Regulation of mouse hepatic ATP-citrate lyase activity by dietary fat evidence for the presence of inactive enzyme

The induction of ATP-citrate lyase activity in mouse liver by dietary carbohydrate (glucose) is markedly reduced by including in the diet a source of polyunsaturated fatty acids. Within 72 h after changing from a standard mouse chow diet to a high carbohydrate diet containing 15% (w/w) of hydrogenated cottonseed oil (as a source of saturated fatty acids), the activity of mouse liver ATP-citrate lyase per milligram cytosolic protein was approx. 3-fold higher than that from mice fed a similar diet containing 15% (w/w) of corn oil. The rate of synthesis of ATP-citrate lyase relative to that for total protein and the rate of degradation of the enzyme were similar for both dietary groups. Elevated levels of enzyme activity in the hydrogenated cottonseed oil-fed livers were not accompanied by a similar increase in the amount of enzyme protein. To explain such findings, we propose that the activity of hepatic ATP-citrate lyase is regulated by dietary polyunsaturated fatty acids through a mechanism involving the conversion of a catalytically active form of the enzyme to a catalytically inactive form. A reversal of this conversion (inactive-active)_is evident within 72 h of removing the mice from the corn oil diet and placing them on the hydrogenated cottonseed oil diet. Futhermore, the conversion appears to be independent of the in vivo rate of synthesis of the enzyme.     

The influence of diet on the lipogenic response to thyroxine in rat liver.

ATP citrate lyase, acetyl-CoA synthetase, malic enzyme and hexose monophosphate dehydrogenase activities and rates of $\text{denovo}$ synthesis of long chain fatty acids from labeled acetate and citrate were measured in cell-free fractions of liver from rats fed various diets, with and without D- or L- thyroxine. Diets containign sucrose (vs. isocaloric glucose) or lard (vs. isocaloric corn oil) stimulated hepatic lipogenesis both in control and in thyroxine-treated rats. The lipogenic response to thyroxine was greatly modified by diet, except for an invariable rise in malic enzyme activity. With diets providing less than 6% of calories as linoleic acid, thyroxine increased fatty acid synthesis, depleted liver glycogen and retarded growth; when linoleic acid was increased to 16% of calories, thyroxine had no effect on fatty acid synthesis or growth and liver glycogen depletion was significantly attenuated. This response to dietary linoleic acid suggests that these phenomena may be largely secondary to the increased requirement for essential fatty acid in thyrotoxicosis. Further study should reveal the extent to which observed effects of excess thyroid hormone are amenable to control by dietary polyunsaturated fat.     

Cholesterol homeostasis in guinea pigs fed saturated and polyunsaturated fat diets

Whole body sterol balance, hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity, hepatic low-density lipoprotein (LDL) receptor levels and net tissue cholesterol concentrations were determined in guinea pigs fed either a corn oil- or lard-based purified diet for 6-7 weeks. In comparison to the saturated lard diet, the polyunsaturated corn oil diet resulted in a 34% reduction in plasma total cholesterol levels (P less than 0.02) and a 40% lower triacylglycerol level (P less than 0.02). Feeding the corn oil diet altered very-low-density lipoprotein (VLDL) and LDL composition; the percent cholesterol ester in both particles was decreased and the relative percentages of VLDL triacylglycerol and LDL phospholipid increased. The ratio of surface to core components of LDL from corn oil-fed guinea pigs was significantly higher compared to LDL from animals fed lard. Dietary fat quality had no effect on fecal neutral or acidic steroid excretion, net tissue accumulation of cholesterol, whole body cholesterol synthesis or gallbladder bile composition. Consistent with these results was the finding that fat quality did not alter either expressed (non-phosphorylated) or total hepatic HMG-CoA reductase activities. The hepatic concentrations of free and esterified cholesterol were significantly increased in corn oil-fed animals, as were cholesterol concentrations in intestine, adipose tissue, muscle and total carcass. Analysis of receptor-mediated LDL binding to isolated hepatic membranes demonstrated that the polyunsaturated corn-oil based diet caused a 1.9-fold increase in receptor levels (P less than 0.02). The data indicate that the hypocholesterolemic effects of dietary polyunsaturated fat in the guinea pig are not attributable to changes in endogenous cholesterol synthesis or catabolism but rather may result from a redistribution of plasma cholesterol to body tissue due to an increase in tissue LDL receptors.     

Suppression of hepatic fatty acid synthase by feeding alpha-linolenic acid rich perilla oil lowers plasma triacylglycerol level in rats

This study was performed to determine the effects of dietary perilla oil, a n-3 alpha-linolenic acid (ALA) source, on hepatic lipogenesis as a possible mechanism of lowering triacylglycerol (TG) levels. Male Sprague-Dawley rats were trained for a 3-hour feeding protocol and fed one of five semipurified diets as follows: 1% (w/w) corn oil control diet, or one of four diets supplemented with 10% each of beef tallow, corn oil, perilla oil, and fish oil. Two separate experiments were performed to compare the effects of feeding periods, 4 weeks and 4 days. Hepatic and plasma TG levels were decreased in rats fed perilla oil and fish oil diets, compared with corn oil and beef tallow diets. The activities of hepatic lipogenic enzymes such as fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase, and malic enzyme were suppressed in the fish oil, perilla oil, and corn oil-fed groups, and the effect was the most significant in the fish oil-fed group. Also, the activities of glycolytic enzymes, glucokinase, and L-pyruvate kinase showed the similar trend as that of lipogenic enzymes. The activity of FAS, the key regulatory enzyme in lipogenesis, was positively correlated with hepatic and plasma TG levels and reduced significantly in the perilla oil-fed group compared with corn oil-fed group. In addition, the FAS activity was negatively correlated with the hepatic microsomal content of EPA and DHA. In conclusion, suppression of FAS plays a significant role in the hypolipidemic effects observed in rats fed ALA rich perilla oil and these effects were associated with the increase of hepatic microsomal EPA and DHA contents.     

Effect of essential fatty acid deficiency on release of triglycerides by the perfused rat liver

Studies are reported on release of triglycerides during perfusion of livers of male Sprague-Dawley rats fed a fat-free diet or diets containing hydrogenated coconut oil or corn oil. Perfusions were carried out with Krebs-Ringer bicarbonate buffer containing albumin with and without infusion of oleate or linoleate. Infusion with sodium oleate or linoleate caused an accumulation of triglycerides in the livers of the corn oil-fed animals and stimulated the release of triglycerides into the perfusing medium. In similar experiments with essential fatty acid-deficient animals, which were fed fat-free diets or diets containing hydrogenated coconut oil, there was no increase in secretion of triglycerides into the perfusate, and the amount of triglyceride which accumulated in the liver was greater than in the livers of the control (corn oil-fed) animals. Tracer experiments with oleate-1-(14)C or linoleate-1-(14)C also showed that with livers of essential fatty acid-deficient animals, secretion of triglyceride into the perfusate was not stimulated by infusion of fatty acids into the perfusing medium. It is concluded that impairment of the secretion of triglycerides is a factor in the accumulation of fat in the livers of essential fatty acid-deficient animals.     

Attenuation of mammary duct development by menhaden oil in BALB/c mice

The predominant polyunsaturated fatty acids of the n-6 family found in corn oil (CO) are crucial for normal mammary duct formation when fed to animals. However, as shown here, not all polyunsaturated fatty acids are equally effective in stimulating mammary gland development. The n-3 fatty acids in a 10% menhaden oil (MO) diet fed to mice effectively reduced both the diameter and the length of the growing mammary ducts. Previously, we demonstrated a similar reduction in duct growth by feeding a 10% fat diet high in those saturated fats found in hydrogenated cotton seed oil. The inhibited rate of duct maturation caused by hydrogenated cotton seed oil was reversed when the mice were allowed to mature on a diet containing n-6 fatty acids prior to feeding the saturated fat diet. The addition of 1% CO to a 9% hydrogenated cotton seed oil diet fed to immature mice was also sufficient to restore duct growth. Mice fed menhaden oil diets, on the other hand, continued to show impaired ductal growth well into adulthood. Examination of the ovaries from MO-fed mice as compared with CO-fed mice revealed significantly fewer corpora lutea. When exogenous progesterone was given to MO-fed mice, ductal growth was partially restored, but not to the extent seen in mice fed corn oil diets. Investigation of the fatty acid contents of livers of these mice revealed reduced amounts of arachidonate (20:4) in MO-fed mice when compared with CO-fed animals. The addition of 1% CO to the 9% MO diets did not alter the arachidonate content, indicating a block in the conversion of linoleate (18:2) to 20:4 by the n-3 fatty acids. Hence, dietary n-6 fatty acids are essential for normal mammary ductal development when fed prior to maturation. Although saturated rats are ineffective, n-3 fatty acids can partially substitute for the required n-6 fatty acids in both ductal and ovarian development.     

Effects of dietary fat on mammary development relative to age and hormones in BALB/c mice

Earlier studies reported that mammary ducts grew faster if the 10% fat in the diet was composed of oils containing polyunsaturated fatty acids (corn oil: CO) compared to hydrogenated cottonseed oil (HCTO), which is devoid of such fatty acids. These experiments were primarily carried out in immature mice and left unanswered questions regarding the effects of dietary fats on more differentiated stages of mammary development. The use of transplanted ducts permitted the study of mammary growth rates in adult mice. If the diet was started when the animals were adults, there was no difference in the growth rate of those fed HCTO diet compared to those fed CO diet. However, when the diets were fed to immature mice, the mammary gland grew slower in mice fed the HCTO diet, confirming our earlier observations. The HCTO and CO diets caused no difference in the growth rate or morphology of fine ducts and alveoli that developed during pregnancy. Furthermore, no differences were seen in female mice following 6 weeks of progesterone administration begun at 3 weeks of age. Experiments that used male mice to examine the initial stages of mammary duct growth also showed that the effect of dietary fat was not observed when estrogen (E) or E and progesterone (P) were injected. In addition, there was no effect of dietary fat in ovariectomized 3-week-old females when any dose of E was administered from 0.01 to 1 microgram/day. Examination of the ovaries from mice fed either HCTO or CO diets from 3 to 9 weeks or 3 to 13 weeks of age showed that mice fed HCTO diet did not develop corpora lutea, while those fed CO diet had normal appearing ovaries. The HCTO diet inhibits normal maturation of the follicle and corpus luteum formation. We conclude that the effect of the dietary fat on the developing mouse is on the maturation of the ovary and subsequently on mammary growth.     

Olive oil increases the hepatic triacylglycerol content in mice by a distinct influence on the synthesis and oxidation of fatty acids

Diet supplementation with olive oil exerts beneficial effects on an organism, even if an increase in the level of hepatic lipids has been concomitantly observed. This study was therefore designed to investigate whether the stimulation of lipogenesis was responsible for the olive oil-induced hepatic fat accumulation. In mice fed for 8 weeks with an olive oil-enriched diet, an increase of about 2.6 fold in the level of liver triglycerides was found in comparison to animals fed with a corn oil-containing diet. Despite that, no increase in the activities of cytosolic lipogenic enzymes or of the mitochondrial tricarboxylate carrier was found; on the contrary, a decrease in the activity of carnitine palmitoyltransferase I was observed. This impairment of fatty acid oxidation, which was not apparent in corn oil-fed animals, may have had a role in the increase of hepatic lipid content found in the olive oil-fed mice.     

The influence of estrogen on hepatic cholesterol metabolism and biliary lipid secretion in rats fed fish oil

Both estrogen and dietary n-3 polyunsaturated fatty acids are known to be hypocholesterolemic, but appear to exert their effects by different mechanisms. In this study, the interaction between dietary fish oil (rich in n-3 polyunsaturated fatty acids) and estrogen in the regulation of hepatic cholesterol metabolism and biliary lipid secretion in rats was studied. Rats fed a low fat or a fish oil-supplemented diet for 21 days were injected with 17alpha-ethinyl estradiol (5 mg/kg body weight) or the vehicle only (control rats) once per day for 3 consecutive days. Estrogen-treatment led to a marked reduction in plasma cholesterol levels in fish oil-fed rats, which was greater than that observed with either estrogen or dietary fish oil alone. The expression of mRNA for cholesterol 7alpha-hydroxylase was decreased by estrogen in rats fed a low fat or a fish oil-supplemented diet, while the output of cholesterol (micromol/h/kg b.wt.) in the bile was unchanged in both groups. Cholesterol levels in the liver were increased by estrogen in rats given either diet, but there was a significant shift from cholesterol esterification to cholesteryl ester hydrolysis only in the fish oil-fed animals. Estrogen increased the concentration of cholesterol (micromol/ml) in the bile in rats fed the fish oil, but not the low fat diet. However, the cholesterol saturation index was unaffected. The output and concentration of total bile acid was also unaffected, but changes in the distribution of the individual bile acids were observed with estrogen treatment in both low fat and fish oil-fed groups. These results show that interaction between estrogen-treatment and dietary n-3 polyunsaturated fatty acids causes changes in hepatic cholesterol metabolism and biliary lipid secretion in rats, but does not increase the excretion of cholesterol from the body.     

Regulation of guinea pig hepatic acyl-coa:cholesterol acyltransferase activity by dietary fat saturation and cholesterol

We measured the interactive effects of dietary cholesterol and fat on the regulation of hepatic acyl-CoA:cholesterol acyltransferase (ACAT) activity and its relationship to hepatic microsomal lipid composition in guinea pigs fed 15 g/100 g (w/w) fat diets (corn oil, olive oil, or lard) with 0.01, 0.08, 0.17, or 0.33 g/100 g (w/w) added cholesterol. Guinea pigs exhibited a dose dependent increase in hepatic microsomal ACAT activity, with increasing levels of cholesterol intake (P < 0.001) in all dietary fat groups. Animals fed monounsaturated olive oil had the highest hepatic ACAT activity with the exception of the 0.33 g/100 g cholesterol diet (P < 0.001). There were no differences in ACAT activity with intake of polyunsaturated corn oil or saturated lard. Dietary cholesterol resulted in increased microsomal free cholesterol (FC) concentrations in a dose dependent manner but had no effects on microsomal phosphatidylcholine (PC) concentrations. Guinea pigs fed olive oil generally had the highest microsomal FC/PC molar ratios, and hepatic ACAT activities correlated significantly with this parameter. After modification of the lipid compositions of the microsomes from guinea pigs fed the 12 test diets with FC/PC liposome treatment, microsomal ACAT activities remained significantly related to the microsomal FC/PC molar ratios, and dietary fat type did not affect this correlation. Our findings do not support the hypothesis that the stimulation of hepatic ACAT activity with cholesterol intake is enhanced by polyunsaturated fat intake. The data demonstrate that although dietary fat type and cholesterol amount have differential effects on hepatic ACAT activity, substrate availability, expressed as microsomal FC/PC molar ratio, is a major regulator of hepatic microsomal ACAT activity.     

Alteration of rat adipose tissue lipolytic response to norepinephrine by dietary fatty acid manipulation.

The present study clearly shows that, by feeding rats a semi-synthetic diet of known composition enriched with saturated fatty acids, the epididymal fat pad responsiveness to norepinephrine $\text{in}\text{vitro}$ can be abolished relative to fat pads from animals fed a similar diet but enriched with polyunsaturated fatty acids. Addition of varying concentrations of norepinephrine to the incubation medium produced a clear dose-response relationship in fat pads from animals fed diet enriched with polyunsaturated fatty acids while no effect of norepinephrine was apparent at any dose level in fat tissue from animals fed saturated fatty acids. These changes in lipolytic responsiveness were concurrent with alterations in fatty acid compositions of adipose tissue phospholipids and triglycerides as well as in total tissue contents of phospholipids and cholesterol.     

Oxidative stress in mice

The aim of this study was to analyze the effect of high dietary Fe on liver antioxidant status in mice fed a corn-oil-enriched diet. Male Balb/c mice were fed for 3 wk with a standard diet enriched with 5% by weight of corn oil with adequate Fe (FCO diet) or supplemented with 1% carbonyl Fe (FCOFe diet). The control group was fed a standard diet. The high-Fe diet induced a twofold increase of hepatic Fe level. However, an increase of thymic Fe level has been induced solely by dietary fat. The hepatic copper (Cu) level slightly decreased in the FCO diet. In the spleen, the high-Fe diet-induced increase of Fe level was negatively correlated with the Cu level. The antioxidant status was influenced by both dietary fat and Fe. Mice fed corn-oil-enriched diets had a higher concentration of thiobarbituric acid-reactive substances (TBARS), with a greater increase in the FCOFe diet. Fatty acid analysis showed decreased n−3 and n−6/n−3 ratio, particularly in the FCOFe diet. Hepatic Cu/Zn superoxide dismutase (CuZn-SOD) activity was decreased in FCO diet, and Fe supplementation caused a further decrease in the enzyme activity. These results suggest that feeding with corn oil-enriched diet increases oxidative damage by decreasing antioxidant enzyme defense. The high-Fe diet additionally affects the antioxidant defense system, further increasing the tissue's susceptibility to lipid peroxidation. Additionally, both corn-oil- and Fe-enriched diets have increased the Cu requirement in mice.     

Delta-aminolevulinate dehydratase, a zinc dependent enzyme

Erythrocyte and liver tissue δ-aminolevulinate dehydratase activity was determined in rats fed a semipurified diet under controlled nutritional intake of zinc and copper. A significant decrease in enzymatic activity was observed in animals fed low zinc diet, while dietary copper had no effect. $\text{In vitro}$ addition of zinc to the erythrocyte preparations obtained from rats on low zinc diet produced a slight increase in enzymatic activity. It appears that, even though zinc may be the metal ion activator of δ-aminolevulinate dehydratase, the requirement of this metal is at the site of synthesis of this enzyme.     

Effects on drug metabolism of carbaryl and 1-naphthol in the mouse

The effects of carbyl and 1-naphthol on hepatic microsomal drug-metabolizing enzyme systems were investigated. The agents were fed at a level of 25 mmol/kg of feed to groups of young male Swiss-Webster mice for 14-day periods. Body weight was depressed by carbaryl, but not by 1-naphthol. The rates of $\text{in vitro}$ metabolism of aniline and benzphetamine were greater than control rates in livers of mice fed carbaryl, but the rate of $\text{in vivo}$ hydrolysis of the carbamate insecticide Zectran was decreased by carbaryl feeding. Administration of 1-naphthol did not change the rates of $\text{in vitro}$ metabolism of either aniline or benzphetamine. Hepatic microsomal concentrations of cytochromes P-450 and b₅ were increased by carbaryl, but feeding of 1-naphthol did not affect levels of either cytochrome. Radiolabeled pentobarbital disappeared from the blood of carbaryl-fed mice more rapidly than from the blood of control animals, and carbaryl-fed mice slept a shorter period of time than controls following pentobarbital administration. The LD50 of an acute oral dose of carbaryl was increased two-fold by feeding carbaryl for 14 days. It was concluded that carbaryl is a weak inducer of hepatic microsomal drug-metabolizing activity, and that the effects observed are not likely due to 1-naphthol.     

The effect of dietary fat on lipogenesis in mammary gland and liver from lactating and virgin mice

1. Virgin and lactating C(3)H mice maintained on laboratory chow were transferred to a high-fat (15% corn oil) or a fat-free diet 3 days before being killed. 2. The linoleate content of liver, mammary gland and milk was decreased in lactating mice given the fat-free diet but was increased in those fed on the high-fat diet. Changes in linoleate content and mammary gland followed a similar but much less marked trend in virgin animals. 3. Hepatic fatty acid synthesis in lactating and virgin mice fed on the fat-free diet was higher than in corresponding animals fed on either the chow or the high-fat diet. The lipogenic capacity of livers from mice fed on either the chow or the high-fat diet was greater in lactating than in virgin animals. These changes in hepatic lipogenic capacity were accompanied by alterations in the specific activities of certain enzymes involved in fat synthesis. 4. Mammary gland from virgin and lactating animals showed no such adaptation to dietary fat. Results indicate that fatty acid synthesis in neither mammary-gland parenchymal cells nor mammary-gland adipose cells can be influenced by dietary fat in the same way as in the hepatocyte.     

The DNA damage checkpoint protein ATM promotes hepatocellular apoptosis and fibrosis in a mouse model of non-alcoholic fatty liver disease

Steatoapoptosis is a hallmark of non-alcoholic fatty liver disease (NAFLD) and is an important factor in liver disease progression. We hypothesized that increased reactive oxygen species resulting from excess dietary fat contribute to liver disease by causing DNA damage and apoptotic cell death, and tested this by investigating the effects of feeding mice high fat or standard diets for 8 weeks. High fat diet feeding resulted in increased hepatic H₂O₂, superoxide production, and expression of oxidative stress response genes, confirming that the high fat diet induced hepatic oxidative stress. High fat diet feeding also increased hepatic steatosis, hepatitis and DNA damage as exemplified by an increase in the percentage of 8-hydroxyguanosine (8-OHG) positive hepatocytes in high fat diet fed mice. Consistent with reports that the DNA damage checkpoint kinase Ataxia Telangiectasia Mutated (ATM) is activated by oxidative stress, ATM phosphorylation was induced in the livers of wild type mice following high fat diet feeding. We therefore examined the effects of high fat diet feeding in Atm-deficient mice. The prevalence of apoptosis and expression of the pro-apoptotic factor PUMA were significantly reduced in Atm-deficient mice fed the high fat diet when compared with wild type controls. Furthermore, high fat diet fed Atm^−/− mice had significantly less hepatic fibrosis than Atm^+/+ or Atm^+/− mice fed the same diet. Together, these data demonstrate a prominent role for the ATM pathway in the response to hepatic fat accumulation and link ATM activation to fatty liver-induced steatoapoptosis and fibrosis, key features of NAFLD progression.     

The DNA damage checkpoint protein ATM promotes hepatocellular apoptosis and fibrosis in a mouse model of non-alcoholic fatty liver disease

Steatoapoptosis is a hallmark of non-alcoholic fatty liver disease (NAFLD) and is an important factor in liver disease progression. We hypothesized that increased reactive oxygen species resulting from excess dietary fat contribute to liver disease by causing DNA damage and apoptotic cell death, and tested this by investigating the effects of feeding mice high fat or standard diets for 8 weeks. High fat diet feeding resulted in increased hepatic H₂O₂, superoxide production, and expression of oxidative stress response genes, confirming that the high fat diet induced hepatic oxidative stress. High fat diet feeding also increased hepatic steatosis, hepatitis and DNA damage as exemplified by an increase in the percentage of 8-hydroxyguanosine (8-OHG) positive hepatocytes in high fat diet fed mice. Consistent with reports that the DNA damage checkpoint kinase Ataxia Telangiectasia Mutated (ATM) is activated by oxidative stress, ATM phosphorylation was induced in the livers of wild type mice following high fat diet feeding. We therefore examined the effects of high fat diet feeding in Atm-deficient mice. The prevalence of apoptosis and expression of the pro-apoptotic factor PUMA were significantly reduced in Atm-deficient mice fed the high fat diet when compared with wild type controls. Furthermore, high fat diet fed Atm^?/? mice had significantly less hepatic fibrosis than Atm^+/+ or Atm^+/? mice fed the same diet. Together, these data demonstrate a prominent role for the ATM pathway in the response to hepatic fat accumulation and link ATM activation to fatty liver-induced steatoapoptosis and fibrosis, key features of NAFLD progression.     

Hepatic and adipose tissue lipogenic enzyme mRNA levels are suppressed by high fat diets in the rat

Small changes in lipogenic enzyme activity induced by dietary fats of different composition may, over the long term, have significant impact on the development of obesity. We have investigated the effect of high fat diets (45% of calories as fat) on abundance of mRNA encoding fatty acid synthetase (FAS) and glycerophosphate dehydrogenase (GPDH) in male Sprague-Dawley rats. When caloric intake was equal, the relative amount of hepatic FAS mRNA was greater in rats fed a saturated compared to a polyunsaturated fat diet. This difference could not be attributed to diet-induced changes in plasma insulin concentration. However, both fat diets suppressed hepatic FAS mRNA compared to a sucrose diet. Close correlation between FAS specific activity and the relative amount of mRNA suggested that regulation was mainly at a pre-translational level. Adipose tissue FAS mRNA was suppressed by the two fat diets equally while GPDH mRNA was unaffected by dietary composition. Retroperitoneal fat pads were significantly larger in rats fed saturated compared to those fed polyunsaturated fat for 26 weeks. We concluded that dietary saturated fats fail to suppress hepatic de novo lipogenesis as effectively as polyunsaturated fats, which may have implications for the prevention of obesity in humans.     

The prostaglandin outflow from perfused mesenteric vasculature of rats fed different fats

The effects of dietary n-6 polyunsaturated fatty acids and replacement with saturated fat or fish oil on the prostaglandin outflow from perfused mesenteric vasculature in rats were studied. Seventy-two weanling male rats were fed ad libitum a semi-synthetic diet supplemented with 10% by weight of oil, composed wholly of n-6 fatty acid-rich evening primrose oil, or replaced partly or completely (25, 50, 75 or 100%) by n-6 fatty acid-deficient fish oil or hydrogenated coconut oil for 8 weeks. The outflows of 6-keto-PGF1 alpha, thromboxane B2, and prostaglandin E from the perfused mesenteric vasculature were measured at 60 min-time point after starting the perfusion. In general, the release of prostanoids from the mesenteric vasculature was significantly reduced in rats fed a diet in which evening primrose oil was partly or completely replaced by either hydrogenated coconut or fish oil. This was probably due to the insufficient conversion of linoleic acid to arachidonic acid. The extent of reduction was greater in fish oil-fed than in hydrogenated coconut oil-fed rats, while the levels of arachidonic acid in aortic phospholipids were similar between these two groups. This result implies that the greater reduction of prostaglandin synthesis in rats fed fish oil was due to the inhibitory effect of eicosapentaenoic and docosahexaenoic acids in fish oil on the conversion of arachidonate to eicosanoids.     

High density lipoprotein accumulation in perfusates of isolated livers of African green monkeys. Effects of saturated versus polyunsaturated dietary fat

To determine whether altered hepatic secretion of HDL is part of the mechanism by which polyunsaturated fat lowers plasma HDL concentration, we have studied HDL secretion in the isolated perfused livers of African green monkeys fed an atherogenic diet containing either safflower oil as the polyunsaturated fat or butter as the saturated fat. During recirculating perfusion with a lipoprotein-free medium, livers from safflower oil-fed animals produced 21% less HDL mass on the average than those from butter-fed animals. Newly secreted hepatic HDL were characterized after their isolation and subfractionation by a combination of agarose column chromatography and density gradient ultracentrifugation. In both diet groups the HDL were heterogeneous in size, morphology, and composition and consisted of discoidal particles ranging in diameter from greater than 200 A to as little as 50 A. Large, discoidal particles that were rich in apoE and apoA-I were separated from small particles that were poor in apoE but rich in apoA-I. All hepatic HDL subfractions contained only small amounts of cholesteryl ester and triglyceride. The hepatic particles resembled in composition and structure the large variety of HDL particles found in the plasma of patients with the familial deficiency of lecithin:cholesterol acyltransferase. Accordingly, perfusate LCAT activity was measured and found to be 2% or less than that in monkey plasma. We conclude that the perfused monkey liver produces a variety of nascent HDL that are relatively unmodified by the post-secretory metabolic events which normally occur in blood plasma in vivo, and that livers of polyunsaturated fat-fed monkeys secrete fewer plasma HDL precursor particles than do those of saturated fat-fed monkeys.