or whether saturated fat, or differences in acyl group chain length in this fat, might be responsible. Therefore, we fed rats diets differing only in amounts and kinds of fat, and measured triacylglycerol secretion rates and liver concentrations of triacylglycerols and cholesteryl esters, for comparison with our earlier measurements of plasma high density lipoprotein subpopulations in rats fed exactly the same diets. The purified diets contained either no fat, 5% by weight hydrogenated coconut oil, 5% hydrogenated cottonseed oil, or each of these three diets supplemented with 1% safflower oil, or 5% corn oil. We also fed some rats a nonpurified stock diet for comparison with literature reports. The present results indicate that the metabolic responses to essential fatty acid deficiency described above are definitely due to essential fatty acid-deficiency and not to the presence or chain length of acyl groups in saturated fat in the diet.

Induction of long-lasting hypercholesterolemia in the rat fed a cystine-enriched diet

The influence of dietary excess (5%) of L-cystine on rat plasma lipoproteins was examined. After only one week of cystine feeding, an increase in the plasma cholesterol level and a decrease in triglyceride levels were observed. The increase in cholesterol level became greater when the duration of cystine-enriched diet increased until eight weeks (+131% after eight weeks), but no further increase occurred between 8 and 20 weeks. This change was essentially due to the progressive increase in cholesterol levels in high density lipoproteins (HDL) and in lipoproteins isolated between 1.040 and 1.063 g/ml, i.e., certain low density lipoproteins (LDL2), and containing mainly apoE-rich lipoproteins (HDL1). The decrease in plasma triglycerides resulted from that of chylomicrons and very low density lipoproteins (VLDL). The effects observed after four or eight weeks of cystine feeding were maintained for eight weeks after replacing the cystine diet by the standard diet. Ingestion of the standard diet containing either cholestyramine (2%) or probucol (0.25%) following eight weeks of cystine feeding significantly decreased plasma cholesterol levels. It is concluded that cystine-fed rats are a useful tool of investigation for understanding mechanisms leading to increased plasma cholesterol level and for hypocholesterolemic drug trials.