Dietary effect of omega-3 type polyunsaturated fatty acids on serum and liver lipid levels in rats.

The dietary effect of omega-3 type highly polyunsaturated fatty acid concentrate (PUFA mix) was investigated on cholesterol and triglyceride levels in the serum and liver, and high density lipoprotein cholesterol (HDL-cholesterol) levels in the serum. The PUFA mix prepared from squid liver oil contained about 75% of total omega-3 type fatty acids. In rats fed the normal diet to which 3% PUFA mix was added, the levels of triglyceride, total cholesterol and phospholipid in the serum markedly decreased as compared to rats fed a 3% methyl-oleate diet. However, lipid peroxide values in the liver and serum increased in rats fed PUFA mix-diets. In the hypercholesterolemic rats, a 5% PUFA mix-diet caused growth retardation and a corresponding reduction in food intake. Lipid peroxide in the liver and serum were more elevated in rats fed diets containing 1, 3 and 5% PUFA mix than in rats fed diets containing 5% oleate or 5% linoleate. In all the rats on PUFA mix-diets, there were depression of serum total cholesterol and elevation of serum HDL-cholesterol. The ratio of HDL-cholesterol to total cholesterol increased in proportion to the amounts of dietary PUFA mix. Total cholesterol level in the liver was depressed after PUFA mix feeding.

Differential effects of dietary eicosapentaenoic and docosahexaenoic fatty acids on lowering of triglyceride and cholesterol levels in the serum of rats on hypercholesterolemic diet.

This investigation was attempted in order to further clarify the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on lipid metabolism in rats. Ninety-three percent ethyleicosapentaenoate (EPAconc) and 91% ethyl-docosahexaenoate (DHAconc) were used and supplied at the 3% level to a hypercholesterolemic basal diet which contained 5% lard. Four experimental diets were prepared from (1) 5% olive oil, (2) 2% olive oil +3% ethyl-linoleate, (3) 2% olive oil +3% EPAconc, and (4) 2% olive oil +3% DHAconc plus hypercholesterolemic basal diet. Young male rats were fed on these diets for respective periods of 10 and 20 days. Concentrations of serum lipids in rats fed on the diets (2), (3) and (4) were compared to those of the control group (diet (1]. Serum total cholesterol level was significantly lower only in the animals fed on DHAconc, whereas serum triglyceride concentration was significantly lower only in the animals fed on EPAconc. Serum phospholipid level was significantly lowered both in the animals fed on either EPAconc or DHAconc. Serum lipid peroxide concentration was elevated in these two groups of animals, while serum alpha-tocopherol concentration was lower in both groups of animals fed on EPAconc and DHAconc, respectively, although these findings were less marked in the rats on the EPAconc diet. From these findings, it is postulated that EPA and DHA have different effects on lipid metabolism in rats with hypercholesterolemia experimentally induced.

Further studies on the reduction of vitamin A content in the livers of rats given polychlorinated biphenyls.

Further investigations on the reduction of vitamin A content in the liver of rats fed a 0.1% PCB diet were conducted. The first experiment, in which rats were fed a 0.1% PCB diet for 8 weeks and vitamin A in the liver was determined at 2-week intervals, suggested that a significant decrease of vitamin A in the liver might occur within 2 weeks of PCB ingestion. In the second experiment a significant reduction of vitamin A content per gram of liver, but not per whole liver, in rats fed a 0.1% PCB diet was observed on the 3rd day of PCB ingestion, and then on the 6th day the difference between the control group and the PCB-fed group became much more remarkable. But thereafter no further reduction was seen, indicating a lower limit of vitamin A concentration in the liver of rats fed PCB. It was found that retinol binding protein in the serum of rats fed the 0.1% PCB diet decreased to one-half that of the control group on the 10th day of PCB ingestion, suggesting also a marked reduction in serum vitamin A level. Another experiment revealed that a decrease in hepatic vitamin A occurred even at low PCB levels, but serum phospholipid did not respond at all to any PCB level examined until 7 days after PCB ingestion began. The mechanisms of sensitive response of vitamin A in the animals fed PCB are briefly discussed.

Effect of indigestible polysaccharides on pancreatic exocrine secretion and biliary output.

The present study was designed to determine the effect of purified viscous polysaccharides on pancreatic exocrine secretion and biliary output. Male Sprague-Dawley rats aged 5 weeks were fed either on the control diet which contained no fiber or on the experimental diets that contained 5% indigestible polysaccharides (agar, kappa-carrageenan, Na-alginate and konjac mannan). After pretreatment with each diet for 2 weeks, the diet was discontinued overnight, and the animals were then allowed to eat 4 g of the test diet in 1 h. Immediately after this, a polyethylene tube was placed in the common bile duct, under anesthesia. Combined, free drained pancreatic-bile juice was collected for the following 1 h. Long-term (2 weeks) administration of Na-alginate and konjac mannan gave rise to increases in the volume of secreted juice and in the output of total bile acids, amylase and protease, whereas that of agar and kappa-carrageenan had no affect. Since a single dose of Na-alginate and konjac mannan was ineffective as regards pancreatic-bile secretion, the elevated secretion observed over prolonged periods may result from processes of adaptation against highly viscous polysaccharides.

Mixed function oxidases in response to different types of dietary lipids in rats.

The influence of dietary lipids on the liver microsomal mixed function oxidase system and on pentobarbital-induced sleeping time was studied in rats. Giving diets containing (g/kg) 150 olive oil, 150 lard or 150 soya-bean oil for 21 d (Expt 1) increased the cytochrome P-450 content in the order: olive oil less than lard less than soya-bean oil. When diets containing (g/kg) 150 lard, 150 soya-bean oil, 150 sardine oil or an equal mixture of 50 of each oil were given for 15 d (Expt 2), the cytochrome P-450 content and aminopyrine N-demethylase activity were significantly higher in the sardine-oil and mixed-oil groups than in the lard group, and the activity of aminopyrine N-demethylase was also significantly higher in the soya-bean oil group compared with the lard group. A significantly higher activity of NADPH-cytochrome c reductase (EC 1.6.2.5) was observed in the sardine-oil group than in the other three groups. Aniline hydroxylase activity and cytochrome b5 content remained unchanged in all the groups. Pentobarbital-induced sleeping time measured on day 15 (Expt 2) varied inversely with the changes in cytochrome P-450 content and aminopyrine N-demethylase activity in the three single-fat groups, but not in the mixed-oil group, reflecting liver microsomal metabolic activity for pentobarbital in vivo. From these results, it appears that high intakes of polyunsaturated fatty acids (18:2n-6, 18:3n-3, 20:5n-3 and 22:6n-3) stimulate the liver microsomal mixed function oxidase system.

Effect of viscous indigestible polysaccharides on pancreatic-biliary secretion and digestive organs in rats.

Effects of viscous indigestible polysaccharides on the pancreas exocrine function were investigated in growing rats. Rats were fed a nonfiber diet or a diet containing approximately 5% of one of the following fibers: apple pectin, lambda-carrageenan, locust bean gum, gum xanthan, guar gum or sodium (Na) alginate. Pancreatic-bile secretion was found to be elevated in rats fed for 2 wk the highly viscous polysaccharides, sodium alginate, locust bean gum, gum xanthan and guar gum. The polysaccharides may have interfered with the digestion and absorption of nutrients, resulting in a decreased digestibility and an enlargement of digestive organs. When alginic acid and calcium alginate, insoluble polysaccharides that did not contribute to viscosity, were given to rats, they had no effect on pancreatic and biliary secretion compared with sodium alginate. The results demonstrate that consumption of viscous indigestible polysaccharides leads to changes in the exocrine pancreatic-biliary function and may depress the process of digestion and absorption. Rats may compensate for the inefficiency of digestion and absorption with a hyperplasia/hypertrophy of digestive organs and an increased secretion of digestive juice.