Influence of medium-chain triglycerides on lipid metabolism in the chick

The effect of corn oil, coconut oil, and medium-chain triglyceride (MCT, a glyceride mixture consisting almost exclusively of fatty acids of 8 and 10 carbons in length) ingestion on lipid metabolism was studied in chicks. In chicks fed cholesterol-free diets, MCT ingestion elevated plasma total lipids and cholesterol and depressed liver total lipids and cholesterol when compared to chicks receiving the corn oil diet. As a consequence of the opposite effects of MCT ingestion on plasma and liver cholesterol and total lipids, the plasma-liver cholesterol pool was not altered. When cholesterol was included in the diets, dietary MCT depressed liver and plasma total lipids and cholesterol as compared with corn oil, consequently also lowered the plasmaliver cholesterol pool. The in vitro cholesterol and fatty acid synthesis from acetate-1-¹⁴C was higher in liver slices from chicks fed MCT than in those from chicks fed corn oil. The percentage of radioactivity from acetate-1-¹⁴C incorporated into the carboxyl carbon of fatty acids by liver slices was not altered by MCT feeding, indicating that the increased acetate incorporation represented de novo fatty acid synthesis. The conversion of palmitate-1-¹⁴C to C₁₈ acids was increased in liver of chicks fed MCT, implying that fatty acid chain elongating activity was also increased. Studies on the conversion of stearate-2-¹⁴C to mono- and di-unsaturated C₁₈ acids showed that hepatic fatty acid desaturation activity was enhanced by MCT feeding. Data are presented on the plasma and liver fatty acid composition of chicks fed MCT-, corn oil-, or coconut oil-supplemented diets. The principles of laboratory animal care, as promulgated by the National Society for Medical Research, were observed.     

Influence of medium-chain triglycerides on lipid metabolism in the rat

Lipid metabolism was studied in rats fed diets containing corn oil, coconut oil, or medium-chain triglyceride (MCT), a glyceride mixture containing fatty acids of 8 and 10 carbons in length. The ingestion of MCT-supplemented, cholesterolfree diets depressed plasma and liver total lipids and cholesterol as compared with corn oil-supplemented diets. In rats fed cholesterol-containing diets, plasma cholesterol levels were not influenced by dietary MCT, but liver cholesterol levels were significantly lower than in animals fed corn oil. In vitro cholesterol synthesis from acetate-1-¹⁴C was lower in liver slices of rats that consumed MCT than in similar preparations from corn oil-fed rats. Studies of fatty acid carboxyl labeling from acetate-1-¹⁴C and the conversion of palmitate-1-¹⁴C to C₁₈ acids by liver slices showed that chain-lengthening activity is greater in the liver tissue of rats fed MCT than in the liver of animals fed corn oil. The hepatic fatty acid desaturation mechanisms, evaluated by measuring the conversion of stearate-2-¹⁴C to oleate, was also enhanced by feeding MCT. Adipose tissue of rats fed MCT converts acetate-1-¹⁴C to fatty acids at a much faster rate than does tissue from animals fed corn oil. Evidence is presented to show that the enhanced incorporation of acetate into fatty acids by the adipose tissue of rats fed MCT represents de novo synthesis of fatty acids and not chain-lengthening activity. Data are also presented on the fatty acid composition of plasma, liver, and adipose tissue lipids of rats fed the different fats under study.     

Acetoacetate metabolism of rats fed high fat or restricted calorie diets

Ethyl-¹⁴C-acetoacetate was used to trace oxidation and metabolism of acetoacetate when rats were fed a high fat diet (80% of total calories from beef tallow or corn oil, carbohydrate free), a high carbohydrate diet (2% corn oil) or a high carbohydrate diet with restriction of calories to one half of ad lib. consumption for two weeks. The rate of expiration of¹⁴CO₂ in all groups of animals did not differ significantly and was not related to plasma concentration of acetoacetate. The high fat diets slightly enhanced the oxidation of acetoacetate to¹⁴CO₂ over a 3 hr period compared to other diets. Incorporation of acetoacetate into fatty acids did not differ significantly among groups. Rats fed the high carbohydrate diet ad lib. incorporated into liver cholesterol more acetoacetate than did any other group, but dietary unsaturated fat resulted in greater incorporation of acetoacetate into cholesterol than saturated fat. High calorie and high beef tallow groups were ketonemic but the low concentration of plasma acetoacetate in rats fed a high corn oil diet indicates that unsaturated fatty acids are not ketogenic. The data show that utilization of acetoacetate is not significantly reduced in a ketonemic condition and support the premise that overproduction of ketone bodies is the cause of ketonemia. Rats appeared to be normal during the two-week period when no carbohydrate was included in the diet. Presented at the AOCS Meeting, Chicago, October, 1967.     

Oxidative susceptibility of low density lipoprotein from rabbits fed atherogenic diets containing coconut,palm, or soybean oils

The oxidative susceptibilities of low density lipoproteins (LDL) isolated from rabbits fed high-fat atherogenic diets containing coconut, palm, or soybean oils were investigated. New Zealand white rabbits were fed atherogenic semisynthetic diets containing 0.5% cholesterol and either (i) 13% coconut oil and 2% corn oil (CNO), (ii) 15% refined, bleached, and deodorized palm olein (RBDPO), (iii) 15% crude palm olein (CPO), (iv) 15% soybean oil (SO), or (v) 15% refined, bleached, and deodorized palm olein without cholesterol supplementation [RBDPO(wc)], for a period of twelve weeks. Total fatty acid compositions of the plasma and LDL were found to be modulated (but not too drastically) by the nature of the dietary fats. Cholesterol supplementation significantly increased the plasma level of vitamin E and effectively altered the plasma composition of long-chain fatty acids in favor of increasing oleic acid. Oxidative susceptibilities of LDL samples were determined by Cu²⁺-catalyzed oxidation which provide the lag times and lag-phase slopes. The plasma LDL from all palm oil diets [RBDPO, CPO, and RBDPO(wc)] were shown to be equally resistant to the oxidation, and the LDL from SO-fed rabbits were most susceptible, followed by the LDL from the CNO-fed rabbits. These results reflect a relationship between the oxidative susceptibility of LDL due to a combination of the levels of polyun-saturated fatty acids and vitamin E. Based on a paper presented at the PORIM International Palm Oil Congress (PIPOC) held in Kuala Lumpur, Malaysia, 1993.     

Dietary lipid,fatty acid synthesis and cholesterol metabolism in aging rats

Male and female rats were fed diets containing 2% of calories as corn oil or that plus 40% of calories as beef tallow or corn oil. After 3, 6, 12 and 18 months groups were given 4-¹⁴C-cholesterol ip, and feces were collected for 9 days. Just prior to necropsy³H-acetate was administered ip. Samples of serum, liver, heart and carcass were obtained for analysis. Concentrations of fatty acids and cholesterol, synthesis of those and recovery of ring-labeled steroid are reported. Mortality from acute respiratory disease was very high in male rats fed beef tallow or low fat diets and very low in those fed the corn oil diet. In females, only beef tallow diet resulted in a high mortality rate, and this was lower and at a later age than in males. The most notable effects of age were in relation to fatty acid synthesis and presence of¹⁴C-acidic steroid in the carcass. In 3-month-old rats both fats depressed fatty acid synthesis in comparison to the low fat diet. At later ages beef fat ceased to depress fatty acid synthesis in both sexes. Corn oil continued to depress fatty acid synthesis up to 12 months in males and 18 months in females. The presence of¹⁴C-acidic steroid in carcass was substantial in 6-month-old rats and constituted ca. 40% of recovered¹⁴C in 18-month-old rats. The possibility that the increase in acetate incorporation into fatty acids with age in fat feeding is related to chain elongation rather than de novo synthesis is discussed. Both the presence and amount of acidic steroid in the carcass are notable and may be of importance in constructing models of cholesterol turnover. Presented in part at the AOCS Sterol Symposium, April 1970, and the Federation of American Societies for Experimental Biology, April 1971. Scientific Series Paper No. 1536, Colorado Agricultural Experiment Station.     

Lipid and fatty acid profiles in rats consuming different high-fat ketogenic diets

High-fat ketogenic diets are used to treat intractable seizures in children, but little is known of the mechanism by which these diets work or whether fats rich in n−3 polyunsaturates might be beneficial. Tissue lipid and fatty acid profiles were determined in rats consuming very high fat (80 weight%), low-carbohydrate ketogenic diets containing either medium-chain triglyceride, flaxseed oil, butter, or an equal combination of these three fat sources. Ketogenic diets containing butter markedly raised liver triglyceride but had no effect on plasma cholesterol. Unlike the other fats, flaxseed oil in the ketogenic diet did not raise brain cholesterol. Brain total and free fatty acid profiles remained similar in all groups, but there was an increase in the proportion of arachidonate in brain total lipids in the medium-chain triglyceride group, while the two groups consuming flaxseed oil had significantly lower arachidonate in brain, liver, and plasma. The very high dietary intake of α-linolenate in the flaxseed group did not change docosahexaenoate levels in the brain. Our previous report based on these diets showed that although ketosis is higher in rats consuming a ketogenic diet based on medium-chain triglyceride oil, seizure resistance in the pentylenetetrazol model is not clearly related to the degree of ketosis achieved. In combination with our present data from the same seizure study, it appears that ketogenic diets with widely differing effects on tissue lipids and fatty acid profiles can confer a similar amount of seizure protection.     

Biliary and fecal steroid excretion in rats fed partially hydrogenated soybean oil

Male Wistar rats were fed cholesterol-free or cholesterol-enriched diets containing partially hydrogenated soybean oil with different levels of trans-fatty acids or unhydrogenated soybean oil at the 10% level. The linoleic acid content of hydrogenated fat diets was adjusted to 3.6% of the total energy. Hydrogenated fat diets contained 29% and 41% trans-acids, mainly as t-18:1. Trans-fats exerted no untoward effects on growth parameters, but increased liver weight. Dietary hydrogenated fats influenced neither the concentration nor composition of biliary steroids, irrespective of the presence or absence of cholesterol in the diet. In rats fed a cholesterol-free diet, daily fecal output of neutral and acidic steroids was enhanced by hydrogenated fats and the magnitude of augmentation was proportional to the dietary level of trans-fatty acids. The increased fecal steroid excretion corresponded to an increase in total excreta. Hydrogenated fats also tended to enhance bile acid excretion when feeding a cholesterol-enriched diet. The results suggest that dietary trans-fatty acids, in relation to cis-polyunsaturated fatty acids, provoke demonstrable change in steroid homeodynamics.     

The effects of fat-free,saturated and polyunsaturated fat diets on rat liver and plasma lipids

The liver and plasma lipids and fatty acid composition of rats fed synthetic diets of differing fat type and content were studied. All animals were starved for 48 hr and then refed a high carbohydrate, fat-free diet for 48 hr. They were then divided into three groups and fed for an additional 48 hrs the following: group 1, the fat-free diet; group 2, a diet containing 44% of calories from corn oil; and group 3, a diet containing 44% calories from completely hydrogenated soybean oil. The total lipid concentration of the liver in the animals on the fat-free diet was elevated at 72 and 96 hr. The addition of either saturated or unsaturated fat in the diet at 48 hr prevented this accumulation. The total phospholipid and cholesterol concentrations of the liver were relatively uninfluenced by any diet in this study. Plasma total fatty acid concentration was elevated at 72 hr in the animals on a fat-free diet compared to those fed the stock diet, starved for 48 hr or fed the fat-containing diets. By 96 hr, however plasma fatty acid concentrations in all groups were similar to those in animals fed only the stock diet. The release of de novo synthesized fatty acids into plasma from the liver was strongly inhibited by dietary fat, either saturated or polyunsaturated. With the fat-free diet there was a significant increase in the saturated and monounsaturated fatty acids in both liver and plasma. The addition of corn oil to the diet facilitated a reversion of the fatty acid composition in liver and plasma to that found in the animals fed the stock diet ad libitum, but saturated fat did not. No effect of diet on the fatty acid composition of the red cells was observed during the course of this study. Exogenous saturated fatty acids, although similar chemically to the fatty acids synthesized by the liver, may have physiological actions that differ from endogenously synthesized fat.     

Species variation in the atherogenic profile of monkeys: Relationship between dietary fats,lipoproteins, and platelet aggregation

Because lipoproteins and platelet aggregation have been implicated in atherogenesis, relative differences in the response of these variables to dietary fat saturation were compared in three species of monkeys differing in their susceptibility to atherosclerosis (cebus, rhesus, and squirrel monkeys). Both long-term (8–12 years) and short-term (8 weeks) responses to diets containing 31% fat calories were examined in the same monkeys. As expected, long-term feeding of coconut oil by comparison to corn oil produced significantly higher plasma concentrations of total cholesterol, LDL cholesterol, apoB, and triglycerides, as well as higher ratios of LDL/HDL cholesterol and apo B/apo A-I. These responses were characteristic of all species with cebus being most responsive and rhesus the least. The shortterm plasma cholesterol response to animal fats (butter, lard, beef tallow) was significantly less than that to coconut oil. When fish oil was substituted for two-thirds of either corn oil or coconut oil, exceptional decreases occurred in plasma cholesterol and triglycerides, as well as in HDL cholesterol and apo A-I concentrations despite the fact that the fish oil diets contained more saturated fat and less polyenes than the corn oil diet. Platelet aggregation tended to increase with saturated fat consumption and greatly decreased with fish oil intake in all monkeys, although cebus monkeys were ten-fold more resistant to platelet aggregation than the other two species. The molecular species of platelet phosphatidylcholine (PC) varied with both the dietary fat fed and species of monkey. An inverse correlation (r=−0.60; p<0.001) was found between changes in one such PC molecular species (18∶0−20∶4) induced by diet and the platelet aggregation threshold. These results demonstrate that the lipemic and platelet responses to dietary saturated fat depend upon both the type of fat (i.e., the specific combination of dietary fatty acids, including the chain length of saturated fatty acids and the degree of polyunsaturation) and the species of monkey (genetic component) in which the response is elicited.     

The hypercholesterolemic effect of dietary coconut fatversus corn oil in hypo- or hyperresponsive rabbits is not exerted through influencing cholesterol absorption

In two inbred strains of rabbits with high or low response of plasma cholesterol to dietary saturatedversus polyunsaturated fatty acids, the efficiency of intestinal cholesterol absorption was measured. The feeding of a cholesterol-free purified diet containing saturated fatty acids in the form of coconut fat, when compared with a diet containing corn oil as polyunsaturated fatty acids, did not influence the efficiency of cholesterol absorption in the two rabbit strains. Irrespective of the dietary fat source, the hyperresponsive rabbits absorbed cholesterol more efficiently. It is concluded that the hypercholesterolemic effect of dietary coconut fatversus corn oil is not exerted by influencing cholesterol absorption.     

Separate effects of dietary protein and fat on serum cholesterol levels: another view of amino acid content of proteins

Casein or soy protein with vegetable or animal fat were used to determine the dietary protein or fat effects and their possible interaction on serum cholesterol levels. Young, male New Zealand white rabbits with a mean weight of 2.1 kg were divided into groups of six and fed one of four different diets containing 20% of the calories as protein, 30% as fat (according to dietary guidelines for the United States) and 50% as carbohydrate. The diets contained casein or soy (lysine/arginine ratio = 2.2 or 0.9, respectively) as the protein sources with fat from either almond oil or butter. There was no significant difference in weight gain among the diet groups. Total serum cholesterol level was highest among animals fed the diet containing butter with casein (177 +/- 25 mg/dl) or soy protein (189 +/- 50 mg/dl), it was intermediate in animals fed the vegetable oil with casein (121 +/- 14 mg/dl), and lowest in the soy protein with vegetable oil group (58 +/- 12 mg/dl). There was a significant difference in serum cholesterol levels due to the protein effect when vegetable oil was used (p less than 0.05) but not with butter. There was also a significant fat effect on serum cholesterol when the diet contained soy protein (p less than 0.005) but not when the protein was casein. No significant interaction was observed between the dietary fat and protein sources on serum cholesterol levels, which suggests that dietary protein and fat independently affect the levels of serum cholesterol. Thus, dietary protein has a significant effect on serum cholesterol levels and may be a factor in the low levels of serum cholesterol observed among vegetarians and in humans of Third World countries where the diets is primarily of vegetable origin.     

Effect of dietary fat upon aflatoxicosis in rats fed torula yeast containing diet

This study was designed to study the possible interrelationships between Torula yeast, vitamin E, and the dietary fat source on aflatoxin-induced tumors. Rats were fed Torula yeast-containing basal diets which included 1.7 ppm aflatoxin B₁ with either lard, corn oil or no fat, and with or without vitamin E supplements for 3 months. Thereafter, the respective diets without aflatoxin were fed for ca. 9 months. Animals receiving the vitamin E-deficient diets had a high mortality. Although the vitamin E-deficient, aflatoxin-treated rats had lower wt gains than did the vitamin E-deficient controls, they lived twice as long. In addition, regardless of the dietary fat source, the kidneys and adrenals of these vitamin E-deficient, aflatoxin-supplemented rats were found to be significantly heavier than the controls, and plasma cholesterol levels were elevated. Increased amounts of liver lipid were observed in response to aflatoxin in both corn oil-fed and fat-deficient rats. No such differences were observed in the responses of the vitamin E-supplemented groups to aflatoxin. On the corn oil diet, aflatoxin administration resulted in an increased deposition of polyunsaturated fatty acids in cholesteryl ester and phospholipid fractions in livers of vitamin E-deficient rats and the phospholipid fraction of vitamin E-sufficient rats. The vitamin E-deficient rats exhibited necrosis of the liver, which was alleviated when aflatoxin was included in the diet, and calcification of the kidneys, which was potentiated by the dietary aflatoxin. No tumors were observed in these animals. In animals maintained on vitamin E-sufficient diets for 1 year, growth was depressed as a result of aflatoxin administration with the greatest depression occurring in the group fed corn oil. Spleen wt were decreased in all groups given aflatoxin. However, there were no changes in either plasma or liver cholesterol or total liver lipids which could be attributed to aflatoxin administration. When aflatoxin was fed with lard, the cholesteryl ester, triglyceride, and free fatty acid fractions of plasma had decreased amounts of the C20:4 acid. In the cholesteryl ester fraction only, this change was accompanied by increased levels of C16:0, C18:0, and C18:1 acids. In the liver phospholipids, there were increased levels of mono- and polyunsaturated fatty acids and decreases in the saturated fatty acids. All of the animals receiving aflatoxin exhibited severe necrosis and tumor formation in the kidneys; the animals fed lard had the highest level of involvement and those in the fat-free group the least. Liver pathology was the least marked among the rats fed the fat-free diet. Since aflatoxin-induced tumors are rich in lipids, the fat-free diet may be protective to the animal.     

The effect of dietary fat level and quality on plasma lipoprotein lipids and plasma fatty acids in normocholesterolemic subjects

This study examined the effect on the plasma lipids and plasma phospholipid and cholesteryl ester fatty acids of changing from a typical western diet to a very low fat (VLF) vegetarian diet containing one egg/day. The effect of the addition of saturated, monounsaturated or polyunsaturated fat (PUFA) to the VLF diet was also examined. Three groups of 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fat) for two weeks, and then in the next two weeks the dietary fat in each group was increased by 10% energy/week using butter, olive oil or safflower oil. The fat replaced dietary carbohydrate. The VLF diet reduced both the low density lipoprotein (LDL)-and high density lipoprotein (HDL)-cholesterol levels; addition of the monounsaturated fats and PUFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet led to significant reductions in the proportion of linoleic acid (18∶2ω6) and eicosapentaenoic acid (20∶5ω3) and to increases in palmitoleic (16∶1), eicosatrienoic (20∶3ω6) and arachidonic acids (20∶4ω6) in both phospholipids and cholesteryl esters. Addition of butter reversed the changes seen on the VLF diet, with the exception of 16∶1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18∶1 and significant decreases in all ω3 PUFA except 22∶6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18∶2 and 20∶4ω6 and significant decreases in 18∶1, 20∶5ω3 and 22∶5ω3. These results indicate that the reduction of saturated fat content of the diet (<6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturated fat, reduced the total plasma cholesterol levels by approximately 12% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deteterious since populations which habitually consume these diets have low rates of coronary heart disease. The addition of safflower oil or olive oil to a VLF diet produced favorable changes in the lipoprotein lipid profile compared with the addition of butter. The VLF diets and diets rich in butter, olive oil or safflower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma. This suggests that advice on plasma lipid lowering should also take into account the effect of the diet on the fatty acid profile of the plasma lipids.     

Dietary fat and fatty acids modulate cholesterol cholelithiasis in the hamster

We tested two hypotheses, i) whether the type and the amount of fat in the diet will affect the formation of cholesterol gallstones in the hamsters, and ii) whether palmitic acid, a major fatty acid component of butterfat, can act as a potentiator of cholesterol cholelithiasis in the hamster. Young, male golden Syrian hamsters (Sasco) were fed a semipurified diet containing casein, corn starch, cellulose and cholesterol (0.3%) to which various types and amounts of fat (butterfat, olive oil, menhaden oil, corn oil) were added. All diets contained 2% corn oil to supply essential fatty acids to the growing hamsters. No deaths or illness occurred during the experiment. Animals fed the semipurified diet plus 4% butterfat (group 1) had a gallstone incidence of 63%. Replacement of butterfat with either olive oil, corn oil or menhaden oil prevented the formation of cholesterol gallstones entirely (groups 2–4). When total butterfat was increased from 4% to 8% (group 8), the incidence of cholesterol gallstones increased to 80%. Substitution of 4% olive oil (group 5), corn oil (group 6), or menhaden oil (group 7) for the additional 4% butterfat significantly reduced gallstones to 35%, 45% and 30%, respectively. The replacement of 4% butterfat with 1.2% palmitic acid gave the highest incidence of cholesterol gallstones (95%). These results suggest that butterfat (and one of its components, palmitic acid) intensifies gallstone formation in this model whereas mono- and polyunsaturated fats act as inhibitors of cholesterol cholelithiasis. A fatty acid, possibly palmitic acid, appears to act as lithogen in our model.     

Dietary α-linolenic acid lowers postprandial lipid levels with increase of eicosapentaenoic and docosahexaenoic acid contents in rat hepatic membrane

This study was designed to examine the effects of dietary n−3 and n−6 polyunsaturated fatty acids (PUFA) on postprandial lipid levels and fatty acid composition of hepatic membranes. Male Sprague-Dawley rats were trained for a 3−h feeding protocol and fed one of five semipurified diets: one fat-free diet or one of four diets supplemented with 10% (by weight) each of corn oil, beef tallow, perilla oil, and fish oil. Two separate experiments were performed, 4-wk long-term and 4-d short-term feeding models, to compare the effects of feeding periods. Postprandial plasma lipid was affected by dietary fats. Triacylglycerol (TG) and total cholesterol levels were decreased in rats fed perilla oil and fish oil diets compared with corn oil and beef tallow diets. Hepatic TG and total cholesterol levels were also reduced by fish oil and perilla oil diets. Fatty acid composition of hepatic microsomal fraction reflected dietary fatty acids and their metabolic conversion. The major fatty acids of rats fed the beef tallow diet were palmitic, stearic, and oleic. Similarly, linoleic acid (LA) and arachidonic acid in the corn oil group, α-linolenic acid (ALA) and eicosapentaenoic acid (EPA) in the perilla oil group, and palmitic acid and docosahexaenoic acid (DHA) in the fish oil group were detected in high proportions. Both long- and short-term feeding experiments showed similar results. In addition, microsomal DHA content was negatively correlated with plasma lipid levels. Hepatic lipid levels were also negatively correlated with EPA and DHA contents. These results suggest that n−3 ALA has more of a hypolipidemic effect than n−6 LA and that the hypolipidemic effect of n−3 PUFA may be partly related to the increase of EPA and DHA in hepatic membrane.     

Effects of low casein and fish oil on hyperlipidemia and proteinuria in nephritic rats

The effects of amino acid-fortified low casein and fish oil (FO) diets on hyperlipidemia and proteinuria were studied in rats with nephrotoxic serum nephritis. After an antiserum injection, rats were maintained for 14 d on four different experimental diets: a 20% casein diet containing corn oil (CO) or FO, or an 8% casein diet supplemented with cystine plus threonine containing CO or FO. The 8% casein diets reduced urinary protein excretion in nephritic rats without inducing severe growth retardation or fatty liver compared with the basal 20% casein diets. Both the 8% casein diet and the FO diet decreased serum cholesterol, triglyceride and phospholipid levels in nephritic rats, and nonesterified fatty acid levels were decreased by FO feeding. In nephritic animals, hepatic cholesterol synthesis was decreased by the 8% casein diets compared with the 20% casein diets, and tended to be reduced by FO feeding between groups at the same casein levels. No effect of diet was observed on fatty acid synthesis among the nephritic rats. FO administration to the nephritic animals suppressed fecal steroid excretion. While lipoprotein lipase activity was unchanged among the nephritic rats, hepatic triglyceride lipase activity was reduced by either the 8% casein or FO diet. The results suggest that the hypolipidemic action of low casein diets may, at least in part, be due to reduced hepatic cholesterol synthesis and suppressed triglyceride secretion from the liver. They also suggest that the hypolipidemic action of FO may, at least in part, be due to reduced hepatic cholesterol synthesis and decreased fatty acid mobilization from peripheral adipose tissue.     

Tracer experiments to assess metabolic conversions of polyunsaturated fatty acids

Fifteen groups of rats were maintained on diets free of fat or supplemented with different levels of linoleate, arachidonate or linolenate. After 100 days on the diets the rats were sacrificed and liver slices were incubated with acetate-1-¹⁴C. The individual fatty acids were separated by gas chromatography and their radioactivity was determined by liquid scintillation counting. The C₂₀ esters were separated by GLC, collected, and the structures of the components were determined by ozonolysis. The acetate incorporation into the various polyunsaturated fatty acids was influenced by the previous dietary conditioning. The distributions of radioactivity indicated that metabolic reactions taking place in the rat liver are modified by dietary supply of essential fatty acids. Presented at the AOCS meeting, Houston, 1965.     

Dietary lipid,fatty acid oxidation and incorporation of carbon into cholesterol

Female rats (200 g) were fed a nutritionally adequate diet containing 1% by weight of corn oil (low-fat, LF), 21% of corn oil (CO) or 20% of beef tallow plus 1% of corn oil (BT) for two weeks. Food was removed for 8–12 hr, then each rat was refed for 1 hr. Each rat was injected ip with Na-³H-acetate and U-¹⁴C-Na-palmitate, (P),-oleate (O) or-linoleate (L). Expired CO₂ was collected for 2 hr. Liver, heart and serum were obtained for analysis of total lipid¹⁴C and³H and cholesterol¹⁴C and³H. Oxidation of L was twice as great as O or P when the LF diet was fed. CO and BT diets doubled oxidation of O to equal L, and increased oxidation of P, 50%. In liver and serum P was retained to a greater extent than O or L on BT and CO diets. Incorporation of acetate into total lipid was highest on LF diet and reduced by feeding either CO or BT. Incorporation of acetate into cholesterol was greater when BT or CO was fed than for LF.¹⁴C was incorporated into cholesterol in such small amounts that it was barely detectable and could not be counted accurately. Conclusions are that (a) dietary fat affects rate of oxidation of uniformly labeled palmitate and oleate, but not linoleate, (b) acetate is a more ready precursor to cholesterol than is fatty acid carbon, and (c) the acetate incorporated into cholesterol when polyunsaturated fat is fed is not derived directly from fatty acid carbon. The failure of incorporation of fatty acid carbon into cholesterol within 2 hr of administration opens the question of compartmentation of acetate as to its metabolic source. Colorado Agricultural Experiment Station Scientific Series Paper No. 1510.     

Effect of dietary safflower oil upon lipogenesis in neonatal lamb

The effect of dietary safflower oil upon lipogenesis has been investigated in neonatal lambs. Preliminary experiments with lambs suckled by their mothers showed that there was a 10-fold increase in the rate of incorporation of [¹⁴C] from acetate into fatty acids in adipose tissue slices during the first 10 days post partum. Barely detectable rates of [¹⁴C] acetate incorporation into fatty acids were found in liver slices from lambs during the same period. In lambs given cows' milk from birth until 11 days of age, there was also a 10-fold increase in the rate of lipogenesis in adipose tissue slices. Supplementing the diet of cows' milk with safflower oil (5 ml/lamb/day) resulted in significantly lower rates of lipogenesis in adipose tissue slices from 11 day old lambs. Administration of safflower oil had no effect upon the concentration of unesterified fatty acids, including linoleic acid, in the lamb adipose tissue slices. The data show that lipogenesis in ovine adipose tissue, like that in rodent liver and adipose tissue, is sensitive to dietary polyunsaturated fatty acids, and that, for the neonatal lamb, the effect of polyunsaturated fatty acids upon lipogenesis is not dependent upon an increase in the tissue concentration of polyunsaturated fatty acids.     

Thermal acclimation and dietary lipids alter the composition,but not fluidity,of trout sperm plasma membrane

The effect of a long-term adaptation of rainbow trout to 8 and 18°C combined with a corn oil-or a fish oil-supplemented diet on the characteristics of the spermatozoan plasma membrane was investigated. The experiment lasted up to 22 mon during which spermatozoa were collected from the mature males. Spermatozoan plasma membranes were isolated by nitrogen cavitation, and the cholesterol content, phospholipid composition and fatty acid pattern were investigated. Membrane viscosity was assessed on whole cells by electron spin resonance using spin-labeled phospholipids. Neither diet nor rearing temperature influenced the cholesterol content of the plasma membrane nor the phospholipid class distribution. The rearing temperature of the broodstock only slightly affected the phospholipid fatty acids. A minor decrease in 18∶0 and increase in monounsaturated fatty acids was observed for the cold-adapted fish. These modifications were not sufficient to affect membrane fluidity, and we conclude that trout spermatozoa do not display any homeoviscous adaptations in these conditions. On the contrary, the dietary fatty acid intake greatly modified the fatty acid profile of plasma membrane phospholipids. The fish oil-fed trout displayed a much higher n−3/n−6 fatty acid ratio than did the corn oil-fed ones, but the 22∶6n−3 levels remained unchanged. Modifications in plasma membrane composition by the diet were obtained although neither of the two diets was deficient in essential fatty acids. The enrichment in n−3 fatty acids, however, did not affect plasma membrane fluidity which was unchanged by the diets.