Positional distribution on n−3 fatty acids in triacylglycerols from rat adipose tissue during fish oil feeding

The present study was designed to investigate the metabolism of the n−3 olyunsaturated fatty acids (PUFA) in adipose tissue and its dependence upon dietary factors. Changes in the positional distribution of the fatty acids in triacylglycerols from retroperitoneal adipose tissue were studied as a function of time on rats fed for 4 wk a diet enriched with fish oil. The stereospecific analysis of triacylglycerols was based on random formation ofrac-1,2-diacylglycerols by Grignard degradation. This was followed by synthesis ofrac-phosphatidic acids and treatment with phospholipase A₂. In the triacylglycerols of the fish oil diet, 57% of the total n−3 fatty acids were in position 3,i.e., two-thirds of 22∶5n−3 and 22∶5n−3 were esterified insn-3 position, whereas 22∶6n−3 was equally distributed in positions 2 and 3. After 4 wk of feeding fish oil, the fatty acid composition of adipose tissue triacylglycerols reached a steady state. Half of the n−3 fatty acids were found in position 3, namely 75% of 22∶5n−3, 50% of 20∶5n−3 and 18∶4n−3 and 45% of 22∶6n−3, the latter being equally distributed in positions 2 and 3. This pattern of distribution resembled that found in triacylglycerols of the fish oil diet, except for a higher proportion of 20∶5n−3 in adipose tissue in position 1 at the expense of position 3. Throughout the 4-wk period of fish oil feeding, the distribution pattern of minor n−3 fatty acids (18∶4n−3 and 22∶5n−3) in adipose tissue triacylglycerols remained unchanged. On the other hand, at the onset of fish oil feeding, 20∶5n−3 and 22∶6n−3 became concentrated in position 3, but thereafter 20∶5n−3 was progressively incorporated into position 1 and 22∶6n−3 into position 2. We thus conclude that n−3 fatty acids are differentially esterified in triacylglycerols of white adipose tissue. Despite the complex sequence of hydrolysis and acylation steps involved, the positional distribution of n−3 fatty acids was found to be similar in both the fish oil diet and the stored fat, in contrast to what was observed for nonessential fatty acids.     

Identification and quantification of prostaglandin E3 in renal medullary tissue of three strains of rats fed fish oil

Three strains of rats were fed a fish oil diet to verify their ability to incorporate and convert dietary eicosapentaenoic acid (20∶5ω3) into trienoic prostaglandins. Our results show that such conversion indeed occurs in kidney medullae homogenates. Specifically, the presence of prostaglandin E₃ (PGE₃) was established by gas chromatographic-mass spectrometric (GC-MS) analysis. That compound was conclusively identified by comparison of fragment ions and their relative intensities with those obtained from authentic PGE₃. Further evidence was provided by studying the recovery of exogenously added PGE₃. The crude ethyl acetate extracts of the medullary homogenates were methylated and cleaned up by liquid-gel chromatography with Lipidex-5000 prior to conversion to PGB₃ for GC-MS analysis. The PGE₃ was quantified by selected ion monitoring (SIM) with [3,3,4,4-²H₄PGE₂ as internal standard. The levels of PGE₃ were similar, about 3 ng/mg of wet tissue, in the 3 strains of rats. Identical in vivo conversion of the 20∶5ω3 fatty acid to PGE₃ could not be positively established by analysis of pooled urine specimens.     

Control of metabolism in brown adipose tissue

Cells and mitochondria were isolated from brown adipose tissue of the adult hamster. Isolated mitochondria did not show respiratory control. Reversed electron transport was demonstrated and the oxidation rates of various substrates were compared. α-Glycerophosphate gave the highest oxidative rate with isolated mitochondria. The low basal respiration of isolated brown fat cells could be stimulated by catecholamines, oleate, succinate,a-glycerol phosphate and uncoupling agents. Only norepinephrine or oleate induced respiration was sensitive to inhibition by oligomycin, but this inhibition could not be released by uncoupling agents. Neither atractyloside nor (+) decanoylcarnitine were found to affect respiration, suggesting that mitochondrial nucleotide exchange is slow and that fatty acid oxidation might be carnitine independent. In resting brown fat cells, ATP amounts to 75% of the total adenine nucleotides. NE or oleate caused a small decrease of ATP and a corresponding increase of ADP. Oligomycin caused a partial depletion of ATP content, but subsequent NE addition increased ATP back to control values. This effect was abolished by arsenite. Similarly, uncoupling agents diminished the ATP level which was increased only slightly by NE. Arsenite alone decreased ATP levels to a small extent but a rapid depletion occurred upon subsequent NE addition while respiration was inhibited. Thus, substrate level phosphorylation may be the major energy producing reaction for the generation of ATP and GTP for the activation of fatty acids. Norepinephrine addition to brown fat cells caused an oxidation of pyridine nucleotides, a reduction of flavoproteins and an oxidation of cytochrome b. In constras, succinate produced a reduction of all the components of the respiratory chain. The bioenergetic basis of thermogenesis in brown fat is its high respiratory rate. The rapid respiration induced by norepinephrine or fatty acids appears to be characterized by a low yeild of ATP from oxidative phosphorylation and may be controlled by fatty acid mediated release of energy coupling, possibly by an indirect mechanism. One of nine papers to be published from the Symposium “Brown Adipose Tissue,” presented at the AOCS-AACC Joint Meeting, Washington, D. C., March 1968. This work was done during the tenure of an Established Investigatorship from the American Heart Association.     

Bioenergenetics of brown adipose tissue 1

Examination of the effect of 2,4-dinitrophenol (DNP) in vivo on the brown adipose tissue of cold-exposed rats as well as the effect of DNP and dicumarol in vitro, indicates that brown fat does possess a functional electron transport-coupled phosphorylating system. Moreover, the fact that a norepinephrineinduced thermogenic response (in vivo) can be elicited from the brown fat after DNP administration implies that the effect of norepinephrine (NE) is not primarily due to stimulation of an adenosine triphosphatase system. Furthermore, since the magnitude of the NE-stimulated temperature increase is not diminished by prior treatment with DNP, it appears that the effect of NE is not achieved through any significant degree of uncoupling by the released fatty acids. Alternatively, our data suggest that under basal conditions (i.e., when the animal is not stimulated by cold stress or NE) the heat production (oxygen consumption) of the brown fat is limited by the availability of substrate rather than ADP. Conversely, it is proposed that under states of cold stress or NE infusion the thermogenic effect is induced through stimulation of lipolysis and consequent enhancement of substrate accessible for mitochondrial oxidation. One of nine papers to be published from the Symposium “Brown Adipose Tissue,” presented at the AOCS-AACC Joint Meeting, March 1968.     

The effect of dietary fish oil on muscle and adipose tissue lipoprotein lipase

The activity of lipoprotein lipase (LPL) in the adipose tissue and skeletal muscle of rats fed glucose- or fructose-based diets containing fish oil, corn oil or tallow was examined. In addition, heart LPL activity was measured in rats fed a glucose-based diet containing either corn oil or fish oil. Adipose tissue LPL activity was unaffected by dietary fat. In both heart and skeletal muscle, LPL activity was higher in rats fed the fish oil diet. These results suggest that increased removal of triglyceride by muscle may contribute to the blood triglyceride lowering effect of dietary fish oil.     

The structure of the triacylglycerols of meadowfoam oil

The triacylglycerols of meadowfoam oil have been resolved by HPLC in the silver ion and reversed-phase modes, and by the two techniques used in a complementary fashion. The fractions obtained were collected and quantified by gas chromatography of their methyl esters in the presence of an internal standard. Silver ion chromatography gave a distinctive resolution in which fractions differing solely in the position and chain-length of a single monoenoic fatty acyl group were resolved, the order of elution being 11−20∶1, 5−20∶1, 13−22∶1, 5−18∶1 and 9−18∶1. Reversed-phase chromatography also gave fractions containing single positional isomers, (11−20∶1<5−20∶1<13−22∶1<5−22∶1), but the pattern was more difficult to discern since fractions containing 22∶2 tended to overlap with those containing 20∶1. The species (5−20∶1)(5−20∶1)(22∶2), (5−20∶1)(5−20∶1)(5−20∶1) and (5−20∶1)(5−20∶1)(13−20∶1) were found to be the most abundant, and together comprised 67% of the total. A small but significant trilinolein fraction was detected and its presence may have biosynthetic implications.     

In vivo incorporation of lauric acid into rat adipose tissue triacylglycerols

An in vivo approach was taken to examine fatty acid esterification in adipose tissue using a coconut oilenriched diet. Rats were fed a diet containing cocounut oil (50% lauric acid) for six weeks. Triacylglycerols from perirenal adipose tissue were fractionated by silver nitrate-thin layer chromatography and, then, preparative gas chromatography. The distribution of 169 triacylglycerol types accounting for 97% of total triacylglycerols was determined. There was evidence for a very high content of mixed triacylglycerols composed of intermediate (12∶0 and 14∶0) and long acyl moieties. No significant differences were observed between the experimental distribution of triacylglycerol types and the random distribution, calculated from the total fatty acid composition. This indicated that most long chain triacylglycerols stored before coconut oil feeding would have been rearranged after the six weeks of coconut oil feeding. The experimental proportion of trilauroylglycerol reached 2%, as expected from its random proportion, and the proportions of dilauroylacylglycerols were slightly higher than the random values. Present results were compared with those previously obtained from triacylglycerols of adipose tissue of rats fed a low-fat standard diet (1,2). From our results and those of other authors, it is suggested that lauric acid is a good substrate forsn-glycero-3-phosphate acyltransferase and diacylglycerol acyltransferase in rat adipose tissue.     

Lipoprotein lipase in rats fed fish oil: Apparent relationship to plasma insulin levels

To investigate the role of lipoprotein lipase (LPL) and hepatic lipase in the triacylglycerol lowering effects of fish oil, rats were fed lard (L), corn oil (CO) or menhaden oil (MO) as the primary fat source in otherwise identical diets. After 2 weeks, soleus muscle LPL differed between groups (MO>CO>L). Hepatic lipase did not differ between CO- and MO-fed rats but was elevated in L-fed rats. Adipose LPL did not differ between diet groups. Total epididymal fat weight was reduced in MO-fed rats. There was a significant positive correlation between adipose tissue weight and plasma free fatty acids. MO-fed rats had lower plasma insulin levels. Insulin was directly correlated with plasma triacylglycerol and glucose, consistent with a hyperinsulinemic, insulin-resistant state in CO-and L-fed rats, and a protective effect with MO feeding. In addition, insulin was directly correlated with adipose LPL. A negative relationship between soleus muscle LPL and insulin approached significance. Soleus muscle LPL was significantly inversely correlated with triacylglycerol. The data indicate that increased skeletal muscle LPL, in response to MO or a MO-induced decrease in insulin, may contribute to the triacylglycerol-lowering effects of fish oil. Decreased fat weight and adipose LPL and increased soleus muscle LPL and decreased plasma triacylglycerol suggest a shift from fat deposition to oxidation with MO feeding. The lack of response of hepatic lipase to MO feeding suggests that this enzyme does not contribute to the fish oil-stimulated lowering of plasma triacyglycerolvia hepatic reuptake of very low density lipoproteins or other triacylglycerol-rich lipoproteins.     

Lymphatic fatty acids from rats fed human milk and formula supplemented with fish oil

Absorption of long-chain polyunsaturated fatty acids from human milk and formula supplemented with fish oil was studied to determine if the distribution route into lymphatic triacylglycerol (TAG) and phospholipid (PL) varies with the dietary source. Rats were intraduodenally infused with human milk or formula containing graded amounts of fish oil (0, 0.5, or 1.0 g/100 mL), and the mesenteric lymph was collected. Arachidonic acid (20∶4n−6) levels in lymphatic TAG and PL were highest from animals fed human milk. In the animals infused with formula containing fish oil, as the amount of eicosapentaenoic acid (EPA, 20∶5n−3) infused increased, there was essentially an equal increase of EPA associated with both lymphatic TAG and PL. Animals intraduodenally infused with human milk or formula without fish oil had only minor levels (less than 1%) of EPA in the lymph. In the fish oil-treated animals, as the amount of docosahexaenoic acid (DHA, 22∶6n−3) infused increased, there was a 16-fold increase in DHA associated with lymphatic TAG, but only a 3-fold increase in DHA associated with lymphatic PL. The highest level of DHA in rats infused with human milk was observed in lymphatic PL. Hence, fish oil can be added to formula as a source of long-chain polyunsaturated fatty acids, but the distribution of fatty acids into lymphatic TAG and PL is not the same as that observed with human milk.     

Effects of dietary triacylglycerol structure on triacylglycerols of resultant chylomicrons from fish oil- and seal oil-fed rats

We investigated the influence of the intramolecular fatty acid distribution of dietary triacyl-sn-glycerols (TAG) rich in n-3 polyunsaturated fatty acids (PUFA) on the structure of chylomicron TAG. Fish oil and seal oil, comparable in fatty acid compositions but with different contents of major n-3 PUFA esterified at thesn-2 position (20:5n-3, 46.6%, and 5.3%; 22:6n-3, 75.5%, and 3.8%, respectively), were fed to rats. Mesenteric lymph was collected and the chylomicrons were isolated by ultracentrifugation. The fatty acid composition of chylomicrons largely reflected the fatty acid composition of the oils administered. The intramolecular fatty acid distributions of the TAG fed were reflected in the chylomicron TAG as the fraction of the total contents observed in thesn-2 position of 20:5n-3 were 23.6 and 13.3%, and of 22:6n-3 were 30.6 and 5.4% for resultant chylomicrons following fish oil and seal oil administration, respectively. Thus, after seal oil administration, significant higher load of n-3 PUFA was esterified in thesn-1,3 positions of chylomicron TAG compared with fish oil administration (P<0.05).     

Some aspects of fatty acid metabolism in brown adipose tissue

The action of catecholamines on white and brown adipose tissue is compared. The available evidence indicates that lipolysis is initiated in both tissues by hormonal action. There are, however, some differences in the behavior of the lipolytic process in the two tissues in their response to theophylline, nicotinic acid and insulin which remain unexplained. It would appear that the release of free fatty acids triggers the stimulation of O₂ consumption in both tissues. In brown adipose tissue no evidence has been obtained to indicate that the increased O₂ consumption is geared to the production of ATP for the purpose of reesterification of the released free fatty acids, as is the case in white adipose tissue. One of nine papers to be published from the Symposium “Brown Adipose Tissue,” presented at the AOCS-AACC Joint Meeting, Washington, D.C., March 1968.     

Positional analysis of triacylglycerols from bovine adipose tissue lipids varying in degree of unsaturation

The objective of this study was to demonstrate that changing the fatty acid composition of bovine adipose tissue concurrently changed (i) proportions of triacylglycerol species, (ii) fatty acid composition of triacylglycerol species, and (iii) positional distribution of the component fatty acids of the triacylglycerol species. To achieve this, we took advantage of adipose tissue lipids, from cattle fed in Australia and Japan, that varied widely in fatty acid composition and melting points. Treatment groups produced in Australia were cattle fed: a cornbased diet (MUFA1); a grain-based diet containing whole cottonseed (SFA); a grain-based diet containing protected cottonseed oil (PUFA); and a grain-based diet that resulted in high contents of trans fatty acids (TFA). Treatment groups produced in Japan (MUFA2 and MUFA3) were diets of unknown composition fed for over 300 d. The MUFA1, MUFA2, and MUFA3 samples all were rich in monounsaturated fatty acids, varying only in the proportions of the individual monounsaturates. The SFA, PUFA, and TFA samples had relatively high concentrations of stearic acid (18:0), PUFA, and TFA, respectively. Slip points (indicative of melting points) were 45.1, 41.5, 38.5, 30.7, 28.4, and 22.8°C, for the SFA, TFA, PUFA, MUFA1, MUFA2, and MUFA3 groups, respectively (P<0.05). Triacylglycerols were separated by high-performance liquid chromatography on a silver nitrate-impregnated column into sn-1,2,3-saturated fatty acid triacylglycerol (SSS); [triacylglycerols containing two saturated acids and one trans-monounsaturated fatty acid (SSMt sn-positions unknown)]; sn-1-saturated, 2-monounsaturated, 3-saturated triacylglycerol (SMS); sn-1-saturated, 2-monounsaturated, 3-trans-monounsaturated triacylglycerol (SMMt); sn-1-saturated, 2,3-monounsaturated fatty acid triacylglycerol (SMM); sn-1-saturated, 2-polyunsaturated, 3-trans-monounsaturated triacylglycerol; sn-1,2,3-monounsaturated fatty acid triacylglycerol (MMM); and sn-1-saturated, 2-polyunsaturated, 3-monounsaturated triacylglycerol. Fatty acid methyl esters of each triacylglycerol species also were determined, and further analysis indicated sn-2, and sn-1/3 positions. As the percentage oleic acid increased in the total lipid extract, the proportions of SMM and MMM increased (e.g., from 31.4 and 2.4% in the SFA group to 55.4 and 17.8% in the MUFA3 group). The elevated 18:0 in the SFA group (26%) was reflected in increased percentages of SSS and SSM, and caused an increase in the proportion of 18:0 in all triacylglycerol species relative to the other treatment groups. The percentage of 18:0 in the sn-1/3 positions was elevated markedly in the SMS fraction of the SFA group (to 44%); this would account for the high melting point of the fat of these animals. We conclude that long-term feeding of cattle is sufficient to produce significant alterations in fatty acid composition in bovine adipose tissue. Alterations in the fatty acid composition of bovine adipose tissue changed both the distribution and the composition of the triacylglycerol species, which, in turn, accounted for marked differences in melting points among treatment groups.     

Circum-annual changes in triglyceride fatty acids of bat brown adipose tissue

A circum-annual study of the fatty acids of brown adipose tissue triglycerides ofEptesicus fuscus has demonstrated a rhythmic pattern of change. This is seen as a reciprocal shift of the levels of oleic and linoleic acids. Oleic acid levels are lower during the summer months and higher in the winter months. Levels of palmitic and linoleic acids reach maximal values in midsummer and fall significantly during the winter. Homogenates of brown adipose tissue produce more¹⁴CO₂ from 1-¹⁴C-palmitic acid than from 1-¹⁴C-oleic acid when incubated at temperatures below 20C. The formation of¹⁴CO₂ from either substrate was maximal in the neighborhood of 30C, and the temperature effect was enhanced by stimulation with DL-carnitine. It is proposed that the rhythmic change in brown adipose tissue triglyceride composition is a reflection of the different rates of fatty acid oxidation and the absence of normal food intake for extended periods of time.     

Identification of methyl-branched fatty acids from the triacylglycerols of subcutaneous adipose tissue of lambs

A concentrate of branched chain fatty acids (as methyl esters) was prepared from the triacylglycerols of subcutaneous adipose tissue lipids of lambs receiving a carbohydrate-rich (cereal) diet. This was accomplished by procedures which allowed the removal of unsaturated components by peroxidation and straight chain saturated components by urea-adduct formation. The concentrate was analyzed by high resolution gas chromatography in combination with mass spectrometry and was shown to consist of a complex mixture of saturated methyl-substituted fatty acids. Methyl substitution occurred on even-numbered carbon atoms (relative to the carboxyl group) and the chain lengths of the acids ranged from 10 to 18 carbon atoms. Acids with one methyl substituent in the fatty acyl chain were most abundant; di-, tri- and tetramethyl-substituted acids were also present. The biosynthesis of these methyl-substituted acids is discussed briefly.     

Mid‐infrared spectroscopy and multivariate curve resolution for analyzing human adipose tissue triacylglycerols

The aim of this study was to evaluate use of infrared spectroscopy for measuring adipose tissue triacylglycerols (TAGs) with analysis by multivariate curve resolution (MCR). The mid‐infrared spectrum was measured with an attenuated total reflection accessory from a lipid droplet pressed from adipose tissue. The obtained spectra were characteristic of pure TAG spectra and water and protein contamination could be easily identified from specific spectral regions. MCR analysis of the olefinic (?C? H) stretch (3006 cm^?1), resolved the different contributions of monounsaturated (MUFA) and polyunsaturated (PUFA) double bonds. Similar MCR analysis of the trans (HC?CH? ) region (966 cm^?1), resolved the differing contributions of isolated trans isomers (transFA) and CLA. The PUFA double bond content of 16 subjects was negatively correlated with concentrations of serum total cholesterol R = ?0.498 (p = 0.050) and triacylglycerols R = ?0.609, (p = 0.016). The transFA content exhibited a negative, although non‐significant, correlation to high‐density lipoprotein (HDL)‐cholesterol (R = ?0.483, p = 0.068). The present study shows that MCR analysis of adipose tissue TAG infrared spectra can be used to estimate differences in the fatty acid (FA) profiles in population studies. Infrared spectroscopy in combination with MCR provides a robust method for assessing a FA profile of human adipose tissue. Practical applications: This study has highlighted the use of MCR to enhance the information obtained from infrared spectra. This new approach provides a robust method for assessing a FA profile of human adipose tissue lipids.     

Reduction in triacylglycerol levels by fish oil correlates with free fatty acid levels inad libitum fed rats

Rats were fed (for 2 or 6 wk) purified diets containing lard (LD) or menhaden oil (MO) at two levels of dietary fat,i.e., at 11.5 and 20.8% of energy in the low fat (LF) and the medium fat (MF) diets, respectively. Following the diet period, rats were sacrificed after either an overnight fast or after uninterruptedad libitum feeding. The studies were designed to investigate the dependence of our previously reported effects of MO,i.e. the reduction of plasma free fatty acid (FFA) levels and accumulation of hepatic triacylglycerols, on the dietary fat concentration and the nutritional state of the animal at the time of sacrifice. Reductions in plasma triacylglycerol and cholesterol levels in MO-fed relative to LD-fed rats were observed under all conditions. FFA levels were consistently reduced by MO-feeding at both dietary fat concentrations, but only when blood was sampled fromad libitum fed rats. Under these conditions there was a significant positive relationship between plasma FFA and triacylglycerol concentrations. Reduction in plasma FFA levels may be an additional mechanism associated with the triacylglycerol-lowering effect of fish oil (FO). The LF and MF MO diets caused a rise in plasma glucose levels with no significant change in insulin concentration, indicating that the reduction of FFA by MO was not related to changes in insulin concentration or insulin sensitivity. The MO diets had no effect on skeletal muscle or epididymal adipose tissue lipoprotein lipase activity, demonstrating that catabolism of triacylglycerol-rich lipoproteins contributes little, if any, to the MO-dependent reductions of plasma triacylglycerol and FFA. The previously reported accumulation of hepatic triacylglycerols after high fat (HF; 30% of energy) MO-feeding was not observed with the LF or MF MO diets, suggesting that the apparent direct inhibition of triacylglycerol secretion by FO imposes a rate-limitation only when feeding HF diets.     

Serum lipids in spontaneously hypertensive rats and sprague-dawley rats fed menhaden oil

Dietary n-3 fatty acids, abundant in fish oil, exert a variety of effects that attenuate cardiovascular disease. In this study, we assessed the effect of fish oil (menhaden oil) on the serum lipid profile in hypertensive and normotensive rats. Spontaneously hypertensive rats (SHR) or Sprague-Dawley rats (SD) were fed either standard powdered diet (L-485), or L-485+5% menhaden oil (MO) or L-485+5% corn oil (CO) from weaning through eight months of age. Systolic blood pressure (BP) was periodically determined on SHR. Serum lipid profiles were performed at eight months on sample taken from the exposed hearts of anesthetized, fasted rats. SHR, compared with SD (diets combined) had significantly lower triaclyglycerols (TG), higher cholesterol (CHOL), higher high density lipoprotein cholesterol (HDL CHOL), higher low density lipoprotein cholesterol (LDL CHOL), and a higher LDL:HDL ratio. Comparison among diets (strains combined) revealed that rats fed MO had the lowest values for TG, CHOL, LDL and LDL:HDL; HDL did no vary with diet. SHR were less responsive to diet-induced changes than were SD; no decrease in TG, LDL or LDL:HDL was observed in SHR, nor was degree of hypertension altered in SHR by the MO or CO diet. In summary, MO is more effective than CO in shifting the lipid profile of rats toward one that is less atherogenic. However, the SD rat is more susceptible to diet-induced lipid modification than is the SHR.     

Myocardial lipids and nucleotides of rats fed olive oil or rapeseed oil

After 1 week, the level of myocardial fatty acids was 4 times greater in young rats fed high erucic rapessed oil than in those fed olive oil. The proportion of erucic acid was 5.6% in the mitochondrial fraction, 15.1% in the microsomal fraction, and 34.8% in the floating fat fraction. This incorporation of erucic acid into triglycerides of the floating fat was evidence of esterification. The changes in the mitochondrial lipids did not alter the content of adenine nucleotides of the myocardium nor its apparent capacity to oxidize substrates.     

Enhanced survival to endotoxin in guinea pigs fed IV fish oil emulsion

Improved survival to endotoxin has been demonstrated in rats pretreated with cyclooxygenase inhibitors or made essential fatty acid deficient, implying that excessive ω6 fatty acids, possibly through their eicosanoid products, contribute to mortality. Following endotoxin administration, we also have shown improvement in survival with oral diets supplemented with fish oil. This study sought to explore whether parenteral fish oil ameliorates the adverse impact of endotoxin. Male Hartley-strain guinea pigs were obtained at a body weight of 500 g and fed a normal laboratory diet. Central venous lines through which the animals received either a 10% safflower oil emulsion (n=11) or a 10% fish oil emulsion (n=11) during two, 24-hr periods separated by two days were inserted. Two days after the second infusion, endotoxin (0.35 mg/100 g b.w.), was given intraperitoneally, and survival was noted. The animals received a total of 25.4 g of IV fat per kg b.w., including 5.3 g of eicosapentaenoic acid per kg b.w., for the fish oil group. From six hr after endotoxin through four days, there was better survival in the fish oil group (p<.006). Final mortality showed 7/11 fish-fed vs 2/11 safflower-fed animals surviving. We conclude that the administration of parenteral fish oil, even for a brief time, can have a profound effect on subsequent survival to endotoxin.