EFA-deficient Rats Research Articles

Lung surfactant and fatty acid composition of lung tissue and lavage of rats fed diets containing different lipids.

Two nutritional models, essential fatty acid (EFA) deficiency and the feeding of saturated vs unsaturated fats, were used to determine the effects of dietary lipids on the fatty acid composition of rat lung and lavage. Semipurified diets containing 7% corn oil, 7% hydrogenated coconut oil (EFA-deficient), 10% butter or 10% safflower oil were fed to dams during lactation and thereafter to their offspring for a total of 24 weeks. Lipids were extracted from the lung lavage and lung tissue and their fatty acid composition was determined. The content of dipalmitoylphosphatidylcholine (DPPC), the main surfactant in the lungs, was also determined. The results show that the levels of DPPC in the lungs of rats fed 10% butter decreased although the decrease in the EFA-deficient rats was greater. Comparing rats fed butter with those fed corn oil, there were also modifications in the fatty acid composition of the total lipids and phospholipids of lung tissue and lavage as well as in phosphatidyl-choline, phosphatidylethanolamine and phosphatidylinositol + phosphatidylserine fractions isolated from the lung tissue. The changes in fatty acid composition were somewhat fewer in rats fed butter then in those fed an EFA-deficient diet. The results suggest that a marginal EFA deficiency produced in rats by long-term feeding of 10% butter may account for the reduction in DPPC levels and in the changes in fatty acid composition in the lung tissue and lavage.

Effect of essential fatty acid deficiency on the epidermal sphingolipids of the rat

The epidermal sphingolipids from rats maintained on either a rat stock diet or a fat-free diet have been analyzed. Thin-layer Chromatographic analyses have revealed glucosylceramides, acylglucosylceramides and four fractions of ceramides, one of which proved to be an acylceramide. The relative amounts of the glucosylceramides, acylglucosylceramides and acylceramides were increased in the essential fatty acid-deficient epidermis while one ceramide fraction was diminished. The other two ceramide fractions remained unchanged. The acylceramides and acylglucosylceramides from normal rat epidermis both contained long-chain ω-hydroxy acids in amide linkage to sphingosine bases and high proportions of linoleic acid in ester linkage. The linoleate, which is known to be crucial for the formation and maintenance of the epidermal water barrier, was replaced by oleate in the essential fatty acid-deficient rats.

Studies of the effects of essential fatty acid deficiency in the rat.

We report a model of prostaglandin depletion induced in rats by fasting for 11 days, followed by institution of an essential fatty acid-deficient diet. Urinary prostaglandin E, 2 weeks after this diet had been implemented, was 22 +/- 2 ng/24 hours compared to 113 +/- 8.5 ng/24 hours in controls (P less than 0.01). There was no difference in 24-hour urine volume or solute excretion in controls and essential fatty acid-deficient rats. Five hours after administration of NaCl, 10 mM/kg, essential fatty acid-deficient diet rats excreted 1.85 +/- 0.78 ml urine compared to 6.42 +/- 2.26 ml in control (p less than 0.01) with Na+ excretion 447 +/- 273 muEq in essential fatty acid-deficient rats vs 1483 +/- 366 muEq in control (P less than 0.01). Intravenous isotonic NaCl, 1.5% body weight, resulted in increased urine flow rate in control rats from 8.3 +/- 2 microliter/min to 28.7 +/- 8.8 microliter/min with sodium excretion increasing from 0.19 +/- 0.2 to 3.3 +/- 0.9 muEq/min. In the essential fatty acid-deficient diet animals, there was no significant change in flow rate, 6.07 +/- 2.43 to 9.85 +/- 4.29 microliter/min, or sodium excretion, 0.09 +/- 0.03 to 0.40 +/- 0.24 muEq, after saline infusion. There was no difference in the glomerular filtration rate of plasma aldosterone in the two groups after the salt load. When given a water load, 3 ml/100 g body weight, essential fatty acid-deficient diet rats excreted 2.5 +/- 0.7 ml in 5 hours compared to 6.3 +/- 1.4 ml in controls (P less than 0.01). The defect in water excretion was not due to increased sensitivity to antidiuretic hormone, since similar sensitivity to this hormone was demonstrated in the essential fatty acid-deficient diet and control rats during a water diuresis. When isotonic saline was substituted for drinking water, there was an increase in systolic blood pressure in essential fatty acid-deficient diet rats from 124 +/- 2 to 142 +/- 3 mm Hg over 9 days (P less than 0.01) compared to 122 +/- 2 before and 122 +/- 2 mm Hg after saline drinking in controls. The administration of linoleic acid for 4 days increased urinary prostaglandin E excretion to 114 +/- 15 ng/24 hours from 23 +/- 4 (P less than 0.01), and the alterations in the ability to excrete a sodium and water load were reversed. In essential fatty acid-deficient diet animals made hypertensive by 9 days of saline drinking, the institution of linoleic acid to the diet normalized the blood pressure despite the continued administration of saline. These studies demonstrate that essential fatty acid-deficient diet animals develop salt-sensitive hypertension with a combined defect in both sodium and water excretion which is reversed following correction of the essential fatty acid deficiency.

Characteristics of the formation of the platelet lipoxygenase product from endogenous arachidonic acid.

The concentration of 12-hydroxyeicosatetraenoic acid (12-HETE) formed in rat platelets aggregated by collagen suspension increased continuously during a 115-min incubation period, whereas the concentration of TXB2 or PGF2 alpha reached the maximum within 3 min and stayed at the plateau for the remaining incubation period. These data indicate that platelet lipoxygenase is not completely inactivated as is cyclooxygenase by the oxidizing agent. Platelets of essential fatty acid deficient (EFAD) rats resuspended in plasma of control rats produced more 12-HETE than platelet-rich plasma (PRP) of EFAD rats, whereas platelets of control rats resuspended in plasma of EFAD rats formed less 12-HETE than PRP of control rats. However, the concentration of TXB2 or PGF2 alpha produced was not changed in both cases implying that platelet cyclooxygenase preferentially utilizes arachidonic acid (AA) derived from platelet lipids. Radioactivity of phosphatidylcholine (2-arachidonyl-1-14C) suspended in the plasma of PRP was incorporated into 12-HETE but not to TXB2, indicating again that only lipoxygenase can utilize AA derived from plasma phospholipids. The significance of this observation is that the effects of platelet lipoxygenase products, although their physiological roles are not known, would be much more persistent than cyclooxygenase products after platelets are stimulated or aggregated in vivo.

Triacylglycerol Secretion in Rats: Effects of Essential Fatty Acids and Influence of Dietary Sucrose, Glucose or Fructose

The rate of triacylglycerol (TG) secretion into plasma was determined in vivo in essential-fatty-acid(EFA)-adequate and EFA-deficient rats fed for 8–10 weeks on diets containing either sucrose, glucose or fructose (66.5% wt/wt) as the sole source of carbohydrate. The rate of TG secretion was increased in EFA-deficient rats, irrespective of the type of dietary carbohydrate. The secretion rate in EFA-deficient rats fed fructose was 50% higher than the rate in similar animals fed glucose or sucrose, although in the EFA-adequate rats, the secretion rate with fructose was not significantly higher than with sucrose or glucose. The concentrations of triacylglycerols and cholesteryl esters in plasma were generally reduced in EFA deficiency, whereas the concentrations of these lipids in liver were increased. Plasma free fatty acid concentrations were unchanged. The fatty acid composition of plasma and hepatic lipids was altered both by EFA deficiency and to a smaller extent by the type of dietary carbohydrate. The concentration of plasma glucagon was reduced in the deficient animals, although plasma insulin concentration was not affected. The resulting increase in the plasma insulin:glucagon molar ratio may explain some of the alterations in lipid concentrations and in lipid metabolism observed in EFA deficiency.triacylglycerol secretion EFA deficiency dietary carbohydrate insulin glucagon lipid compositions

Cholesteryl ester hydrolase activity in adrenal homogenates from normal and essential fatty acid-deficient female rats.

Cholesteryl ester hydrolase was assayed in adrenal homogenates from mature female rats fed a control (corn oil-containing) or essential fatty acid (EFA)-deficient diet. Cholesteryl ester of 16:0, 18:0, 18:1, 18:2(n-6), 20:4(n-6) and 22:4(n-6) were used as substrates. In control rats, the unsaturated esters were hydrolyzed more rapidly than the saturated esters and cholesteryl arachidonate was the preferred substrate of the six investigated; cholesteryl oleate elicited the highest activity in the deficient group. Polyunsaturated esters were hydrolyzed at a significantly lower rate by homogenates from EFA-deficient rats than by those from control animals. The esters of 18:1, 18:2(n-6) and 20:4(n-6) were hydrolyzed more extensively in relation to their concentrations in adrenal tissue than were cholesteryl esters of 16:0, 18:0 and 22:4(n-6). This difference was more pronounced in control than in EFA-deficient rats. No simple relationship of adrenal cholesteryl ester hydrolase activity to ester fatty acid structure or to nutritional essentiality was evident.

Increased proliferation of the epithelium of the proximal alimentary tract of EFA-deficient rats: A light and electron microscopy study

Rats of a Wistar strain fed a lipid-poor diet which is deficient in essential fatty acids (EFA) developed hyperkeratosis and increased cell proliferation of the stratified squamous epithelium of the upper alimentary tract. The frequency and severity of hyperkeratosis was significantly increased in the forestomach in both male and female EFA-deficient rats but, in the esophagus, only in the male, whereas hyperkeratosis was not seen in mouth epithelium. In EFA-deficient rats, the mitotic index was increased in the epithelium of palate and tongue ( P < 0.001), as well as in esophagus ( P < 0.025) and forestomach ( P < 0.005). Sex-linked differences in the mitotic index were noted, being higher in female than in male rats, in both control and experimental animals. Electron microscopy showed that in the epithelium of the forestomach of the EFA-deficient rat the squamous cells presented decreased number of desmosomes, widening of the intercellular spaces, diminution of surface folds, and increased binding of ruthenium red. This suggested that the surface of these cells was altered in the EFA-deficient condition. Present observations indicated that cell proliferation and differentiation of the stratified squamous epithelium of the upper alimentary tract are upset in various degrees in EFA-deficient rats.

Metabolic changes in scaly lesions of rat skin produced by essential fatty acid deficiency.

Marked changes in the structure and metabolism of lipids were observed at scaly lesions induced in the skin of rats by the feeding for four months of a diet deficient in essential fatty acids. The concentration of neutral lipids increased in the experimental skin specimens with the exception of free cholesterol. Analysis of fatty acids in the skin lipids of these essential fatty acid deficient rats showed a marked increase in monoenoic and eicosatrienoic acids, with a concomitant decrease in linoleic and arachidonic acids. Incubation of skin specimens from the essential fatty acid deficient rats with [2-3H]glycerol and [1-14C]acetate showed a marked increase in the incorporation of both precursors into all lipid classes. Particularly, their incorporations into phosphatidylcholine were predominant compared to other lipid classes. With regard to the molecular species of phosphatidylcholine, saturated-monoenoic and monoenoic-monoenoic species were highly synthesized in the skin from essential fatty acid deficient animals, and the synthesis of saturated-dienoic and tetraenoic species was very low with either precursor. Significant decreases in these labelings were also noted in saturated-saturated species. Addition of prostaglandin E2 to the incubation medium did not significantly affect the metabolism of any of the lipid classes in the skin from the essential fatty acid deficient rats. The present results, therefore, suggest that phosphatidylcholine containing linoleic acid may be a key lipid in the epidermal barrier function.

Effects of essential fatty acid deficiency on the induction of liver microsomal membranes by phenobarbital: an ultrastructural and biochemical investigation.

The essential fatty acids, particularly arachidonic, are important components of intracellular membrane systems. Their absence during dietary manipulation has been postulated to cause alterations in both composition and function of membranes and associated enzyme systems. In the current investigation, the effect of essential fatty acid deficiency on the induction of hepatic microsomal membranes my phenobarbital was studied. Control rats were fed a standard chow diet and either injected daily for 4 days with phenobarbital or with a placebo. Experimental animals were given an essential fatty acid-deficient (EFAD) diet and similarly injected with either phenobarbital or placebo. Following the above regimens, liver tissue was obtained for electron microscopy and biochemical membrane analysis. Control animals given phenobarbital displayed a marked proliferation of smooth endoplasmic reticulum in comparison to placebo controls. In contrast, EFAD rats did not exhibit an endoplasmic reticulum response to phenobarbital injection and appeared to recover from the drug administration injection more slowly than control animals. The alterations in fatty acid composition characteristic of an EFAD diet were observed in the microsomal membranes of the deficient animals. The concentrations of palmitic, palmitoleic, oleic, and 5,8,11-eicosatrienoic acids were significantly increased above that found in control animals. Concentrations of linoleic and arachidonic acids were reduced. Phenobarbital administration significantly increased the concentrations of palmitic, linoleic, and arachidonic acids in microsomal fractions of chow-fed animals but not in EFAD animals. Conversely, eicosatrienoic acid concentrations increased in phenobarbital-treated EFAD animals but not in chow-fed, drug-injected rats. The triene/tetraene ratio reflected these alterations. Essential fatty acid deficiency causes biochemical alterations of the hepatic microsomal membranes which are exaggerated by the administration of phenobarbital. These compositional changes appear to alter the functional ability of the membranes to proliferate in response to phenobarbital and, thereby, inhibit the efficaceous metabolism of this drug.

Interrelationship between dietary trans Fatty acids and the 6- and 9-desaturases in the rat.

Studies are reported on the effects of dietary trans fatty acids on the 6- and 9-acyl desaturase activities in the liver microsomes of rats fed essential fatty acid (EFA)-deficient and non-EFA-deficient diets. In experiment I, weanling male rats were fed a semisynthetic diet with either 10% safflower oil (SAF) or 10% hydrogenated coconut oil (HCO). At the age of one year, half of the dietary fat was replaced by a supplement containing elaidate, linolelaidate and cis, trans-trans,cis-18:2 (TRANS) for 12 weeks. In experiment II, male rats which were kept from weaning on a 10% (SAF + TRANS, or 5% HCO + 5% TRANS. Feeding TRANS depressed the 6-desaturase activity in the liver microsomes, especially in the EFA-deficient rats (HCO + TRANS group of experiment I). Unlike the 6-deaturase activity, the 9-desaturase activity was not inhibited by the dietary trans fatty acids and was significantly stimulated in the non-EFA-deficient rats (SAF + TRANS group of experiment I and HCO + TRANS groups of experiment II). This was evidence by incubation reaction and by comparisons of fatty acid consumptions and microsomal fatty acid levels, showing extra biosynthesis of 16:1 and 18:1 when TRANS was fed. The biosynthesis of essential (n-6) fatty acids was depressed by the TRANS supplement in EFA-deficient as well as in non-EFA-deficient animals.

Essential fatty acid supplemented diet increases renal excretion of prostaglandin E2 and water in essential fatty acid deficient rats.

Weanling male rats were fed an essential fatty acid (EFA)-deficient diet for 25 weeks and then switched to an EFA-supplemented diet for 3 weeks. Control rats received the EFA-supplemented diet for 25 weeks and then the EFA-deficient diet for 3 weeks. Throughout the last 19 weeks, the rats were housed in metabolic cages once a week for a 24-hr period. urinary excretion of prostaglandin E2 (PGE2) was estimated by radioimmunoassay. Throughout a period of 12 weeks (weeks 13-24) water consumption increased ca. 60%, and urine output and PGE2 excretion decreased ca. 45% and 70%, respectively, in the EFA-deficient rats, Feeding EFA-supplemented diet to the EFA-deficient rats for 3 weeks decreased the water consumption and raised the urine output to that observed in the controls. However, the urine output was corrected within 1 day whereas the water consumption was not corrected until the second measurement 8 days after the dietary change. The PGE2 excretion increased more than 9-fold (from 18 +/- 8 ng/24 hr to 165 +/- 51 ng/24 hr) 1 day after EFA-supplementation, followed by a decrease to 86 +/- 29 ng/24 hr over the following 24 weeks. On the basis of the present data, it is suggested that EFA deficiency in rats causes diminished PGE2 excretion, which can be normalized by EFA supplementation. The normalization of the urine flow may, in part, be caused by the concomitant considerable increase in endogenous PGE2 synthesis.

Incorporation into lipid classes of products from microsomal desaturation of isomeric trans-octadecenoic acids.

The microsomal desaturation of positional isomers of trans-octadecenoic acids is effected by the delta 9-desaturase and, with concomitant geometric isomerization, cis,trans- and cis,cis-octadecadienoic acids of unusual structure are formed. Incorporation of the substrates and their products into lipids varied from 50.5% for incubations with 14-18:1 to 81.0% for 6-81:1. A detailed study of the composition of each of the major lipid classes, i.e., phospholipids, triacylglycerol and cholesteryl esters, as well as the composition of the free fatty acid fraction, revealed a complex picture. Generally, the c,c-18:2 products were enriched in the phospholipids fraction, whereas the c,t-18:2 appeared preferentially in cholesteryl esters. The 18:1 substrates themselves did not show marked preferences for any of the lipid classes. Phospholipase A2 action on phosphatidylcholine and phosphatidylethanolamine demonstrated enrichment of the c,c- and the c,t-18:2 products in the 2-position, whereas the 18:1 substrates were preferentially inserted into the 1-positions. The c,c- and c,t-18:2 formed by desaturation of t11-18:1 varied from this pattern, probably due to their conjugated double bond structures. Linoleic acid, c9,c12-18:2, formed during desaturation of t12-18:1, surprisingly showed enrichment in the 1-position of phosphatidylcholine. Incubation experiments with t5- and t6-isomers using liver microsomes from rats fed a corn-oil-supplemented diet showed conversion and incorporation rates similar to the rates obtained with microsomes from EFA-deficient rats. The fatty acid composition of lipid classes and the distribution of products and substrate between the 1- and 2-positions of phosphatidylcholine also agreed with results obtained using microsomes from EFA-deficient rats.

The composition of alkanes in exhaled air of rats as a result of lipid peroxidation in vivo Effects of dietary fatty acids, vitamin E and selenium

Alkane production in exhaled air of rats has been studied as an index of lipid peroxidation in vivo in these animals. The effect of feeding essential fatty acid-deficient rats varying levels of n A, n-6 and n-7 polyunsaturated fatty acids for various periods of time has been studied with regard to the composition of the alkanes produced as well as the fatty acid composition of liver phospholipids and liver and adipose tissue triacylglycerols. It was found that the fatty acid composition of liver lipids depended markedly on the nature and the quantity of polyunsaturated fatty acid in the diet. The composition of the alkanes produced on stimulation of lipid peroxidation in vivo by inhalation of small, non-lethal doses of carbon tetrachloride corresponded closely to the fatty acid composition of the liver phospholipids. The results strongly suggest that the alkanes produced as a result of lipid peroxidation in vivo originate from the methyl end of the fatty acid administered. So ethane is produced from n-3 acid, propane from n-4 acid, pentane from n-6 acid and hexane from n-7 acid. The amounts of a specific alkane produced increase as its corresponding fatty acid, as present in the liver phospholipids, increases. There sare indications that relatively more ethane than pentane is produced on stimulation of the in vivo lipid peroxidation although there are considerably more n-6 fatty acids than n-3 fatty acids present in the liver phospholipids.

Insulin and glucagon secretion in essential fatty acid deficient rats

Insulin and glucagon secretion in response to common secretagogues were ascertained in the perfused pancreas isolated from essential fatty acid deficient rats. The pattern of insulin secretory response to glucose (16.7 mmol/L) by isolated rat pancreas perfused for 30 min was biphasic in EFA-deficient and control rat pancreas. The amplitude of glucose-stimulated acute secretion (phase I) was significantly greater (p less than 0.01) in magnitude and amplitude in EFA-deficient rats than in the control rats. There was no significant difference in the second phase of glucose-stimulated insulin secretion in the two groups. Glucagon secretion in EFA-deficient and control rats was inhibited by glucose (16.7 mmol/l). Glucagon secretion induced by L-arginine (10 mmol/l) was not significantly different in EFA-deficient and in control rat pancreata (p greater than 0.05). However, arginine (10 mmol/l)-stimulated insulin release was significantly higher in EFA-deficient than in control rats. Growth hormone (100 mumol/l)-induced glucagon and insulin secretion was variable in the two groups but significantly higher than basal secretion. The level of L-leucine (10 mmol/l)-stimulated glucagon and insulin secretion in EFA-deficient rats was minimal but significant. Our results show that isolated pancreata of rats devoid of precursors for endogenous prostaglandin synthesis secreted insulin and glucagon in response to common secretagogues. On the basis of our data, it is concluded that endogenous prostaglandins are probably not obligatory for normal secretory functions of islets of Langerhans.

Abnormal cell proliferation and differentiation and urothelial tumorigenesis in essential fatty acid deficient (EFAD) rats

Data provided by several investigators is showing conclusively that the mechanisms regulating normal proliferation and differentiation of certain cell populations are upset in EFAD rats. In most studies, a significant increase in the mitotic index was recorded. This has been seen in squamous keratinizing epithelia of the skin and upper alimentary tract (tongue, esophagus and forestomach). Also, an increase of cell proliferation was found in the gastric glands and intestinal crypts of the EFAD mice and rats. Study of the mitotic index of most organs of the EFAD rat is under investigation in our laboratory. Though, a more dynamic approach to evaluating changes in cell proliferation in EFAD such as was carried on by McCullough et al., 28 using cell labeling, will open leads for understanding the role of EFA and presumably their biological active products, such as prostaglandins, in controlling the cell cycle of various populations. Yet, it is apparent that most cell populations characterized by active renewal, and in which mitoses are normally abundant, such as covering epithelia 23 are particularly responsive to the EFAD condition. The recognition of urothelial tumors in a small, though significant number of EFAD rats, and the large incidence of atypical hyperplasias suggest that in this nutritional condition abnormal proliferation and tumorigenesis of the transitional epithelium (urothelium) of the urinary passages is favored. The study of the pathology, life span and longevity of the chronically EFA-deficient rat is showing that: (1) Proliferation and differentiation of certain cell populations are abnormal and, as for urothelial cells, neoplastic in nature and (2) these changes increase in frequency with aging.

Essential fatty acids, prostaglandins and heart function

Coronary flow (q cor), spontaneous frequency (f) and contractile force (F) of isolated, perfused hearts of rats fed a diet containing mixtures of various fats are positively related to the amount of linoleic acid in the diet. The production of prostacyclin (the main prostaglandin formed in the heart) of isolated, perfused hearts of essential fatty acid deficient rats is about 0.3 ng min −1 g −1 (dry weight), while that of isolated hearts of rats fed a diet with 5 en% sunflowerseed oil (containing 70% 18:2 ( n-6)) is about 4 ng min −1 g −1; this production does not further increase in hearts of rats fed larger amounts of sunflowerseed oil. Feeding rats a diet with 35 en% linseed oil (with 52% 18:3( n-3)) for 8 weeks results in a 50% decrease in prostacyclin production of their isolated hearts, but does not significantly influence q cor, f or F. Intraperitoneal injection of acetylsalicyclic acid (83 μmol kg −1) or indomethacin (28 μmol kg −1) in rats completely inhibits the PGI 2 release from their isolated hearts and decreases q cor and f, but does not influence F. The observed effects on heart function are syntematic but moderate, and may in vivo be surpassed by regulatory influences. They show, however, that dietary essential fatty acids have definite effects on cardiac function which can partly be explained via an influence on prostaglandin synthesis and, for the other part, probably via influences on membrane composition and fluidity. The latter suggestion needs further investigation.

Inhibition of desaturation of palmitic, linoleic and eicosa-8,11,14-trienoic acids in vitro by isomeric CIS-octadecenoic acids

The effects of the positional isomers of cis-18 : 1 acids on the desaturation of 18 : 2 ω6 → 18 : 3 ω6 ( Δ 6 desaturase), 20 : 3 ω6 → 20 : 4 ω6 ( Δ 5 desaturase) and 16 : 0 → 16 : 1 ( Δ 9 desaturase) were investigated using essential fatty acid deficient rat liver microsomes. The isomeric cis-18 : 1 acids were found to be inhibitory for the Δ 6, Δ 5 and Δ 9 desaturases, and the position of the double bond is important in determining the degree of inhibition. The effects of the several cis-18 : 1 isomers on Δ 6 and Δ 5 desaturases were parallel in magnitude exept for the cis- Δ 6 isomer which gave 17.5% inhibition for Δ 6 desaturase and no inhibition for Δ 5 desaturase. The strongest inhibitor for Δ 5 desaturase ( cis- Δ 8 18 : 1) was also the most potent inhibitor for Δ 5 desaturase, and the weakest inhibitor for Δ 6 desaturase ( cis- Δ 3 18 : 1) was the least effective inhibitor on Δ 5 desaturase. The Δ 9 desaturase was maximally inhibited by cis- Δ 10 and Δ 11 18 : 1 isomers. The cis-18 : 1 acid isomers in partially hydrogenated edible fats may have effects on the lipid metabolism through their inhibitory effects on the desaturases.

Glutathione peroxidase activity in vitamin e and essential fatty acid-deficient rats.

Gluthathione peroxidase (EC 1.11.1.9, GSHPx) activity was measured in whole liver, in hepatic cytosol and in whole mitochondria from normal rats and from rats subjected to experimentally induced vitamin e and/or essential fatty acid (EFA) deficiency. The animals were fed and raised on the specific diets for 6 months. The GSHPx activity was significantly decreased in all samples of EFA-deficient rats. This group exhibited a significant increased 29:3omega9 content and to low 20:4omega6 content. In rats fed a vitamin E-deficient diet, the GSHP x activity was significantly decreased in hepatic cytosol. When the data of all experimental groups were pooled the specific GSHP x activities of the hepatic cytosol correlated significantly to that of whole mitochondria. The specific GSHP x activity of the whole liver, the mitochondrial and the cytosol fractions were found higher in female than in male rats in controls as well as in deficient animals. This difference was affected by the EFA deficiency. In EFA-deficient mitochondria the sex difference in enzymic activity was decreased (half of normal difference). In EFA-deficient cytosol the difference was increased (double of normal difference). However, the total hepatic GSHPx activities were not significantly higher in female than in male rats in any of the groups studied. Thus, EFA deficiency is added to the list of factors influencing the GSHPx activity. It is concluded that it is not possible to use GSHPx activity as a marker for the selenium status in domestic animals such as suggested previously. Thus, selenium is only one of the factors governing the GSHPx level.

Prostaglandin synthesis by adult heart myocytes

Adult cardiac myocytes, prepared by proteolytic disaggregation of left ventricular tissue of rats or dogs, were incubated with [1- 14C]-arachidonic acid for periods up to 90 min at 37°C. Ethyl acetate extracts of the acidified media containing carrier prostaglandins were subjected to thin layer silicic acid chromatography for separations of prostacyclin and thromboxane derivatives and classical prostaglandings (PG). Synthesis of prostaglandins was evaluated by gas and thin layer radiochromatography. Unperturbed rat heart myocytes synthesized prostaglandins linearly during the 90 min incubation and these included predominantly PGE 2 and its metabolites (PGA 2-PGB 2) and equal levels of prostacyclins (determined as 6-keto PGF 1α) thromboxane B 2 and PGF 2α. Dog heart myocytes, in contrast, produced largely 6-keto PGF 1α and PGD 2 with lesser amounts of other PGs. Incorporation of labeled arachidonate into these PGs inhibited by indomethacin or eicosatetryenoic acid, and was enhanced by incubation of cells with methylprednisolone, a phospholipase A 2 inhibitor, or by using cells from essential fatty acid-deficient rats.

Structural and biochemical effects of essential fatty acid deficiency on peripheral nerve.

The effect of postweaning essential fatty acid (EFA) deficiency on the peripheral nerve was studied in groups of rats. At 325 days, the characteristic biochemical changes of EFA deficiency were present in isolated peripheral myelin, although to a lesser degree than reported in non-neural tissues. There was no significant difference between control and deficient groups in number or size distributions of myelinated fibers (MFs) in muscle and sensory nerves, in the incidence of teased fiber abnormalities, in rates of axonal transport of dopamine-beta-hydroxylase and acetylcholinesterase, or in conduction velocity and compound action potentials of peripheral nerve in vivo or in vitro. Four weeks after a standard sciatic crush injury, the median MF diameter in regenerated peroneal nerves was significantly smaller in EFA-deficient rats than in control rats, but this difference was no longer significant at 18 weeks. At 18 weeks, EFA-deficient and control regenerated nerves showed similar myelin periodicity and relationship of axonal area to number of myelin lamellae. We conclude that acquired EFA deficiency in the rat leads to biochemically abnormal peripheral myelin, but that this state is unaccompanied by clinical, physiological, or morphological evidence of neuropathy.