Mercury inhibition of fatty acid synthesis in chicks.

Male chicks were fed a commercial ration and were given drinking water which contained 0, 50, 100, 150, 200 or 300 mug of mercury/ml as mercuric chloride from hatching to 3 weeks of age. In one experiment, the mercuric chloride was administered by injection into the abdominal cavity rather than in the drinking water. At 3 weeks the chicks were killed, and the livers were removed and weighed. The activity of fatty acid synthetase in the 800 X gav supernatant fractions of the liver homogenates and in vivo incorporation of [14C]acetate into liver and carcass fatty acids and respiratory 14CO2 was determined as indicated. Administration of mercury at a treatment level of 300 mug/ml of drinking water depressed growth, feed and water consumption, liver weight, hepatic fatty acid synthetase activity, and in vivo incorporation of [14C]acetate into liver and carcass fatty acids, and increased the production of respiratory 14CO2 as compared with controls. In experiments in which graded doses of mercury were administered, body weights, liver weights, and feed and water intakes of the chicks receiving 0, 50 and 100 mug of mercury/ml of drinking water were similar to each other, but these parameters were severely depressed by 200 mug of mercury/ml of drinking water. Mercury caused a dose-related decrease of fatty acid synthetase activity. Incorporation of [14C]acetate into carcass fatty acid was depressed by 50 and 200 mug of mercury/ml of drinking water; incorporation into liver fatty acids and production of respiratory 14CO2 was not affected by mercury. Intra-abdominal injection of 6 mg of mercury/100 g body weight (as mercuric chloride) into well alimented chicks depressed hepatic fatty acid synthetase activity at 1 h post-injection. The data are consistent with the hypothesis that a portion of the effects of mercury on fatty acid synthesis are direct rather than a secondary effect of inanition.     

Effect of aflatoxin B1 on lipids of rat tissues.

The effect of aflatoxin B1 on lipids of liver, kidney, adipose and plasma of rats was studied. A single dose administration (6 mg/kg body weight) increased liver and kidney weights and their total lipids within 24 h. Increase in liver lipids was confined mainly to phospholipid and cholesterol, whereas triglycerides showed a significant decrease. Adipose tissue triglycerides were, however, increased. Plasma showed decreases in triglycerides, free fatty acids and cholesterol. Incorporation studies with palmitate-1-14C revealed increased incorporation in adipose tissue lipids and decreased incorporation in liver and plasma lipids, thereby indicating an increased synthesis of lipids in adipose. Their mobilization to plasma was, however, inhibited, hence the low levels of triglyceride in liver. But the adrenals showed hypo-activity upon aflatoxin B1 administration.     

Contribution of omega-oxidation to fatty acid oxidation by liver of rat and monkey.

Contributions of omega-oxidation to overall fatty acid oxidation in slices from livers of ketotic alloxan diabetic rats and of fasted monkeys are estimated. Estimates are made from a comparison of the distribution of 14C in glucose formed by the slices from omega-14C-labeled compared to 2-14C-labeled fatty acids of even numbers of carbon atoms and from [1-14C]acetate compared to [2-14C]acetate. These estimates are based on the fact that 1) the dicarboxylic acid formed via omega-oxidation of a omega-14C-labeled fatty acid will yield [1-14C]acetate and [1-14C]succinate on subsequent beta-oxidation, if beta-oxidation is assumed to proceed to completion; 2) only [2-14C]acetate will be formed if the fatty acid is metabolized solely via beta-oxidation; and 3) 14C from [1-14C]acetate and [1-14C]succinate is incorporated into carbons 3 and 4 of glucose and 14C from [2-14C]acetate is incorporated into all six carbons of glucose. From the distributions found, the contribution of omega-oxidation to the initial oxidation of palmitate by liver slices is estimated to between 8% and 11%, and the oxidation of laurate between 17% and 21%. Distributions of 14C in glucose formed from 14C-labeled palmitate infused into fasted and diabetic rats do not permit quantitative estimation of the contribution of omega-oxidation to fatty acid oxidation in vivo. However, the distributions found also indicate that, of the fatty acid metabolized by the whole animal in the environment of glucose formation, at most, only a minor portion is initially oxidized via omega-oxidation. As such, omega-oxidation cannot contribute more than a small extent to the formation of glucose.     

Influence of dietary sources of fat on lipid synthesis in mink (Mustela vison) mammary tissue

• 1.1. The fatty acid composition of the triglyceride fraction of mink milk sampled during mid-lactation (day 28 post partum) from two nursing mink was compared to that of plasma samples and to the fatty acid composition of the feed rations used.
• 2.2. Chemical analysis of the triglyceride composition of mink milk demonstrated only minute concentrations of fatty acids with a chain length below C₁₄.
• 3.3. The saturated C_16:0- and C_18:0-unit fatty acids in mink milk made up for 24–40% of the total amount of fatty acids extracted, the remainder being represented by mono and polyunsaturated long-chain (C₁₆-C₂₄) fatty acids.
• 4.4. Preliminary in vitro experiments proved the incorporation of¹⁴C-labelled glucose, acetate or palmitate into triacylglycerols in cultures of mink mammary tissue to be linear for at least 2 hr.
• 5.5. The in vitro capacity for de novo fatty acid synthesis in mink mammary tissue using 14C-labelled glucose or acetate was low, i.e. ranging from 0.096–0.109 nmol/g (fresh tissue)/min, and amounted to only about 5% of that obtained in the case of [¹⁴C]palmitic acid incubation.
• 6.6. Following ¹⁴C-labeIled acetic or palmitic acid incubation of mink mammary tissue neither desaturation nor chain elongation was observed.
• 7.7. In response to long-term feeding on rations with two different sources of animal fat (F = fish oil or L = lard) the influence of compositional changes in dietary neutral lipids on the fatty acid composition of the lipids of mink milk is discussed.

     

Metabolic Turnover of Fatty Acids and Acylglycerols in Rat Sciatic Nerve

To explain the discrepancy between the low level and high metabolic activity of endoneurial free fatty acids (FFAs) and triacylglycerol (TG), levels of de novo synthesized FFA and acylglycerols were measured in rat sciatic endoneurium at various intervals after endoneurial microinjection of [14C]acetate. Soon after injection (less than 10 min), the [14C]acetate was metabolized to FFA and incorporated into diacylglycerol (DG), TG, sterols, ceramides, and various phospholipids. The proportions of 14C-labeled FFA, DG, TG, and ceramides to total 14C-labeled lipids decreased, whereas those of phospholipids and cerebrosides increased with time after injection. These findings suggest that rapid turnover of FFA and TG may contribute to their low level in sciatic endoneurium. The de novo synthesized fatty acids were largely incorporated into phosphatidylcholine (approximately 50% of total 14C-labeled phospholipids), probably via the cytidine nucleotide pathway using 1,2-DG as a metabolic intermediate. Hydrolysis of [14C]phosphatidylcholine revealed that fatty acids were labeled at both the C-1 (approximately 43%) and C-2 (approximately 57%) positions. On the other hand, a temporal association between decreased amounts of 14C-label in ceramides and increased amounts of 14C-label in sphingomyelin and galactocerebrosides supports the hypothesis that peripheral nerve galactocerebroside is derived, in vivo, from ceramide via acylation of sphingosine. This exclusive labeling of endoneurial lipids by endoneurial microinjection of labeled precursor provides a unique model for studying synthesis and metabolic turnover of membrane lipids in experimental neuropathies.     

Incorporation of acetate-1-14C into lipids by the perfused liver of normal, X-irradiated, or partially hepatectomized rats

In order to study lipid metabolism in the liver without interference due to transport from and to the liver the isolated livers of normal, X-irradiated, and partially hepatectomized rats were perfused with acetate-1-(14)C and the distribution of radioactivity in total lipids, total fatty acids, individual lipids, and fatty acids of individual lipids was determined. In X-irradiated animals, an increased incorporation of acetate into many lipids, particularly into cholesterol, was observed. Lipids in the liver of the partially hepatectomized rats exhibited a marked increase in triglyceride content together with a decreased rate of incorporation into all but the phospholipid fractions. It is concluded that the increase usually observed in lipid pontent of the regenerating liver is due to the changes in transcort rather than to changes in synthesis. The changes observed in irradiated liver could be the result of alterations in the metabolism of precursors common to most lipids.     

In vitro and in vivo synthesis of long-chain fatty acids from (1-14C) acetate in the renal papillae of rats.

1. The relationship between the rate of [1-14C] acetate incorporation into the fatty acids of renal papillary lipids and the acetate concentration in the medium has been measured. 2. [1-14C] acetate was incorporated mainly into fatty acids of phospholipids and triacylglycerols. Only a few per cent of the radioactivity was found in the free fatty acid fraction. 3. The major part of the [1-14C] acetate was found to be incorporated by a chain elongation of prevalent fatty acids. The major component of the poly-unsaturated fatty acids in triacylglycerols and the major product of fatty acid synthesis from [1-14C] acetate in vitro was demonstrated by mass spectrometry to be docosa-7,10,13,16-tetraenoic acid. 4. The radioactivity of docosa-7,10,13,16-tetraenoic acid accounted for 40% of total radioactivity in triacylglycerol fatty acids (lipid droplet fraction) and 20% of total radioactivity in membrane phospholipid fatty acids.     

Relative significance of exogenous and de novo synthesized fatty acids in the formation of rumen microbial lipids in vitro

Mixed rumen microorganisms (MRM) or suspensions of rumen Holotrich protozoa obtained from a sheep were incubated anaerobically with [1-(14)C]linoleic acid, [U-(14)C]glucose, or [1-(14)C]acetate. With MRM, the total amount of fatty acids present did not change after incubation. An increase in fatty acids esterified into sterolesters (SE) and polar lipids at the expense of free fatty acids was observed. This effect was intensified by the addition of fermentable carbohydrate to the incubations. Radioactivity from [1-(14)C]linoleic acid was incorporated into SE and polar lipids with both MRM and Holotrich protozoa. With MRM the order of incorporation of radioactivity was as follows: SE > phosphatidylethanolamine > phosphatidylcholine. With Holotrich protozoa, the order of incorporation was phosphatidylcholine > phosphatidylethanolamine > SE. With MRM the radioactivity remaining in the free fatty acids and that incorporated into SE was mainly associated with saturated fatty acids, but a considerable part of the radioactivity in the polar lipids was associated with dienoic fatty acids. This effect of hydrogenation prior to incorporation was also noted with Holotrich protozoa but to a much lesser extent. Small amounts of radioactivity from [U-(14)C]glucose and [1-(14)C]acetate were incorporated into rumen microbial lipids. With protozoa incubated with [U-(14)C]glucose, the major part of incorporated radioactivity was present in the glycerol moiety of the lipids. From the amounts of lipid classes present, their radioactivity, and fatty acid composition, estimates were made of the amounts of higher fatty acids directly incorporated into microbial lipids and the amounts synthesized de novo from glucose or acetate. It is concluded that the amounts directly incorporated may be greater than the amounts synthesized de novo.     

Alterations in cholesterol and fatty acid biosynthesis in rat liver homogenates by aryloxy acids (Short Communication)

2,4-Dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid inhibited the incorporation of [2-(14)C]mevalonate into cholesterol and non-saponifiable lipids. Both compounds inhibited the conversion of [1-(14)C]isopentenyl pyrophosphate into cholesterol and the synthesis of cholesterol and fatty acids from [2-(14)C]acetate. There was no inhibition of the conversion of [1-(14)C]mevalonate into CO(2). At low concentrations (0.5mm) of the compounds there was a stimulation of acetate incorporation into fatty acids.     

Effects of the selective herbicide fluazifop on fatty acid synthesis in pea (Pisum sativum) and barley (Hordeum vulgare).

Concentrations of fluazifop-butyl sprayed on intact plants caused large decreases in the incorporation of radioactivity from [1-14C]acetate into lipids of barley (Hordeum vulgare) leaves and stems, but did not affect leaves or stems of pea (Pisum sativum). Labelling of all acyl lipids, but not pigments, was reduced. The effects of the active acid form, fluazifop, were also determined in leaf pieces and chloroplasts. Concentrations of (R,S)-fluazifop up to 100 microM had no affect upon quality or quantity of fatty acids produced from [1-14C]acetate in pea. In barley, however, 100 microM-(R,S)-fluazifop caused 89% (leaf) or 100% (chloroplasts) inhibition in labelling of fatty acids from [1-14C]acetate. Lower concentrations of fluazifop (less than 25 microM) caused incomplete inhibition and significant decreases in the proportion of C18 fatty acids synthesized, particularly by isolated chloroplasts. Synthesis of fatty acids from [2-14C]malonate was also inhibited (59%) in barley leaf tissue by 100 microM-(R,S)-fluazifop. The labelling pattern of products showed that elongation reactions were unaffected by the herbicide, but synthesis de novo was specifically diminished. By using resolved stereoisomers, it was found that the (R) isomer was the form which inhibited fatty acid synthesis, a finding that is in agreement with its herbicidal activity. These results suggest that inhibition of fatty acid synthesis de novo forms the basis for the selective mode of action of fluazifop.     

Folic acid metabolism in vitamin B12-deficient sheep. Depletion of liver folates

1. Metabolism of folate was studied in six ewes in an advanced state of vitamin B(12) deficiency as judged by voluntary food intake and in their pair-fed controls receiving vitamin B(12). A group of four animals that were maintained throughout the experiment at pasture was also studied. 2. After 34-40 weeks on the cobalt-deficient diet urinary excretion of formiminoglutamate by four deficient animals was about 3.2mmol/day and this was not significantly decreased by injection of three of them with about 4.5mug of [2-(14)C]folate/kg body weight per day for 5 days. Three days after the last injection retention of [2-(14)C]folate by the livers of the deficient animals (5.5% of the dose) was lower than that of their pair-fed controls (26% of the dose) but there was no evidence of net retention of injected folate in the livers of either group. Urinary excretion of (14)C indicated that renal clearance of folate may have been impaired in very severe vitamin B(12) deficiency. 3. As estimated by microbiological assays total folates in the livers of animals at pasture (12.9mug/g) included about 24% of 5-methyltetrahydrofolate as compared with about 72% of a total of 12.5mug/g in three further ewes fed on a stock diet of wheaten hay-chaff and lucerne-chaff. Liver folates of vitamin B(12)-deficient animals (0.5mug/g) included about 88% of 5-methyltetrahydrofolate as compared with about 51% of a total of 5.2mug/g in pair-fed animals treated with vitamin B(12). 4. Chromatography of liver folates of the pair-fed animals permitted quantitative estimates of the pteroylglutamates present. The results showed that the vitamin B(12)-deficient livers were more severely depleted of tetrahydrofolates and formyltetrahydrofolates than of methyltetrahydrofolates and that as the deficiency developed they were more severely depleted of the higher polyglutamates than of the monoglutamate within each of these classes. Results from animals injected with [2-(14)C]folate indicated an impairment of the exchange between pteroylmonoglutamates and pteroylpolyglutamates in the livers of deficient animals. 5. In vitamin B(12)-deficient animals with food intakes below 200g/day some of the liver folates were not completely reduced and some degradation of pteroylpolyglutamates was detected. The latter condition may have been associated with fatty liver. 6. The results are discussed in relation to current theories of vitamin B(12)-folate interactions.     

Alterations in the developmental patterns of enzymes in chicken embryos infected with West Nile virus.

Infection of chicken embryos with West Nile (WN) virus, a group B togavirus containing structural lipids, caused a rapidly developing hypertriglyceridemia. Changes in the activity of several hepatic regulatory enzymes in glycolytic and lipogenic pathways occurred during infection. Compared to control values in embryos of the same age (16 days), an 8.8-fold increase in the specific activity of ATP-citrate lyase and a 5.6-fold increase in that of hexokinase were observed on the third day of WN virus infection. Hexose monophosphate shunt dehydrogenase specific activities were elevated twofold in virus-infected livers. Activities of malic enzyme and phosphofructokinase were also elevated in WN virus-infected livers. Malate dehydrogenase and NADP-linked isocitrate dehydrogenase levels showed little or no change during infection. The levels of pyruvate kinase and lactate dehydrogenase were decreased in virus-infected livers. Hepatic acetyl-CoA carboxylase activity was at least twofold higher in virus-infected embryos; however, following removal of low-molecular-weight compounds, the specific activities of this enzyme from infected and control embryos were virtually identical. The results of mixing experiments suggest that the low levels of carboxylase activity in control embryos may be due to the presence of enzyme inhibitor(s) which can be removed by gel filtration.The incorporation of radiolabeled precursors into cellular lipids by liver minces from virus-infected and uninfected embryos was measured. There was a twofold increase in carbohydrate incorporation in virus-infected liver as compared to uninfected liver; [¹⁴C]pyruvic acid was incorporated into lipids to the greatest extent. [1-¹⁴C]acetic acid, [U-¹⁴C]alanine, and [U-¹⁴C]leucine were incorporated very poorly in both infected and control livers. Twice as much [1-¹⁴C]oleic acid or [1-¹⁴C oleic]triolein was incorporated in WN-infected livers as in control. The relative distribution of neutral and polar lipids formed from each precursor was generally similar in infected and uninfected livers as determined by thin-layer chromatography of radiolabeled lipids. Except for a threefold increase in oxidation of [¹⁴C]glucose by virus-infected livers, the oxidations of carbohydrates and fatty acids were similar in infected and uninfected livers. The pentose phosphate pathway appears to be the major pathway utilized in glucose oxidation for both control and virus-infected livers. The results indicate that enhanced flux of metabolites into lipids reflects a virus-induced alteration in embryonic development: The enzyme patterns of infected embryos are more characteristic of older embryos or even newly hatched chicks.     

Itaconic acid: An inhibitor of isocitrate lyase in Tetrahymena pyriformis in vitro and in vivo

The succinate analog itaconic acid was observed to be a competitive inhibitor of the glyoxylate cycle specific enzyme isocitrate lyase (EC 4.1.3.1) in cell-free extracts of Tetrahymena pyriformis. Itaconic acid also inhibited net in vivo glycogen synthesis from glyoxylate cycle-dependent precursors such as acetate but not from glyoxylate cycle-independent precursors such as fructose. The effect of itaconic acid on the incorporation of ¹⁴C into glycogen from various ¹⁴C-labeled precursors was also consistent with inhibition of isocitrate lyase by this compound. Another analog of succinate which shares a common metabolic fate with itaconic acid, mesaconic acid, had no effect on isocitrate lyase activity in vitro or on ¹⁴C-labeled precursor incorporation into glycogen in vivo. In addition, itaconic acid did not affect gluconeogenesis from lactate in isolated perfused rat livers, a system lacking the enzyme isocitrate lyase. These results are taken as evidence that itaconic acid is an inhibitor of glyoxylate cycle-dependent glyconeogenesis Tetrahymena pyriformis via specific competitive inhibition of isocitrate lyase activity.     

Further Characterization of Tissue Distribution and Metabolism of [14C]Aflatoxin B1 in Chickens

The distribution and metabolism of [(14)C]aflatoxin B(1) in chicken tissues were further investigated. Previously dried and frozen ethyl acetate extracts of liver, heart, gizzard, breast, leg, blood, and fecal samples were obtained from either layer or broiler chickens fed subclinical levels of [(14)C]aflatoxin B(1). Treatment of these extracts with either carboxypeptidase A, leucine aminopeptidase, pepsin, or trypsin revealed that an average of 50% of the (14)C detected in the acetate extracts was a liberated peptide (or amino acid) conjugate of [(14)C]aflatoxin B(2a). When a prepared standard of B(2a) was made by incubation of B(1) with cold dilute aqueous HCl, the R(f) values and absorbance maxima were identical with those of the tissue extracts after enzymatic treatment.     

Evidence of secondary poisoning of free-ranging riparian mustelids by anticoagulant rodenticides in France: implications for conservation of European mink (Mustela lutreola)

Because of the rapid decline of the endangered European mink (Mustela lutreola) populations in France, a national conservation program has been put into action, including research to understand the causes of decline. As part of this research, concentrations of eight anticoagulant rodenticides were examined in livers from 122 carcasses of four species of free-ranging mustelids collected between 1990 and 2002 in southwestern France. Bromadiolone residue was found in all species and 9% of the sample (one of 31 European mink, three of 47 American mink [Mustela vison], five of 33 polecats [Mustela putorius], and two of 11 European otters [Lutra lutra]). Liver concentrations ranged from 0.6 mug/g to 9.0 mug/g. Chlorophacinone residue was found in two species and 4% of the sample (in four of the American mink and in one of the otters), with liver concentrations ranging from 3.4 mug/g to 8.5 mug/g. Two polecats and one American mink had lesions and liver residues indicating bromadiolone was directly responsible for their death. However, most of our study animals survived secondary poisoning until they were caught; this study certainly underestimates the extent of fatal exposure of mustelids to rodenticides. Moreover, anticoagulant poisoning could increase their vulnerability to other causes of death. The current status of the endangered European mink population is such that any additional risk factor for mortality is important, and it is thus urgent to monitor and reduce the extensive use of bromadiolone and chlorophacinone against field rodents in France.     

Effects of unsaturated fatty acid deprivation on neutral lipid synthesis in Saccharomyces cerevisiae

The effects of unsaturated fatty acid deprivation on lipid synthesis in Saccharomyces cerevisiae strain GL7 were determined by following the incorporation of [14C]acetate. Compared to yeast cells grown with oleic acid, unsaturated fatty acid-deprived cells contained 200 times as much 14C label in squalene, with correspondingly less label in 2,3-oxidosqualene and 2,3;22,23-dioxidosqualene. Cells deprived of either methionine or cholesterol did not accumulate squalene, demonstrating that the effect of unsaturated fatty acid starvation on squalene oxidation was not due to an inhibition of cell growth. Cells deprived of olefinic supplements displayed additional changes in lipid metabolism: (i) an increase in 14C-labeled diacylglycerides, (ii) a decrease in 14C-labeled triacylglycerides, and (iii) increased levels of 14C-labeled decanoic and dodecanoic fatty acids. The changes in squalene oxidation and acylglyceride metabolism in unsaturated fatty acid-deprived cells were readily reversed by adding oleic acid. Pulse-chase studies demonstrated that the [14C]squalene and 14C-labeled diacylglycerides which accumulated during starvation were further metabolized when cells were resupplemented with oleic acid. These results demonstrate that unsaturated fatty acids are essential for normal lipid metabolism in yeasts.     

Regulation of lipid synthesis in soybeans by two benzoic Acid herbicides

The effects of 3-nitro-2,5-dichlorobenzoic acid (dinoben) and 3-amino-2,4-dichlorobenzoic acid (chloramben) on lipid formation and on the incorporation of various substrates into lipids by intact seeds and subcellular fractions of germinating soybean (Glycine max [L.] Merr. ;Amsoy') were studied. Dinoben (20 mug/ml) inhibited synthesis of total lipids 67%, neutral lipids 73%, glycolipids 51%, and phospholipids 39% in germinating seeds. When polar lipids were analyzed further, inhibition of individual lipid classes was also observed. Chloramben (20 mug/ml) stimulated total lipid synthesis 25%. With the exception of the mitochondrial fraction where malonate thiokinase was absent, dinoben inhibited up to 99% the incorporation of acetate and malonate into lipids, but did not inhibit acetyl-CoA and malonyl-CoA incorporation. Chloramben stimulated the incorporation of all substrates tested into lipids by all fractions except the mitochondrial fraction when malonate was the substrate. When dinoben and chloramben were used in combinations, chloramben did not reverse the inhibitory effect of dinoben.It is concluded that the dinoben inhibitory effect is specific and is associated with the acetate and malonate thiokinase systems. The chloramben effect is stimulatory to either acetyl-CoA carboxylase or fatty acid synthetase or both.     

Rapid activation and inactivation of fatty acid synthesis from glucose in vivo

The flux of glucose carbon to total body fatty acids was measured in unanesthetized mice either after fasting or 50-80 min after they nibbled a small test meal containing 120 mg of glucose (fasted-refed). Flux was calculated from plasma [(14)C]glucose specific activity curves and from total body (14)C-labeled fatty acid 30 min after intravenous injection of tracer [(14)C]glucose. Mobilization of liver glycogen, changes in the body glucose pool size, and total flux of carbon through the glucose pool during periods of fasting and refeeding were defined. Liver glycogen was almost completely depleted 8 hr after food removal. Body glucose pool size fell during fasting and increased after refeeding the test meal. Irreversible disposal rate of glucose C varied directly with body glucose pool size; but flux of glucose C into fatty acids increased exponentially as body glucose concentration increased. Within an hour after nibbling a small test meal, the flux of glucose C into total body fatty acids increased 700% in mice previously starved for 24 hr. However, flux of glucose C into fatty acids in postabsorptive mice (food removed for 2 hr; livers rich in glycogen) was only about 2% of the value calculated from published studies in which the incorporation of an intubated [(14)C]glucose load into total body fatty acid was measured in mice. A possible explanation for this phenomenon is presented.     

Effects of ethynyloestradiol on the metabolism of [1-14C]-oleate by perfused livers and hepatocytes from female rats

Normal female rats were given 15mug of ethynyloestradiol/kg body wt. for 14 days and were killed on day 15 after starvation for 12-14h. The livers were isolated and were perfused with a medium containing washed bovine erythrocytes, bovine serum albumin, glucose and [1-(14)C]oleic acid; 414mumol of oleate were infused/h during a 3h experimental period. The output of bile and the flow of perfusate/g of liver were decreased in livers from animals pretreated with ethynyloestradiol, whereas the liver weight was increased slightly. The rates of uptake and of utilization of [1-(14)C]oleate were measured when the concentration of unesterified fatty acid in the perfusate plasma was constant. The uptake of unesterified fatty acid was unaffected by pretreatment of the animal with oestrogen; however, the rate of incorporation of [1-(14)C]oleate into hepatic and perfusate triacylglycerol was stimulated, whereas the rate of conversion into ketone bodies was impaired by treatment of the rat with ethynyloestradiol. Pretreatment of the rat with ethynyloestradiol increased the output of very-low-density lipoprotein triacylglycerol, cholesterol, phospholipid and protein. The production of (14)CO(2) and the incorporation of radioactivity into phospholipid, cholesteryl ester and diacylglycerol was unaffected by treatment with the steroid. The net output of glucose by livers from oestrogen-treated rats was impaired despite the apparent increased quantities of glycogen in the liver. The overall effect of pretreatment with oestrogen on hepatic metabolism of fatty acids is the channeling of [1-(14)C]oleate into synthesis and increased output of triacylglycerol as a moiety of the very-low-density lipoprotein, whereas ketogenesis is decreased. The effect of ethynyloestradiol on the liver is apparently independent of the nutritional state of the animal from which the liver was obtained. It is pertinent that hepatocytes prepared from livers of fed rats that had been treated with ethynyloestradiol produced fewer ketone bodies and secreted more triacylglycerol than did hepatocytes prepared from control animals. In these respects, the effects of the steroid were similar in livers from fed or starved (12-14h) rats. Oestrogens may possibly inhibit hepatic oxidation of fatty acid, making more fatty acid available for the synthesis of triacylglycerol, or may stimulate the biosynthesis of triacylglycerol, or may be active on both metabolic pathways.     

Effect of antimicrobials on cholesterol synthesis and content in liver and small intestines.

The antimicrobials tetracycline, ampicillin and bactrim (cotrimoxazole) decreased HMG CoA reductase activity in liver and small intestines of albino rats. Diminished incorporation of 1, 2, 14C acetate into cholesterol of small intestines in bactrim group was noted. There was a significant fall in cholesterol content of liver, duodenum, jejunum and ileum of the bactrim group and jejunum only in tetracycline group.