Effect of epinephrine on the oxidative desaturation of fatty acids in the rat

Relationship between fatty acids and the endocrine and neuroendocrine system

Significant interactions exist between fatty acids and the endocrine system. Dietary fatty acids alter both hormone and neuropeptide concentrations and also their receptors. In addition, hormones affect the metabolism of fatty acids and the fatty acid composition of tissue lipids. The principal hormones involved in lipid metabolism are insulin, glucagon, catecholamines, cortisol and growth hormone. The concentrations of these hormones are altered in chronic degenerative conditions such as diabetes and cardiovascular disease, which in turn leads to alterations in tissue lipids. Lipogenesis and lipolysis, which modulate fatty acid concentrations in plasma and tissues, are under hormonal control. Neuropeptides are also involved in lipid metabolism in brain and other tissues. Polyunsaturated fatty acids are also precursors for eicosanoids including prostaglandins, leucotrienes, and thromboxanes, which have hormone-like activities. Fatty acids in turn affect the endocrine system. Saturated and trans fatty acids decrease insulin concentration leading to insulin resistance. In contrast, polyunsaturated fatty acids increase plasma insulin concentration and decrease insulin resistance. In humans, omega3 polyunsaturated fatty acids alter the levels of opioid peptides in plasma. Free fatty acids have been reported to inhibit glucagon release. Fatty acids also affect receptors for hormones and neuropeptides.

Hormonal modulation of delta6 and delta5 desaturases: case of diabetes

Animal biosynthesis of high polyunsaturated fatty acids from linoleic, alpha-linolenic and oleic acids is mainly modulated by the delta6 and delta5 desaturases through dietary and hormonal stimulated mechanisms. From hormones, only insulin activates both enzymes. In experimental diabetes mellitus type-1, the depressed delta6 desaturase is restored by insulin stimulation of the gene expression of its mRNA. However, cAMP or cycloheximide injection prevents this effect. The depression of delta6 and delta5 desaturases in diabetes is rapidly correlated by lower contents of arachidonic acid and higher contents of linoleic in almost all the tissues except brain. However, docosahexaenoic n-3 acid enhancement, mainly in liver phospholipids, is not explained yet. In experimental non-insulin dependent diabetes, the effect upon the delta6 and delta5 desaturases is not clear. From all other hormones glucagon, adrenaline, glucocorticoids, mineralocorticoids, oestriol, oestradiol, testosterone and ACTH depress both desaturases, and a few hormones: progesterone, cortexolone and pregnanediol are inactive.

Effect of ursodeoxycholic acid on prostaglandin metabolism and microsomal membranes in alcoholic fatty liver

The aim of the present study was to evaluate the effect of ursodeoxycholic acid (UDCA) on prostaglandin and fatty acid metabolism and the possible relation of these substances to the development of alcoholic fatty liver in rats. The effects of UDCA (40 mg/kg/day, 30 days) were studied in rats pair-fed a high-fat diet (52% of calories as fat) with daily ethanol (4 g/kg/day, 30 days) intragastric intubation. The livers of ethanol-treated animals were characterized by fatty dystrophy. Liver triglyceride and cholesterol ester contents and the activities of serum marker enzymes, alanine aminotransferase and gamma-glutamyltransferase, were significantly increased. Ethanol enhanced phosphoinositol and sphingomyelin content in liver microsomes and lowered prostaglandin E(2) (PGE(2)) concentration in the liver. An increase in the percentage of monoenoic fatty acids and a decrease in the n-6 acid family in liver phospholipids, linoleoyl-CoA desaturase, and PGE(2) synthase activities in liver microsomes were observed in ethanol-treated rats. Treatment with UDCA improved liver morphologic characteristics, decreased triglyceride and cholesterol ester contents, increased the PGE(2) level, and normalized linoleoyl-CoA desaturase and PGE(2) synthase activities, as well as phospholipid and fatty acid patterns in the liver. The activities of the serum marker enzymes were decreased in the ethanol- and UDCA-treated group. Ursodeoxycholic acid lowered the viscosity of the microsomal membrane, as assessed by both fluorescence probe techniques and the saturated/unsaturated fatty acid ratio. We propose that the hepatoprotective effect of UDCA in alcoholic fatty liver is related to the stabilization of microsomal membranes, the prevention of a decrease in essential fatty acids and PGE(2) in the liver, and, probably, an improvement in biochemical processes controlled by PGE(2).

Effect of dietary supplementation with black currant seed oil on the immune response of healthy elderly subjects

BACKGROUND

We have shown that the age-associated increase in prostaglandin E(2) production contributes to the decline in T cell-mediated function with age. Black currant seed oil (BCSO), rich in both gamma-linolenic (18:3n-6) and alpha-linolenic (18:3n-3) acids, has been shown to modulate membrane lipid composition and eicosanoid production.

OBJECTIVE

Our objectives were to 1) test whether dietary supplementation with BCSO can improve the immune response of healthy elderly subjects, and 2) determine whether the altered immune response is mediated by a change in the factors closely associated with T cell activation.

DESIGN

A randomized, double-blind, placebo-controlled (soybean oil) study was conducted to examine the effect of 2 mo of BCSO supplementation on the immune response of 40 healthy subjects aged >/=65 y. In vivo immune function was determined by delayed-type hypersensitivity skin response. Peripheral blood mononuclear cells (PBMCs) were tested for in vitro immune response.

RESULTS

In subjects supplemented with BCSO, the total diameter of induration at 24 h and individual responses to tetanus toxoid and Trichophyton mentagrophytes were significantly higher than their baseline values. The change in response to tetanus toxoid was significantly different from that of the placebo group. The BCSO group showed a significant increase in proliferative response of PBMCs to the T cell mitogen phytohemagglutinin that was not significantly different from that observed in the placebo group. BCSO had no effect on concanavalin A-induced mitogenic response, interleukin 2 and -1beta production, and PBMC membrane fluidity. Prostaglandin E(2) production was significantly reduced in the BCSO-supplemented group, and this change was significantly different from that of the placebo group.

CONCLUSION

BCSO has a moderate immune-enhancing effect attributable to its ability to reduce prostaglandin E(2) production.

Abnormal metabolism of polyunsaturated fatty acids in adrenal glands of diabetic rats

Studies carried out on the adrenal glands of experimental diabetic rats have shown an important inhibition in polyenoic fatty acid biosynthesis. This effect was demonstrated by testing the activities of long-chain fatty acyl-CoA synthetase, the delta 5- and delta 6-desaturases of the (n-6) essential fatty-acid series and the delta 6-desaturase of the (n-3) series in liver and adrenal microsomes. The depression in desaturating activity in the insulin-deprived animals was independent of that produced on acyl-CoA-thioester biosynthesis. Experiments measuring the incorporation and transformation of [1-14C]eicosa-8,11,14-trienoic acid in adrenocortical cells isolated from streptozotocin-diabetic animals demonstrated a significant inhibition of arachidonic acid biosynthesis compared to controls. Insulin injections in diabetic rats partially restored the delta 5- and delta 6-desaturase activities. This effect could result from direct action by the hormone since the restoration was reproduced when arachidonic acid biosynthesis was measured after insulin was added to the incubation medium of adrenocortical cells isolated from diabetic animals. The results of the present study provide new information about the implication of this abnormal metabolism in the adrenal gland of diabetic rats.

Effect of phosphatidylethanolamine and its constituent base on the metabolism of linoleic acid in rat liver

Dietary phosphatidylethanolamine (PE) contributes the circulatory and hepatic free-ethanolamine in rats (Ikeda et al. (1987) Biochim. Biophys. Acta 921, 245). A role for circulatory ethanolamine has not been defined; however, our recent studies have shown that exogenous ethanolamine influences cholesterol and linoleic acid metabolism in rats (Imaizumi et al. (1983) J. Nutr. 113, 2403). In order to understand the role of dietary PE the effects of PE and its base on the hepatic metabolism of linoleic acid were investigated in vivo and in primary cultured hepatocytes in rats. Dietary PE increased the plasmic level of ethanolamine from 37 to 52 microM and decreased the ratio of arachidonate to linoleate in hepatic phospholipids. Activity of hepatic delta 6-desaturase decreased in rats given PE and the desaturation of [14C]linoleate in the cultured hepatocytes decreased by the addition of ethanolamine. Secretion [14C]linoleate labeled very-low-density lipoprotein from the cultured hepatocytes decreased by the addition of ethanolamine. Dietary PE caused an increased formation of CO2 from [14C]acetate by liver slices, and ethanolamine added to the hepatocytes caused an increased oxidation of [14C]linoleate and a suppression of fatty acid synthesis from [3H]serine. These results suggest that ethanolamine derived from the dietary PE plays a regulatory role in the linoleate metabolism in the liver.

Effect of magnesium deficiency on delta 6 desaturase activity and fatty acid composition of rat liver microsomes

Experimental Mg2+ deficiency was induced in a group of rats by feeding them a Mg2+-deficient diet for 23 days. They were pair-fed to compare with a control group of rats fed a Mg2+-sufficient diet. In the Mg2+-deficient group the plasma total cholesterol and triglyceride levels were increased while HDL-cholesterol was decreased. In the Mg2+-deficient group the plasma level of thiobarbituric acid reacting substances (TBARS) used as a measure for lipid peroxidation was increased. The increase was attributed to the increased cytosolic Ca2+ in Mg2+-deficiency which can cause: 1) increase of hydro and endoperoxide levels as a consequence of the increase of arachidonic acid release and eicosanoid synthesis in Mg2+-deficiency, and 2) inhibition of the mitochondrial respiratory activity and activation of Ca2+-dependent proteases which may activate the conversion of xanthine dehydrogenase to xanthine oxidase which generates active O2 species. In the Mg2+-deficient group, the fatty acid composition of the liver microsomes indicated a slower rate of conversion of linoleic acid to arachidonic acid which was consistent with the decrease of delta 6 desaturase activity in liver microsomes of Mg2+-deficient rats as measured in vitro. The decrease of delta 6 desaturase activity was attributed to the lower concentration of actual enzyme molecules as a result of the decreased rate of protein synthesis in Mg2+-deficiency. The possible effects of the increased catecholamine release in Mg2+-deficiency are discussed.

Alternative lipids to usual omega 6 PUFAS: gamma-linolenic acid, alpha-linolenic acid, stearidonic acid, EPA, etc

The intravenous administration of parenteral fat emulsions is widely used in total parenteral nutrition (TPN) to supply essential fatty acids and concentrated energy in a relatively small volume of isotonic solution. They contain very high amounts of linoleic acid and usually about 8% of alpha-linolenic acid calculated in the fat phase (10 or 20% of the total emulsion). Most of the time one emulsion is given as the sole source of fat, giving direct venous entry to a fatty acid composition substantially different from that encountered in a normal diet. Since the latter greatly influences the fatty acid composition of phospholipids which are critical determinants of membrane structural properties influencing a variety of membrane functions (Fig. 1) (enzyme activity, membrane transport, receptor function) and functional precursors of intracellular and intercellular mediators (diacylglycerols, prostaglandins, leukotrienes, hydroxy fatty acids), do we provide the right fatty acid at the right place and the right time for efficient cell cell interaction? In other words, given the three roles of fatty acids--energetic, structural, functional--are we using the best strategy to avoid imbalances between the three roles?

Epinephrine effect on arachidonic acid biosynthesis in isolated adrenocortical cells

The in vivo and in vitro effect of epinephrine on the incorporation and desaturation of [1-14C]eicosa-8,11,14-trienoic acid was studied in isolated adrenocortical cells of rats. Control cells incubated at different substrate concentrations and for different periods of time were able to incorporate eicosatrienoic acid and to desaturate it to arachidonic acid. The ultrastructural study demonstrated that most of the cells belonged to the zona fasciculata and presented a good preservation. When the cells were isolated from rats killed 7 and 12 h after the administration of a single dose of epinephrine, a decrease in the incorporation and desaturation of 20:3n6 was observed. The effect on the desaturation was independent from the incorporation of the acid, and it was also observed in the microsomes of the decapsulated adrenal gland from rats treated with epinephrine. The fine structure of adrenocortical cells did not show changes after the treatment with epinephrine. The addition of the hormone to the incubation medium containing cells isolated from untreated rats produced no effect on arachidonic acid biosynthesis, indicating that the effect of epinephrine would be indirect, through either a metabolic or a hormone mediator.

Effect of environmental temperature changes on liver delta 6 and delta 5 fatty acid desaturases depressed by hyperglycidic diet on male rats

Male rats maintained on a control diet at 24 C and shifted to 12 C for five days showed no modification in delta 6 or delta 5 desaturase activity. When delta 6 and delta 5 desaturase activities were diminished by a hyperglycidic diet, shifting to cold increased both enzymatic activities. In general, modifications observed in liver microsomal fatty acid composition are consistent with those associated with the enzymatic desaturation activity.

Effect of malonyl-CoA on delta 6 desaturation activity of rat liver microsomes

The effect of malonyl-CoA on linoleic acid desaturation and elongation reactions of rat liver microsomes was studied. Under strict desaturation conditions, the in vitro microsomal conversion of linoleic acid to gamma-linolenic acid is time-dependent. When malonyl-CoA was added to the aforementioned incubation medium, linoleic acid was desaturated to gamma-linolenic acid and elongated to its higher homologues. Under these conditions, delta 6 desaturation activity, calculated by adding gamma-18:3, 20:3 and 20:4 acids, was neither inhibited nor activated by malonyl-CoA. These results indicate that the elongation of gamma-linolenyl-CoA coupled to the desaturation of linoleic acid did not modify delta 6 desaturase activity.

Effect of epinephrine on the oxidative desaturation of fatty acids in the rat adrenal gland

Delta-6 and delta 5 desaturation activity of rat adrenal gland microsomes was studied to determine the effect of microsomal protein and the substrate saturation curves. This tissue has a very active delta 6 desaturase for linoleic and alpha-linolenic acids. The administration of epinephrine (1 mg/kg body weight) 12 hr before killing, produced approximately a 50% decrease in desaturation of [1-14C]linoleic acid to gamma-linolenic acid, [1-14C]alpha-linolenic acid to octadeca-6,9,12,15-tetraenoic acid and [1-14C]eicosa-8,11,14-trienoic acid to arachidonic acid. A 30% decrease in delta 5 desaturation activity was also shown after 7 hr of epinephrine treatment. The changes on the oxidative desaturation of the same fatty acids in liver microsomes were similar. No changes were observed in the total fatty acid composition of adrenal microsomes 12 hr after epinephrine treatment. Mechanisms of action of the hormone on the biosynthesis of polyunsaturated fatty acids in the adrenal gland are discussed.

Dexamethasone blocks arachidonate biosynthesis in isolated hepatocytes and cultured hepatoma cells

The effect of dexamethasone on the incorporation and conversion of [1-14C]eicosa-8,11,14-trienoic acid to arachidonic acid in isolated hepatocytes and in hepatoma tissue culture (HTC) cells was studied. In both kinds of cells, no changes in the exogenous acid incorporation were found when the hormone was added to the incubation media at 0.1 or 0.2 mM concentration, while the biosynthesis of arachidonic acid was significantly depressed. The effect on the biosynthesis was faster in isolated normal liver cells (60 min) than in tumoral cells (120 min) and reached an inhibition of ca. 50% after 3 hr of treatment. The addition of cycloheximide (10(-6) M) also caused a marked decrease in the biosynthesis of this polyunsaturated fatty acid, but when dexamethasone was added to the media simultaneously with cycloheximide, a synergistic action was not observed. The results obtained show that protein synthesis would be involved in the modulation of the biosynthesis of arachidonic acid by glucocorticoids. The changes in the delta 5 desaturation of labeled 20:3 omega 6 to arachidonic acid correlated with changes in the fatty acid composition in isolated cells.

Studies on the half-life and the distribution of stearoyl-CoA desaturase in the housefly

The half-life of the stearoyl-CoA desaturase was determined by using houseflies injected with puromycin. The LD50 for puromycin was determined to be 1.55 micrograms/mg body wt for both sexes. By following the decay in specific activity of the desaturase after puromycin injection, the half-life of this enzyme in 4-day-old females was calculated to be 9.35 hr, while in 1-day-old females it was 3.38 hr. The inhibition curve for the 3-day-old males never reached 100%, and a biphasic curve was observed. The early phase resulted in a half-life of the desaturase of 2.41 hr, while the latter phase had a half-life of 8.45 hr. In general, it appeared that the half-life of the desaturase increased with age in either sex. Studies on the distribution of desaturase activity within the housefly showed that most of the activity was present in the integument; however, in the female, the onset of ovarian development seemed to shift the distribution of desaturase from the integument, towards the internal tissues. In the male, there appeared to be equal amounts of desaturase in integument and the fat body plus internal tissues at day 2, but by day 5 most of the activity was associated with the integument. The high specific activity and high percentage of total desaturase activity associated with integument coupled with the shift of distribution of desaturase in females during the onset of ovarian development may be indicative of a close correlation of the desaturase with alkene synthesis and possibly sex pheromone production.

Studies on the regulation of arachidonic acid synthesis in isolated rat liver cells

Isolated liver cells from rats fed a diet deficient in essential fatty acids were used to study the oxidation, esterification and, especially, the desaturation and chain elongation of [1-14C]linoleic acid. 14C-labelled arachidonic acid (20:4) and smaller amounts of eicosatrienoic acid (20:3) were recovered mainly in the phospholipids, while gamma-linolenic acid (18:3) was found in both the phospholipids and the triacylglycerol fraction. Lactate strongly increased the formation of arachidonic acid, which was found mainly in the phosphatidylcholine and the phosphatidylinositol fractions. Lactate reduced the amounts of gamma-linolenic acid. Glucagon and (+)-decanoylcarnitine reduced the formation of arachidonic acid, and (+)-decanoylcarnitine increased the incorporation of gamma-linolenic acid especially, in the triacylglycerol fraction. Increasing concentrations of the [1-14C]linoleic acid substrate increased the formation of arachidonic acid and of the other chain-elongated or desaturated fatty acids. Lactate also stimulated the formation of arachidonic acid in liver cells from animals fed adequate amounts of essential fatty acids. It is suggested that dietary and hormonal factors which can change the intracellular levels of malonyl-CoA may influence both the ratio of arachidonic acid/gamma-linolenic acid formed and the total amounts of desaturated and chain-elongated fatty acids formed from linoleic acid.

Changes in fatty acyl chain composition of rat heart phospholipids induced by noradrenaline

The effect of noradrenaline on fatty acyl chain composition of the rat heart phospholipids was studied in vivo. The rats received increasing amounts of noradrenaline for 15 days. The noradrenaline stress caused significant alterations in the fatty acyl chain composition of the two major phospholipids in heart muscle, whereas the phospholipid content remained unchanged. In phosphatidylcholine, there was 50% diminution in linoleic acid and a decrease in oleic acid with a concomitant increase in stearic, arachidonic and docosahexaenoic acids. In phosphatidylethanolamine, the docosahexaenoic acid increased by 25% accompanied by a decrease in oleic and arachidonic acids. The possible causes and consequences of these changes are discussed.

Effect of epinephrine and dibutyryl cyclic AMP on delta 5-desaturation activity of rat liver microsomes

The effect of epinephrine and dibutyryl cyclic AMP on the oxidative desaturation of [1-14C]-eicosatrienoic acid to arachidonic acid of rat liver microsomes has been studied. Epinephrine, at a dose of 1 mg/kg/body weight, produced a significant decrease on delta 5-desaturation activity 3 hr after the injection. This effect was maintained up to 12 hr and reached the control values 48 hr after the hormone administration. Dibutyryl cyclic AMP treatment for 24 hr (5 mg/8 hr/100 g body weight) also produced a significant decrease of the conversion of eicosatrienoic acid to arachidonic acid in rat liver microsomes. The effect of epinephrine on delta 5-desaturation activity was postulated to be evoked through an increase of the intracellular concentration of cyclic AMP.

Polyenoic acid metabolism in cultured human skin fibroblasts

The incorporation of [1-14C]linoleic acid, and [1-14C]linolenic acid into cellular lipids of cultured human skin fibroblasts was studied. Cultured cells took up both labeled fatty acids at nearly the same rate and incorporated them into a variety of lipid classes. At the end of 1 hr incubation with [1-14C]linoleic acid, radioactivity was found in the triacylglycerol (TG) and choline phosphoglyceride (CPG) pools preferentially. Incorporation into the TG fraction decreased rapidly, while the uptake into CPG, serine phosphoglyceride (SPG), and ethanolamine phosphoglyceride (EPG) fractions increased progressively with longer incubation times. Similar results were obtained with [1-14C]linolenic acid as precursor. At the end of 24 hr, desaturation and chain elongation of 18:3 n-3 was more extensive than conversion of 18:2 n-6 to higher polyenoic acids. During pulse-chase experiments with either fatty acid precursor, the incorporated radioactivity was progressively lost from cellular lipids, particularly from the TG and CPG fractions, but continued to increase in the SPG and EPG pools. The similar labeling pattern of cellular phospholipids with linoleic or linolenic acids, and data from pulse-chase studies suggest that a direct transfer of fatty acids from CPG to EPG is a likely pathway in fibroblast cultures. Incorporation into the EPG pool during the pulse-chase experiments paralleled extensive desaturation and elongation of linoleic acid to 20:4 n-6, and 22:4 n-6; and of linolenic acid into 22.5 n-3 and 22:6 n-3.

Thermogenic mechanisms and their control

The alterations in properties of mitochondria and of plasma membrane of brown adipose tissue and skeletal muscle of cold-acclimated rats are reviewed in order to bring out any adaptive changes which are related to the mechanism of nonshivering thermogenesis, and thus to the enhanced calorigenic action of catecholamines known to exist in these animals. Since prevention of the morphological changes in the mitochondria by treatment of the animals with oxytetracycline during acclimation to cold also prevents the development of the enhanced calorigenic response to the catecholamines it is concluded that the changes noted are either a cause of the development of the increased capacity for nonshivering thermogenesis during acclimation to cold or are secondary to the operation of nonshivering thermogenesis.

Regulatory function of delta6 desaturate -- key enzyme of polyunsaturated fatty acid synthesis

The delta6 desaturation of unsaturated acyl-CoA is the first reaction involved in the normal biosynthesis of all polyunsaturated fatty acids families in animal microsomes. Due to this key position it can regulate the biosynthesis of the fatty acids of the series. The reaction is modified by competition with substrates and products, ATP, and acyl-CoA acceptors. Dietary glucose and fructose inhibit the enzyme whereas protein diets and essential fatty acid deficient diets enhance the reaction independently of hormonal effects. The enzyme is sensitive to hormones concentration. Insulin enhance the reaction but the effect is eliminated by protein synthesis inhibition. Hyperglucemic hormones as glucagon, and epinephrine depress the activity of the delta6 desaturase by reactions triggers by an increase of cAMP concentration. The lateral relation of linoleic or alpha-linolenic microsomal elongation is insensitive to insulin, glucagon, epinephrine and protein. All these effects have been proved by either in vivo experiments or cell culture using linoleic or alpha-linolenic acids as substrates.

Comparative effect of glucagon, dibutyryl cyclic AMP, and epinephrine on the desaturation and elongation of linoleic acid by rat liver microsomes

The effect of glucagon, dibutyryl cyclic adenosine 3',5'-monophosphate, and epinephrine on the biosynthesis of polyunsaturated fatty acids of the linoleic acid family was studied. The incubations were performed with rat liver microsomes and labeled linoleic acid under desaturating and elongating conditions. Under desaturating conditions linoleic acid was converted to gamma-linolenic acid, whereas under elongating conditions it was converted to 20:2omega6. Glucagon, dibutyryl cyclic AMP, and epinephrine decreased the oxidative desaturation of linoleic acid to gamma-linolenic acid while the elongating reaction was not modified in the experimental conditions tested. Consequently, the results support the hypothesis that the oxidative desaturation of linoleic acid to gamma-linolenic acid is the main controllable step in the biosynthesis of polyunsaturated fatty acids of the linoleic acid family in the microsomes.