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.

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.

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 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.

Unsaturated fatty acids esterified in 2-acyl-l-lysophosphatidylcholine bound to albumin are more efficiently taken up by the young rat brain than the unesterified form.

The aim of the present study was to investigate whether unsaturated 2-acyl-lysophosphatidylcholine bound to plasma albumin is a relevant delivery form of unsaturated fatty acids to the developing brain. Twenty-day-old rats were perfused for 30 s with labeled palmitic, oleic, linoleic, and arachidonic acids in either their unesterified form or esterified in 2-acyl-lysophosphatidylcholine labeled on the choline and fatty acid moieties. Both forms were bound to albumin. Incorporation in brain lipid classes was followed within 1 h. The brain uptake of the unesterified fatty acids reached a plateau at 5-15 min and was maximal for arachidonic acid (0.45% of the perfused dose). The brain uptake of palmitoyl-lysophosphatidylcholine was similar to that of palmitic acid, whereas that of other lysophosphatidylcholines increased with the degree of unsaturation (rate and maximal uptake) and was six- to 10-fold higher than that of the corresponding unesterified fatty acid. 2-Acyl-lysophosphatidylcholines were taken up without prior hydrolysis and reacylated into doubly labeled phosphatidylcholine, which was the most labeled lipid class, whereas lipid distribution of the unesterified fatty acid was more diversified. Partial hydrolysis of 2-acyl-lysophosphatidylcholine occurred in the brain tissue, and redistribution of the fatty acyl moiety into other phospholipid classes was also observed and was the highest for arachidonic acid. In this case, the percentage of esterification of this fatty acid in phosphatidylinositol (expressed as a percentage of the total lipid fraction) was relatively lower than that observed when the unesterified form was used.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic fate of sphingomyelin of high-density lipoprotein in rat plasma.

The metabolic fate of high density lipoprotein (HDL) sphingomyelin in plasma was studied in rats over a 24-hr period after injection of HDL containing sphingomyelin which was 14C-labeled in the stearic (18:0) or lignoceric acid (24:0) moiety and 3H-labeled in the choline methyl groups. Decay of label in plasma followed three phases. The first two phases were similar for both isotopes and both types of sphingomyelin (t1/2 approximately 10 and 110 min). However, during the third phase (from 10 hr after injection), 3H label disappeared more slowly than 14C label from 18:0 sphingomyelin, whereas the 3H/14C ratio remained relatively constant when 24:0 sphingomyelin was used. Intact, doubly-labeled 18:0 sphingomyelin disappeared from HDL rapidly (t1/2 = 38 min) by tissue uptake and by transfer to very low density lipoprotein (VLDL). VLDL contained up to 12% of the sphingomyelin 1 hr after injection. This is the first demonstration of a transfer in vivo of sphingomyelin from HDL to VLDL. A similarly rapid transfer was also observed in vitro. Some nontritiated, [14C]18:0 or [14C]24:0 sphingomyelin was redistributed more slowly into HDL. Doubly-labeled phosphatidylcholine appeared in VLDL and HDL within 1 hr after injection and reached 1.8 and 2.1% of the injected 14C and 3H in VLDL at 1 hr, and 4.8 and 6.9% in HDL at 3 hr, respectively.

Time-course of utilization of [stearic or lignoceric acid]sphingomyelin from high-density lipoprotein by rat tissues.

Utilization of stearic and lignoceric acids supplied by high-density lipoprotein (HDL) sphingomyelin to different tissues was followed for 24 h after rats were injected with HDL containing [[1-14C]stearic (18:0) or [1-14C]lignoceric (24:0) acid [Me-3H]choline]sphingomyelin. Both isotopes reached a maximum in tissue lipids 3-12 h after injection and were recovered mainly in the liver (30%) and small intestine (3%), whereas the other tissues contained approx. 1% or less of the injected dose. All the tissues were able to take up some intact sphingomyelin from HDL and hydrolyze it. In the lung and erythrocytes, the 3H:14C ratio of sphingomyelin remained unchanged throughout the studied period, while an increase in the isotopic ratio was observed in the kidney due to the 3H choline moiety re-used for synthesis of new sphingomyelin. Conversely, the isotopic ratio of sphingomyelin decreased in the liver, indicating a saving of the 14C-labelled fatty acids, especially 24:0. Furthermore, [24:0]ceramide in the liver remained at a high level (6% of the injected dose), whereas [18:0]ceramide decreased to 1%. When the tissues were examined 24 h after injection, the proportion of the 14C linked to sphingomyelin in the total 14C was always higher for both kinds of sphingomyelin than the molar proportion of sphingomyelin in the whole of lipid classes. However, in the majority of the extra-hepatic tissues, more [14C]18:0 than [14C]24:0 was recovered in sphingomyelin, and more 14C radioactivity from 18:0 than from 24:0 was redistributed in the other lipids. The choline moiety from both kinds of sphingomyelin was re-used to synthesize phosphatidylcholine, especially in the liver (up to 20% of the injected dose). All these results show that utilization of sphingomyelin from HDL by tissues normally occurs in vivo and that this phenomenon should be taken into account in the study of the phospholipid turnover of cell membranes. They also show that metabolism of sphingomyelin from HDL in the liver and other tissues is dependent on the sphingomyelin acyl moiety.

Utilization of high-density lipoprotein sphingomyelin by the developing and mature brain in the rat.

Utilization of very long chain saturated fatty acids by brain was studied by injecting 20-day-old and adult rats with high-density lipoprotein containing [stearic or lignoceric acid-14C, (methyl-3H)choline]sphingomyelin. Labeling was followed for 24 h. Very small amounts of 14C were recovered in the brain of all rats, and there was no preferential uptake of lignoceric acid. Approximately 20% of the entrapped 14C was located in the form of unchanged sphingomyelin 24 h after injection. This result shows that the rat brain utilizes very little very long chain fatty acids (greater than or equal to 20 C atoms) from high-density lipoprotein sphingomyelin, even during the myelinating period. The [3H]choline moiety from sphingomyelin was recovered in brain phosphatidylcholine in a higher proportion in comparison with the 14C uptake. The brain 3H increased throughout the studied period in all experiments, but was much higher in the myelinating brain than in the mature brain. From the radioactivity distribution in liver and plasma lipids, it is clear that the choline 3H in the brain originates from either double-labeled phosphatidylcholine of lipoproteins or tritiated lysophosphatidylcholine bound to albumin, both synthesized by the liver.

Turnover and uptake of double-labelled high-density lipoprotein sphingomyelin in the adult rat.

Rat HDL containing [stearic acid-14C, (methyl-3H)choline]sphingomyelin was prepared by incubating labelled sphingomyelin liposomes with serum. HDL was then separated by ultracentrifugation and purified by gel-filtration chromatography. The maximum transfer was reached when 1.5 microliter sphingomyelin was incubated in the presence of 1 ml of serum at 37 degrees C for 1 h. When transfer was limited to a 5-7% increase in HDL mass, no significant change was observed in the HDL electrophoretic pattern, and rats could therefore be injected with this type of HDL under physiological conditions. Plasma radioactivity decay was followed for 24 h, and the recovery of both isotopes in 11 tissues was studied 24 h after the injection. The decay in plasma of both isotopes followed three exponential phases. During the first two phases, both isotopes disappeared with the same velocity (t1/2 = 12.8 and 98-105 min for the first and second phases, respectively). 10 h after injection, 3H had disappeared more slowly than 14C (t1/2 = 862 and 502 min for 3H and 14C, respectively) and 24 h after injection, only 1.5% of 14C and 2.5% of 3H remained in the plasma. This radioactivity was located mainly in HDL (80-85% for 3H and 14C), with a 3H/14C ratio close to that of injected sphingomyelin, and in VLDL, with the same isotopic ratio as that of liver lipids. Some 3H was associated with non-lipoprotein proteins. 17.5% of 3H and 23.4% of 14C were recovered in the liver, 1.6% of each isotope in erythrocytes, and 1.4% of 3H and 0.6% of 14C in kidney. Less than 1% of each isotope was recovered in each of the other tissues. Phosphatidylcholine was the lipid most labelled, and in several tissues sphingomyelin had a 3H/14C ratio close to that of injected sphingomyelin, showing an uptake without prior hydrolysis.