Effect of dietary fat saturation of absorption and intestinal secretion of cholesterol by the hypercholesterolemic rat

The fate of an oral dose of [4-¹⁴C] cholesterol given to rats grown on diets with 20% safflower oil or 20% hydrogenated coconut oil was determined by analysis of digestive tract, feces and tissues. The pattern of isotope distribution did not support the view that rats fed a saturated fat absorb less cholesterol than those fed an unsaturated fat. Fasted animals growth on the diet with 5% of these two fats and beef fallow showed no clear difference in the amount of digitonin-peecipitable sterol in their intestines. A shorter transit time for intestinal contents was observed with the saturated fat groups. It is concluded that neither absorption of cholesterol from the gut nor secretion of β-hydroxy sterol into the gut accounts for the hypocholesterolemic effect of polyunsaturated fat. Journal Paper No. 4951 AES, Purdue University.     

Fatty acid composition of rat hearts as influenced by age and dietary fatty acids

Fatty acid composition of neutral and polar lipid fractions from rat hearts was determined in rats of different ages as their diet source changed. Piebald rats were weaned at 21 days and were fed standard lab chow. Lipids from rat hearts, mothers milk and lab chow were purified on a Sephadex G-25 fine column and separated into neutral and polar lipid fractions by silicic acid column chromatography. These lipid fractions were then hydrolyzed and methylated with BF₃ in methanol, prior to gas liquid chromatographic separation on a 1/8 in. × 10 ft aluminum column of 15% EGS on 80–100 mesh acid-washed Chromosorb W. Three major fatty acids in the neutral lipid fraction comprised 72% of total neutral lipid fatty acids from young hearts. At sexual maturity (at least 74 days old) C_18∶1 was the major fatty acid, followed by C_16∶0 and C_18∶0. The same three fatty acids comprised 83% of total polar lipid fatty acids, but C_18∶0 was the major fatty acid, followed by C_16∶0 and C_18∶1. The fatty acid composition of dietary lipids influenced the total neutral lipid fatty acid composition of the rat heart, but had little influence on the fatty acid composition of the polar lipid fraction. Presented in part at the AOCS Meeting, New Orleans, April 1970.     

Response of docosapentaenoic acids of rat heart phospholipids to dietary fat

Groups of male Holtzman strain rats were fed from weanling one of the following diets: 20% hydrogenated soybean fat (20% HF), and 20% HF plus 2%, 3% and 4% corn oil, respectively, for 20 weeks. The animals were killed, and the heart phospholipid fractions isolated by chromatographic procedures. The levels and distribution of the docosapolyenoic acids, especially 22∶5ω3, were compared among the animals fed the corn oil supplemented and nonsupplemented diets. Although dietary linolenate (18∶3ω3) level was very low in the nonsupplemented diet, 22∶5ω3 accounted for 8.4% of the total fatty acids of heart total phospholipids when this diet was fed-half the level of total eicosatetraenoic acids. The amounts of 22∶5ω3 were decreased by corn oil supplementation of the diet and got down to the “normal” range of 2.0–2.5% at corn oil supplementation levels greater than 2%. The docosapolyenoic acids were confined largely to the phosphatidylcholine and phosphatidylethanolamine classes of phospholipids. These findings are discussed from the standpoint of the structural role of the phospholipids in the heart subcellular fractions.     

Effect of dietary bile acids,cholesterol, and β-sitosterol upon formation of coprostanol and 7-dehydroxylation of bile acids by rat

During studies of sterol metabolism in the rat, the fecal neutral sterol fraction was analyzed by a combination of thin layer chromatography and gas liquid chromatography. On a stock diet of rat chow supplemented with 5% corn oil, the rats excreted 14.5 mg/day of total neutral sterols. Coprostanol comprised 35% (5 mg/day) of this fraction. When the diet was supplemented with 0.5% sodium taurochenodeoxycholate, the amount of coprostanol in the feces remained the same as in the controls (3.2 mg/day, 32%). The addition of 0.5% sodium taurocholate to the diet resulted in a fivefold reduction of coprostanol formation (0.6 mg/day, 8%). When 1.2% cholesterol was added to the stock diet, the amount of coprostanol present in the feces decreased to an average of 11% compared to controls, but the absolute amount formed was greater (35 mg/day). On a diet enriched with 0.8% β-sitosterol, the rats, on the average, converted 23% of the cholesterol to coprostanol. Feeding diets enriched with sodium taurochenodeoxycholate and sodium taurocholate reduced the 7-dehydroxylation of primary bile acids in the feces by 28% and 42%, respectively. The conversion of primary bile acids to secondary bile acids in the feces of control, cholesterol, and β-sitosterol fed rats was the same (64%).     

Effect of dietary fat on the lipid composition and utilization of short-chain fatty acids by rat colonocytes

The objective of the present studies was to examine the effect of dietary fat on the lipid composition of rat colonocytes and their utilization of short-chain fatty acids (SCFA). Rats were fed 14% beef fat, fish oil or safflower oil plus 2% corn oil in a semi-synthetic base diet for 4 wk. Colonocytes were isolated and their lipid composition was examined. Feeding beef fat and fish oil resulted in an increase in monounsaturated fatty acids and a reduction in ω-6 fatty acids. Feeding fish oil resulted in an enrichment with ω-3 fatty acids. These was no dietary influence on the amount of either cholesterol or phospholipids of colonocytes. Fish oil feeding resulted in significant increase in colonocyte free fatty acids (FFA) as compared to other diets. Dietary fat was found to have no effect on SCFA utilization by colonocytes. Colonocytes were found to utilize SCFA in the order of butyrate ≥acetate ≥propionate. The presence of acetate and propionate in the medium had no effect on the rate of butyrate utilization.     

Modification of in vitro rat adrenal corticosteroidogenesis by dietary fat

Three groups of male weanling Holtzman rats were maintained, ad libitum, for 4 and 8 weeks on 1 of 3 diets: Purina Chow, hydrogenated soybean fat, and milk fat diets. The fats were added at the level of 36% total calories in the case of the hydrogenated soybean and milk fat diets. Adrenal homogenates prepared from tissues of each group of animals at the end of the dietary periods were used to measure the relative abilities to synthesize corticosteroids from endogenous substrates. Endogenous free cholesterol levels were found adequate to sustain the level of corticosteroids obtained. No concomitant cholesteryl ester hydrolysis was observed under the experimental conditions used. The adrenal synthetic ability for the three dietary groups was in the order milk fat > Purina Chow > hydrogenated milk fat. This order appeared not to be a reflection of the essential fatty acid status of the animals in the three dietary groups. The possible basis for this trend, and the implications of the findings for carbohydrate, protein, and lipid metabolism in the animal are indicated. Presented in part at the AOCS Meeting, New Orleans, April 1973.     

The effect of dietary fat on the glyceride structure of rat carcass fat

Carcass fats were obtained from weanling rats fed a complete diet for 8 weeks, which consisted of 2% cottonseed oil and 10% of the following fats: (1) corn oil; (2) the fatty acids of corn oil; (3) triricinolein; (4) ricinoleic acid; (5) the hydrogenated fatty acids of castor oil ; and (6) commercial hydrogenated shortening. The fats were subjected to both pancreatic lipase and nonspecific hydrolysis ; the resulting acids converted into methyl esters by conventional methods, and subjected to gas Chromatographie analysis. From these data, the positional distri-bution of the component fatty acids, glyceride types, and isomeric forms were calculated. The results indicated a preferential placement of un-saturated acids in the 2- position of the carcass triglycerides and that the carcass fat composition in terms of unsaturated (U) and saturated (S) fatty acid composition is not greatly influenced by the S and U compositions of the dietary fat. It was found that hydroxy acids or their tri-esters are metabolized much the same as are normal triglycerides and exert no particular in-fluence upon the fat structure of the rat. Some type of relationship between the dietary U and the U₃ in the carcass fat appears to be present. The glycerides of the carcass fats examined here are essentially a random mixture of the major glyceride types, but the isomeric forms (SUS, S SU, USU and UUS) are a definite non-random mixture. Carried out at the Food Res. Div., Armour & Co., and at The Burnsides Research Laboratory under research grant No. EF 225 from the National Institutes of Health, U. S. Public Health Service, and Deparmtent of Health, Education, and Welfare.     

Fecal bile acid excretion and composition in response to changes in dietary wheat bran,fat and calcium in the rat

The effect and possible interactive influence of different dietary amounts of wheat bran, fat and calcium on the fecal excretion, concentration and composition of bile acids was studied in Fischer-344 rats. The fecal bile acids were analyzed using gas-liquid chromatography. Dietary wheat bran increased both total bile acid excretion and fecal weight without changes in fecal bile acid concentration. The proportion of fecal hyodeoxycholic acid decreased with increasing dietary fiber, whereas that of lithocholic and deoxycholic acids increased significantly with fiber intake. The percent content of fecal chenodeoxycholic acid did not change. Increasing dietary fat led to an increase in bile acid excretion without changes in either fecal weight or bile acid concentration. In contrast, the level of dietary calcium did not affect the total excretion of bile acids. However, since calcium increased the fecal weight, it consequently diluted bile acids and decreased their fecal concentration. Dietary fat and calcium had no influence on fecal bile acid composition. There were no interactive effects of wheat bran, fat and calcium on fecal bile acids. The finding in this study that dietary fiber, fat and calcium induce significant changes in fecal bile acids may be of relevance to the potential of bile acids to promote carcinogenesis.     

Influence of dietary fat composition on intestinal absorption in the rat

Omega-3 fatty acids influence the function of the intestinal brush border membrane. For example, the omega-3 fatty acid eicosapentaenoic acid (20∶5ω3) has an antiabsorptive effect on jejunal uptake of glucose. This study was undertaken to determine whether the effect of feeding α-linolenic acid (18∶3ω3) or EPA plus docosahexaenoic acid (22∶6ω3) on intestinal absorption of nutrients was influenced by the major source of dietary lipid, hydrogenated beef tallow or safflower oil. Thein vitro intestinal uptake of glucose, fatty acids and cholesterol was examined in rats fed isocaloric diets for 2 weeks: beef tallow, beef tallow + linolenic acid, beef tallow + eicosapentaenoic acid/docosahexaenoic acid, safflower oil, safflower oil + linolenic acid, or safflower oil + eicosapentaenic acid/docosahexaenoic acid. Eicosapentaenoic acid/docosahexaenoic acid reduced jejunal uptake of 10 and 20 mM glucose only when fed with beef tallow, and not when fed with safflower oil. Linolenic acid had no effect on glucose uptake, regardless of whether it was fed with beef tallow or safflower oil. The jejunal uptake a long-chain fatty acids (18∶0, 18∶2ω6, 18∶3ω3, 20∶4ω6, 20∶5ω3 and 22∶6ω3) and cholesterol was lower in salfflower oil than with beef tallow. When eicosapentaenoic acid/docosahexaenoic acid was given with beef tallow (but not with safflower oil), there was lower uptake of 18∶0, 20∶5ω3 and cholesterol. The demonstration of the inhibitory effect of linolenic acid or eicosapentaenoic acid/docosahexaenoic acid on cholesterol uptake required the feeding of a saturated fatty acid diet (beef tallow). These changes in uptake were not explained by differences in the animals’ food intake, body weight gain or intestinal weight. Feeding safflower oil was associated with an approximately 25% increase in the jejunal and ileal mucosal surface area, but this increase was prevented by combining linolenic acid or eicosapentaenoic acid/docosahexaenoic acid with safflower oil. Different inhibitory patterns were observed when mixtures of fatty acids were present together in the incubation medium, rather than in the diet: for example, when 18∶0 was in the incubation medium with 20∶4ω6, the uptake of 20∶4ω6 was reduced, whereas the uptake was unaffected by 18∶2ω6 or 20∶5ω3. Thus, (1) the inhibitory effect of eicosapentaenoic acid/docosahexaenoic acid on jejunal uptake of glucose, fatty acids and cholesterol was influenced by the major dietary lipid, saturated (beef tallow) or polyunsaturated fatty acid (safflower oil); and (2) different omega-3 fatty acids (linolenic acid versus eicosapentaenoic acid/docosahexaenoic acid) have a variable influence on the intestinal absorption of nutrients.     

Regulation of very low density lipoprotein apo B metabolism by dietary fat saturation and chain length in the guinea pig

Studies investigated the effects of dietary fatty acid composition and saturation on the regulation of very low density lipoprotein (VLDL) apo B flux, clearance, and conversion to low density lipoprotein (LDL) in guinea pigs fed semipurified diets containing 15% (w/w) corn oil (CO), lard (LA), or palm kernel oil (PK). Plasma cholesterol levels were highest with dietary PK (3.1±1.0 mmol/L) followed by LA (2.4±0.4 mmol/L) and CO (1.6±0.4 mmol/L) intake. VLDL particles were larger (P<0.05) in the LA (78±7 nm) and PK (69±10 nm) groups compared to animals fed CO (49±5 nm). VLDL-apo B fractional catabolic rates (FCR) were highest in guinea pigs fed the LA diet (P<0.05) and VLDL apo B flux, estimated from VLDL ¹²⁵I-apo B turnover kinetics, were higher in LA compared to PK or CO fed guinea pigs. In the case of PK consumption, the kinetic estimates of VLDL apo B flux significantly underestimated rates compared to direct VLDL apo B secretion measurements and LDL turnover analyses. These data demonstrate that differences in the composition and amount of saturated fatty acids have differential effects on VLDL apo B flux, catabolism, and conversion to LDL which, together with changes in LDL receptor-mediated catabolism, determine plasma LDL cholesterol levels in guinea pigs. The data also indicate that kinetic analysis of VLDL metabolism in PK fed animals is inaccurate possibly due to the presence of a small, nonequilibrating pool of newly synthesized VLDL which is rapidly converted to LDL.     

Effects of dietary fat and fatty acids on sterol balance in hamsters

Sterol balance studies, using both isotopic and chromatographic techniques, were carried out in hamsters fed semipurified diets to detect changes in sterol metabolism during the early period of the lithogenic stimulus. The balance studies examined animals in the first two weeks on the experimental lithogenic diets. The variables were as follows: dose of cholesterol (group 1, 0.05% vs. group 2, 0.2%); dietary fat (fatty acid) (group 2, butterfat vs. group 4, palmitic acid); source of hamster [group 2, Sasco (Omaha, NE) vs. group 3, Charles River (Wilmington, MA)]; average weight of animals (group 4, 60 g vs. group 5, 119 g). Animals in groups 1, 2, 3 and 5 maintained almost constant weight throughout the two-week balance study. Liver and plasma cholesterol levels increased in groups 2–5 with increasing dose of dietary cholesterol. The highest levels were found in group 4 (liver cholesterol, 32.7 mg/g; plasma cholesterol, 367 mg/dL). Sterol balance measurements showed that bile acid synthesis remained low (range 0.55–1.01 mg/d) for all groups regardless of the intake of dietary cholesterol (range, 3.27–20.90 mg/d). The dietary cholesterol absorbed from the intestine (range, 2.91–18.91 mg/d) was stored in the liver; this storage was reflected in the negative values for cholesterol balance for all groups (range, −0.70 to −14.97 mg/d). These studies did not reveal any correlations between parameters of sterol balance and cholelithiasis.     

Effects of clofibrate and tiadenol on the elimination of lipids and bile acids in rat bile

The aim of the work presented here was to compare the biliary elimination of cholesterol and the different bile acids of rats that had been made hypolipidemic by short-term treatments with clofibrate or tiadenol. Both treatments induced a significant decrease in cholesterol output in the bile. The analysis of the different bile acids showed a decrease in dihydroxylated acids elimination (especially CDC acid) without any difference between the 2 sexes. This decrease was associated with an increase in cholic acid excretion. These results are directly correlated with the dose of the administered hypolipidemic drug. The drugs caused a significant increase in the ratio of trihydroxylated acids to dihydroxylated acids. The maximal effect on the concentration of the biliary acids of the bile and on the output was obtained, for both drugs, with a treatment of 200 mg/kg/day. Clofibrate had a greater effect than tiadenol at this dose. Both drugs show a greater effect on lowering serum lipid levels in female animals when compared to males, whereas elimination of bile cholesterol and modifications of bile acids were greater in male animals than female animals.     

Effects of fatty acids on gap junctional communication: Possible role in tumor promotion by dietary fat

Dietary lipids, in particular unsaturated fat, promote the development of many experimental tumors. However, no mechanisms to fully explain these effects have been elucidated. Recent reports, which we summarize here, suggest a role for gap junction-mediated intercellular communication in the process of tumor promotion. We also review tumor-promoting effects of dietary fat on experimental, particularly mammary, carcinogenesis. Our main focus is to review recent data examining the inhibitory effects of unsaturated fatty acids on metabolic cooperation in Chinese hamster V79 cells. These data suggest that inhibition of junctional communication may be involved mechanistically in the promotion of tumors by high levels of dietary unsaturated fat. Finally, potential mechanisms by which unsaturated fatty acids inhibit metabolic cooperation are examined. Presented at the symposium on “Specialty Lipids and Their Biofunctionality” at the annual meeting of the American Oil Chemists' Society, Philadelphia, May 1985.     

Analysis of fecal neutral steroids and bile acids in humans on constant fat diet

A method is described for the separation and quantification of fecal neutral steroids and fecal bile acids. The fecal extract is separated into the neutral steroid fraction and bile acid fraction with ionexchange resin columns. The principal neutral steroids and bile acids are then separated and quantitated by thin-layer chromatography. Values for the fecal neutral steroids, cholesterol, coprostanol and coprostanone and fecal bile acids, deoxycholic acid and lithocholic acid of 5 subjects on a constant fat diet for a 3-week period are presented.     

Dietary squalene increases tissue sterols and fecal bile acids in the rat

Feeding 1% squalene increased markedly the concentrations of squalene and methyl sterols in each serum lipoprotein class, intestinal mucosa, liver and also in adipose tissue. It also increased cholesterol concentration of the liver and serum VLDL, and esterified cholesterol in serum LDL as well as fecal bile acids. The results suggest that absorbed dietary squalene contributes to some extent to the squalene content of adipose tissue, effectively increases the overall cholesterol synthesis and enhances cholesterol elimination preferentially as fecal bile acids.     

Comparative bioavailability of dietary alpha-linolenic and docosahexaenoic acids in the growing rat

Animal and human studies have indicated that developing mammals fed only α-linolenic acid (18∶3n−3) have lower docosahexaenoic acid (22∶6n−3) content in brain and tissue phospholipids when compared with mammals fed 18∶3n−3 plus 22∶6n−3. The aim of this study was to test the hypothesis that low bioavailability of dietary 18∶−3 to be converted to 22∶6n−3 could partly explain this difference in fatty acid accretion. For that purpose, we determined the partitioning of dietary 18∶3n−3 and 22∶6n−3 between total n−3 fatty acid body accumulation, excretion, and disappearance (difference between the intake and the sum of total n−3 fatty acids accumulated and excreted). This was assessed using the quantitative method of whole-body fatty acid balance in growing rats fed the same amount of a 5% fat diet supplying either 18∶3n−3 or 22∶6n−3 at a level of 0.45% of dietary energy (i.e., 200 mg/100 g diet). We found that 58.9% of the total amount of 18∶3n−3 ingested disappeared, 0.4% was excreted in feces, 21.2% accumulated as 18∶3n−3 (50% in total fats and 46% in the carcass-skin compartment), and 17.2% accumulated as long-chain derivatives (14% as 22∶6n−3 and 3.2% as 20∶5n−3+22∶5n−3). Similar results were obtained from the docosahexaenoate balance (as % of the total amount ingested): disappearance, 64.5%; excretion, 0.5%; total accumulation, 35% with 30.1% as 22∶6n−3. Thus, rats fed docosahexaenoate accumulated a twofold higher amount of 22∶6n−3, which was mainly deposited in the carcass-skin compartment (68%). Similar proportions of disappearance of dietary 18∶−3 and 22∶6n−3 lead us to speculate that these two n−3 polyunsaturated fatty acids were β-oxidized in the same amount.     

Action of three bile acids on hepatic and intestinal cholesterogenesis in the rat

Incorporation of [1¹⁴−C] acetate into cholesterol by subcellular particles from the liver and the small intestine of rats with a biliary diversion and a duodenal perfusion of sodium taurocholate, taurochenodeoxycholate or taurodehydrocholate, was studied in vitro. In the liver, taurochenodeoxycholate prevented the increase of cholesterol synthesis induced by biliary drainage. Taurocholate had no action on cholesterol synthesis at any time, day or night. Intestinal synthesis of cholesterol was reduced by taurocholate and taurochenodeoxycholate but was not modified by taurodehydrocholate infusion.     

Effect of age on plasma bile acids and lipid components in the rat

With increasing age, total plasma bile acid contents increased in rats over a period of 11 months, and also total plasma cholesterol and carcass fat contents increased in the same manner. Plasma showing high bile acid levels at 11 months was found by means of high performance liquid chromatography to contain cholic acid as one of the major components, chenodeoxycholic acid and trace deoxycholic acid. These results suggest that there are close relationships between the plasma bile acids and age-dependent changes of lipid components in the rat.     

Effects of ferulic andp-coumaric acids in nutrient culture of cucumber leaf expansion as influenced by pH

Cucumber seedlings were grown in 5 mM MES [2-(N-morpholino)ethanesulfonic acid] -buffered nutrient solutions adjusted to a pH of 5.5, 6.25, or 7.0. Nutrient solutions were changed on alternate days. Seedlings were treated for a two-day period with various concentrations (0–1 mM) of ferulic acid,p-coumaric acid, or mixtures of these phenolic acids when 16 days old. Leaf growth, dry weight, and water utilization of the seedlings; pH of the solutions; and disappearance of the phenolic acids from nutrient solutions were monitored. Leaf area expansion of cucumber seedlings was inhibited by both ferulic andp-coumaric acid, and the magnitude of these inhibitions was influenced by concentration and pH. Inhibition of leaf area expansion was greater at pH 5.5 and nominal at pH 7.O. Ferulic acid was more inhibitory thanp-coumaric acid. The effect of pH on growth was best described by data for mean relative rates of leaf expansion. For example, the mean relative rates of leaf expansion by both acids at 0.5 mM for the 16- to 18-day growth period (treatment period) were reduced by 45, 31, and 8% for the pH 5.5, 6.25, and 7.0 treatments, respectively. The dry weight of seedlings at harvest (day 22) was significantly reduced for seedlings grown in the pH 5.5 and 6.25 treatments, but not for the pH 7.0 treatment. There was, however, one exception; the dry weight of seedlings treated withp-coumaric acid solutions adjusted to a pH of 5.5 was not significantly reduced. Water utilization by the seedlings was reduced by both ferulic andp-coumaric acid. Again, the impact of ferulic acid was greater thanp-coumaric acid. The effect of ferulic acid on water utlization decreased with increasing pH of the nutrient solution. The pH effects were not so consistent forp-coumaric acid. The effects of equimolar mixtures of the two phenolic acids were additive for all variables measured. There was a linear correlation between mean relative rates of leaf expansion and water utilization.Paper No. 9693 of the Journal Series of the North Carolina Agricultural Research Sevice, Raleigh, North Carolina. Mention of a trademark or a propriety product does not constitute a guarantee or warranty of the product by the Agricultural Research Service and does not imply its approval to the exclusion of other products that may be suitable.