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PubMed1967

Fracture planes in an ice-bilayer model membrane system.

Experiments with transferred stearate layers were performed to determine the location of fracture planes in frozen ice-lipid systems. Bilayers and multilayers of carbon-14-labeled stearate were frozen in contact with an aqueous phase and then fractured. The distribution of radioactivity on both sides of the fracture showed that the stearate layers were cleaved apart predominantly in the plane of their hydrocarbon tails. Because bilayers split in this manner, it was possible to measure time-dependent exchange of label between the layers. Exchange occurred with a half-time of 50 minutes in the presence of calcium and 25 minutes in the absence of calcium. Since stearate bilayers and multilayers are models of hydrophobically stabilized structures, the strong influence of their hydrophobic region on the fracture plane provides an explanation of how the freeze-etch technique of electron microscopy can expose inner, hydrophobic faces of cell membranes.

Carbon Isotopes↗

PubMed1985

Influence of calcium addition on growth of highly purified syntrophic cultures degrading long-chain Fatty acids.

Two highly purified syntrophic associations resulting in acetogenesis from stearate (SM) and oleate (OM) were obtained from the sludges of a sewage digestor. In both cases, Methanospirillum hungatei together with short, motile, gram-negative, nonfluorescent rods morphologically similar to Syntrophomonas wolfei were identified by microscopic examination. Besides growing on volatile fatty acids (butyrate through caproate), both cultures grew on oleate (C(18:1)) and numerous even-numbered, saturated long-chain fatty acids (LCFA [decanoate through stearate]). In addition, during growth on LCFA, supplementation of the culture media with calcium chloride was an absolute requirement. The sole difference between the associations was observed when SM and OM cultures were transferred from a stearate to an oleate medium. The SM culture needed 10 days before starting to degrade oleate, whereas the OM culture grew immediately, but the OM culture also grew immediately when transferred to stearate medium. Saturated LCFA degradation occurred in the presence of equinormal amounts of calcium (fatty acid/Ca ratio, 2). On the other hand, OM degradation only took place in the presence of an equimolar amount of calcium (fatty acid/Ca ratio, 1). These observations are discussed by considering the solubility constants of LCFA as calcium salts and the toxicity of the free acids against microorganisms.

Journal Article↗

PubMed1994

Measurement of fractional lipid synthesis using deuterated water (2H2O) and mass isotopomer analysis.

Fractional biosynthesis of palmitate, stearate, and cholesterol was determined with deuterated water (2H2O) using mass isotopomer analysis in Hep G2 and MCA sarcoma cells in culture. The method employed differs from previous ones in that the number of deuterium atoms from 2H2O incorporated into newly synthesized molecules was determined and not assumed. After correction for background natural abundances, the isotopomer distribution due to deuterium incorporation in fatty acids and cholesterol was shown to follow a simple binomial distribution depending on the deuterium enrichment in water (p) and the maximum number of deuterium atoms incorporated per molecule (N). Under a wide range of 2H2O enrichments, N could be determined to be 17 for palmitate, 20 for stearate, and 20 for cholesterol by regression analysis or from a series of consecutive mass isotopomer ratios. The fraction derived from de novo synthesis was given by the ratio of the observed to the theoretical deuterium enrichment, which is the product (N x p). The new synthesized fraction of palmitate and stearate by Hep G2 cells for the length of the experiment was found to be 77 and 65%, respectively. These values were confirmed by experiments with [U-13C]glucose as the precursor. In MCA sarcoma cells grown in lipid-poor medium, the average values for fractional synthesis of palmitate, stearate, and cholesterol were 70, 35, and 70%, respectively. This approach should be generally applicable to the simultaneous determined of fractional synthesis of a number of compounds with either deuterium or 13C tracers. Its application is only limited by the accuracy of mass spectrometric analysis.

Animals↗

PubMed1996

Copper intestinal absorption in the rat: effect of free fatty acids and triglycerides.

The absorption of some minerals has been shown to be affected by the presence of unhydrolyzed dietary triglycerides and free fatty acids generated from their partial hydrolysis. Since copper (Cu) can form poorly soluble soaps with long-chain fatty acids, we examined whether the uptake of Cu from the intestinal lumen is altered by the presence of fatty acids and triglycerides using an in vivo jejunal perfusion procedure. Long-chain fatty acids palmitate and stearate at 1.0 mM reduced Cu absorption rates compared with infusates without either fatty acid or triglycerides (means +/- SEM, controls: 104.4 +/- 8.8 pmole/min x cm vs palmitate: 12.5 +/- 17.6, P < 0.01; stearate:37.2 +/- 25.6, P < 0.05). Medium chain free fatty acids had no effect on Cu absorption (caprylate: 90.6 +/- 14.9, not significant; caproate: 69.5 +/- 14.2, not significant). Similarly, neither an emulsion of medium chain nor long-chain triglycerides at a total 1.0 or 2.5 mM concentration altered Cu absorption. The inhibitory effect of palmitate and stearate on Cu absorption was accompanied by a reduction in lumen-to-mucosa water influx (controls: 5.33 +/- 0.26 microl/min x cm vs palmitate: 3.20 +/- 0.70, P < 0.01; stearate: 3.36 +/- 0.52, P < 0.01). The data are consistent with a potential impairment of Cu intestinal absorption by long-chain free fatty acids which may accumulate in the jejunum following excessive fat intake and/or lipid malabsorption.

Animals↗

PubMed2000

Transport of heptafluorostearate across model membranes. Membrane transport of long-chain fatty acid anions I.

Heptafluorostearic acid, an isogeometric derivative of stearic acid, has a pK(a) value of about 0.5. To evaluate the suitability of heptafluorostearate as model compound for anions of long-chain fatty acids in membrane transport, monolayer and liposome studies were performed with lipid mixtures containing phospholipids;-cholesterol-heptafluorostearate or stearate (100:40:20 molar ratios). Transfer of heptafluorostearate and stearate from liposomes to bovine serum albumin (BSA) was followed by measuring the intrinsic fluorescence of BSA. The percentage of heptafluorostearate, equivalent to the amount placed in their outer monolayer, transferred from liposomes (120;-130 nm diameter) to BSA was 55.7 +/- 3.7% within 10 min at 25 degrees C and 55 +/- 2% within 5 min at 37 degrees C. Slow transfer of 22.7 +/- 2.5% of heptafluorostearate at 25 degrees C followed with a half-life of 2.3 +/- 0.4 h and of 20 +/- 4% at 37 degrees C with a half-life of 0.9 +/- 0.1 h until the final equilibrium distributions between BSA and liposomes were reached, 79 +/- 6% to 21 +/- 5% at 25 degrees C and 75 +/- 5% to 25 +/- 4% at 37 degrees C. The pseudounimolecular rate constants for flip-flop of heptafluorostearate equal k(FF,25) = 0.24 +/- 0.05 h(-) and k(FF,37) = 0.6 +/- 0.1 h(-), respectively. By comparison, transfer of stearate required only 3 min to reach equilibrium distribution. The difference between heptafluorostearate and stearate may be explained by a rapid flip-flop movement of the un-ionized fatty acids which exist in different concentrations in accordance with their pK(a) values. Half-life of flip-flop of heptafluorostearate makes it suitable to study mediated membrane transport of long-chain fatty acid anions.

Animals↗

PubMed1975

Absorption of erythromycin. A cross-over study in healthy volunteers.

The absorptions of 6 erythromycin preparations were compared in a cross-over study in healthy humans. In a single-dose study, 500 mg of each preparation was, after an overnight fast, given to 10 volunteers. The two enterosoluble preparations of erythromycin base studied were absorbed slowly, and the peak serum concentration (1.5-2 mg/l) was achieved only at 4 h. The absorption of the stearates was quick, but especially one of them was poorly absorbed, the serum concentration being always below 1 mg/l. Both of the two estolates gave highest apparent concentrations, and the maximum serum level (2-2.5 mg/l) was achieved at 2 h, but the concentration of active erythromycin remains unknown. In the second part of the study, two erythromycin stearates and one base preparation were given at 6-h interval in a cross-over fashion, each for 4 days. On the 4th day, blood samples were analyzed. The erythromycin base gave higher serum concentrations than did the two stearates, which were equivalent. It seems doubtful that the erythromycin stearate at the dose of 250 mg every 6th hour would give satisfactory serum levels of erythromycin which would be effective against most bacteria during the whole treatment.

Biopharmaceutics↗

PubMed2002

The effect of formulation on reduced radioiodide thyroid uptake.

UNLABELLED: This investigation compared in vitro dissolution profiles from sodium iodide capsules with radioiodide thyroid uptake in patients with thyroid abnormalities, using sodium iodide capsules prepared with a formulation exhibiting complete release of radioiodide in vitro and a formulation exhibiting incomplete release. METHODS: In vitro dissolution profiles for radioactive sodium iodide capsules with 2 different formulations were determined using the U.S. Pharmacopeia (USP) XXIV dissolution test. The 2 formulations studied in vitro were sodium phosphate dibasic powder with 1% magnesium stearate and calcium phosphate dibasic powder with 3% magnesium stearate. The thyroid uptake of radioiodide from capsules exhibiting complete release or incomplete release of radioiodide was determined in patients with thyroid disorders. RESULTS: In the dissolution studies, by 20 min after initiation of the test, >95% of the radioactive iodide was released from capsules of sodium phosphate dibasic powder. The capsules of calcium phosphate dibasic powder reached 75% at 65 min, with no further release occurring thereafter. In the in vivo studies, the mean thyroid uptake at 1 h for sodium phosphate dibasic powder with 1% magnesium stearate (complete-release formulation) was 12.7%, compared with 9.3% for calcium phosphate dibasic powder with 3% magnesium stearate (incomplete-release formulation) (P < 0.05). At 24 h, the value was 56.6% for the complete-release formulation, compared with 50.3% for the incomplete-release formulation (P < 0.01, Wilcoxon signed rank test). At 1 h, the abdominal activity for the complete-release formulation was 3.4%, compared with 8.8% for the incomplete-release formulation (P < 0.01). At 24 h, the value was 0.4% for the complete-release formulation, compared with 1.0% for the incomplete-release formulation (P < 0.01). CONCLUSION: The data suggest that the incomplete dissolution profile observed in vitro may correlate with reduced bioavailability of radioiodide in vivo. The USP dissolution test can be applied to radioiodide sodium iodide capsules as a quality assurance procedure.

Adult↗

PubMed2004

[Study of the strength of compacts of mixed dry binders consisting of powdered cellulose and directly compressible lactose].

The paper studied the strength of compacts of dry binders consisting of powdered cellulose and directly compressible lactose. The powdered cellulose employed was Arbocel A300, the directly compressible lactose, Pharmatosa DCL 21. The first step of the evaluation comprised the tensile strength of compacts and sensitivity of dry binders alone to an addition of magnesium stearate. The same method of evaluation was then used for mixed dry binders from Arbocel A300 and Pharmatosa DCL 21 in ratios of 3:1, 1:1 and 1:3. The tested concentrations of magnesium stearate were 0.4 and 0.8%. Sensitivity of dry binders to an addition of the lubricant was evaluated by means of lubricant sensitivity ratio (LSR) values. The compacts with the highest strength and at the same time the lowest sensitivity to an addition of magnesium stearate were produced using a mixture of Arbocel A300 and Pharmatosa DCL 21 in a ratio of 1:3. The evaluation also included the commercially produced mixed dry binder Cellactosa 80, in which higher sensitivity to an addition of stearate than in a mixture of Arbocel A300 and Pharmatosa DCL 21 in a ratio of 1:3 was found.

Cellulose↗

PubMed2004

Spectroscopic investigation of the aggregation state of amphotericin B during loading, freeze-drying, and reconstitution of polymeric micelles.

PURPOSE: To investigate the relative aggregation state of amphotericin B (AmB) during loading and reconstitution of polymeric micelles. METHODS: Hexanoate and stearate derivatives of PEO-b-p (L-Asp) were prepared. The polymers and AmB were dissolved in methanol (MeOH). Milli-Q water was then added slowly, and the MeOH was removed via rotary evaporation. The solutions were freeze-dried in the presence of trehalose. During micelle preparation, the aggregation state of AmB was assessed using absorption spectroscopy. Upon reconstitution, the samples were analyzed using vapor-pressure osmometry, size-exclusion chromatography (SEC), and absorption spectroscopy. The absorption spectrum of AmB in the presence of the block copolymers was compared to that of AmB alone under the same conditions. RESULTS: AmB was loaded into micelles prepared from acyl derivatives of PEO-b-p (L-Asp). Absorption spectroscopy indicated that the aggregation state was preserved during the loading process. AmB exists in a self-aggregated state in polymeric micelles containing hexanoate ester cores and in a relatively monomeric state in polymeric micelles containing stearate ester cores. Vapor-pressure osmometry confirmed the isotonicity of the formulations, while SEC indicated that the micelles were approximately 10(6) g/mol. CONCLUSIONS: Depending on the polymer structure and assembly conditions, it is possible to encapsulate AmB in a relatively nonaggregated or aggregated state in micelles prepared from acyl derivatives of PEO-b-p (L-Asp). In polymeric micelles containing stearate side chains, AmB was loaded in a nearly monomeric state, possibly due to interaction with the stearate side chains. The final aggregation state of the drug is preserved during lyophilization and reconstitution of polymeric micelles prepared by a novel solvent evaporation procedure.

Amphotericin B↗

PubMed2006

[Studies of the properties of tablets made from directly compressible starch and its mixtures with directly compressible lactose].

The paper studies the strength and disintegration time of compacts made from directly compressible Starch 1500 and its mixtures with directly compressible lactose Pharmatosa DCL 15 in different relative proportions in dependence on the added lubricant magnesium stearate and the model active ingredient ascorbic acid. The dry binders under study differ in their mechanisms of compression and thus in their sensitivity to the addition of the lubricant, which is manifested in decreased strengths of the compacts as well as the mechanism of disintegration of the compacts. The mixtures of substances under study were in the relative representations of 1:3, 1:1 and 3:1. The employed concentration of the lubricant magnesium stearate was 0.4%, that of ascorbic acid, 50%. The study has confirmed and quantitatively evaluated the sensitivity of directly compressible starch to the addition of magnesium stearate. A higher share of directly compressible lactose in the mixture decreased the sensitivity of tableting material to the addition of the lubricant and shortened disintegration time. The presence of stearate did not negatively influence disintegration time, with an exception of the mixture of Starch 1500 and Pharmatosa DCL 15 1:3. An addition of the model active ingredient ascorbic acid decreased the strength of the compacts and shortened the disintegration time in all tableting materials tested.

Lactose↗

PubMed1975

Long chain fatty acid binding to human plasma albumin.

The binding of six physiologically important long chain fatty acids to defatted human plasma albumin was measured at 37 degrees in a calcium-free Krebs-Ringer phosphate buffer, pH 7.4. The data were analyzed in terms of multiple stepwise equilibria. With the saturated acids, the magnitude of the equilibrium (association) constants, Ki, increased as the chain length increased: laurate smaller than myristate smaller than palmitate smaller than stearate. Oleate was bound more tightly than stearate; by contrast, linoleate was bound less tightly than stearate. The equilibrium constants, K1 through K12, ranged from 2.4 times 10-6 - 3.5 times 10-3 m-1 for laurate to 2.6 times 10-8 - 3.5 times 10-5 m-1 for oleate. Successive values of Ki decrease for each of the acids, indicating that major cooperative binding effects do not occur over the physiological range of fatty acid concentrations. In no case could the Ki be segregated into distinct classes, suggesting that any grouping of albumin binding sites is somewhat arbitrary. The results were inconclusive concerning whether premicellar association of unbound fatty acid occurs. Although corrections for premicellar association produced very little change in the Ki values for myristate, they raised the Ki for palmitate and stearate by 300 to 700 per cent. A sigmoidal relationship was obtained when the logarithm of Ki was plotted against chain length for the saturated fatty acids containing 6 to 18 carbon atoms, indicating that the binding energy is not simply a statistical process dependent only on the fatty acid chain length. This selectivity that albumin contributes to the binding process may be due to varying degrees of configurational adaptability of its binding sites as the fatty acid increases in length.

Fatty Acids↗

PubMed1981

The pharmacokinetics of two erythromycin esters in plasma and in saliva following oral administration in humans.

An improved highly sensitive fluorimetric methods has been employed to measure plasma and saliva levels of erythromycin propionate and stearate in eight healthy volunteers following a single oral dose of 7.5 mg/kg. The plasma curves exhibited a mean half-life of 5.22 +/- s. e. m., 0.86 h-1 for the propionate and 2.97 +/- 0.22 h-1 for the stearate. Peak levels were reached at the 2nd h (4.07 +/- 0.29 microgram/ml for the propionate; 2.15 +/- 0.14 microgram/ml for the stearate). The area under the total plasma concentration curve was about 3-fold higher in the case of propionate. The concentration in saliva was about 20% of the corresponding concentration in plasma for the propionate and about 25% for the stearate. A significant positive correlation was observed between plasma and saliva levels for both macrolides.

Administration, Oral↗

PubMed1996

Irreversible inhibition of hepatic fatty acid salt uptake by photoaffinity labeling with 11, 11-azistearate.

In order to have a model compound for detection of proteins involved in transport and metabolism of long-chain fatty acid salts by photoaffinity labeling 11,11-azistearate and 11,11-azi[G-3H]stearate (specific radioactivity 2.78 TBq/mmol) were synthesized. The suitability of 11,11-azi[G-3H]stearate for photoaffinity labeling was demonstrated by incorporation into BSA (bovine serum albumin) and H-FABP (hepatic fatty acid salt-binding protein) of rat liver. Repeated photoaffinity labeling resulted in a clear decrease of the binding capacities of both proteins. Labeling of protein mixtures with 11,11-azi[G-3H]stearate showed that binding proteins for long-chain fatty acid salts interact specifically with this probe. Photoaffinity labeling of isolated hepatocytes using 300 microM 11,11-azistearate in the presence of 100 microM BSA resulted in the irreversible inhibition of the uptake of stearate and its analogue 2,2,3,3,18,18,18-heptafluorostearate nearly to the same extent of about 30%. Irreversible inhibition of the uptake of long-chain fatty acid salts by photoaffinity labeling did not alter the mediated transport of cholyltaurine and has no effect on the uptake of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, a compound that crosses the hepatocyte membrane by simple diffusion. The irreversible inhibition of membrane transport by photoaffinity labeling demonstrates the existence of a specific transport system for the uptake of long-chain fatty acid salts into hepatocytes.

Affinity Labels↗

PubMed1998

Hepatic secretion of VLDL fatty acids during stimulated lipogenesis in men.

Fatty acids (FA) that are utilized for triglyceride (TG) synthesis in the liver and principally from two sources: FA synthesized de novo in the liver and preformed FA. We have measured the contribution from the two sources to very low density lipoprotein (VLDL) TG synthesis individually for palmitate, oleate, stearate, and linoleate (approximately 98% of the total FA of VLDL TG (VLDL TGFA)) by isotopomer analysis. Five healthy men were studied in the basal state, and 1 (day 1) and 4 days (day 4) after the start of a hypercaloric carbohydrate-enriched diet (approximately 2.5 times energy expenditure). The secretion of de novo palmitate was increased 15- and 43-fold after 1 and 4 days of hyperalimentation (2.6+/-1.2 (basal state), 40.8+/-20.0 (day 1), and 113.3+/-42.0 micromol/kg per d (day 4)). Even though 4 days of hyperalimentation increased the secretion of de novo stearate 43-fold and de novo oleate 70-fold (stearate; 0.2+/-0.2 (basal), 8.6+/-3.3 micromol/kg per d (day 4), oleate; 0.4+/-0.4 (basal), 28.2+/-12.7 micromol/kg per d (day 4)), palmitate accounted for 75-85% of all the de novo VLDL TGFA. One day of carbohydrate hyperalimentation tended to decrease the secretion while 4 days increased the secretion of all preformed FA in VLDL TG. The rate of secretion of preformed palmitate and oleate were almost identical (palmitate; 80.2+/-22.2 (basal), 45.1+/-23.8 (day 1), and 256.2+/-74.1 micromol/kg per d (day 4), oleate; 95.2+/-22.8 (basal), 46.2+/-24.2 (day 1), and 356.8+/-74.1 micromol/kg per d (day 4)) and collectively these two FA accounted for 80-90% of the secretion from the preformed source. Palmitate is the predominant product of acute and prolonged carbohydrate mediated lipogenesis in the human liver. The pathway of further elongation and subsequent desaturation of de novo synthesized palmitate to generate stearate and oleate is inducible but, quantitatively, of minor significance in hepatic lipogenesis.

Dietary Carbohydrates↗

PubMed1979

Effect of microcrystalline cellulose on liquid penetration in and disintegration of directly compressed tablets.

The penetration of isooctane and water into tablets of microcrystalline cellulose, dibasic calcium phosphate dihydrate, spray-crystallized maltose-dextrose, and blends of microcrystalline cellulose with one of the other excipients were studied. The isooctane penetrations occurred according to the Washburn equation and were not affected by the presence of 0.5 or 1.0% magnesium stearate. The inhibition of aqueous penetration into tablets resulting from hydrophobic magnesium stearate was less pronounced for vehicles like dibasic calcium phosphate, which exhibited extensive brittle fracture under compression. Microcrystalline cellulose tablets, both with and without magnesium stearate, exhibited extremely fast aqueous penetration even at low porosities, caused by breaking of the hydrogen bonds and subsequent widening of the pores. Ratios between water uptake and original pore volume up to 20 were obtained for microcrystalline cellulose tablets. This unique property was, however, suppressed by the presence of fast dissolving and highly soluble excipients like dextrose, resulting in an antagonistic disintegration behavior of tablets compressed at pressures over 10,000 N/cm2. Improved disintegration properties were obtained by blending microcrystalline cellulose with an insoluble vehicle such as dibasic calcium phosphate dihydrate.

Calcium Phosphates↗

PubMed1996

The plasma borne free fatty acids rapidly enter the hepatocellular nuclei.

Long-chain free fatty acids (FA) were shown to exert a regulatory function in the nucleus. However, the route of their entry remains uncertain. The aim of the present study was to examine whether the extracellular FA enter the hepatocellular nuclei. The experiments were carried out in vivo and in vitro. Intravenous administration of albumin-bound [14C]-palmitic and [14C]-linoleic acid resulted in rapid accumulation of the labels in the nuclear lipids. Unesterified [14C]-palmitic acid represented 22.4 +/- 1.7 and [14C]-linoleic acid 17.6 +/- 1.3 percent of the total lipid radioactivity. In vitro, confocal laser scanning microscopy was used to examine 12-NBD-stearate (a fluorescent derivative of stearate) translocation into the nuclei of isolated hepatocytes. It was found that 12-NBD stearate enters the nucleus and that this uptake depends on the extracellular and/or cytoplasmic concentration. It is concluded that factors (e.g. dietary) leading to alterations in the plasma FA composition and content can result in rapid changes of the nuclear FA pool and thus regulate certain nuclear processes.

4-Chloro-7-nitrobenzofurazan↗

PubMed2000

Effects of norepinephrine on the metabolism of fatty acids with different chain lengths in the perfused rat liver.

The effects of norepinephrine on ketogenesis in isolated hepatocytes have been reported as ranging from stimulation to inhibition. The present work was planned with the aim of clarifying these discrepancies. The experimental system was the once-through perfused liver from fasted and fed rats. Fatty acids with chain lengths varying from 8-18 were infused. The effects of norepinephrine depended on the metabolic state of the rat and on the nature of the fatty acid. Norepinephrine clearly inhibited ketogenesis from long-chain fatty acids (stearate > palmitate > oleate), but had little effect on ketogenesis from medium-chain fatty acids (octanoate and laureate). With palmitate the decrease in oxygen uptake was restricted to the substrate stimulated portion; with stearate, the decrease exceeded the substrate stimulated portion; with oleate, oxygen uptake was transiently inhibited. Withdrawal of Ca2+ attenuated the inhibitory effects. 14CO2 production from [1-14C]oleate was inhibited. Net uptake of the fatty acids was not affected by norepinephrine. In livers from fed rats, oxygen uptake and ketogenesis from stearate were only transiently inhibited. The conclusions are: (a) in the fasted state norepinephrine reduces ketogenesis and respiration by means of a Ca2+-dependent mechanism; (b) the degree of inhibition varies with the chain length and the degree of saturation of the fatty acids; (c) norepinephrine favours esterification of the activated long-chain fatty acids in detriment to oxidation; (d) in the fed state the stimulatory action of norepinephrine on glycogen catabolism induces conditions which are able to reverse inhibition of ketogenesis and oxygen uptake.

Acetoacetates↗

PubMed1976

Subcellular membrane fatty acids of rat heart after cold acclimation or thyroxine.

Relative percent changes in fatty acid (FA) composition of heart mitochondria and microsomes from 30-day-warm-acclimated and cold-acclimated rats were determined by gas chromatography. Rats in both environmental groups received thyroxine (T4) (1 mg/kg per day) or propylthiouracil (PTU) (5 mg/rat per day) for 10 days prior to sacrifice. Mitochondrial total unsaturated fatty acids (TUFA) decreased in cold-acclimated rats relative to warm-acclimated controls but not in cold-acclimated animals receiving PTU. In mitochondria of the T4-treated warm-acclimated group, the relative content of linoleate decreased and that of stearate increased. Heart microsomes from warm-acclimated rats receiving T4 showed large increases in the percentage content of palmitate and stearate accompanied by reductions in linoleate and arachidonate. In cold-acclimated control rats, the relative content of stearate was elevated in both membrane fractions. The results suggested that thyroid hormones may decrease the TUFA composition of heart subcellular membranes by a relative increase in percent stearic acid and decrease in percent linoleic acid. Similar FA changes in these membranes in cold-acclimated rats may be related to the action of thyroid hormones.

Acclimatization↗