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.     

Lipid synthesis in germinating Tradescantia pollen

Synthesis of neutral and polar lipids in pollen of Tradescantia paludosa during germination and tube growth was studied by the incorporation of acetate-[1-¹⁴C] into lipids in the presence and absence of inhibitors of RNA and protein synthesis. The proteins required for the synthesis of both neutral lipids and phospholipids are not made de novo during germination but are already present in the mature ungerminated pollen grain and they are functionally stable during the first 2 hr of pollen growth.     

Lipid metabolism in brain tissue explants

Abstract— Tissue explants from frontal lobes of rat brain were used for the study of cerebral fatty acid metabolism. After tissues had been maintained in serum-supplemented medium, a lipid-free medium was substituted and metabolic studies were carried out. Under these conditions explants continued to take up lipid precursors for at least 48 h, as judged by incorporation of dl -[2-¹⁴C]mevalonic acid into cellular lipids. [l-¹⁴C]Stearic acid and [l-¹⁴C]palmitic acid were bound to cells as the free fatty acids, or incorporated into neutral lipids (particularly triglycerides), glycolipids and phospholipids. In the galactolipid fraction, cerebrosides were the principal radioactive lipids. Choline phosphoglycerides, ethanolamine phosphoglycerides, inositol phosphoglycerides and serine phosphoglycerides were the principal radioactive phospholipids. Fatty acids were incorporated into cellular lipids either unchanged or after desaturation, chain elongation, or both. Maximum incorporation of stearate occurred in tissues derived from 3-day-old animals. With increasing age the uptake of fatty acid dropped sharply. When the labelling of lipids as a function of time was followed in 3-day-old animals, triglycerides and choline phosphoglycerides were the first fractions to take up labelled stearate. Labelling of cerebrosides occurred slowly, only becoming evident after 24 h. These studies exemplify the usefulness of tissue explants for prolonged metabolic studies in normal and pathological specimens of brain.     

Manoalide,a Phospholipase A2 Inhibitor,Inhibits Arachidonate Incorporation and Turnover in Brain Phospholipids of the Awake Rat

The Fatty Acid method was used to determine whether incorporation of plasma radiolabeled arachidonic acid into brain phospholipids is controlled by phospholipase A₂. Awake rats received an i.v. injection of a phospholipase A₂ inhibitor, manoalide (10 mg/kg), and then were infused i.v. with [1-¹⁴C]arachidonate or [³H]arachidonate. Animals were killed after infusion by microwave irradiation, and tracer distribution was analyzed in brain phospholipid, neutral lipid and acyl-CoA pools. Calcium-independent phospholipase A₂ activity in brain homogenate was reduced by manoalide, whereas phospholipase C activity was unaffected. At 60 min but not at 20 or 40 min after its injection, manoalide had significantly decreased by 50% incorporation of unesterified arachidonate into and turnover within brain phospholipids, taking into account dilution of the brain arachidonoyl-CoA pool by recycled arachidonate. Manoalide also increased by 100% the net rate of unesterified arachidonate incorporation into brain triacylglycerol. This study indicates that manoalide can be used to inhibit brain phospholipase A₂ in vivo, and that phospholipase A₂ plays a critical role in arachidonate turnover in brain phospholipids and neutral lipids.     

ASSEMBLY OF LIPIDS INTO MEMBRANES IN ACANTHAMOEBA PALESTINENSIS : I. Observations on the Specificity and Stability of Choline-14C and Glycerol-3H as Labels for Membrane Phospholipids

In order to determine the feasibility of using radioactive precursors as markers for membrane phospholipids in Acanthamoeba palestinensis, the characteristics of phospholipids labeled with choline-¹⁴C and glycerol-³H were examined. Choline-¹⁴C was found to be a specific label for phosphatidyl choline. There was a turnover of the radioactive moiety of phosphatidyl choline at a rate that varied with the concentration of nonradioactive choline added to the growth medium. Radioactivity was lost from labeled phosphatidyl choline into the acid-soluble intracellular pool and from the pool into the extracellular medium. This loss of radioactivity from cells leveled off and an equilibrium was reached between the label in the cells and in the medium. Radioactive choline was incorporated into phosphatidyl choline by cell-free microsomal suspensions. This incorporation leveled off with the attainment of an equilibrium between the choline-¹⁴C in the reaction mixture and the choline-¹⁴C moiety of phosphatidyl choline in the microsomal membranes. Therefore, a choline exchange reaction may occur in cell-free membranes, as well as living A. palestinensis. In contrast to choline-¹⁴C, the apparent turnover of glycerol-³H-labeled phospholipids was not affected by large concentrations of nonradioactive choline or glycerol in the medium. The radioactivity in lipids labeled with glycerol-³H consisted of 33% neutral lipids and 67% phospholipids. Phospholipids labeled with glycerol-³H turned over slowly, with a concomitant increase in the percentage of label in neutral lipids, indicating a conversion of phospholipids to neutral lipids. Because most (~96%) of the glycerol-³H recovered from microsomal membranes was in phospholipids, whereas only a minor component (~2%) of the glycerol-³H was in the phospholipids isolated from nonmembrane lipids, glycerol-³H was judged to be a specific marker for membrane phospholipids.     

Effect of hypoglycemia on the brain free fatty acid level and the uptake of fatty acids by phospholipids

The effect of hypoglycemia on the uptake of [1-¹⁴C]arachidonate and [1-¹⁴C]oleate into a synaptosomal and microsomal glycerophospholipids was investigated. In the presence of ATP, Mg²⁺ and CoA, rat brain synaptosomes and micorsomes catalyze the transfer of arachidonate and oleatc into glycerophospholipids. Arachidonate was mainly incorporated into phosphatidylinositol (PI) and phosphatidylcholine (PC), whereas oleate was incorporated into phosphatidylcholine and phosphatidylethanolamine (PE).Hypoglycemia was produced by intraperitoneal injection of 10 or 100 units of crystalline insulin per kg body weight. Two hours after injection the blood glucose level decreased to 10–20 mg%. The content of brain phospholipids was slightly decreased but the change was not statistically significant. The level of free fatty acids (FFA) was increased. More pronounced and reproducible changes were found when hypoglycemia was produced by injection of 100 units of insulin per/kg body weight. Changes in brain cortex were similar to those observed in microsomes and synaptosomes. Hypoglycemia affected the incorporation of arachidonic acid into glycerophospholipids of brain membranes. Uptake of [1-¹⁴C]arachidonate was decreased selectively by 50% (into phosphatidic acid /PA/) when hypogiycemia was produced by injection of 10 units of insulin per kg body weight. The Higher dose of insulin 100 units per kg body weight produced a 20% inhibition of arachidonate incorporation into synaptosomal PI and a 13% decrease of incorporation into microsomal phosphatidylcholine. Incorporation of [1-¹⁴C]oleate into membrane phospholipids was not changed by hypoglycemic insult. It is proposed that the disturbances in fatty acid level, particularly arachidonate, and decreased uptake of arachidonic acid by synaptosomal glycerophospholipids may be responsible for alteration of membrane function and changes of synaptic processes.     

Axonal transport of phospholipids in rabbit optic pathway

The uptake of different labeled precursors, their incorporation into lipids, and transport along the rabbit optic pathway [ipsilateral retina and optic nerve (ON), and contralateral optic tract (OT), lateral geniculate body (LGB), and superior colliculus (SC)] were investigated. Albino rabbits were used. The following radioactive precursors, either combined or separately, dissolved in 50 l of saline containing 15% BSA, were injected into vitreous body: [2-³H]glycerol (50 Ci), [1-¹⁴C]palmitate (15 Ci), and [1-¹⁴C]linoleate (7.5 Ci). Animals were killed at different time intervals from 1 hr up to 24 days. The radioactivity of total lipids and of different phospholipid classes from total tissue was measured. One hour after the administration of precursors, the radioactivity into the retina was high and the incorporation of [³H]glycerol and [¹⁴C]palmitate increased until 12 hr and 24 hr, respectively. The incorporation of [¹⁴C]linoleate reached a maximum on the second day. The phospholipids of LGB and SC were intensively labeled after 4–8 hr, and their radioactivity increased up to the 10th day after injection, independent of the precursor employed. The results obtained indicate that the labeled hydrophilic and hydrophobic precursors used were actively incorporated into the retina. The phospholipids were later transported at a rapid rate along the optic pathway.A preliminary report of this study has been presented at the Satellite ISN Meeting, Istanbul, September 8–10, 1979.     

Biosynthesis of lipids in chloroplasts isolated from jack pine needles

Suspensions of isolated pine needle chloroplasts were shown to incorporate galactose from UDP galactose-[¹⁴C] into galactolipids. The incorporation of the label among galactolipids was always considerably higher in the monogalactosyl diglycerides than in the digalactosyl diglycerides. The galactosyl incorporation into both galactolipid fractions was optimal at pH 8.0 and was inhibited by sulphydryl reagents (p-chloromercuribenzoate, N-ethyl maleimide and CdCl₂). The chloroplast preparations were also able to biosynthesize various phospholipids and galactolipids from palmitoyl-[1-¹⁴C]-CoA; the major portion of the label appeared in phosphatidyl choline. The incorporation of palmitic-[1-¹⁴C] acid into various lipids was very poor compared to that of palmitoyl-[1-¹⁴C]-CoA. However, addition of ATP and CoA markedly stimulated lipid biosynthesis from palmitic-[1-¹⁴C] acid, suggesting the presence of activating enzymes. These chloroplast suspensions did not show any de novo fatty acid synthesis.     

Total polar lipid biosynthesis during growth of Crotalaria juncea pollen tubes

[1-¹⁴C]-Acetate incorporation into total and polar lipids was studied in the growing pollen tubes of Crotalaria juncea. Ungerminated pollen had phosphatidyl inositol, phosphatidyl serine, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol, monogalactosyl diglyceride, digalactosyl diglyceride, sulpholipid and steryl glycosides. In the growing pollen tubes considerable [1-¹⁴C]-acetate incorporation was observed into the individual polar lipids. The exogenous carbon source significantly influenced lipid biosynthesis. Boric acid (20mg/l.) promoted both pollen tube growth and acetate incorporation into phospholipids. In comparison to 5′-adenosine monophosphate, cyclic-3′,5′-adenosine monophosphate (cAMP) promoted tube growth and also enhanced phospho-and glycolipid biosynthesis. The regulation of membrane component biosynthesis by cAMP is suggested.     

Reserve lipid accumulation and translocation of 14C in the photosynthetically active and senescent shoot parts of Dicranum elongatum

Lipid metabolism of the subarctic moss Dicranum elongatum was studied by feeding the moss with 2-¹⁴C-acetate and, after extraction of the lipids, counting the ¹⁴C-content of different lipid fractions immediately after feeding or after chase periods. Translocation of ¹⁴C after ¹⁴C-feeding was studied with autoradiography. Both low temperature (+6°C) and drought (at +23°C) resulted in increased incorporation of ¹⁴C into the neutral lipid (NL) fraction and decreased incorporation of ¹⁴C into the glycolipid (GL) fraction of the green shoot part of the moss. The distribution of radioactivity between the NL classes suggests that diacylglycerols (1, 2-DAG) and common triacylglycerols (cTAG) are turned into acetylenic triacylglycerols (aTAG), which are accumulated preferentially. The decrease in the radioactivity of the GL fraction was due to two unknown fractions, whereas ¹⁴C incorporation into the chloroplast membrane lipids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG), was very low throughout the experiments. The phospho-lipid (PL) fraction accounted for 48–63% of total lipid radioactivity at both low and high temperatures. 2-¹⁴C-acetate feeding to the senescent moss part resulted in vigorous ¹⁴C incorporation into the lipids, especially into the reserve TAGs. Electron microscopic examination showed the presence of plastids, which explains the capability of the senescent part of the moss for lipid synthesis. The fact that transport of ¹⁴C from 2-¹⁴C-acetate took place upwards and downwards in the moss shoot, together with the capability for lipid synthesis of the senescent moss part, supports the suggestion that the senescent moss part plays a role as an energy store.     

The effect of cadmium on lipid and fatty acid biosynthesis in tomato leaves

This research aims to examine the effect of cadmium uptake on lipid composition and fatty acid biosynthesis, in young leaves of tomato treated seedlings (Lycopersicon esculentum cv. Ibiza F1). Results in membrane lipids investigations revealed that high cadmium concentrations affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the unsaturated fatty acid content, resulting in a lower degree of fatty acid unsaturation. The level of lipid peroxides was significantly enhanced at high Cd concentrations. Studies of the lipid metabolism using radioactive labelling with [1-¹⁴C]acetate as a major precursor of lipid biosynthesis, showed that levels of radioactivity incorporation in total lipids as well as in all lipid classes were lowered by Cd doses. In total lipid fatty acids, [1-¹⁴C]acetate incorporation was reduced in tri-unsaturated fatty acids (C16:3 and C18:3); While it was enhanced in the palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0) and linoleic (C18:2) acids. [1-¹⁴C]acetate incorporation into C16:3 and C18:3 of galactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)] and some phospholipids [phosphatidylcholine (PC) and phosphatidylglycerol (PG)] was inhibited by Cd stress. Our results showed that in tomato plants, cadmium stress provoked an inhibition of polar lipid biosynthesis and reduced fatty acid desaturation process.     

Reduced labeling of brain phosphatidylinositol,triacylglycerols, and diacylglycerols by [1-14C]arachidonic acid after electroconvulsive shock: Potentiation of the effect by adrenergic drugs and comparison with palmitic acid labeling

The effect of electroconvulsive shock on the labeling of phospholipids and neutral lipids in mice brains was examined after intracerebral injection of [1-¹⁴C] arachidonic acid or [1-¹⁴C]palmitic acid. Electroconvulsive shock reduced greatly the removal of radiolabeled arachidonic acid from the free fatty acid pool. At the same time, the incorporation of arachidonic acid was partially inhibited in triacylglycerol, diacylglycerol, and phosphatidylinositol, whereas the incorporation of [1-¹⁴C]palmitic acid was not affected. Pretreatment with desipramine and pargyline potentiated the lipid effect of electroconvulsive shock in neutral glycerides. These electroconvulsive shock-induced changes reflect alterations in the metabolism of intracerebrally injected arachidonic acid, but not of similarly injected palmitic acid. From the available data whether decreased ATP, enzyme inhibition or other factors are involved cannot be ascertained. Moreover, the electroconvulsive shock-enhanced endogenous free arachidonic acid may possibly dilute the injected radiolabeled fatty acid, thus decreasing its availability for arachidonoyl-coenzyme A synthesis. Hence, a partial inhibition of the activation-acylation of these fatty acids, primarily arachidonic acid, also may be involved in the seizure-induced accumulation of free fatty acids in the brain.     

Cadmium stress induces changes in the lipid composition and biosynthesis in tomato (<Emphasis Type="Italic">Lycopersicon esculentum</Emphasis> Mill.) leaves

The effects of cadmium (Cd) stress on lipid composition and biosynthesis were investigated in young leaves of ten-day-old tomato seedlings (Lycopersicon esculentum Mill. cv. Ibiza F1). Cd was found to be mainly accumulated in roots, but a severe inhibition of biomass production occurred in leaves, even at its low concentration (1.0 μM). Seven days after Cd treatment, the membrane lipids were extracted and separated on silica-gel thin layer chromatography (TLC). Fatty acid methyl esters were analyzed by FID-GC on a capillary column. Our results showed that Cd stress decreased the quantities of all lipids classes (phospholipids, galactolipids and neutral lipids). Likewise, there was also a decline in the levels of tri-unsaturated fatty acids, such as linolenic (C18:3) and hexadecatrienoic (C16:3) acids. The linolenic acid (C18:3) decreased in monogalactosyldiacylglycerol (MGDG) and all phospholipids, while hexadecatrienoinic acid (C16:3) declined mainly in MGDG. Moreover, Cd at high concentrations (25.0 and 50.0 μM) significantly enhanced the levels of lipid peroxides. Radiolabelling experiments were carried out by laying down microdroplets of [1-¹⁴C]acetate–a major precursor of lipid biosynthesis–on attached leaves of the control and Cd-treated plants. After incubation for 1, 2, 12 and 24 h, the leaves were harvested and lipids extracted and analysed. Cd stress was found to decrease the incorporation of [1-¹⁴C]acetate in total lipids. The biosynthesis of total lipids was altered with 25.0 and 50.0 μM Cd. The decline in the incorporation of [1-¹⁴C]acetate due to Cd stress was observed in all lipid classes. There was also a substantial decline in the incorporation of [1-¹⁴C]acetate in tri-unsaturated fatty acids. The results indicate that Cd treatment induces an oxidative stress by inhibiting the chloroplastic and extrachloroplastic lipid-biosynthesis pathways as well as lipid peroxidation.     

THE INCORPORATION OF [1-14C]ACETATE INTO UNESTERIFIED FATTY ACIDS IN RAT CEREBRAL CORTEX IN VIVO

—The incorporation of [1-¹⁴C]acetate into unesterified fatty acids and into the fatty acids of neutral glycerides and of phospholipids has been measured in rat cerebral cortex in vivo. The most rapid incorporation is seen in the unesterified fatty acids which have a turnover time of 5-6 min. It is suggested that unesterified fatty acids are precursors to neutral glycerides and phospholipids rather than being derived from them by lipase activity.     

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.     

Effects of acute hypoxia on incorporation of [1-14C]arachidonic acid into glycerolipids of rat brain

The effects of 1 min of acute hypoxic treatment (1% O₂ in N₂) on incorporation of [1-¹⁴C]arachidonic acid into brain lipids of 16-day-old rats were investigated at 3, 6, and 12 min after intracerebral injection of the labeled fatty acid. The hypoxic-hypoxia condition associated with convulsive seizures caused a decrease in the conversion of labeled arachidonate to its acyl-CoA as well as incorporation of the label into the brain phospholipids. Among the phospholipids, there was a specific decrease in the labeling of diacylglycerophosphoinositol (GPI), and this change was accompanied by an increase in labeling of the diacylglycerols. These results indicate that metabolism of the long-chain fatty acids and some glycero-lipids in brain are vulnerable to acute hypoxic treatment.     

Distribution and metabolism of arachidonic and docosahexaenoic acids in rat pineal cells. Effect of norepinephrine

The time-course incorporation of 10 μM [¹⁴C]arachidonic (AA) and docosahexaenoic (DHA) acids into glycerolipids was studied in rat pineal cells. The incorporation of both labeled fatty acids into total lipids was approximately equal, but their distribution profiles among the various cell lipids showed marked differences. The esterification of [¹⁴C]DHA in the neutral lipids, triacylglycerols (TAG) and cholesterol esters (CE), was 2-fold higher than that of [¹⁴C]AA whereas the opposite could be observed in total phospholipids (PL). The order of incorporation into PL was phosphatidylcholine (PC) > phosphatidylinositol (PI) = phosphatidylethanolamine (PE) for [¹⁴C]AA and PC = PE for [¹⁴C]DHA, the incorporation of both fatty acids being not detected in phosphatidylserine (PS) and that of DHA not in PI. When using 0.5 μM [³H] fatty acids, the respective distribution patterns resembled that of fatty acids at 10 μM, except for a lower proportion in TAG. The stimulation of ³H-labeled cells by 100 μM norepinephrine induced a 170% increase of basal release of [³H]AA into the medium, while [³H]DHA was virtually not released. However, the analysis of cell labeling revealed that both [³H] fatty acid levels were decreased in PL and increased in TAG. These findings suggest different involvement for AA and DHA in the pineal function. The preferential incorporation of DHA in TAG suggests that TAG might play an important role in the pineal enrichment with DHA. The absence of DHA release after NE stimulation, which however cannot be ascertained, may raise the question of the role of DHA in NE transduction.     

Phospholipid synthesis in aging potato tuber tissue

The effect of activation (“aging”) of potato tuber slices on their phospholipid metabolism was investigated. Aged slices were incubated with ¹⁴C labeled choline, ethanolamine, methionine, serine, and acetate. In all cases, the incorporation of radioactivity into the lipid fraction increased with the length of time the slices were aged. This incorporation was shown to be true synthesis and not exchange between precursors and existing phospholipids.

The increased incorporation of labeled choline into lipids was mainly due to an increase in its uptake by the tissue, the presence of actidione during aging prevented this increased uptake. The increase in the incorporation of labeled acetate into lipids resulted from the development of a fatty acid synthetase during aging. In the case of ethanolamine, both its uptake into the tissue and its incorporation into the lipid fraction increased.

The phospholipids formed from these precursors were identified by paper and thin-layer chromatography. The major compound formed from choline was lecithin, while phosphatidylethanolamine and a small amount of lecithin were formed from ethanolamine.

     

Effects of desmethylimipramine and diphenylpropene derivatives on synthesis of rat brain lipids in vivo

The effects of antidepressant compounds on the synthesis of brain lipids from [1-¹⁴C] acetate $\text{in vivo}$ in 15 day old rats have been investigated. Compounds used included the drug desmethylimipramine (DMI), the tetrabenazine antagonist 3-methylamino-1:1-diphenylprop-1-ene (II) and the primary (I) and tertiary (III) amine analogues of (II). Compound (II), the most potent tetrabenazine antagonist in the diphenylpropene series, significantly increased lipogenesis, whereas the remaining compounds did not. The results from fractionation of the lipid extract from rats treated with (II) indicated that the incorporation of radioactivity from [1-¹⁴C] acetate increased proportionally in all neutral lipids and phospholipids. Tetrabenazine also increased brain lipogenesis $\text{in vivo}$ and altered the distribution within lipid classes of radioactivity from [1-¹⁴C] acetate. Using [¹⁴C] labelled compound, the concentration of (II) in the brain under the present experimental conditions has been determined.     

A COMPARATIVE STUDY OF THE METABOLISM OF DE NOVO SYNTHESIZED FATTY ACIDS FROM ACETATE AND GLUCOSE, AND EXOGENOUS FATTY ACIDS, IN SLICES OF RABBIT CEREBRAL CORTEX DURING DEVELOPMENT

Slices of rabbit cerebral cortex, from the foetal stage to the adult have been used to compare lipid synthesis from fatty acids synthesized de novo from [U-¹⁴C]glucose and [1-¹⁴C]acetate, with lipid synthesis from exogenous albumin-bound [1-¹⁴C]palmitate. Incorporation into cellular lipid has been determined in terms of DNA, protein, wet wt. of tissue and wet weight of whole brain. On a wet wt. basis, maximum incorporation of glucose carbon into lipid occurred in the foetal brain while lipid synthesis from acetate and palmitate was maximum at 4–14 days after birth. Glucose and acetate were incorporated into a diversity of lipids (with increasing amounts of phosphatidylcholine synthesized during maturation), while palmitate was incorporated into the free fatty acid and triglyceride fractions. A greater proportion of acetate was incorporated into fatty acids of chain-length longer than C16 compared with the incorporation of palmitate. However, on a molar basis de novo synthesized and exogenous palmitate were elongated, desaturated and incorporated into phospholipids at a similar rate, while exogenous palmitate was incorporated to a greater extent than de nova synthesized fatty acid into the triglyceride fraction. This difference in metabolism may be due to the different size of the non-esterified fatty acid pool in the two situations. At the period of their most active formation, the very long-chain fatty acids may be synthesized from a pool of the C18 series of fatty acids (saturated and monoenoic) not in equilibrium with the bulk of C₁₈ acids in cerebral lipids. This could be a pool of acyl groups derived from ethanolamine phospholipids.