Further investigations of the incorporation of [1-14C]acetate into the lipids of the silkworm Bombyx mori L

1. After the injection of sodium [1-¹⁴C]acetate, the highest incorporation of ¹⁴C into the lipids of the silkworm was observed after 24hr. 2. The specific radioactivity of the palmitic acid fraction was greater and increased more rapidly than that of the stearic acid fraction, which was consistent with the precursor–product relationship to be expected on the basis of current concepts of fatty acid synthesis in vivo. 3. The results indicate the probability of synthesis of lipid components in tissues other than the fat body. 4. Fractionation studies indicate considerable differences in the rate of incorporation of [1-¹⁴C]acetate into neutral lipids and phospholipids between larvae and pupae as well as among tissues of larvae. 5. The rate of incorporation of [1-¹⁴C]acetate remains constant throughout pupal development.     

Preincubation stimulates fatty acid synthesis by liver slices and isolated hypatocytes from fasted and diabetic rats.

We have observed that preincubation of 48 hour-fasted or alloxan diabetic rat liver slices, with no exogenous energy supply, for 3 hours resulted in an increased rate of incorporation of [1-¹⁴C] acetate into fatty acids and cholesterol during the following 2 hours. This preincubation effect was enhanced by the presence of glucose (25mM) in or prevented by the addition of dibutyryl cyclic adenosine 3′,5′ monophosphate (10^?4M) to the preincubation medium. Preincubation of normal rat liver slices did not change their rate of incorporation of [1-¹⁴C] acetate into fatty acids or cholesterol. The rate of ¹⁴CO₂ synthesized by normal, fasted or diabetic liver slices was little affected by preincubation. The preincubation effect, i.e. enhanced fatty acid synthesis was also observed in suspensions of hepatocytes from fasted and diabetic rats, preincubated for 2 hours, followed by a 1 hour incubation with either [1-¹⁴C] acetate or [³H] H₂O as precursor. We conclude from these data that there is concurrent and coordinated short- and long-term regulation of fatty acid biosynthesis in fasted and diabetic rat livers. Further, we suggest that the release of inhibition by preincubation of these tissues provides a useful tool for studying the coordinated control     

Evidence for negative feedback control of cholesterogenesis from mevalonate in liver: Absence in the intestine of guinea pigs fed A 0,5 % cholesterol diet

The in vitro rate of incorporation of [2-¹⁴C]-acetate and [2-¹⁴C]-mevalonate into cholesterol of liver, ileum and caecum was determined in guinea pigs. In control animals, contrary to the situation observed when acetate was used as precursor, the rate of conversion of mevalonate to cholesterol was higher in liver than in intestine. In this latter tissue, the cholesterogenesis varied depending on the portion tested. The distribution of radiolabel derived from mevalonate between esterified and unesterified cholesterol differed among the various tissues. In cholesterol-fed guinea pigs, the plasma, liver, intestine and aorta cholesterol contents increased significantly. In addition, a negative feedback control existed for hepatic cholesterol synthesis for mevalonate and acetate. This control was absent in intestinal tissues.     

The hypothermic hamster brain: Its water and electrolyte content and perfusion

The data suggest that cold swelling of the brain does not occur in hypothermic hamsters for up to 48 hr or in the hypothermic rat for 2 hr. It may be possible that the adaptation of the Na⁺,K⁺-activated ATPase system as well as lipid changes occurs during the 6- to 8-hr induction period of hypothermia in the hamster. The absence of swelling in the rat, a species which does not hibernate, may be due to both the lack of hypercapnia and the brevity of the hypothermic period. It is noteworthy that in the hamster the distribution of cardiac output to the brain and the respiratory centers of the brain system is unaffected by hypothermia of up to 18 hr. Actual perfusion is, however, dramatically reduced. The data suggest that the helium-cold hypothermic hamster retains the ability to maintain solute gradients in hypothermia, and that hypothermic death is not due to an increase in cerebral water content or in the percentage of cardiac output received by the brain.     

The metabolism of dl-(1,6-14C)lipoic acid in the rat

dl-[1,6-¹⁴C]Lipoic acid was synthesized and administered to rats or incubated in vitro with rat liver systems. The urinary excretion of radioactivity after labeled lipoate was administered intraperitoneally at a level of 0.5 mg/100 g body weight was maximal at 3–6 hr, with 60% of the injected radioactivity recovered within 24 hr. Respiratory ¹⁴CO₂ from the same animals is maximal at 3 hr, after which it falls off markedly. Approximately 30% of the injected radioactivity was recovered as ¹⁴CO₂ within 24 hr. The excretion of radioactivity after lipoate was administered by stomach tube was similar to that after intraperitoneal injection. Localization of radioactivity in the body was greatest in liver, intestinal contents, and muscle in all cases. Ionexchange and paper chromatographies of 24-hr pooled urine revealed several watersoluble radioactive metabolites. Incubation of [¹⁴C]lipoate with homogenates or mitochondrial preparations in vitro resulted in the production of ¹⁴CO₂, which was decreased by incubation with unlabeled fatty acids and unaffected by the addition of carnitine or (+)-decanoylcarnitine. The rat, like certain bacteria, metabolizes lipoate via β-oxidation of the valeric acid side chain and by other metabolic reactions on the dithiolane ring, which render the molecule more water soluble.     

Relative importance of acetate, acetoacetate and D-beta-OH-butyrate in the transport of acetyl CoA from the mitochondria to the cytoplasm for fatty acid synthesis in mice.

Mice were injected intravenously with either 3-¹⁴C acetoacetate, 3-¹⁴C D-β-OH-butyrate or 1-¹⁴C acetate and the radioactivity of the fatty acids was measured. In liver, the values obtained for acetoacetate and β-OH-butyrate were identical and slightly higher than those for acetate. In carcass and adipose tissue, the values obtained for the β-OH-butyrate were lower than for the other two. In particle-free supernatant of liver and adipose tissue, almost no radioactivity was obtained from β-OH-butyrate, and only the acetoacetate and the acetate were used efficiently (in vitro studies). The incorporation of acetate and acetoacetate by adipose tissue supernatant is higher than that of citrate by liver supernatant.The cytoplasmic acetoacetyl CoA synthetase and acetyl CoA synthetase activity was found to be higher in adipose tissue than in the liver. β-OH-butyryl CoA synthetase was found to be much less active than the other two synthetases. Acetoacetyl CoA thiolase is very active in the mitochondria and supernatant of adipose tissue.Our results show that, in mice adipose tissue in particular, where the citrate-cleavage enzyme is not very active, acetyl CoA is probably transformed into acetoacetate so that it can leave the mitochondria to participate in cytoplasmic fatty acid synthesis.     

Metabolic effects of acetate in perfused rat liver studies on ketogenesis,glucose output,lactate uptake and lipogenesis

1. Livers from fed male rats were perfused in situ in a non-recirculating system with whole rat blood containing acetate at six concentrations, from 0.04 to 1.5 μmol/ml, to cover the physiological range encountered in the hapatic portal venous blood in vivo. 2. Below a concentration of 0.25 μmol/ml there was net production of acetate by the liver, while above it there was ner uptake with a fractional extraction of 40%. 3.No relationship was observed between blood [acetate] and hepatic ketogenesis, the ration [3-hydroxybutyrate]/[acetoacetate] or glucose output, either at low fatty acid concentration s or during oleate infusion. 4. Following the increase in serum fatty acid concentration, induced by oleate infusion, there were suquential incresase in ketogenesis and the ratio of [3-hydroxybutyrate]/[acetoacetate] while glucose output rose and lactate uptake fell significantly after in redox state. 5. There was a highly significant negative correlation between blood [acetate] and hepatic lactate uptake during oleate infusion. At the highest acetate concentration of 1.5 μmol/ml there was a small net hepatic lactate output. After oleate infusion ceased, lactate uptake increased, but the negative correlation between blood [acetate] and hepatic lactate uptake persisted. 6. Livers were also perfused with iether [1-¹⁴C]acetate or [U-¹⁴C]lactate at a concentration of acetate of either 0.3 or 1.3 μmol/ml of blood. With [1-¹⁴C]acetate, most of the radioactivity was recovered as fatty acids at the lower concentration of blood acetate. At the higher blood [acetate] a considerably smaller proportion of the radioactivity was recovered in lipids. With [U-¹⁴C]lactate the reverse pattern obtained i.e., recovery was greater at the high concentration of acetate and fell at the low concentration. Fatty acid biosynthesis, measured with ³H₂O, was stimulated from 2.4 to 6.6 μmol of fatty acid/g of liver per h by high blood [acetate] although the contribution of (acetate+lactate) to synthesis remained constant at 33–38% of the total. 7. These results emphasize the important role of the liver in regulating blood acetate concentrations and indicate that it can be major hepatic substrate. Acetate taken up by the liver appeared to compete directly with lactate, for lipogenesis and metabolism and acetate uptake was inhibited by raised bloodd [lactate].     

Studies on lipogenesis in vivo: Fatty acid and cholesterol synthesis in hyperglycaemic-obese mice

1. Lipogenesis has been studied in intact genetically obese mice by measuring the incorporation of a single oral dose of 250mg. of [U-¹⁴C]glucose into fatty acid and cholesterol in the liver and extrahepatic tissues. Studies were also carried out with [U-¹⁴C]glucose added to the diet and fed for 24hr. With either method of isotope administration, the conversion of [U-¹⁴C]glucose into fatty acid was greatly elevated in the livers of the obese mice. In contrast, conversion of the single dose of [¹⁴C]glucose into fatty acid in extrahepatic tissues of obese mice was only half that occurring in the non-obese litter mates. When [¹⁴C]glucose was given in the diet for 24hr. the total accumulation of labelled fatty acid in extrahepatic tissues of obese mice was slightly less than in the non-obese. Uptake of labelled glucose and conversion into fatty acid in adipose tissue of the obese mice decreased with age. 2. Conversion of the single dose of [¹⁴C]glucose into liver cholesterol was comparable in obese and non-obese mice fed on a purified low-fat diet. However, obese mice given this diet for 12 weeks accumulated 1·54% of cholesterol in the liver compared with 0·29% in the non-obese litter mates. This accumulation apparently resulted from a decrease in removal of cholesterol from the liver, rather than an increased synthesis. 3. Conversion of the single dose of [¹⁴C]glucose into extrahepatic fatty acid was decreased by 18hr. starvation proportionally as much in obese as in non-obese mice. The decrease in liver fatty acid synthesis caused by starvation also was considerable in obese mice, although somewhat less marked than in the non-obese. 4. The metabolic derangements in the liver could be more fundamental to the development of the obesity than the changes seen in extrahepatic tissues.     

Tissue-specific extravasation of albumin-bound Evans blue in hypothermic and rewarmed rats

The effects of hypothermia and rewarming on endothelial integrity were examined in intestines, kidney, heart, gastrocnemius muscle, liver, spleen, and brain by measuring albumin-bound Evans blue loss from the vasculature. Ten groups of twelve rats, normothermic with no pentobarbital, normothermic sampled at 2, 3, or 4 h after pentobarbital, hypothermic to 20, 25, or 30 degrees C, and rewarmed from 20, 25, or 30 degrees C, were cooled in copper coils through which water circulated. Hypothermic rats were cooled to the desired core temperature and maintained there for 1 h; rewarmed rats were cooled to the same core temperatures, maintained there for 1 h, and then rewarmed. Following Evans blue administration, animals were euthanized with methoxyflurane, tissues removed, and Evans blue extracted. Because hypothermia and rewarming significantly decrease blood flow, organ-specific flow rates for hypothermic and rewarmed tissues were used to predict extravasation. Hypothermia decreased extravasation in tissues with continuous endothelium (brain, muscle) and increased it in tissues with discontinuous endothelium (liver, lung, spleen). All tissues exhibited significant (p < 0.05) differences from normothermic controls. These differences are attributed to a combination of anesthesia, flow, and (or) change in endothelial permeability, suggesting that appropriate choice of organ and temperature would facilitate testing pharmacological means of promoting return to normal perfusion.     

Linoleic acid biosynthesis in the pea aphid,Acyrthosiphon pisum (Harris)

The pea aphid Acyrthosiphon pisum (Harris) incorporated [1-¹⁴C]acetate into a phospholipid dienoic fatty acid in a time-dependent manner. In 2-h incubations, the incorporation of radioactivity into the 18:2 fraction was minimal, whereas after 45 h 18:2 was the major fatty acid labeled. Ozonolysis of the isolated dienoic fatty acid methyl ester followed by radio-gas-liquid chromatography showed that radioactivity was associated with fragments containing carbons 1–9 and 13–18. These data established the location of the double bonds in the 9,12 positions and indicated that the entire molecule was labeled from [1-¹⁴C]acetate. Tetracycline-treated aphids synthesized linoleic acid in the same proportions as untreated controls. Scanning electron microscopy showed that over 50% of the treated insects had greatly reduced numbers of intracellular symbiotes or lacked them or most of the existing symbiotes had an abnormal appearance. Therefore, we conclude that intracellular symbiotes are not involved in the biosynthesis of linoleic acid in the pea aphid.     

Inhibition of fatty acid synthesis by RMI 14,514 (5-tetradecyloxy-2-furoic acid)

RMI 14,514 strongly inhibited the incorporation of label from [1-¹⁴C]acetyl-CoA into fatty acids by rat liver homogenates. No inhibition was observed when [2-¹⁴C]malonyl-CoA was used as the labeled fatty acid precursor. These results suggest that the drug inhibits $\text{de novo}$ fatty acid biosynthesis at the step mediated by acetyl-CoA carboxylase. The data presented in this communication support earlier reports that RMI 14,514 probablyexerts its hypolipidemic effects by inhibition of fatty acid biosynthesis.     

Metabolism of tween-Fatty Acid esters by cultured soybean cells : kinetics of incorporation into lipids, subsequent turnover, and associated changes in endogenous Fatty Acid synthesis

Uptake of Tween-fatty acid esters and incorporation of the fatty acids into lipids by soybean (Glycine max [L.] Merr.) suspension cultures was investigated, together with subsequent turnover of the incorporated fatty acids and associated changes in endogenous fatty acid synthesis. Tween uptake was saturable, and fatty acids were rapidly transferred from Tweens to all acylated lipids. Patterns of incorporation into glycerolipids were similar in cells treated with Tweens carrying [1-¹⁴C]-fatty acids and in cells treated with [1-¹⁴C]acetate, indicating that exogenous fatty acids were used for glycerolipid synthesis essentially as if they had been made by the cell. In Tween-treated cells neutral lipids (which include Tweens) initially accounted for the majority of lipid radioactivity. Radioactivity was then rapidly transferred to glycerolipids. A transient pool of free fatty acids accounting for up to 10% of lipid radioactivity was observed. This was consistent with the hypothesis that fatty acids are transferred from Tweens to lipids by deacylation of the Tweens, creating a pool of free fatty acids which are then used for lipid synthesis. Sterols were only slightly labeled in cells treated with Tweens, but accounted for nearly 50% of lipid radioactivity in cells treated with acetate. This suggested very little degradation and reutilization of the radioactive fatty acids in cells treated with Tweens. In cells treated with either [1-¹⁴C]acetate or Tween-[1-¹⁴C]-18:1, 70% of the initial fatty acid radioactivity remained in fatty acids after a 100 hour chase. By contrast, fatty acids not normally present disappeared more rapidly, suggesting differential treatment of such fatty acids compared with those normally present. Cells which had incorporated large amounts of exogenous fatty acids altered fatty acid synthesis in three distinct ways: (a) amounts of [1-¹⁴C]acetate incorporated into fatty acids were reduced; (b) cells incorporating exogenous unsaturated fatty acids increased the proportion of [1-¹⁴C]acetate partitioned into saturated fatty acids, while the converse was true of cells which had incorporated exogenous saturated fatty acids; (c) desaturation of 18:1 to 18:2 and 18:3 was reduced in cells which had incorporated unsaturated fatty acids. These results suggest that Tween-fatty acid esters will be useful for supplying fatty acids to cells for a variety of studies related to fatty acid or membrane metabolism.     

Studies in lipogenesis in vivo: Fatty acid and cholesterol synthesis during starvation and re-feeding

1. Lipogenesis in vivo has been studied in mice given a 250mg. meal of [U-¹⁴C]glucose (2·5μc) or given an intraperitoneal injection of 25μg. of [U-¹⁴C]glucose (2·0μc). 2. The ability to convert a [U-¹⁴C]glucose meal into fatty acid was not significantly depressed by 6–7hr. of starvation. In contrast, incorporation of ¹⁴C into fatty acid in the liver after the intraperitoneal dose of [¹⁴C]glucose was depressed by 80% and by more than 90% by 1 and 2hr. of starvation respectively. Carcass fatty acid synthesis from the [U-¹⁴C]glucose meal was not depressed by 12hr. of starvation, whereas from the tracer dose of [U-¹⁴C]glucose the depression in incorporation was 80% after 6hr. of starvation. 3. Re-feeding for 3 days, after 3 days' starvation, raised fatty acid synthesis and cholesterol synthesis in the liver fivefold and tenfold respectively above the levels in non-starved control mice. These increases were associated with an increased amount of both fatty acid and cholesterol in the liver. 4. After 18hr. of starvation incorporation of a [U-¹⁴C]glucose meal into carcass and liver glycogen were both increased threefold.     

Short-chain fatty acid metabolism in temperate marine herbivorous fish

Short-chain fatty acids (SCFAs) were identified and estimated in the gut of three herbivorous fish containing gut endosymbionts, the herring cale Odax cyanomelas (Richardson, 1850) (Family Odacidae), the butterfish O. pullus (Bloch and Schneider, 1801) (Family Odacidae) and the sea carp Crinodus lophodon (Günther, 1859) (Family Aplodactylidae). The highest concentrations of short-chain fatty acids were in the posterior region of the intestine in all species. In O. cyanomelas 85% of the total short-chain fatty acids were found in this region. There was a positive correlation between the distribution of short-chain fatty acids and the microorganisms, suggesting that the short-chain fatty acids were end products of microbial anaerobic metabolism. The major short-chain fatty acid in all three species was acetate, the concentration of which ranged from 20 to 29 mmol·1^-1 in the posterior intestine. Lower concentrations of propionate and butyrate were also found. Additionally, valerate was found in the odacids. The ratio of acetate: propionate:butyrate:valerate in the gut section containing the highest concentration of short-chain fatty acids was 83:8:9:1 in O. cyanomelas, 64:21:14:1 in O. pullus and 74:17:9:0 in C. lophodon. Acetate was present in the blood of O. cyanomelas and C. lophodon at concentrations of 1.74±0.17 and 1.79±0.20 mmol·l^-1, respectively. The presence of the enzyme necessary to activate acetate, acetyl CoA synthetase, in the major tissues of both O. cyanomelas and C. lophodon indicates that these fishes are able to utilise acetate produced in the gut. The highest activity of acetyl CoA synthetase, 3.55±0.51 and 6.48±3.18 nmol·s^-1·g tissue^-1 in O. cyanomelas and C. lophodon, respectively, was found in the kidney. Acetyl CoA hydrolase activity was detected in the liver, heart, muscle, gut and kidney of O. cyanomelas and C. lophodon. The highest activity was in the liver of both species, 91.22±9.03 and 57.35±7.15 nmol·s^-1·g tissue^-1 in O. cyanomelas and C. lophodon, respectively. The presence of acetyl CoA hydrolase in tissues of O. cyanomelas and C. lophodon raises the possibility that some of the acetate in the blood could arise from hydrolysis of endogenously produced acetyl CoA. The results strongly support the hypothesis that short-chain fatty acids produced by endosymbionts in the posterior intestine are used as a blood fuel either for energy purposes or for lipid synthesis by the host fish.Abbreviations DTNB 5,5-dithiobis [2-nitrobenzoic acid] - SCUBA self contained underwater breathing apparatus - SCFA short-chain fatty acid - TCA trichloroacetic acid - TRIS TRIS (hydroxymethyl) amino-methane     

The incorporation of [1-14C]acetate into the methyl ketones that occur in steam-distillates of bovine milk fat

1. The ¹⁴C-labelling of the fatty acids and the methyl ketones in steam-distillates of milk fat from a lactating cow that had been injected intravenously with [1-¹⁴C]acetate was determined. 2. The labelling patterns of the C₆–C₁₆ fatty acids and the corresponding methyl ketones with one fewer carbon atoms were similar, particularly so for the C₅–C₁₀ compounds at 9 and 22hr. after the injection of [1-¹⁴C]acetate. The isolation of ¹⁴C-labelled methyl ketones in the range C₃–C₁₅ is evidence that the β-oxo acid precursors, which are glyceride-bound in the milk fat, are synthesized in the mammary gland from acetate. The absence of heptadecan-2-one in steam-distillates and the extremely low specific radioactivity of stearic acid are further evidence for this biosynthetic pathway. 3. The specific radioactivities of the C₅–C₁₅ methyl ketones were higher (with the exception of C₉ methyl ketone in the second milking) than the specific activities of the corresponding fatty acids with one more carbon atom. This is consistent with the methyl ketone precursors' being formed during the biosynthesis of fatty acids rather than being products of β-oxidation of fatty acids.     

The synthesis of phosvitin in vitro by slices of liver from the laying hen

1. Slices of liver from laying hens incorporated Na₂¹⁴CO₃ and NaH₂³²PO₄ into phosvitin. Slices of liver from immature birds did not do so to any appreciable extent. The ³²P was incorporated into O-phosphorylserine in the phosvitin molecule. 2. Kidney, spleen, muscle, large and small intestine, ovary and oviduct from laying birds did not incorporate Na₂¹⁴CO₃ into phosvitin. 3. Slices of liver from laying hens carried out a net synthesis of phosphoprotein under the standard conditions of incubation. Slices from the livers of immature pullets did not do so. 4. Liver from the laying hen incorporated [2-¹⁴C]glycine, [3-¹⁴C]serine and [2-¹⁴C]glutamic acid into phosvitin. Part of the glycine was shown to be present as serine in the final product. 5. Slices of liver from immature birds treated with oestradiol synthesized phosvitin from [2-¹⁴C]glycine, but the addition of oestrogens in vitro to slices from untreated immature birds did not promote synthesis during a 3 hr. incubation period.     

In vivo study of cholesterol turnover in tissues of adult sows

The in vivo study of free and esterified cholesterol turnover was carried out in 15 tissues of adult Large White sows maintained at a constant weight for 10–12 weeks. They received a single intravenous injection either of [1-¹⁴C] acetate, or of an autologous red cell suspension or of plasma, previously labelled in vitro (for red cells) or in vivo (for plasma) with tritiated cholesterol.The tissues can be separated into four groups according to their relative rate of free cholesterol exchange between plasma and tissues. The liver and the lungs have a very fast exchange rate whereas the brain and the spinal cord have a very slow one. The whole lipoprotein particle transfer — an exclusive model for the esterified cholesterol transport from plasma to tissues — has been found in all sow tissues. When [1-¹⁴C] acetate is used as a substrate for cholesterol synthesis, lungs, adrenal glands and heart do not seem — or at an extremely low rate — to convert acetate into cholesterol whereas an intense cholesterol synthesis takes place in the small intestine. Its contribution to cholesterol synthesis in sows — taking into account the cholesterol transfer processes — reaches 70 per cent.     

The effects of specific lipogenic substrates and metabolic inhibitors on de Novo fatty acid synthesis in isolated hepatocytes from chow-fed female rats

The effects of glucose (10 mm), glycerol (3 mm), and lactate/pyruvate (10 mm) on the incorporation of ³H from ³H₂O into fatty acids were studied in isolated hepatocytes prepared from chow-fed female rats. Lactate/pyruvate markedly increased lipogenic rates, while glucose and glycerol did not significantly affect rates of lipogenesis. In cells incubated with lactate/pyruvate plus glycerol, the increase in ³H incorporation was greater than observed with lactate/pyruvate alone. In hepatocytes isolated from 24-h starved rats, lactate/pyruvate again increased de novo fatty acid synthesis to a greater extent than either glucose or glycerol. Glycerol significantly increased lipogenesis compared to the endogenous rates and when incubated with lactate/pyruvate produced an increase above lactate/pyruvate alone. (?)-Hydroxycitrate, a potent inhibitor of ATP-citrate lyase (EC 4.1.3.8), and agaric acid, an inhibitor of tricarboxylate anion translocation, were studied in hepatocytes to determine their effects on lipogenesis by measuring ³H₂O, [1-¹⁴C]acetate, and [2-¹⁴C]lactate incorporation into fatty acids. ³H incorporation into fatty acids was markedly inhibited by both inhibitors with agaric acid (60 μm) producing the greater inhibition. (?)-Hydroxycitrate (2 mm) increased acetate incorporation into fatty acids from [1-¹⁴C]acetate and agaric acid produced a strong inhibitory effect. Combined effects of (?)-hydroxycitrate and agaric acid on lipogenesis from [1-¹⁴C]acetate showed an inhibitory response to a lesser extent than with agaric acid alone. With substrate concentrations of acetate present, there was no significant increase in rates of lipogenesis from [1-¹⁴C]acetate and the increase previously observed with (?)-hydroxycitrate alone was minimized. Agaric acid significantly inhibited fatty acid synthesis from acetate in the presence of exogenous substrate, but the effect was decreased in comparison to rates with only endogenous substrate present. With [2-¹⁴C]lactate as the lipogenic precursor, agaric acid and (?)-hydroxycitrate strongly inhibited fatty acid synthesis. However, agaric acid despite its lower concentration (60 μm vs 2 mm) was twice as effective as (?)-hydroxycitrate. A similar pattern was observed when substrate concentrations of lactate/pyruvate (10 mm) were added to the incubations. When (?)-hydroxycitrate and agaric acid were simultaneously incubated in the presence of endogenous substrate, there was an additive effect of the inhibitors on decreasing fatty acid synthesis. Results are discussed in relation to the origin of substrate for hepatic lipogenesis and whether specific metabolites increase lipogenic rates.     

Fatty acid synthesis by slices from developing leaves

Fatty acid synthesis was studied in successive leaf sections from the base to the tip of developing barley (Hordeum vulgare L.), maize (Zea mays L.), rye grass (Lolium perenne L.) and wheat (Triticum aestivium L.) leaves. The basal regions of the leaves had the lowest rates of fatty acid synthesis and accumulated small amounts of very long chain fatty acids. Fatty acid synthesis was highest in the middle leaf sections in all four plants. Linolenic acid synthesis from [1-¹⁴C]acetate was highest in the distal leaf sections of rye grass. The labelling of the fatty acids of individual lipids of rye grass was examined and it was found that [¹⁴C]linolenic acid was highest in the galactolipids. Synthesis of this acid in the galactolipids was most active in leaf segment C. Only traces of [¹⁴C]linolenic acid were ever found in phosphatidylcholine and it is concluded that this phospholipid cannot serve as a substrate for linoleic acid desaturation in rye grass. The synthesis of fatty acids was sensitive to arsenite, fluoride and the herbicide EPTC. The latter was only inhibitory towards those leaf segments which made very long chain fatty acids. Formation of fatty acids from [1-¹⁴C]acetate was also studied in chloroplasts prepared from successive leaf sections of rye grass. Chloroplasts isolated from the middle leaf sections had the highest activity. Palmitic and oleic acids were the main fatty acid products in all chloroplast preparations. Linolenic acid synthesis was highest in chlorplasts isolated from the distal leaf sections of rye grass.     

Influence of short-term hypothermia upon the normal or ischaemic dog kidney.

Dog kidneys were subjected to 1 hr of normothermic ischaemia, maintained for 3 hr in hypothermia with autologous heparinised blood, or underwent a combination of these two treatments and were examined either immediately after the trauma or at different periods up to 1 week after autotransplantation. Clearance tests, tubular amino acid and sugar transport, cortical Na⁺K⁺-ATPase levels, acid phosphatase liberated into the renal circulation, and morphology were investigated. The results obtained (i) confirmed the severe, but slowly and progressively reversible lesion after ischaemia; (ii) revealed the functional impairment with almost normal morphology after hypothermia; and (iii) indicated the immediate and irreparable deterioration of renal function after ischaemic kidneys were subjected to short-term hypothermic treatment of this type.