The interaction of dietary fatty acid and cholesterol on catecholamine-stimulated adenylate cyclase activity in the rat heart

Endothelial lipase increases eNOS activating capacity of high-density lipoprotein

Endothelial lipase (EL) changes structural and functional properties of high-density lipoprotein (HDL). HDL is a relevant modulator of endothelial nitric oxide synthase (eNOS) activity, but the effect of EL on HDL induced eNOS-activation has not yet been investigated. Here, we examined the impact of EL-modified HDL (EL-HDL) on eNOS activity, subcellular trafficking, and eNOS- dependent vasorelaxation. EL-HDL and empty virus (EV)-HDL as control were isolated from human serum incubated with EL-overexpressing or EV infected HepG2 cells. EL-HDL exhibited higher capacity to induce eNOS phosphorylation at Ser1177 and eNOS activity in EA.hy 926 cells, as well as eNOS-dependent vasorelaxation of mouse aortic rings compared to control HDL. As revealed by confocal and structured illumination-microscopy EL-HDL-driven induction of eNOS was accompanied by an increased eNOS-GFP targeting to the plasma membrane and a lower eNOS-GFP colocalization with Golgi and mitochondria. Widefield microscopy of filipin stained cells revealed that EL-HDL lowered cellular free cholesterol (FC) and as found by thin-layer chromatography increased cellular cholesterol ester (CE) content. Additionally, cholesterol efflux capacity, acyl-coenzyme A: cholesterol acyltransferase activity, and HDL particle uptake were comparable between EL-HDL and control HDL. In conclusion, EL increases eNOS activating capacity of HDL, a phenomenon accompanied by an enrichment of the plasma membrane eNOS pool, a decreased cell membrane FC and increased cellular CE content.

A preliminary approach to creating an overview of lactoferrin multi-functionality utilizing a text mining method

Lactoferrin is a multi-functional metal-binding glycoprotein that exhibits many biological functions of interest to many researchers from the fields of clinical medicine, dentistry, pharmacology, veterinary medicine, nutrition and milk science. To date, a number of academic reports concerning the biological activities of lactoferrin have been published and are easily accessible through public data repositories. However, as the literature is expanding daily, this presents challenges in understanding the larger picture of lactoferrin function and mechanisms. In order to overcome the "analysis paralysis" associated with lactoferrin information, we attempted to apply a text mining method to the accumulated lactoferrin literature. To this end, we used the information extraction system GENPAC (provided by Nalapro Technologies Inc., Tokyo). This information extraction system uses natural language processing and text mining technology. This system analyzes the sentences and titles from abstracts stored in the PubMed database, and can automatically extract binary relations that consist of interactions between genes/proteins, chemicals and diseases/functions. We expect that such information visualization analysis will be useful in determining novel relationships among a multitude of lactoferrin functions and mechanisms. We have demonstrated the utilization of this method to find pathways of lactoferrin participation in neovascularization, Helicobacter pylori attack on gastric mucosa, atopic dermatitis and lipid metabolism.

Monounsaturatedn-9 fatty acids and adipocyte lipolysis in rats

To investigate the role of the monounsaturatedn-9 fatty acids (MUFA) in the lipolytic activity of adipocytes, a study was carried out in which an increase in MUFA was produced in the tissues by two different methods; by the dietary enrichment of oleic acid or by producing an essential fatty acid deficiency syndrome. For this, forty-five male Sprague–Dawley rats were fed with a normal-energy diet and were subdivided into three groups. The diets varied in the type of dietary fat; palmitic acid, olive oil, or soyabean oil+palmitic acid. At the end of the study measurements were taken of weight, plasma leptin, tissue concentration of fatty acids, fat-cell size in the epididymal and the omental adipose tissues, adipocyte lipolytic activity of both tissues after stimulation with adrenaline, and the capacity of insulin to inhibit lipolysis. The baseline and adrenaline-stimulated lipolytic activity were greater and the anti-lipolytic capacity of insulin lower in the animals undergoing an increase in MUFA in the tissues (palmitic-acid and olive-oil diets). The area under the curve of glycerol, used as an indicator of lipolytic activity, was positively correlated with the concentration of MUFA and negatively with polyunsaturated fatty acids in the adipose tissues. It is concluded that an increase in tissue MUFA, however obtained, induces an increase in lipolytic activity.

Ingestion of guar-gum hydrolysate partially restores calcium absorption in the large intestine lowered by suppression of gastric acid secretion in rats

We examined the effects of feeding guar-gum hydrolysate (GGH), a highly fermentable form of dietary fibre with low viscosity, on Ca absorption in the small and large intestines in rats under conditions in which gastric acid secretion was suppressed by a proton pump inhibitor, omeprazole. We also examined the role of the caecum in influencing these effects. The study was designed in a 2×2×2 factorial arrangement with two diet (GGH-containing (50 g/kg diet) and GGH-free diets) groups, two injection (omeprazole and vehicle) groups and two operation (sham and caecectomy) groups. Apparent Ca absorption was lower in rats administered omeprazole (30 mg/kg body weight per d) for 8 d than in rats administered the vehicle. Ingestion of GGH led to partial restoration of Ca absorption decreased by omeprazole treatment. However, this increment in Ca absorption was not sufficient to meet requirements because the dietary Ca level (3·0 g/kg diet) was the minimum requirement for the intact rats. The small increment in Ca absorption caused by the GGH diet was completely abolished by caecectomy. Soluble Ca pools in the caecal and colonic contents were increased by feeding GGH, and the soluble Ca concentrations were much higher than the Kt values of the Ca active transport system in the large intestine or the serum Ca concentration. These findings suggest that Ca solubilization is not a limiting factor for Ca absorption in the large intestine. Apparent Mg absorption was clearly lower in caecectomized rats than in sham-operated rats, and higher in the GGH-fed groups than in the groups fed on the GGH-free diet, even in the case of caecectomized rats. We conclude that Ca absorption lowered by inhibition of gastric acid secretion is partially restored in rats fed with GGH, but the increment is not sufficient to meet requirements.

Modifications induced by dietary lipid source in adipose tissue phospholipid fatty acids and their consequences in lipid mobilization

The aim of the present work was to assess the influence of dietary lipid source on fatty acid phospholipid profiles and on lipid mobilization. Forty male Wistar rats were divided into four groups and fed on high-fat diets which provided olive oil, sunflower oil, palm oil or beef tallow. All rats received the same amount of energy to avoid hyperphagia and differences in energy intake among groups. Phospholipid fatty acids were determined by GC. Lipolysis was stimulated in subcutaneous and perirenal isolated adipocytes by several lipolytic agents, and assessed by the determination of released glycerol. After 4 weeks of feeding, differences in body and adipose tissue weights were not observed. Dietary regimens caused great changes in adipose tissue phospholipid composition: rats fed on palm oil and beef tallow had higher concentrations of saturated fatty acids and animals fed on olive oil or sunflower oil had greater amounts of oleic and linoleic acids, respectively. These modifications did not lead to important changes in adipocyte lipolysis. Significant differences were only observed between palm-oil- and beef-tallow-fed groups when lipolysis was stimulated by isoproterenol in subcutaneous adipocytes. The fact that our feeding protocol did not induce differences in fat accumulation among groups avoids misinterpretations due to adiposity changes. The differences observed between both saturated-fat-fed groups, therefore, should only be attributable to dietary lipids. Despite this effect, the data from this work indicate that some diet-induced changes in adipose tissue fatty acid composition may have little effect on overall function.

Dietary fatty acids and membrane protein function

In recent years, there has been growing public awareness of the potential health benefits of dietary fatty acids, and of the distinction between the effects of the omega6 and omega3 polyunsaturated fatty acids that are concentrated in vegetable and fish oils, respectively. A part of the biologic effectiveness of the two families of polyunsaturated fatty acids resides in their relative roles as precursors of the eicosanoids. However, we are also beginning to appreciate that as the major components of the hydrophobic core of the membrane bilayer, they can interact with and directly influence the functioning of select integral membrane proteins. Among the most important of these are the enzymes, receptors, and ion channels that are situated in the plasma membrane of the cell, since they carry out the communication and homeostatic processes that are necessary for normal cell function. This review examines current information regarding the effects of diet-induced changes in plasma membrane fatty acid composition on several specific enzymes (adenylate cyclase, 5'-nucleotidase, Na(+)/K(+)-ATPase) and cell-surface receptors (opiate, adrenergic, insulin). Dietary manipulation studies have demonstrated a sensitivity of each to a fatty acid environment that is variably dependent on the nature of the fatty acid(s) and/or source of the membrane. The molecular mechanisms appear to involve fatty acid-dependent effects on protein conformation, on the "fluidity" and/or thickness of the membrane, or on protein synthesis. Together, the results of these studies reinforce the concept that dietary fats have the potential to regulate physiologic function and to further our understanding of how this occurs at a membrane level.

Conceptual foundations of the UCSD Statin Study: a randomized controlled trial assessing the impact of statins on cognition, behavior, and biochemistry

BACKGROUND

Statin cholesterol-lowering drugs are among the most prescribed drugs in the United States. Their cardiac benefits are substantial and well supported. However, there has been persistent controversy regarding possible favorable or adverse effects of statins or of cholesterol reduction on cognition, mood, and behavior (including aggressive or violent behavior).

METHODS

The literature pertaining to the relationship of cholesterol or statins to several noncardiac domains was reviewed, including the link between statins (or cholesterol) and cognition, aggression, and serotonin.

RESULTS

There are reasons to think both favorable and adverse effects of statins and low cholesterol on cognition may pertain; the balance of these factors requires further elucidation. A substantial body of literature links low cholesterol level to aggressive behavior; statin randomized trials have not supported a connection, but they have not been designed to address this issue. A limited number of reports suggest a connection between reduced cholesterol level and reduced serotonin level, but more information is needed with serotonin measures that are practical for clinical use. Whether lipophilic and hydrophilic statins differ in their impact should be assessed.

CONCLUSION

There is a strong need for randomized controlled trial data to more clearly establish the impact of hydrophilic and lipophilic statins on cognition, aggression, and serotonin, as well as on other measures relevant to risks and quality-of-life impact in noncardiac domains.

Membrane physical properties do not explain increased cyclic AMP production in hepatocytes from rats fed menhaden oil

To study the effect of altering plasma membrane fatty acid composition on the glucagon signal transduction pathway, cAMP accumulation was measured in hepatocytes from rats fed diets containing either menhaden oil (MO) or coconut oil (CO). Hepatocytes from MO-fed animals produced significantly more cAMP in response to glucagon and forskolin compared to CO-fed animals. Glucagon receptor number and affinity were similar in MO- and CO-fed rats. Liver plasma membranes from MO-fed animals were enriched in long-chain n-3 fatty acids and contained significantly lower amounts of saturated C10-C16 and 18:1n-9 than CO-fed animals. Membrane physical properties were examined using both Fourier transform infrared spectroscopy (FTIR) and the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). FTIR analysis revealed that below 34 degrees C, CO membranes were more ordered than MO membranes. However, as assay temperature approached 37 degrees C, MO and CO membranes became similarly ordered. DPH polarization values indicated no differences in membrane order at 37 degrees C, whereas membrane order was decreased in CO-fed animals at 25 degrees C. These data indicate the importance of assay temperature in assessing the influence of membrane physical properties on the activity of signal transduction pathways. Whereas increased signal transduction activity has been correlated to reduced membrane order in MO-fed animals, these data indicate that at physiological temperatures membrane order did not vary between groups. Enhanced cAMP accumulation in response to forskolin indicates that adenylate cyclase activity or content may be elevated in MO- vs. CO-fed rats. Enhanced adenylate cyclase activity may result, in part, from changes in specific fatty acids in hepatocyte plasma membranes without demonstrable changes in membrane physical properties.

A simple reproducible model of free radical-injured isolated heart induced by 1,1-diphenyl-2-picryl-hydrazyl (DPPH)

1,1-Diphenyl-2-Picryl-Hydrazyl (DPPH), a stable free radical, has been used for detecting antioxidant activity in chemical analysis. However, it is still unknown if DPPH triggers free radical injury in cardiac tissue. In order to establish a simple free radical-injured isolated heart model, we investigated the action of DPPH on isolated guinea pig heart by Langendorff perfusion and compared it with cardiac effect of superoxide anion (O2.-), generated by the hypoxanthine (HX)-xanthine oxidase (XO) system. Free radical scavengers, dimethyl sulphoxide (DMSO), superoxide dismutase (SOD), and L-cysteine, were also used to analyze the characteristic of the DPPH free radical-derived cardiac dysfunction. In isolated guinea pig hearts, DPPH 100 nM and 250 nM in Krebs-Henseleit solution significantly decreased the left ventricular developed pressure (LVDP) and maximum velocity changes of left ventricular pressure (+/-LVdP/dtmax), elevated the left ventricular end-diastolic pressure (LVEDP), and increased lactate dehydrogenase (LDH) release and thiobarbituric acid-reactive substances (TBARS) formation in cardiac tissue. The cardiac dysfunction induced by DPPH 250 nM was more intense than 100 nM. L-Cysteine improved the DPPH-impaired cardiac function, while DMSO and SOD had no beneficial effect on this injury. The cardiac membrane fluidity was decreased by DPPH. Free radical signals, detected by electron spin resonance (ESR) in the DPPH-injured heart, were reduced by L-cysteine-treatment. These results suggest that DPPH free radical-induced cardiac dysfunction is attributed to neither the superoxide anion nor the hydroxyl radical. In conclusion, our data indicate that DPPH-induced isolated heart dysfunction serves as a simple and reproducible free radical-injured heart model.

Assessing the observed relationship between low cholesterol and violence-related mortality. Implications for suicide risk

Health advocacy groups advise all Americans to restrict their dietary intake of saturated fat and cholesterol as an efficacious and safe way to lower plasma cholesterol concentrations and thus reduce the risk of coronary heart disease and other atherosclerotic disorders. However, accumulating evidence suggests that naturally low or clinically reduced cholesterol is associated with increased nonillness mortality (principally suicide and accidents). Other evidence suggests that such increases in suicide and traumatic death may be mediated by the adverse changes in behavior and mood that sometimes accompany low or reduced cholesterol. These observations provided the rationale for an ongoing series of studies in monkeys designed to explore the hypothesis that alterations in dietary or plasma cholesterol influence behavior and that such effects are potentiated by lipid-induced changes in brain chemistry. In fact, the investigations in monkeys reveal that reductions in plasma cholesterol increase the tendency to engage in impulsive or violent behavior through a mechanism involving central serotonergic activity. It is speculated that the cholesterol-serotonin-behavior association represents a mechanism evolved to increase hunting or competitive foraging behavior in the face of nutritional threats signaled by a decline in total serum cholesterol (TC). The epidemiological and experimental data could be interpreted as having two implications for public health: (1) low-cholesterol may be a marker for risk of suicide or traumatic death and (2) cholesterol lowering may have adverse effects for some individuals under some circumstances.

Mechanisms of adaptive supersensitivity: correlation of guinea pig atrial supersensitivity with modifications in adenylyl cyclase activity

The possibility that the cellular mechanism underlying adaptive supersensitivity in right and left atria of the guinea pig may involve either adenylyl cyclase or components of that transduction process was examined in left and right atria obtained from controls or guinea pigs chronically treated with reserpine. Adenylyl cyclase activity and the abundance of alpha-subunits of several G-proteins (i.e. Gs, Gi, and Go) were quantified using standard techniques. Functional concentrations of Gs and Gi were compared in tissues from control and treated animals using pertussis- or cholera toxin-induced protein ribosylation. Chronic treatment with reserpine did not alter basal levels of adenylyl cyclase activity in left or right atrium but did increase significantly the ability of isoproterenol, 5'-guanylylimido diphosphate, and forskolin to activate adenylyl cyclase in the left atrium compared with the control. In contrast, treatment with reserpine increased the ability of only isoproterenol to active adenylyl cyclase in the right atrium. The increases in enzyme activation were not correlated with any detectable change in the concentrations of G-proteins or beta-adrenoceptors. The correlation between the specificity of changes in responsiveness and increased activation of adenylyl cyclase suggests that the cellular mechanism that underlies the development of adaptive supersensitivity in the guinea pig myocardium may involve a modification of adenylyl cyclase. The data also support the idea that the development of enhanced responsiveness in cardiac muscle may not only involve more than one cellular mechanism but may even differ between right and left atrium and ventricles of the same species.

Brain beta-adrenergic receptor binding in rats with obesity induced by a beef tallow diet

We have previously reported that compared with safflower oil diet, feeding a beef tallow diet leads to a greater accumulation of body fat by reducing sympathetic activities. The present study examined the effects of dietary fats consisting of different fatty acids on alpha1- and beta-adrenergic receptor binding in the hypothalamus and cerebral cortex. Male Sprague-Dawley rats were meal-fed isoenergetic diets based on safflower oil (rich in n-6 polyunsaturated fatty acids) or beef tallow (rich in saturated fatty acids) for 8 weeks. Binding affinities of the beta-adrenergic receptor in the hypothalamus and cortex were significantly lower in the beef tallow diet group, but those of the alpha1-receptor did not differ between the two groups. The polyunsaturated to saturated fatty acid (P/S) ratio and fluidities of plasma membranes in the hypothalamus and cortex were lower in the beef tallow diet group than in the safflower oil diet group. These results suggest that the beef tallow diet decreases membrane fluidity by altering the fatty acid composition of plasma membranes in the hypothalamus and cerebral cortex of rat. Consequently, beta-adrenergic receptor binding affinities in the brain were lower in rats fed the beef tallow diet than in rats fed the safflower oil diet. We recognized that there is possible link between the membrane fluidity and the changes in affinity of beta-adrenoceptors in rat brain.

The influence of dietary cholesterol on cardiac and hepatic Beta-adrenergic receptors in egyptian sand rats

We examined the effects of dietary cholesterol on cardiac and hepatic beta-adrenergic receptor functioning. Age-matched adult desert rodents (Psammomys obesus) were randomized to either a 5% cholesterol diet (CD, n = 20), or normal rabbit chow (RC, n = 18). After a 2-month exposure to the diets, animals were sacrificed and tissue from both heart and liver were retained for radioligand bindings studies. In heart tissue, cholesterol fed animals, relative to controls, showed an increased production of adenosine 3,5>-cyclic monophosphate (cAMP) in response to isoproterenol. Cholesterol supplementation was not associated with an increase in heart beta-adrenergic receptor number. Animals fed the 5% cholesterol diet showed significant increases in the number of beta-adrenergic receptor sites in hepatic tissue (M = 13.2 vs. 10.4 pmol/mg protein, CD and RC, respectively). The increased number of receptor sites in the liver was accompanied by a significant increase in isoproterenol-stimulated cAMP production. Results are supportive of the hypothesis that dietary cholesterol contributes to an upregulation of beta-adrenergic receptor function in cardiac, as well as hepatic tissue. These findings may be relevant to the observations of excessive stress-induced cardiovascular reactivity in persons with high cholesterol levels.

Thyroid status and dietary fatty acids affect beta-adrenoceptor agonist stimulation of tension development in rat myocardium

1. The inotropic responses to the beta-adrenoceptor agonists adrenaline, noradrenaline and isoprenaline were examined in papillary muscles isolated from hypothyroid rats and euthyroid controls that had been fed diets enriched in either n-6 or n-3 fatty acids. 2. In hypothyroid animals fed the n-6 diet, the maximum developed tension in the presence of isoprenaline was only 54% greater than resting tension compared to 160% in euthyroid animals. Maximum tension was 105% greater than resting in hypothyroid animals fed the n-3 diet compared to 399% in controls. Similar responses to adrenaline and noradrenaline were seen, i.e. maximum tension was significantly greater in both hypothyroid and euthyroid animals fed the n-3 diet, but tension was depressed in the hypothyroid state. 3. Binding of the beta-adrenoceptor antagonist [3H]-dihydroalprenolol to ventricular membranes was saturable and of high affinity, irrespective of thyroid state and diet. While binding site density (Bmax) was not affected by the hypothyroid state or diet, binding affinity (Kd) was higher in hypothyroid animals fed the n-6 diet. 4. The inotropic response to forskolin was the same in hypothyroid animals, irrespective of diet, but maximum developed tension was significantly greater in euthyroid animals fed the n-6 compared to the n-3 diet. The dose-response curve for forskolin was shifted to the right in hypothyroid animals fed the n-3 diet indicating a decrease in sensitivity. 5. These results indicate that the depressed contractility in the hypothyroid heart may be due in part to an altered lipid environment of the beta-adrenoceptor complex and that n-3 fatty acids can significantly increase maximum developed tension in the hypothyLroid state.

Effect of a high fat diet on phospholipid class distribution and fatty acid composition in rat liver

1. Long term consumption (20 weeks) of a high fat diet (65% of the energy content as fat) rich in either saturated [30% (w/w) coconut oil] or unsaturated [30% (w/w) sunflower oil] fatty acids resulted in strikingly similar alterations in the phospholipid class distribution and fatty acid composition in the liver of male Wistar rats. 2. The effect of these two diets was compared to a control group maintained on a 2% fat diet (w/w) for the same time interval. 3. In spite of the difference in the PUFA/SFA (polyunsaturated fatty acid/saturated fatty acid) ratio between the two high fat diets (0.1, saturated fatty acid diet; 5.4, unsaturated fatty acid diet), both diets resulted in a similar PUFA/SFA ratio in liver phospholipids, a similar reduction in palmitic acid (16:0), oleic acid (18:1, n-9) and arachidonic acid (20:4, n-6) and an elevation in stearic acid (18:0), linoleic acid (18:2, n-6) and docosahexaenoic acid (22:6, n-3). 4. Further, changes in the phospholipid classes were also similarly affected by both high fat diets.

Reversal of diet-induced changes in adenylate cyclase activity and fatty acid composition of rat submandibular salivary gland lipids

This study sought to determine if the diet-induced changes in submandibular salivary glands can be reversed. Two groups of male weanling Sprague-Dawley rats were fed purified diets containing 9% butter + 1% corn oil (group I, control) or 9% ethyl ester concentrate of n-3 fatty acids + 1% corn oil (group II, experimental). After 5 weeks of feeding the respective diets, rats in group I were divided into two subgroups: Ia, which was maintained on the control diet, and Ib, which was shifted to the experimental diet for the reversal study. The rats in the experimental group were kept on their original diet. After five further weeks of feeding, the rats were killed, and membranes from submandibular glands were prepared and assayed for adenylate cyclase activity and for the fatty acid composition of total phospholipids. Changes characteristic of feeding n-3 fatty acids, including a significant increase in membrane fluidity as measured by the degree of unsaturation of fatty acids, were observed in the total phospholipids of membranes from the experimental group. The adenylate cyclase activity was two- to three-fold higher in membranes of rats fed the experimental diet (group II) than the control diet (group Ia). Whereas the diet-induced changes in fatty acid composition and membrane fluidity were largely reversed (group Ib, reversal study), changes in adenylate cyclase activity were only partially reversed. The results suggest that, in addition to the fatty acid composition and membrane fluidity, other factors may also be important in modifying adenylate cyclase activity.

Effect of dietary fats on some membrane-bound enzyme activities, membrane lipid composition and fatty acid profiles of rat heart sarcolemma

The effect of various dietary fats on membrane lipid composition, fatty acid profiles and membrane-bound enzyme activities of rat cardiac sarcolemma was assessed. Four groups of male weanling Charles Foster Young rats were fed diets containing 20% of groundnut, coconut, safflower or mustard oil for 16 weeks. Cardiac sarcolemma was prepared from each group and the activities of Na+, K(+)-ATPase, 5'-nucleotidase, Ca(2+)-ATPase and acetylcholinesterase were examined. ATPase activities were similar in all groups except the one fed coconut oil, which had the highest activities. Acetylcholinesterase activity was also similar in all the groups, however, it was significantly higher in the group fed mustard oil. No significant changes were observed among the groups in 5'-nucleotidase activity, in the cholesterol-to-phospholipid molar ratio and in sialic acid content. The coconut, safflower and mustard oil diets significantly increased cholesterol and phospholipid contents and the lipid-to-protein ratio of cardiac sarcolemma as compared to feeding the groundnut oil diet. The fatty acid composition of membrane lipids was quite different among the various groups, reflecting the type of dietary fat given. The total unsaturated-to-saturated fatty acid ratio was not different among the various groups; however, the levels of some major fatty acids such as palmitic (16:0), oleic (18:1) and linoleic (18:2) acids were significantly different. Cardiac sarcolemma of the group fed safflower oil had the highest polyunsaturated fatty acid content. The results suggest that dietary fats induce changes not only in the fatty acid composition of the component lipids but also in the activities of sarcolemmal enzymes involved in the regulation of cardiac function.

Changes in beta 1- and beta 2-adrenergic receptor mRNA levels in brown adipose tissue and heart of hypothyroid rats

The aim of the present work was to study the effect of hypothyroidism on the expression of the beta-adrenergic receptor (beta-AR) in interscapular brown adipose tissue and heart. The total density of plasma membrane beta-AR per tissue is decreased by 44% in hypothyroid rat interscapular brown adipose tissue and by 55% in hypothyroid rat heart compared with euthyroid controls. The effects of hypothyroidism on the density of both beta 1- and beta 2-AR subtypes were also determined in competition displacement experiments. The densities of beta 1- and beta 2-AR per tissue are decreased by 50% and 48% respectively in interscapular brown adipose tissue and by 52% and 54% in the heart. Northern blot analysis of poly(A)+ RNA from hypothyroid rat interscapular brown adipose tissue demonstrated that the levels of beta 1- and beta 2-AR mRNA per tissue are decreased by 73% and 58% respectively, whereas in hypothyroid heart, only the beta 1-AR mRNA is decreased, by 43%. The effect of hypothyroidism on the beta 1-AR mRNA is significantly more marked in the interscapular brown adipose tissue than in the heart. These results indicate that beta-AR mRNA levels are differentially regulated in rat interscapular brown adipose tissue and heart, and suggest that the decrease in beta-AR number in interscapular brown adipose tissue and heart of hypothyroid animals may in part be explained by a decreased steady-state level of beta-AR mRNA.

Effects of lindane on fluidity and lipid composition in rat renal cortex membranes

The influence of lindane upon dynamic properties of plasma membranes from rat renal cortex has been investigated using a fluorescence polarization technique. Preincubation with lindane increased membrane fluidity in a manner that is dose-dependent. This increase was higher in brush border membranes than in basolateral membranes. However, a significant decrease of the membrane fluidity was found in brush border membranes when rats were injected with lindane for 12 days. A possible solution to this difference could involve a resistance to membrane disordering by lindane through a regulatory mechanism that would balance the amount of cholesterol and phospholipid classes in the renal cortex membranes of lindane-injected rats.

Influence of lindane on the fluidity of the rat ventral prostate membranes

The influence of lindane upon the dynamic properties of plasma membranes from rat ventral prostate has been investigated using a fluorescence polarization technique. Preincubation with lindane decreased the fluorescence polarization in a dose dependent manner. This effect, which is associated with an increased membrane fluidity, occurred in a very short period of time. Lindane also provoked a number of changes in lipid biosynthesis from acetate in the membrane. Less [1-14C]acetate was incorporated into cholesterol and more into phospholipids when this liposoluble toxicant was added to the preincubation medium. However, not all phospholipid classes were equally increased, because while the rate of acetate incorporation was greater into choline glycerophospholipids than into ethanolamine glycerophospholipids, both were higher than the rates of acetate incorporation into serine glycerophospholipids and sphingomyelin.

Effect of lindane upon the beta-adrenergic stimulation of cyclic AMP accumulation in rat renal cortical tubules caused by alterations in membrane fluidity

The influence of lindane (gamma-hexachlorocyclohexane) on fluidity and lipid composition in rat renal cortical tubules has been investigated. Lindane increased membrane fluidity as measured by a fluorescence polarization technique using the probe diphenylhexatriene. This effect was dose-dependent and was accompanied by a 70% inhibition of the beta-adrenergic stimulatory activity upon cyclic AMP accumulation after 30 min of preincubation with lindane at 25 degrees C. Experiments with increasing concentrations of isoproterenol indicated that the efficacy, but not the potency, of the beta-adrenergic effect upon cyclic AMP accumulation was affected by lindane. Lindane toxicity could also be associated with variations in the incorporation of acetate into various lipid classes. Lindane increased acetate incorporation into phospholipids and decreased that into cholesterol.

Modulation of the beta-adrenergic stimulation of cyclic AMP accumulation in rat prostatic epithelial cells by membrane fluidity

1. The influence of membrane lipid composition on the beta-adrenergic stimulation of cyclic AMP accumulation in rat prostatic epithelial cells was assessed after treating the cells with cholesteryl hemisuccinate (ChH). 2. ChH treatment resulted in a 40% inhibition of the beta-adrenergic response after 30 min of lipid preincubation at 37 degrees C. 3. The inhibitory effect of ChH was dose-dependent and was accompanied by an increase of microviscosity as measured by a fluorescence polarization technique with the probe diphenylhexatriene. 4. Experiments with increasing concentrations of isoproterenol indicated that the efficiency, but not the potency, of the beta-adrenergic response was affected by the increasing of the cholesterol content in the cell membrane.

Effect of dietary fat saturation and cholesterol on low density lipoprotein degradation by mononuclear cells of Cebus monkeys

The mechanism by which dietary unsaturated fatty acids lower low density lipoprotein (LDL) cholesterol is unknown. Unsaturated fatty acids incorporated into the cell membrane can increase membrane fluidity and, as a result, dramatically alter membrane-dependent cell functions. Therefore, we examined the effect of long-term dietary consumption of corn oil and coconut oil with and without cholesterol in amounts equivalent to those of a typical Western diet on the degradation of human LDL by peripheral blood mononuclear cells in Cebus albifrons monkeys. Cellular LDL degradation was dramatically enhanced in the mononuclear cells isolated from animals fed corn oil in comparison with those from animals fed coconut oil. The addition of cholesterol to the diets resulted in a slight attenuation of LDL degradation in the corn oil group while no effect was noted in the coconut oil group. Crossover LDL binding and degradation experiments with LDL isolated from animals fed corn oil diets and coconut oil diets demonstrated increased binding and degradation of LDL in mononuclear cells from animals fed corn oil diets. Enhanced mononuclear cell LDL degradation was accompanied by increased cellular cis-unsaturated fatty acyl content, increased membrane fluidity, and decreased plasma cholesterol. Increased cellular cis-unsaturated fatty acyl content with its concomitant increase in membrane fluidity mirrored the dietary lipid profile of the host animal. A linear relationship was observed between cellular LDL degradation and both cellular cis-unsaturated fatty acyl content and membrane fluidity. These observations parallel results noted in whole-animal LDL catabolic studies with these same animals described elsewhere. These data suggest a novel mechanism by which dietary unsaturated fatty acids exert their LDL-lowering effect.

Effect of dietary trans fatty acids on some membrane-associated enzymes and receptors in rat heart

Three groups of male weanling Sprague-Dawley rats were fed diets containing 20% corn oil, 20% partially hydrogenated soybean oil (PHSBO) or 18% PHSBO + 2% corn oil. PHSBO contained about 48% of its total fatty acids as trans-octadecenoate. Rats were killed after 16-18 weeks of feeding the various diets, hearts were dissected and crude sarcolemma was prepared by differential centrifugation. The activities of ouabain-sensitive (Na+ + K+)ATPase were significantly lower in membranes of rats fed 20% PHSBO than the control rats fed 20% corn oil. The feeding of 2% corn oil with 18% PHSBO resulted in partial restoration of the enzyme activity. The maximum number of [3H]ouabain-binding sites (Bmax) was also lower in cardiac membranes of rats fed 20% PHSBO than those fed 20% corn oil. Similar to (Na+ + K+)-ATPase activity, some restoration of the number of [3H]ouabain-binding sites was observed when 2% corn oil was fed with 18% PHSBO-containing diet. There was no difference in the binding affinity of the radioligand for the receptor among the 3 dietary groups. Adenylate cyclase activities (fluoride-, isoproterenol- and forskolin-stimulated) were lower in membranes of rats fed 20% PHSBO or 18% PHSBO + 2% corn oil than in the control group fed 20% corn oil. Density of the beta-adrenergic receptor was the lowest in cardiac membranes of rats fed 20% PHSBO. The feeding of 2% corn oil with 18% PHSBO resulted in partial restoration of the maximum number of [3H]dihydroalprenolol (DHA)-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary lipids on plasma lipoproteins and fluidity of lymphoid cell membranes in normal and leukemic mice

Mice of the GR/A strain were fed four different isocaloric semipurified diets, enriched in either (1) saturated fatty acids (palm oil), or (2) polyunsaturated fatty acids (corn oil), or (3) palm oil plus cholesterol, or (4) a fat-poor diet containing only a minimal amount of essential fatty acids. We have studied the effects of these dietary lipids on the density profile and composition of the plasma lipoproteins and on the lipid composition and fluidity of (purified) lymphoid cell membranes in healthy mice and in mice bearing a transplanted lymphoid leukemia (GRSL). Tumor development in these mice occurred in the spleen and in ascites. While the fatty acid composition of the VLDL-triacylglycerols still strongly resembled the dietary lipids, the effects of the diets decreased in the order VLDL-triacylglycerols greater than HDL-phospholipids greater than plasma membrane phospholipids. Diet-induced differences in the latter fraction were virtually confined to the content of oleic acid and linoleic acid, and they were too small to affect the membrane fluidity, as measured by fluorescence polarization using the probe 1,6-diphenyl-1,3,5-hexatriene. Healthy mice were almost irresponsive to dietary cholesterol, but in the tumor bearers, where lipoprotein metabolism has been shown to be disturbed, the cholesterol diet caused a substantial increase in the low- and very-low density regions of both blood and ascites plasma lipoproteins. The cholesterol-rich diet also increased the cholesterol/phospholipid molar ratio and lipid structural order (decreased fluidity) in GRSL ascites cell membranes, but not in the splenic GRSL cell membranes. We conclude that the composition of plasma lipoproteins and cell membrane lipids in GR/A mice is subject to exquisite homeostatic control. However, in these low-responders to dietary lipids the development of an ascites tumor may lead to increased responsiveness to dietary cholesterol. The elevated level of membrane cholesterol thus obtained in GRSL ascites cells did not affect the expression of various cell surface antigens or tumor cell growth.

Dietary cholesterol influences cardiac beta-adrenergic receptor adenylate cyclase activity in the marmoset monkey by changes in membrane cholesterol status

The activity of the beta-adrenergic receptor/adenylate cyclase system of the marmoset monkey heart was investigated following dietary cholesterol supplementation (0.5%). After 22 weeks, plasma cholesterol levels in the cholesterol group were more than twice that of the control group. In the cholesterol-fed group, the affinity for ICYP binding to cardiac membranes was elevated more than 2-fold, while the receptor number was decreased by 31%. Isoproterenol, norepinephrine and sodium fluoride stimulated adenylate cyclase activity was significantly higher in the cholesterol-fed group although the fold stimulation over basal levels was not affected. The most prominent change in the cardiac membrane lipids was an increase in the cholesterol to phospholipid ratio in marmoset monkeys fed cholesterol. These results indicate that in the marmoset, membrane cholesterol is an important factor in determining various properties of the cardiac beta-adrenergic receptor particularly receptor affinity which may impact on the response of the beta-adrenergic receptor/adenylate cyclase system of the heart to catecholamines. This result is in agreement with dietary fatty acid supplements designed to increase cardiac membrane cholesterol in this animal species (McMurchie, E.J. et al. (1988) Biochim. Biophys. Acta 937, 347-358). Elevated membrane cholesterol enhances beta-adrenergic receptor affinity and certain aspects of adenylate cyclase activity. This is a likely mechanism whereby atherogenic diets could promote cardiac arrhythmia in non-human primates and indeed in man.

The influence of dietary lipid supplementation on cardiac beta-adrenergic receptor adenylate cyclase activity in the marmoset monkey

Dietary lipid supplements high in either saturated fat derived from sheep kidney fat or unsaturated fat derived from sunflower seed oil, and a low mixed fat reference diet were fed to marmoset monkeys for 20 months and the effects on cardiac membrane lipid composition, and myocardial catecholamine-stimulated adenylate cyclase and beta-adrenergic receptor binding activity were investigated. For cardiac membranes enriched for beta-adrenergic binding activity, the dietary lipid treatment resulted in small changes in the proportion of saturated to unsaturated fatty acids and substantial changes in the (n - 6) to (n - 3) series of unsaturated fatty acids in the membrane phospholipids. The sheep kidney fat diet increased the cholesterol-to-phospholipid ratio in cardiac membranes in comparison to the other diets. This diet also significantly elevated basal and isoproterenol-, epinephrine- and norepinephrine-stimulated adenylate cyclase activity. The value of the dissociation constant (Kd) and the receptor number (Bmax) for the binding of [125I]ICYP to the beta-adrenergic receptor was significantly reduced in marmosets fed the sheep kidney fat diet. These results suggest that dietary lipids can influence the activity of the beta-adrenergic/adenylate cyclase system of the heart. Modulation of this transmembrane signalling system may be induced by changes in the properties of the associated membrane lipids, particularly by alteration in the membrane cholesterol-to-phospholipid ratio. This effect may be limited to those animal species in which the nature of the dietary fatty acid intake may be influencing cardiac membrane cholesterol homeostasis, which is in agreement with previous results in rats following dietary cholesterol supplementation (McMurchie et al. (1987) Biochim. Biophys. Acta 898, 137-153). ICYP, (-)-iodocyanopindolol.