Effects of streptozotocin and dietary fructose on delta-6 desaturation in spontaneously hypertensive rat liver

We have investigated the effects of hypertension associated with diabetes mellitus on polyunsaturated fatty acid biosynthesis. For this purpose, two rat models for these pathologies have been established: a type 1 diabetic hypertensive model obtained by streptozotocin injection to spontaneously hypertensive rat (SHR), followed or not by insulin treatment (experiment 1); a type 2 diabetic hypertensive model by feeding SHR with a fructose enriched diet (experiment 2). Liver gene expression of delta-6 desaturase (D6D), microsomal D6D activities and fatty acid composition of total lipids were estimated. In experiment 1, an increase of linoleic acid (18:2 n-6) level was observed in the streptozotocin group. D6D gene expression appeared depressed in both experimental groups. Insulin did not reverse the streptozotocin effect in SHR, as it does in insulin-dependent diabetic rats. In experiment 2, the results showed a decrease of 18:2 n-6 and of long chain products of desaturation in rats fed on fructose diet. Delta-6 n-3 desaturase activity was significantly increased, whereas gene expression tended to decrease. Feeding fructose induced a significant increase in delta-9 desaturated products, suggesting a stimulation of stearoyl-CoA desaturase. These changes in monounsaturated fatty acids strongly differ from those observed in the streptozotocin experiment, indicating that the effects on lipogenesis of hypertension linked to diabetes differ according to the type of diabetes. Then, these results indicate that the liver steatosis observed during genetic hypertension was reinforced by fructose feeding. All together, the present results showed that hypertension associated to type 1 or type 2 diabetes exacerbated the damage caused by diabetes or hypertension alone on liver lipid metabolism. The metabolic effects induced by fructose being very similar to those found in human NIDDM, SHR fed a fructose-rich diet appears to be an appropriate model for studying the consequences of the combination of hypertension and NIDDM in the metabolic syndrome diseases.

Antihypertensive effects of a dietary unsaturated FA mixture in spontaneously hypertensive rats

The aim of the present study was to investigate whether a mixture of dietary n-6 and n-3 PUFA could lower blood pressure in spontaneously hypertensive rats (SHR) of different ages. In addition, we studied how such a treatment could normalize the FA composition of plasma TAG and cholesterol esters (CE), and of red blood cell (RBC) total lipids. SHR (ages 4, 19, and 50 wk) were fed a normal diet (control groups) or a semisynthetic diet containing a mixture of gamma-linolenic acid (GLA), EPA, and DHA (experimental groups). Systolic blood pressure was measured at regular intervals. After 11 wk of consuming this diet, plasma TAG and CE were separated by TLC and analyzed for their FA composition. Total FA composition of RBC was also determined. The degree to which blood pressure was elevated was reduced in SHR after 11 wk of diet. The largest decrease was obtained with the oldest animals. In RBC, EPA and DHA contents increased. In plasma TAG and CE, EPA, DHA, and GLA increased whereas arachidonic acid decreased. The n-6 and n-3 unsaturated FA mix slowed the development of hypertension in young SHR and decreased blood pressure in adult and aged SHR. In addition, the present treatment altered the n-3 and n-6 PUFA content of SHR lipids to that seen in normotensive rats.

Fat absorption and metabolism in bile duct ligated rats

BACKGROUND

Bile excretion is obstructed in children with extrahepatic bile duct atresia (EHBA) resulting in fat malabsorption and disturbed lipid metabolism.

AIM

Investigate if the bile duct ligated rat exhibits similar deviations as patients with EHBA under different feeding conditions.

METHODS

6 bile duct ligated Wistar rats and 12 matched paired controls were randomised over 3 feeding groups. Rats were killed 16 or 30 days postsurgery. Faeces, blood and livers were collected. Fat absorption was evaluated, markers for cholestasis and the fatty acid composition of serum phospholipids (PL) and cholesterol esters (CE) were determined. Fatty acid desaturation activities in liver microsomes were measured.

RESULTS

Cholestatic bile duct ligated rats have a lower fat absorption coefficient and a lower fraction of 18:2n-6 and 18:3n-3 in serum triglycerides than their controls. This demonstrates that bile duct ligated rats suffer from fat malabsorption. In contrast to the observations in serum triglycerides, 18:2n-6 and 18:3n-3 were not reduced in serum PL and CE of cholestatic rats. Overflow of 18:2n-6 rich biliary PL in the general circulation could contribute to this observation. In agreement with what was found in man, serum PL of cholestatic rats have a higher 16:0/18:0 ratio, increased monoenes and reduced unsaturated fatty acids. However, no differences were observed in microsomal desaturation activities.

CONCLUSION

Cholestatic bile duct ligated rats exhibit similar deviations in serum fatty acid composition as found in patients with EHBA, therefore they can be used as a model for this human disease.

Desaturation and esterification of fatty acids in kidney cells from spontaneously hypertensive rats

In previous studies, several alterations in lipid metabolism have been related to hypertension, but the mechanisms explaining this relationship have not been elucidated. None of the previous works has focused on the lipid metabolism in kidney, which is a key organ in the overall regulation of blood pressure. The aim of the present work was to study the metabolism of polyunsaturated fatty acids, and the possible compositional changes in kidney from hypertensive rats. Radiolabelled linoleic acid (18:2,n-6) and dihomogammalinolenic acid (20:3, n-6) were incubated with isolated kidney cells from spontaneously hypertensive rats (SHR) or the parent normotensive strain (Wistar Kyoto, WKY). The rats were divided into groups of age 9 (young) and 17 (adult) weeks. Cellular uptake, desaturation, chain-elongation, oxidation and distribution into phospholipids and triacylglycerols were measured. Additionally, the lipid composition of kidney was characterized. With each of the labelled fatty acid substrates the uptake in cells from the SHR rats, compared to the WKY rats, was numerically lower in the young group and higher in the adult group. The incorporation of labelled fatty acids into phospholipids was increased and concomitantly decreased in triacylglycerols in cells from adult SHR rats. The delta6-desaturation, measured as the conversion of labelled 18:2(n-6) to 18:3(n-6) was between two and three times increased in cells from the adult rats compared to the young ones, while no difference was found in hypertensives compared to normotensives. Concomitantly, no difference in conversion of labelled 20:3(n-6) to 20:4(n-6) was observed in relation to blood pressure, but, different from delta6-desaturation, the delta5-desaturation was significantly decreased by age. Taken together, this study demonstrates for the first time desaturation of long-chain polyunsaturated fatty acids in isolated kidney cells in suspension and that, contrary to what has been observed in liver, the desaturase activity is unaffected by hypertension. Also different from what has been observed in liver, no blood-pressure-related changes in lipid composition of kidney were found.

Effect of ethanol on polyunsaturated fatty acid biosynthesis in hepatocytes from spontaneously hypertensive rats

BACKGROUND

Polyunsaturated fatty acids (PUFA) play a major role in membrane structures that are modified during alcoholism. PUFA are also precursors of second messengers-eicosanoids-involved in the regulation of blood pressure. Alcohol has been related to hypertension and to alterations in liver PUFA metabolism. We investigated the effects of ethanol on PUFA biogenesis in hepatocytes of Wistar Kyoto (WKY) rats and Spontaneously Hypertensive Rats (SHR). The effects of a diet enriched with n-3 PUFA, which is known to modulate hypertension, were also studied.

METHODS

Isolated hepatocytes from male normotensive Wistar Kyoto (WKY) rats and SHR were incubated for 60 min in the presence of labeled linoleic acid and DGLA, which are precursors of the limiting desaturation steps of PUFA biosynthesis, into a medium containing different concentrations of ethanol. Hepatocytes from SHR that were fed a diet supplemented with n-3 PUFA were incubated with the same precursors.

RESULTS

First, the hepatic biogenesis of PUFA is dependent on the level of ethanol in the incubation medium. Second, Delta5 desaturase was more sensitive than Delta6 desaturase to changes in alcohol concentration. Third, in SHR, a tremendous decrease of arachidonic acid biosynthesis was evidenced in alcohol-intoxicated hepatocytes; the effect was reinforced when ethanol concentration was high, mainly for Delta5 desaturase. Fourth, in the presence of ethanol, the biogenesis of PUFA was altered in isolated hepatocytes from SHR that were fed the diet supplemented with n-3 PUFA, particularly via an inhibition of Delta5 desaturation.

CONCLUSIONS

Our study showed that hepatocyte PUFA biogenesis is dependent on ethanol concentration. Ethanol strongly inhibits the synthesis of PUFA in hepatocytes from SHR, which can explain the deficit of prostaglandin precursors observed in cardiovascular diseases linked to ethanol intoxication. n-3 PUFA supplemented diet reinforces the inhibition of arachidonic acid synthesis, likely by a substrate competition toward Delta5 desaturation. This in vitro approach provides a better understanding of the effects of ethanol on fatty acid metabolism in relation to hypertension.

Brain and hippocampus fatty acid composition in phospholipid classes of aged-relative cognitive deficit rats

The aim of this work was to study the composition of long chain fatty acids and the n-6 and n-3 fatty acid ratios in aged and young Wistar rats in brain and hippocampus, related to relative cognitive deficits. The aged animals showed cognitive deficits during acquisition of a memory task (delayed alternation). In brain, results showed a decrease in palmitoleic and palmitic acid percentages in all the studied phospholipid classes and in the phosphatidylserine and phosphatidylcholine classes, respectively, in old rats, compared to the young ones. There was also an increase in oleic and stearic acid amounts in the sphingomyelin, phosphatidylserine and phosphatidylinositol classes and in the phosphatidylserine and phosphatidylcholine classes, respectively. Arachidonic acid amount was decreased in old rats, compared to the young ones, in the phosphatidylserine and phosphatidylinositol classes. Total n-6 and n-3 fatty acid amounts were both decreased in all phospholipid classes, with a stable n-6/n-3 ratio. Our results confirm that arachidonic acid concentration is decreased in aged rats and that this reduction, more significant in phosphatidylserine and phosphatidylinositol classes, should be related to the fact that low concentrations of arachidonic acid are observed during activation of glutamate receptor.

Dietary docosahexaenoic acid affects stearic acid desaturation in spontaneously hypertensive rats

Docosahexaenoic acid (DHA, 22:6n-3) is an n-3 polyunsaturated fatty acid which attenuates the development of hypertension in spontaneously hypertensive rats (SHR). The effects of DHA on delta-9-desaturase activity in hepatic microsomes and fatty acid composition were examined in young SHR. Two groups of SHR were fed either a DHA-enriched diet or a control diet for 6 wk. Desaturase activity and fatty acid composition were determined in hepatic microsomes following the dietary treatments. Delta-9-desaturase activity was decreased by 53% in DHA-fed SHR and was accompanied by an increase in 16:0 and a reduction in 16:1n-7 content in hepatic microsomes. The DHA diet also increased the levels of eicosapentaenoic acid (20:5n-3) and DHA. The n-6 fatty acid content was also affected in DHA-fed SHR as reflected by a decrease in gamma-linolenic acid (18:3n-6), arachidonic acid (20:4n-6), adrenic acid (22:4n-6), and docosapentaenoic acid (22:5n-6). A higher proportion of dihomo-gamma-linolenic acid (20:3n-6) and a lower proportion of 20:4n-6 is indicative of impaired delta-5-desaturase activity. The alterations in fatty acid composition and metabolism may contribute to the antihypertensive effect of DHA previously reported.

Stearoyl-CoA desaturase 1 coding sequences and antisense RNA affect lipid secretion in transfected chicken LMH hepatoma cells

Hepatic stearoyl CoA desaturase (SCD) activity in chickens from a fat line is higher than that of chickens from a lean line and correlates with plasma triacylglycerol concentrations. Furthermore, in these lines, the hepatic SCD1 mRNA level is positively correlated with the adipose tissue weight. To analyze the contribution of the SCD1 gene in the regulation of adiposity in the early stages of triacylglycerol secretion, SCD1 coding sequence and antisense RNA expression vectors were transfected in LMH cells. After selection, these cells were analyzed with regard to SCD1 expression and lipid secretion. The amounts of secreted triacylglycerols and phospholipids were shown to be higher in LMH cells transfected with the SCD1 gene, but reduced in those transfected with the SCD1 antisense sequences when compared to cells transfected with the vector alone (without SCD1 sequences). These results provide direct evidence that the expression of the SCD1 gene plays a major role in the triacylglycerol and phospholipid secretion process.

Depletion of delta 9 desaturase (EC 1.14.99.5) activity in lactating rat during protein restriction

The effects of protein restriction on the activity of delta9 desaturase (EC 1.14.99.5) were investigated in lactating rats. A control group was fed a balanced diet (20% casein) for 14 days, whereas the experimental groups were fed a low-protein diet (8% casein), supplemented with or without L-methionine (0.4%), for 14 days. The enzyme activity was measured by incubations of hepatic microsomal pellets with (1-14C) stearic acid. Results showed a decreased delta9 desaturase activity, after 2,7 and 14 days of depleted diet, of -50, -40 and -33% respectively, compared with control. The supplementation of the low-protein diet with 0.4% methionine, which favours food consumption as well as growth, did not improve the altered delta9 desaturase activity. Our data evidenced that delta9 desaturase activity is depleted by protein restriction during lactation, when the protein needs are high for the biosynthesis of animal tissues. This change has to be considered as a sign of depressed delta9 desaturase biosynthesis or modifications of enzymatic properties, or both.

5-HT3 receptor-channels coupled with Na+ influx in human T cells: role in T cell activation

The study was conducted on a human (Jurkat) T cell line, loaded with a Na+ fluorescent probe, SBFI/AM. Serotonin and an agonist of 5-HT3 receptor-channels, 2-methyl-5HT, evoked Na+ influx, whereas the agonists of other serotonergic receptor subtypes, i.e., 5-HT1A and 5-HT1B receptors, failed to induce Na+ influx in these cells. By using 3H-BRL43694, an agonist of 5-HT3 receptor-channels, we characterized 5-HT3 lymphocyte receptors which exhibited a density (Bmax) of 300 +/- 20 fmol/10(6) cells and a Kd of 30 nM in Jurkat T cells. The T-cell 5-HT3 receptor-channel is not regulated either by the protein kinase C or by the free intracellular calcium concentrations as the agents known to activate the PKC and to induce increases in intracellular free calcium concentrations failed to influence the free intracellular Na+ concentrations, [Na+]i, in these cells. Furthermore, an increase in [Na+]i, induced by 2-methyl-5HT, via 5-HT3 receptor-channels seems to stimulate T-cell activation by facilitating the progression of T cells from S to G2/M phase of the cell cycle.

Fatty acid desaturase activities and polyunsaturated fatty acid composition in human liver between the seventeenth and thirty-sixth gestational weeks

OBJECTIVE

The aim of the study was to characterize n-3 and n-6 fatty acid delta5- and delta6-desaturase activities and their time course variations in human fetal liver between the 17th and 36th gestational week.

STUDY DESIGN

Twenty-one biologic samples were obtained after legally approved medical abortion, according to French law. The desaturase activities were measured in the 21 liver samples by a radiochemical method by means of reverse-phase high-performance liquid chromatography. The fatty acid composition (percentage by weight) of liver phospholipids was assessed in 16 samples by gas-liquid chromatographic analysis.

RESULTS

Both delta5- and delta6-desaturase activities were significantly expressed between the 17th and 36th gestational weeks. During the second trimester n-6 fatty acid delta5- and delta6-desaturase activities showed opposite patterns of variation; both then remained stable between the 25th and 36th weeks. Delta6-desaturation was higher in n-3 than n-6 fatty acids and peaked at the 18th gestational week. The percentages of linoleic and docosahexaenoic acids in liver microsomes were positively correlated with the gestation age (P < .01), whereas arachidonic acid remained stable.

CONCLUSION

Significant n-3 and n-6 delta5- and delta6-desaturase activities are expressed in human fetal liver as early as the 17th gestational week and are stable throughout the third trimester. Their theoretic capacity evaluated from in vitro measurements appears lower than polyunsaturated fatty acid requirements and is not directly related to liver microsomal membrane fatty acid composition.

Changes in tissue polyunsaturated fatty acids with age, in spontaneously hypertensive rats

The relationship between the biosynthesis of long-chain fatty acids and their distribution in the key organs of hypertension is of considerable interest because of their role in the production of vasoactive eicosanoids and their effects on membrane properties. The present study analyzed the fatty acid compositions of the total lipids in the kidney, aorta, heart, and hepatocytes of 1-, 3-, and 6-mon-old spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar Kyoto rats (WKY) by capillary gas chromatography . The major changes concerned the polyunsaturated fatty acids (PUFA). The percentage of arachidonic acid (AA) was significantly greater in the 1-mon-old SHR kidney than in the WKY kidney, but it was lower at 3 and 6 mon. The percentage of eicosapentaenoic acid was very low in the SHR kidney. The results for the aorta were similar, with marked decreases in 18:2n-6 and 18:3n-3 in SHR aged 1 and 6 mon. Despite a higher proportion of 18:2n-6 and AA at 6 mon, there was no major change in the SHR heart lipids. The fatty acid spectrum in the liver provides additional evidence for the previously reported inhibition of desaturase activities in SHR. Thus, this study shows that the PUFA composition is modified differently in different tissues in SHR, and this may be related to the pathogenesis of hypertension in these animals.

Membrane fluidity and fatty acid metabolism in kidney cells from rats fed purified eicosapentaenoic acid or purified docosahexaenoic acid

Rats were given a supplement (1.5 ml/day) of purified eicosapentaenoic acid (EPA, 20:5,n-3), purified docosahexaenoic acid (DHA, 22:6,n-3)), or corn oil for 10 days. Membrane fluidity, measured as the steady-state fluorescence polarization of diphenylhexatriene (DPH), was approximately 20% lower in kidney cells from rats fed purified EPA than in cells from the DHA-fed or corn-oil fed animals. The level of 20:5(n-3) in kidney phospholipids was 18 times higher in rats fed EPA, and four times higher in those fed DHA as compared to the corn-oil group. The level of arachidonic acid (20:4,n-6) was concomitantly decreased, while linoleic acid (18:2,n-6) was increased in kidney-phospholipids in the n-3 fatty acid fed rats. The proportion of 22:6(n-3) in kidney phospholipids was not affected by EPA supplementation, while the DHA diet slightly increased the level of this fatty acid. The distribution of phospholipid subclasses was significantly altered in that phosphatidylcholine was increased and phosphatidylethanolamine was concomitantly decreased. It is suggested that the decrease in 20:4(n-6) is relatively more important in the regulation of fluidity than a concomitant increase in 20:5(n-3). It is also suggested that the compensatory modifications of the phospholipid subclass distribution as a response to decreased 20:4(n-6)/20:5(n-3) ratio was not sufficient to maintain fluidity when the ratio was as low as in the present study. The incorporation of labelled linolenic acid (18:3,n-3) in phospholipids was decreased in cells from the n-3 supplemented rats. Since endogenous 22:5(n-3) in phospholipids was only increased in the EPA group, 22:6(n-3) only in the DHA group, and 20:5(n-3) in both, it is suggested that the decreased incorporation of labelled 18:3(n-3) into phospholipids of the DHA-fed rats in particular is correlated to the increased level of 22:6(n-3) in the membrane phospholipids. The incorporation of fatty acids into phopholipids may thus show substrate specificity, in that 22:6(n-3) is less exchangable with labelled 18:3(n-3) than is 20:5(n-3). These results demonstrate that increasing levels of n-3 fatty acids in membranes affect the uptake and intracellular metabolism of fatty acids as well as membrane fluidity in the kidney.

Adrenic acid delta4 desaturation and fatty acid composition in the liver of marine-oil fed streptozotocin diabetic rats

The aim of the present study was to assess the effect of streptozotocin diabetes and insulin treatment on adrenic acid delta4 desaturation and fatty acid composition of liver microsomes in Wistar rats fed a fat free semi-synthetic basal diet supplemented with 10% EPA-rich marine oil. Results showed that, in liver microsomes of hyperglycemic rats, the 22:6n-3/22:5n-3 ratio in total lipids was elevated and desaturation of adrenic acid to n-6 docosapentaenoic acid was enhanced. Insulin treatment with 2.0 I.U./100 g body weight-1 twice a day for 3 days resulted in hypoglycemia and suppressed both the increased delta4 n-6 desaturation and 22:6n-3/22:5n-3 ratio. It is concluded that the delta4 desaturation enzyme system, which is activated by experimental diabetes, is regulated by mechanisms different from those regulating delta6 and delta5 desaturations.

Liver microsomal membrane fluidity and microsomal desaturase activities in adult spontaneously hypertensive rats

OBJECTIVE

The purpose of the present study was to investigate liver microsomal membrane fluidity simultaneously with membrane fatty acid composition and desaturase activities in spontaneously hypertensive rats (SHR).

DESIGN AND METHODS

The membrane fluidity was determined, after electron spin resonance (ESR) measurement, in SHR compared with normotensive Wistar-Kyoto (WKY) rats, by calculating the order parameter S from ESR spectra of 5-nitroxide stearate and 10-nitroxide stearate, used as spin-labelled fatty acids. Desaturase activities were measured by incubating SHR and WKY rat liver microsomes with [14C]-radiolabeled fatty acids as substrates for desaturation reactions. The fatty acid composition of liver microsomal membranes was determined by gas-liquid chromatography.

RESULTS

Whereas no significant difference between S of 5-nitroxide stearate was observed for SHR and WKY rats, S of 10-nitroxide stearate was significantly lower in SHR than it was in WKY rat microsomal membrane, indicating that the core microsomal membrane fluidity was higher in SHR. Significant differences between fatty acid compositions were observed for SHR and WKY rat microsomal membranes. Delta9 and n-6 delta6 microsomal desaturase activities were significantly lower in SHR.

CONCLUSION

These results suggest that the higher liver core microsomal membrane fluidity observed in SHR might be dependent on the increased proportion of mono-unsaturated fatty acids. Such observed modifications and the alterations in delta9 and n-6 delta6 desaturase activities suggest that an impaired polyunsaturated fatty acid biosynthesis is related to changes in microsomal membrane fluidity in hypertension.

Fatty acid metabolism, pharmacological nutrients and hypertension

The purpose of the present study was to investigate the effect of a concentrated preparation (EPA 30) containing eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) on the limiting desaturation steps of the polyunsaturated fatty acid biosynthesis in spontaneously hypertensive rats (SHR). Adult SHR were divided into two groups: one group received a standard diet, and the experimental group the standard diet including 0.8% of EPA30 for 9 weeks. Blood pressure was measured at the end of the diets. The desaturase activities and fatty acid composition were determined in isolated hepatocytes. The blood pressure did not decrease in the experimental group. The desaturated products of the n-6 family (gamma-linolenic acid, 18:3 n-6 and arachidonic acid, 20:4 n-6) were lowered in the EPA30 group, when their respective substrates (18:2 n-6 and 20:3 n-6) were increased. EPA and DHA were higher in the experimental group delta 6 n-3, delta 6 n-6 and delta 5 n-6 desaturase activities were depressed approximately 20% in the EPA30 group. EPA30 being an active nutrient on the EFAs cascade, increasing the level of PG3 precursors and decreasing the level of PG2 precursors, favourable conditions have been established to reduce hypertension. The underlying mechanism related to the regulation of desaturase activities by these fatty nutrients remains to be elucidated.

[Polyunsaturated fatty acid biogenesis is impaired in spontaneously hypertensive rat in relation to the pathogenesis of hypertension]

This study was designed to investigate polyunsaturated fatty acid (PUFA) biogenesis in spontaneously hypertensive rats (SHR) during the onset of hypertension. We measured liver desaturase activities, limiting enzymes of linoleic (LA) biosynthesis into arachidonic acid (AA). Fifteen male SHR and 15 male Wistar Kyoto (WKY) normotensive rats were killed at 7.9 or 13 week-old (5 per group). Systolic blood pressure was measured by plethysmography. Liver microsomes were obtained after ultracentrifugation and 5 mg of microsomal proteins incubated during 5 minutes at 37 degrees C with 0.04 mumoles of (1-14C) LA or (2-14C) dihomo-gamma-linolenic acid (DGLA). After fatty acid saponification and methylation, the bioconversion of (1-14C) LA into (1-14C) gamma-linolenic acid (GLA; delta 6 desaturation) and of (2-14C) DGLA into (2-14C) AA (delta 5 desaturation) was determined by measuring the radioactivity shared out between substrate and product of desaturation, after HPLC partition. Fatty acid composition of liver total lipids was calculated after GLC partition. In 7 week-old SHR, blood pressure was closed to that of WKY rats, higher in the 9 week-olds, when hypertension was settled in the 13 week-olds. Delta 6 and delta 5 desaturase activities were lower in SHR than in corresponding WKY. Those impaired desaturase activities increased with the age of rats: delta 6 desaturase activity was 43, 70 and 61% lower in the 7, 9 and 13 week-old SHR, respectively; delta 5 desaturase activity was 14, 48 and 53% lower in the same conditions. We observed a liver storage of total lipids in the 3 groups of SHR. The fatty acid composition of liver total lipids shows a lower proportion of AA and a higher proportion of LA in SHR than in WKY rats, confirming the depletion of the enzymatic systems studied. In summary, LA bioconversion into AA is decreased in liver microsomes of SHR, via the desaturase impairments. This phenomenon is concomitant with the pathogenesis of hypertension and related to the liver fatty acid composition. Such results explain partly the effects of PUFA rich diets administered to hypertensive rats, and clarify the interpretation of such effects.

Influence of spontaneous hypertension on n-3 delta-6-desaturase activity and fatty acid composition of rat hepatocytes

The first rate limiting step in the conversion of alpha-linolenic acid is catalyzed by the delta-6-desaturase enzyme. The activity of such an enzyme was studied in order to investigate the n-3 Polyunsaturated Fatty Acid biogenesis during hypertension. Rat isolated hepatocyte n-3 delta-6-desaturase activity was higher in 1 month old Spontaneously Hypertensive Rats -- prehypertensive period-as compared to normotensive Wistar Kyoto rats, whereas there was no significant differences at 12 months -- hypertensive period-. Our data indicate no correlation between the directly measured enzyme activity and the changes in hepatocyte n-3 fatty acid compositions. The loss of hepatocyte n-3 delta-6-desaturase activity in the Spontaneously Hypertensive Rat may be a key factor in the evolution of hypertension related to aging through altering the eicosanoid balance.

Age-related depletion of linoleic acid desaturation in liver microsomes from young spontaneously hypertensive rats

The present study was designed to investigate the microsomal interconversion of linoleic acid (LA) into arachidonic acid (AA) in young spontaneously hypertensive rats (SHR), in relation to the pathogenesis of hypertension. Our results show lower delta 6 and delta 5 desaturase activities (the limiting steps in the bioconversion of LA into AA) in young SHR, as compared to Wistar Kyoto normotensive rats. This impairment of desaturase activities is raised when the blood pressure increases and is related to the age of animals. The fatty acid composition of liver lipids shows a lower proportion of AA and a higher proportion of LA in SHR than in normotensive rats, confirming the depletion of the enzymatic system studied. Such a loss of desaturase activity may be under the control of hormones involved in the regulation of SHR blood pressure.

Age-related changes in linoleic acid bioconversion by isolated hepatocytes from spontaneously hypertensive and normotensive rats

This study points out the hepatocyte interconversion of the linoleic acid family during hypertension. Hepatocyte delta 6 desaturase activity was higher in 1 month-old spontaneously hypertensive rats than in normotensive controls. A similar tendency was observed in 6 month-old SHR. delta 5 desaturase activity was higher only in 1 month-old spontaneously hypertensive rats as compared to controls. Desaturase activities were particularly high at the age of 6 months. The hepatocyte fatty acid composition showed an impairment of n-6 polyunsaturated fatty acid metabolism in spontaneously hypertensive animals. Changes were greater in the young prehypertensive rats than in adults. A storage of n-3 long chain fatty acids is remarkable in adult hypertensive rats, suggesting an alteration in peroxisomal oxidation. Such modifications may be related to the prostaglandin precursors availability to peripheral tissues such as kidney.

Incorporation of delta 6- and delta 5-desaturation fatty acids in liver microsomal lipid classes of obese Zucker rats fed n - 6 or n - 3 fatty acids

The aim of this work was to study the effect of dietary n - 6 (as borage oil) and of n - 3 (as fish oil) fatty acids on the incorporation--in liver microsomal lipid classes--of fatty acids involved in delta 6- and delta 5-desaturations in obese Zucker rats compared with their lean littermates and with Wistar control rats. We observed that body and liver weights were decreased when obese Zucker rats were fed the fish oil diet. The major part of the radioactivity was recovered, in the obese Zucker rats, into the neutral lipids and especially into the triacylglycerols, while it was recovered into the phospholipid classes, especially into phosphatidylcholine, in the two other strains. Results show, in all phenotypes, an increased alpha-linolenic acid delta 6-desaturation in PL classes when the rats were fed the fish oil diet. However, a decreased linoleic acid delta 6- and delta 5-desaturation was observed in obese Zucker rats fed the fish oil diet. The fish oil diet favours the n - 3 fatty acid biosynthesis and incorporation into liver microsomal lipid classes to the prejudice of the n - 6 fatty acid series. The fatty acid incorporation is simultaneously regulated by the genetical phenotype and dietary fatty acids.

Age-related changes in antioxidant defence mechanisms and peroxidation in isolated hepatocytes from spontaneously hypertensive and normotensive rats

The effects of age and hypertension on the antioxidant defence systems and the lipid peroxidation in rat isolated hepatocytes were studied. Four different age groups (1, 3, 6 and 12 months) were considered in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Age-associated changes were observed on vitamin E status, glutathione (GSH) level, MDA formation and glutathione peroxidase (GSH-Px) activity in both strains. Maximal levels or activities of these parameters were found at 3 and 6 months, except for MDA which was low at 3 months. Then, a fall was observed at 12-month-old compared to 6-month values. In addition, GSH-Px activity was significantly lower in SHR than in WKY rats, except at the age of one month. The decrease of this enzyme activity could induce an increased cellular generation of radical species and lipid peroxidation, which might be link to hypertension.

Adrenic acid delta 4 desaturation and fatty acid composition in liver microsomes of spontaneously diabetic Wistar BB rats

We examined the delta 4 (n-6) desaturation and the fatty acid composition of liver microsomes in the insulin-dependent spontaneously diabetic Wistar Bio-Breeding (BB) rat. The desaturation of adrenic acid to n-6 docosapentaenoic acid was decreased in the normo- and hyperglycemic diabetic rats. Insulin treatment with 1.0 IU. 100 g body weight-1 twice a day for 2 days restored the reduced activity during the hypoglycemic period. The pattern of responses was similar to that of linoleic acid delta 6 and dihomo-gamma-linolenic acid delta 5 desaturases, with a non-parallel relationship between the desaturation system and the glycemia. The microsomal fatty acid composition of BB rat liver reflected only partially to the delta 4 desaturation at different states of glycemia. Factors other than impaired desaturation system are involved in the fatty acid metabolism of spontaneously diabetic rats.

Psychosocial stress, catecholamines, and essential fatty acid metabolism in rats

To examine the effects of psychosocial stress and the "stress hormone," epinephrine, on essential fatty acid metabolism in rats, two studies were conducted. In the first, the effects of four weeks of (i) social isolation and (ii) group housing (control) on liver microsomal delta 6 and delta 5 n-6 desaturase activity were studied in group-reared male normotensive (Wistar Kyoto) and spontaneously hypertensive (SHR) rats (n = 5/group). The second study examined the effects of acute ip epinephrine (0.0, 1.0, 2.0, and 4.0 mg/kg) 6 hr prior to and following an ig dose (4 g/kg) of safflower oil (rich in 18:2n-6, LA) on plasma and liver LA, 20:4n-6 (AA), and LA/AA ratios in adult essential fatty acid deficient Sprague-Dawley rats (n = 6/group). In the first experiment, isolation stress significantly inhibited the activity of delta 6 (P < 0.05) and delta 5 (P < 0.01) desaturase in the normotensive rats and of delta 5 desaturase in the SHR (P < 0.05). In the second study, epinephrine increased plasma and liver LA at doses 1.0 and 2.0 mg/kg in most of the fractions examined, and suppressed AA levels. The response of the LA/AA ratio to epinephrine varied between tissues and among lipid fractions, but increased this ratio at the moderate doses (2.0-4.0 mg/kg) of epinephrine in most cases. These data suggest that psychosocial stressors are capable of inhibiting the rate limiting steps of essential fatty acid metabolism and that this response is more pronounced in the SHR than in the Wistar Kyoto. They also suggest that epinephrine is capable of altering the in vivo metabolism of essential fatty acids in the rat.

Evidence that liver microsomes of human neonates desaturate essential fatty acids

delta 6- and delta 5-Desaturation of essential fatty acids of n-6 and n-3 series are required for the biosynthesis of polyunsaturated fatty acids (PUFAs), which are precursors of eicosanoids and constituents of membrane phospholipids. This pathway could be of special importance during the perinatal period, when PUFAs accretion in the central nervous system is very active. However, experimental evidence of delta 6- and delta 5-desaturase activities in man is very scarce, and no data are available for newborns. We report the delta 6- and delta 5-desaturase activities detected in human liver microsomes from three neonates who died from associated malformations. Radiochemical assays of delta 6- and delta 5-desaturase activities performed with reverse phase HPLC analysis of the products in the n-6 series ranged from 4.8-13.6 to 3.2-16.4 pmol substrate converted.min-1.mg-1 microsomal proteins, respectively. In the n-3 series delta 6-desaturase activity ranged from 5.3 to 12.8 pmol.min-1.mg-1. The relationships between enzyme activities and substrate concentrations suggest excess substrate inhibition for n-6 and not for n-3 fatty acids. These results demonstrate significant delta 6- and delta 5-desaturase activities in human liver of neonates, but this activity was lower than previously reported in adult humans and in mammals, especially rodents.

Age-related changes in delta 6 and delta 5 desaturase activities in rat liver microsomes

Age-related changes in delta 6 desaturation of [1-14C]alpha-linolenic acid and [1-14C]linoleic acid and in delta 5 desaturation of [2-14C]dihomo-gamma-linolenic acid were studied in liver microsomes from Wistar male rats at various ages ranging from 1.5 to 24 mon. Desaturase activities were expressed both as specific activity of liver microsomes and as the capacity of whole liver to desaturate by taking into account the total amount of liver microsomal protein. delta 6 Desaturation of alpha-linolenic acid increased from 1.5 to 3 mon and then decreased linearly up to 24 mon to reach the same desaturation capacity of liver measured at 1.5 mon. The capacity of liver to desaturate linoleic acid increased up to 6 mon and then remained constant, whereas microsomal specific activity was equal at 1.5 and 24 mon of age. The capacity of liver to convert dihomo-gamma-linolenic acid to arachidonic acid by delta 5 desaturation decreased markedly from 1.5 to 3 mon. It then increased to reach, at 24 mon, the same level as that observed at 1.5 mon. Age-related changes in the fatty acid composition of liver microsomal phospholipids at the seven time points studied and of erythrocyte lipids at 1.5 and 24 mon were consistent with the variations in desaturation capacity of liver. In particular, arachidonic acid content in old rats was slightly higher than in young rats whereas contents in linoleic and docosahexaenoic acids varied little throughout the life span.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of salt-loading and spontaneous hypertension on in vitro metabolism of [1-14C]linoleic and [2-14C]dihomo-gamma-linolenic acids

The present study compared the effect of spontaneous hypertension and salt-loading on in vitro metabolism of 18:2n-6 (linoleic acid) and 20:3n-6 (dihomo-gamma-linolenic acid). Ten weanling spontaneously hypertensive rats (SHR) and 10 normotensive Wistar-Kyoto rats (WKY) maintained on a rodent lab chow were given tap water with (n = 5) or without (n = 5) addition of 1% NaCl for 4 weeks. Thereafter, animals were killed and liver microsomes were prepared. Aliquots of microsomes suspended in the phosphate-sucrose buffer containing MgCl2, ATP, CoA, and NADPH were incubated with 0.3 microCi of [1-14C]-18:2n-6 or [2-14C]-20:3n-6 at 37 degrees C for 15 min. The activity of delta 6- and delta 5-desaturases, and the distribution of radioactivity in different lipid fractions and in phospholipid fatty acids were determined. Results showed that both spontaneous hypertension and salt-loading suppressed the desaturation of radiolabeled 18:2n-6 and of 20:3n-6. Incubation of microsomes with [1-14C]-18:2n-6 resulted in 29% of radioactivity being associated with phospholipid fraction, of which 3% was associated with 18:3n-6. Incubation with radiolabeled 20:3n-6 resulted in 30% of the radioactivity being incorporated into phospholipids, of which 50% was associated with 20:4n-6 (arachidonic acid). Salt-loading suppressed the incorporation of radiolabeled fatty acids into phospholipids, more so in SHR than in WKY. Thus, salt-loading not only suppressed the desaturation of 18:2n-6 and 20:3n-6, but also interfered with the acylation of n-6 fatty acids into the phospholipid fraction.

Depletion of delta 9 desaturase (EC 1.14.99.5) enzyme activity in growing rat during dietary protein restriction

The effects of protein restriction on delta 9 desaturase (EC 1.14.99.5) activity were studied in growing rats. A control group was fed on a balanced diet (200 g casein/kg; BD) for 28 d. The experimental group was fed on the low-protein diet (20 g casein/kg; LP) for 26 d, then refed the balanced diet (BD-R) for 2 d. Rats were born to and suckled from normally fed dams. The enzyme activity was measured after 2 and 14 d of LP, and 26 d of LP plus 2 d of BD-R, by incubations in vitro of hepatic microsomal pellets with [1-14C]steric acid. The results indicated a decreased delta 9 desaturase activity after 2 and 14 d of LP of -33 and -43% respectively. Refeeding for 2 d was sufficient to super-repair this activity (+66%). The fatty acid composition of total liver lipids and microsomal phosphatidylethanolamines (PE) and phosphatidylcholines (PC) were also investigated; 18:0 decreased in total liver lipids at 14 d of LP, when 18:1n-9 increased. Stearic acid (18:0) increased in PC at 2 d of LP and in PE at 14 d of LP; oleic acid (18:1n-9) did not change. Therefore, it is concluded that a defect occurred in the bioconversion of 18:0 into 18:1n-9 by delta 9 desaturation during protein depletion. As oleic acid is accumulated in total liver lipids during LP, we speculate that this is due to a decreased oxidation or transport of this fatty acid.

Effect of sodium loading (3% NaCl) on arachidonic acid biosynthesis in rat liver microsomes

Sodium loading increases arachidonic acid (AA) metabolism by way of the prostaglandins(PGs) from series 2. Its effect on AA biosynthesis remains unknown. The purpose of the present study was to investigate the influence of sodium loading on the fatty acid composition of liver and liver microsomes, and the liver microsomal delta-6 and delta-5 desaturations of linoleic acid (LA) into AA. We found a decrease of LA and dihomo-gamma-linolenic acid (DGLA) levels in liver total lipids of Wistar rats receiving hypernatriuretic drinking water (NaCl 3%) for 60 days. At the same time AA increased. DGLA decreased and AA increased in liver microsomal total lipids. 1(14) C-LA delta-6 desaturase and 2(14) C-DGLA delta-5 desaturase activities increased in liver microsomes. These results show that, in addition to its influence on the regulation of glomerular filtration, sodium loading is involved in the regulation of liver AA biosynthesis.

Spontaneous diabetes in bio-breeding rats: evidence for insulin dependent liver microsomal delta 9 stearic acid desaturation

We studied liver microsomal delta 9 stearic acid desaturase activity and fatty acid composition of liver phospholipids and microsomal total lipids in the insulin-dependent spontaneously diabetic adult male Bio-Breeding rat. The diabetic Bio-Breeding rats (3 weeks of diabetes) were killed 48, 17 and 3 h after the last insulin injection (1.0 IU, 100 g body weight-1 day-1). Under these experimental conditions, delta 9 desaturase activity was defective during the normo- and hyper-glycaemic periods and restored during the hypoglycaemic period which followed the insulin injection to the diabetic rats. The fatty acid composition of diabetic rat liver phospholipids and microsomal total lipids were not consistent with delta 9 desaturase activity at the different periods of glycaemia and may be explained by factors other than disturbances of this desaturation.

Altered desaturase activities and fatty acid composition in liver microsomes of spontaneously diabetic Wistar BB rat

We examined the activities of delta 9, delta 6 and delta 5 desaturases and fatty acid composition of liver microsomes in the insulin-dependent spontaneously diabetic adult female Wistar Bio-Breeding (BB) rat. The diabetic BB rats were subcutaneously injected with different doses of protamine zinc insulin in order to be killed in hyper-, normo- or hypo-glycemic states. Desaturase activities, which are partially inhibited by spontaneous diabetes during the normo- and hyper-glycemic periods, were similarly affected by the various insulin treatment; delta 9 desaturase activity being more depressed than the desaturase activities of either delta 6 of delta 5. Insulin treatment with 10 I.U./kg body weight twice a day for 2 days was able to restore the delta 9, delta 6 and delta 5 desaturase activities to control levels during the hypoglycemic period. The microsomal fatty acid composition of BB rats liver was not consistent with the desaturase activities, particularly delta 9 desaturase activity, during the different states of glycemia, indicating that they are not closely linked in a direct cause-effect relationship.

Evidence for insulin dependent hepatic microsomal gamma-linolenic acid chain elongation in spontaneously diabetic Wistar BB rats

We studied hepatic microsomal gamma-linolenoyl-CoA elongation and fatty acid composition of liver microsomes in spontaneously diabetic Wistar BB rats. The liver microsomal gamma-linolenoyl-CoA elongation was decreased in diabetic Wistar BB rats during both normo- and hyperglycemic periods and restored during the hypoglycemic period following insulin treatment. These results are in agreement with our previously reported data on linoleic acid delta 6 and delta 5 desaturations and support the non-parallel relationship between the chain elongation system and the glycemia. The fatty acid composition of BB rat liver microsomes was only partially consistent with the gamma-linolenoyl-CoA elongation activity at the different periods of glycemia, probably because factors other than elongation impairments were involved in the evolution of fatty acid composition.

Elongation and desaturation of arachidonic and eicosapentaenoic acids in rat liver. Effect of clofibrate feeding

The fatty acid elongation-desaturation ability of 5,8,11,14-eicosatetraenoic (20:4(n-6)) and 5,8,11,14,17-eicosapentaenoic (20:5(n-3)) acids was determined in both liver microsomal and light mitochondrial (rich in peroxisomes) fractions of untreated and clofibrate treated rats. The elongation and the subsequent desaturation steps were performed in the corresponding favorable media. 20:5(n-3) elongation was about 2-times more extensive than that of 20:4(n-6). Clofibrate feeding for 10 days resulted in a marked decrease in the elongation rate with the two substrates, while the delta 4 desaturation rate was increased. There were small differences in the elongation rate between the microsomal and light mitochondrial fractions, however, the relative delta 4 desaturation rate was higher in the light mitochondrial fraction than microsomes.

Incorporation into liver microsomal lipids of linoleic and stearic acids and of their respective products of delta 6 and delta 9 desaturation, gamma-linolenic and oleic acids: effect of age and of blackcurrant seed oil

The incorporation of [1-14C]linoleic and [1-14C]stearic acid and of their delta 6 and delta 9 desaturation products (gamma-linolenic and oleic acids, respectively) into different classes of lipids was studied in liver microsomes of rats in function of the diet (blackcurrant seed oil diet, containing gamma-linolenic acid, versus control diet) and in function of age (3, 6 and 9 months). After delta 6 desaturation, total radioactivity was distributed between phospholipids, especially phosphatidylcholine, and neutral lipids. The desaturation product, gamma-linolenic acid, was totally recovered in the phospholipid fraction. Blackcurrant seed oil, which decreased the rate of delta 6 desaturation in 6- and 9-month-old rats, also decreased the incorporation of radioactivity in total phospholipids, especially in phosphatidylcholine. At 6 months of age, after delta 9 desaturation, the majority of radioactivity was recovered in neutral lipids principally as oleic acid, the desaturation product. The precursor, stearic acid, was highly incorporated into phospholipids, especially in rats on a diet of blackcurrant seed oil.

Liver fatty acid composition in the spontaneously diabetic BB rat

The purpose of the present experiment was to investigate if the modulation by insulin of liver microsomal desaturase activities in the spontaneously diabetic adult male Bio-Breeding (BB) rat, with destructive insulitis resembling the lesions described in the human Type I (insulin-dependent) diabetes, corresponds to modifications in fatty acid composition, reflect of changes in fatty acid desaturation. We observed no significant differences between BB rats, during the hyper-(48 h), the normo-(17 h) and the hypo-glycemic (3 h) periods which followed the insulin injection, and control rats for the fatty acid composition of liver total lipids, phosphatidylethanolamines, phosphatidylcholines, triacylglycerols, cholesterol esters and non esterified fatty acids. On the other hand, linoleic acid of BB rats liver phospholipids increased, comparatively to control rats, while arachidonic acid decreased, in agreement with previously reported results on chemical diabetes and consistent with a defective delta 6 desaturation, particularly during the normo-and hyper-glycemic periods, and the fact that control of membrane lipid composition is multifactorial.

Effects of age and dietary essential fatty acids on desaturase activities and on fatty acid composition of liver microsomal phospholipids of adult rats

The combined effects of age and dietary n-6 and n-3 fatty acids were studied in 3-, 6- and 9-month-old rats. At each age, two groups were fed diets containing 5% (w/w) of vegetable oils rich in either 18:3n-6 (borage group) or 18:3n-6 plus 18:4n-3 (black currant group), for a period increasing with age. A control group was fed the essential fatty acids 18:2n-6 and 18:3n-3 only. For each group, delta 6, delta 5 and delta 9 desaturase activities were measured in liver microsomes, and fatty acid composition was determined in microsomal phospholipids. Desaturase activity varied as a function of age and dietary lipids. delta 6 Desaturation of 18:3n-3 was more sensitive to these factors while delta 6 desaturation of 18:2n-6 and delta 9 desaturation were more dependent on season than the other two. Desaturase activity was influenced more by the black currant than by the borage diet, especially at 6 and 9 months of age. A large proportion of arachidonic acid was maintained in the microsomes independent of the diet. Changes in the fatty acid composition did not strictly reflect the differences in desaturase activities. The effects of the two factors (age and diet) on the activities of the desaturases are complex, suggesting that the enzymes are susceptible to other factors as well.

Spontaneous diabetes in BB rats: evidence for insulin dependent liver microsomal delta 6 and delta 5 desaturase activities

We studied linoleic acid delta 5 and dihomo-gamma-linolenic acid delta 5 desaturations, and fatty acid composition, of liver microsomes in the insulin-dependent spontaneously diabetic adult female BB rat. These desaturations were defective along the normo- and hyper-glycemic period and restored during the hypoglycemic period which followed the insulin injection to the diabetic rats. The fatty acid composition of BB rats microsomes was not consistent with the desaturase activities at the different periods of glycemia, probably because other factors than desaturation impairments were involved in the evolution of fatty acid composition.

Metabolism of dicarboxylic acids in rat hepatocytes

[carboxyl-14C]Dodecanedioic acid (DC12) is metabolized in hepatocytes at a rate about two thirds that of [1-14C]palmitate. Shorter dicarboxylates (sebacic (DC10), suberic (DC8), and adipic (DC6) acid) are formed, mainly DC6, less DC8 and only a little DC10. In hepatocytes from clofibrate-treated rats, more polar products account for most of the breakdown products, presumably because the beta-oxidation proceeds all the way to succinate and acetyl-CoA. [carboxyl-14C]Suberic acid (DC8) is oxidized at a rate only one fifth that of dodecanedioic acid. (+)-Decanoylcarnitine inhibits palmitate oxidation but not the oxidation of dodecanedioic acid. At low concentrations of [carboxyl-14C]dodecanedioic acid or of [1-14C]palmitate, acetylsulfanilamide is more efficiently labeled by the former. High concentrations of dodecanedioic acid inhibit palmitate oxidation and the acetylation of sulfanilamide, presumably because their CoA-esters accumulate in the cytosol. These results indicate that medium-chain dicarboxylic acids are beta-oxidized mainly in the peroxisomes.

Liver microsomal delta 6 and delta 5 linoleic acid desaturation in female BB rats

Rat liver microsomal delta 6 and delta 5 desaturation are defective in experimental diabetes, but this defect is correctable with insulin treatment. Rat liver fatty acid composition and delta 6 and delta 5 desaturation were studied in the spontaneously diabetic adult female Bio-Breeding (BB) rat. Control Wistar rats and BB rats (4 weeks of diabetes), that received insulin (1 IU.100 g body weight-1.day-1), were killed 20 h after the last insulin injection. delta 6 and delta 5 desaturase activities were estimated from the incubation of liver microsomes with (1-14C) 18:2, n-6 or (2-14C) 20:3, n-6, respectively, and the fatty acid composition of the liver and microsomal liver lipids were investigated. Under experimental conditions delta 6 and delta 5 desaturase activities were unchanged in the BB rats when compared to the control rats. Impairment of the liver fatty acid composition of diabetic BB rats is not consistent with normal desaturase activity and may be explained by factors other than desaturation disturbance.

The effect of dietary alpha-bromopalmitate on blood lipids in the rat

When alpha-bromopalmitate was fed to rats for 9-30 days, the level of serum triacylglycerol increased up to 2-fold over the concentration of controls. alpha-Bromopalmitate treatment had no effect on concentration of complex lipids in liver, while the triacylglycerol level in heart was significantly enhanced. From metabolic studies using isolated hepatocytes and liver microsomes, it is suggested that the increased serum triacylglycerol level after alpha-bromopalmitate feeding is mainly due to reduced fatty acid oxidation in both liver and peripheral tissues, and to a lesser extent, to inhibited fatty acid uptake and esterification.

Effects of protein level, methionine supplementation and carbohydrate type of the diet on liver lipid and plasma free threonine contents in the lactating rat

Eight groups of 13-15 female rats were fed purified diets after littering. Four groups received a low protein (8% casein) diet (groups 8) and the others, a normal protein (20% casein) diet (groups 20). Carbohydrates were supplied either as starch (groups S) or as starch plus 40% fructose (groups F). Half the animals received a 0.4% methionine supplementation (groups M). Four or five dams per group were sacrificed on days 2, 7 and 14 after littering. The diet intake was increased by methionine supplementation, substitution of starch for fructose and increased protein content, mainly during the second week of lactation. This influenced weight variation of the dams and litter growth. On all days, the plasma levels of cholesterol esters, triglycerides and phospholipids were positively correlated with the dietary protein level. On days 7 and 14, the liver neutral lipid content was increased in rats fed the low protein diets supplemented with methionine (groups 8SM and 8FM) and the normal protein diets containing 40% fructose (groups 20F and 20FM). The plasma free threonine content was positively correlated with the protein level in the diet. On day 14, rats fed a low protein diet had a threonine deficiency, except those in groups 8S and 8F. The plasma free threonine content of these rats was not reduced, possibly due to an impaired utilization of this amino acid. The liver lipidosis observed during lactation, in contrast to that observed during growth with a low protein diet, was not due to a threonine deficiency.

Time-course effects of protein malnutrition on hepatic fatty acids delta 6 and delta 5 desaturation in the growing rat

1. In growing rats, the time-course effects of giving a normal-protein diet (200 g casein/kg; NP) for 52 d, a low-protein diet (20 g casein/kg; LP) for 52 d and a LP diet for 26 d followed by balanced refeeding (200 g casein/kg; BR) for 26 d, on the fatty acid composition of liver total lipids and microsomal phospholipids were investigated together with delta 6- and delta 5-microsomal desaturase activities. 2. The oleic acid content (mg/g tissue) of liver total lipids increased progressively with the LP diet, while linoleic acid was increased only at days 7 and 52. 20:3 omega 6, 20:4 omega 6, 22:5 omega 6 and 22:6 omega 3 fatty acids decreased during the period on the LP diet. BR for 7 d was sufficient to restore the fatty acid composition of total lipids to control values. Changes in the fatty acid composition of liver microsomal L-alpha-phosphatidylcholines were observed only after 52 d on the LP diet; the proportions (% w/w total fatty acids) of 18:0, 20:3 omega 6 and 20:4 omega 6 fatty acids decreased while oleic acid increased. The fatty acid composition of L-alpha-phosphatidylethanolamines was less affected. 3. delta 6- and delta 5-desaturase activities decreased to 20-30% of their original values after 2 d on the LP diet; a smaller deficit prevailed after 14 d but disappeared after 25 d, to appear again after 52 d. As early as day 2 of BR, desaturase activities were greatly recovered and returned to control values at day 13. 4. The present work shows that modifications in microsomal delta 6- and delta 5-desaturase activities are not strictly paralleled by the changes in the composition of fatty acids of liver total lipids and microsomal phospholipids.

[Chronologic studies of the effects of a hypoproteinic diet followed by an equilibrated diet on delta-6 and delta-5 desaturations of linoleic acid in liver microsomes in the rat]

A low protein diet affects amounts of linoleic and arachidonic acids in hepatic microsomal phospholipids of growing rats. Are the changes related to modifications in microsomal delta 6- and delta 5- linoleic acid desaturase activities? Two groups of Wistar rats weighing 80 +/- 5 g at the beginning of the experiment were used: Control group (T) was fed on a 16% gluten + 4% casein diet for 53 days; Experimental group (E) was fed on a 4% gluten + 1% casein diet for 26 days (MP) then Control diet for 27 days (RE). After 2, 14 and 26 days of MP and 2, 15 and 27 days of RE, rats of each group were sacrificed. Protein and water contents of liver, quantitative fatty acid, composition of total lipids in liver and hepatic microsomes were determined. delta 6- and delta 5- linoleic acid desaturase activities were estimated from incubation of liver microsomes with [1-14C] C 18: 2 n-6 or [2(14)C] C 20: 3 n-6 respectively. The low protein diet stops practically ponderal growth. The fatty-acid compositions of microsomal total lipids of E rats were affected in comparison with values of T rats. These modifications persist after 27 days of RE. The C 20: 4 n-6/C 18: 2 n-6 ratio in microsomal total lipids was slightly different between T and E rats but increased strongly during refeeding. Same modifications take place in the fatty-acid composition of hepatic total lipids. After two days of MP, delta 6- and delta 5- desaturase activities were depressed, phenomenon that not persist in the course of MP. These enzyme activities increase to higher values than those of the T after two days of RE.