An apparatus to assay opioid activity in the infused lumen of the intact isolated guinea pig ileum

A modified apparatus is described that provides for the simultaneous bathing of the serosa of an intact piece of isolated guinea pig ileum while allowing infusion of the isolated lumen. The comparative compartmental potency of the opioid agonists morphine, casomorphins, and enkephalins to inhibit electrically driven contractions are described in this system. The rank-order potency for serosally applied opioid agonists was (IC(50) values, nM): [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]-enkephalin (DAMGO) (15)>[D-Ala(2),D-Leu(5)]-enkephalin (DADLE) (35)> or =morphine (46)> or =[D-Ala(2)]-met-enkephalinamide (55)>[D-Ala(2)]-beta-casomorphin[1--4] amide (122)>beta-casomorphin[1--4] amide (940)>met- and leu-enkephalin (>6000). This contrasted to the rank-order potency for the luminally applied opioid agonists: DADLE (63)>DAMGO (135)>[D-Ala(2)]-met-enkephalinamide=morphine (4700)>[D-Ala(2)]-beta-casomorphin[1--4] amide (29000). beta-Casomorphin[1--4] amide, leu-enkephalin and met-enkephalin are mostly inactive when applied luminally. Furthermore, the opioid antagonists, casoxin 4 and [D-Ala(2)]-casoxin 4, when infused into the lumen, significantly overcame the inhibitory effect of morphine added to the serosal side. This model provides an assay and screening system to differentiate between the effects of chemical agents applied via the blood stream (serosa) or food side (lumen) on quiescent or electrically driven gut activity of the nervous plexi or receptor systems of the ileum.

Effects of dietary n-3 fatty acids on contractility, Na+ and K+ currents in a rat cardiomyocyte model of arrhythmia

The n-3 polyunsaturated fatty acids (PUFAs) have been reported to prevent ventricular fibrillation in human clinical studies and in studies involving experimental animals and isolated cardiomyocytes. This study aimed to determine whether dietary n-3 PUFAs could prevent isoproterenol and free radical-induced arrhythmic (asynchronous) contractile activity in adult rat cardiomyocytes and whether whole-cell Na(+) and K(+) currents measured by patch-clamp techniques were affected. Dietary supplementation with fish oil for 3 weeks significantly increased the proportion of total n-3 PUFAs in ventricular membrane phospholipids compared with saturated fat supplementation (18.8 +/- 0.6% vs. 8.1 +/- 1.0%, respectively). Cardiomyocytes from the fish oil group were less susceptible to isoproterenol-induced asynchronous contractile activity than were those from the saturated fat group [EC(50) values: 892 +/- 130 nM, n = 6 and 347 +/- 91 nM, n = 6 (P < 0.05), respectively]. Fish oil supplementation also prolonged the time taken to develop asynchronous contractile activity induced by superoxide and hydrogen peroxide. The voltage dependence of inactivation of Na(+) currents were significantly altered (-73.5 +/- 1.2 mV, n = 5 vs. -76.7 +/- 0.7 mV, n = 5, P < 0.05, for saturated fat and fish oil treated groups, respectively). The voltage dependence of activation of Na(+) and K(+) currents was not significantly affected by the dietary fish oil treatment. These results demonstrate the antiarrhythmic effects of dietary fish oil in a cardiomyocyte model of arrhythmia.

Termination of asynchronous contractile activity in rat atrial myocytes by n-3 polyunsaturated fatty acids

A protective effect of the n-3 polyunsaturated fatty acids (PUFAs) in preventing ventricular fibrillation in experimental animals and cultured cardiomyocytes has been demonstrated in a number of studies. In this study, a possible role for the n-3 PUFAs in the treatment of atrial fibrillation (AF) was investigated at the cellular level using atrial myocytes isolated from young adult rats as the experimental model. Electrically-stimulated, synchronously-contracting myocytes were induced to contract asynchronously by the addition of 10 microM isoproterenol. Asynchronous contractile activity was reduced following acute addition of the n-3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at 10 microM, compared with no fatty acid addition (from 99.0+/-1.0% to 30.7+/-5.2% (p < 0.05) for DHA and 23.8+/-2.8% (p < 0.01) for EPA), while the saturated fatty acid, docosanoic acid (DA) and the methyl ester of DHA (DHA m.e.) did not exert a significant effect on asynchronous contractile activity. Asynchronous contractile activity was also reduced to 1.7+/-1.7% in the presence of the membrane fluidising agent, benzyl alcohol (p < 0.001 vs no fatty acid addition). Cell membrane fluidity was determined by steady state fluorescence anisotropy using the fluorescent probe, TMAP-DPH. Addition of DHA, EPA or benzyl alcohol significantly increased sarcolemmal membrane fluidity (decreased anisotropy, r(ss)) of atrial myocytes compared with no addition of fatty acid (control) (from r(ss) = 0.203+/-0.004 to 0.159+/-0.004 (p < 0.01) for DHA, 0.166+/-0.001 (p < 0.01) for EPA and 0.186+/-0.003 (p < 0.05) for benzyl alcohol, while DA and DHA m.e. were without effect. It is concluded that the n-3 PUFAs exert anti-asynchronous effects in rat atrial myocytes by a mechanism which may involve changes in membrane fluidity.

Membrane fluidity changes are associated with the antiarrhythmic effects of docosahexaenoic acid in adult rat cardiomyocytes

Previous studies using neonatal rat cardiomyocytes have reported antiarrhythmic effects of long-chain polyunsaturated fatty acids (PUFAs). In this study, we examined the effects of the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) on the spontaneous contractile activity and membrane fluidity of adult rat ventricular myocytes. Cardiomyocytes were induced to contract spontaneously by continuous superfusion of a solution containing the arrhythmogenic agents isoproterenol (a beta-adrenergic receptor agonist) or lysophosphatidylcholine. The percentage of cardiomyocytes displaying spontaneous contractions induced by isoproterenol when pretreated with the saturated fatty acid docosanoic acid was 48.1 +/- 7.7%; the percentage for cardiomyocytes pretreated with DHA was 7.1 +/- 2.4% (P < 0.01). DHA significantly prevented lysophosphatidylcholine-induced spontaneous contractions (17.7 +/- 6.5%) compared with treatment with the saturated fatty acid stearic acid (78.0 +/- 7.3%, P < 0.01). The membrane fluidizing agent benzyl alcohol also significantly prevented spontaneous contractions in cardiomyocytes. Membrane fluidity was determined by steady-state fluorescence anisotropy (r(ss)) using the fluorescent probe N-((4-(6-phenyl-1,3,5-hexatrienyl)phenyl)propyl) trimethyl-ammonium p-toluene-sulfonate (TMAP-DPH). DHA and benzyl alcohol dose-dependently decreased the r(ss); however, saturated fatty acids were without effect. These results suggest that the antiarrhythmic mechanisms of the n-3 PUFAs such as DHA may involve changes in membrane fluidity.

Prevention of nerve conduction deficit in diabetic rats by polyunsaturated fatty acids

The influence of diets containing gamma-linolenic acid (GLA; 18:3n-6) on sciatic nerve conduction velocity (NCV) was determined in diabetic rats. NCV was lower in diabetic rats fed diets supplemented with olive oil or sunflower seed oil than in nondiabetic rats; rats supplemented with GLA during a 5-wk diabetic period, however, did not exhibit significantly lower NCV. The mean proportion of the phospholipid fatty acid linoleic acid (18:2n-6) was higher in the sciatic nerves of diabetic rats than in the nondiabetic groups irrespective of dietary lipid treatment. Additionally, the proportion of linoleic acid was higher in the diabetic rats fed sunflower oil than in all other groups. Dietary GLA supplementation did not significantly influence the fatty acid composition of nerve membrane phospholipids and there was no obvious correlation between the fatty acid composition of nerve membrane phospholipids and NCV. The content of fructose and glucose in sciatic nerves was higher, whereas that of myo-inositol was lower, in diabetic rats than in nondiabetic rats; however, this was not significantly influenced by dietary GLA. GLA administration did not significantly influence Na(+)-K(+)-exchanging ATPase or ouabain binding activity in sciatic nerve preparations, both of which remained nonsignificantly different in the diabetic and nondiabetic groups. The results suggest that dietary GLA can prevent the deficit in NCV induced by diabetes and that this effect is independent of the nerve phospholipid fatty acid profile, sugar and polyol content, Na(+)-K(+)-exchanging ATPase activity, and ouabain binding. GLA may prevent the deficit in NCV indirectly, possibly by its role as a precursor of vasodilatory prostaglandins. These results confirm that GLA is the active component of evening primrose oil.

Inhibition of cardiac sodium currents in adult rat myocytes by n-3 polyunsaturated fatty acids

1. The acute effects of n-3 polyunsaturated fatty acids were determined on whole-cell sodium currents recorded in isolated adult rat ventricular myocytes using patch clamp techniques. 2. The n-3 polyunsaturated fatty acids docosahexaenoic acid (22:6, n-3), eicosapentaenoic acid (20:5, n-3) and alpha-linolenic acid (18:3, n-3) dose-dependently blocked the whole-cell sodium currents evoked by a voltage step to -30 mV from a holding potential of -90 mV with EC50 values of 6.0 +/- 1.2, 16.2 +/- 1.3 and 26.6 +/- 1.3 microM, respectively. 3. Docosahexaenoic acid, eicosapentaenoic acid and alpha-linolenic acid at 25 microM shifted the voltage dependence of activation of the sodium current to more positive potentials by 9.2 +/- 2.0, 10.1 +/- 1.1 and 8.3 +/- 0.9 mV, respectively, and shifted the voltage dependence of inactivation to more negative potentials by 22.3 +/- 0.9, 17.1 +/- 3.7 and 20.5 +/- 1.0 mV, respectively. In addition, the membrane fluidising agent benzyl alcohol (10 mM) shifted the voltage dependence of activation to more positive potentials by 7.8 +/- 2.5 mV and shifted the voltage dependence of inactivation to more negative potentials (by -24.6 +/- 3.6 mV). 4. Linoleic acid (18:2, n-6), oleic acid (18:1, n-9) and stearic acid (18:0) were either ineffective or much less potent at blocking the sodium current or changing the voltage dependence of the sodium current compared with the n-3 fatty acids tested. 5. Docosahexaenoic acid, eicosapentaenoic acid, alpha-linolenic acid and benzyl alcohol significantly increased sarcolemmal membrane fluidity as measured by fluorescence anisotropy (steady-state, rss, values of 0.199 +/- 0. 004, 0.204 +/- 0.006, 0.213 +/- 0.005 and 0.214 +/- 0.009, respectively, compared with 0.239 +/- 0.002 for control), whereas stearic, oleic and linoleic acids did not alter fluidity (the rss was not significantly different from control). 6. The potency of the n-3 fatty acids docosahexaenoic acid, eicosapentaenoic acid and alpha-linolenic acid to block cardiac sodium currents is correlated with their ability to produce an increase in membrane fluidity.

Antiarrhythmic fatty acids and antioxidants in animal and cell studies

From the animal and cellular studies that will be discussed in this review, it is apparent that dietary fatty acids and antioxidants play an important role in influencing the development of ventricular tachycardia and potentially lethal ventricular fibrillation. It is this latter disturbance to the rhythmic beating of the heart that is responsible for much of the mortality from coronary heart disease. It is now recognized that diets high in certain polyunsaturated fatty acids (PUFAs) and diets containing antioxidants can afford considerable protection to the heart with regard to the generation of disorders of contractile rhythmicity. The mechanism by which such dietary components confer their cardioprotective effects are now being intensively investigated, particularly with respect to their possible effects on the molecular mechanisms underlying the excitation-contraction coupling process of the myocardial cell. This overview will cover recent studies that have focused on the antiarrhythmic role of PUFAs, particularly those of the n-3 (or omega 3) class with emphasis on experiments performed using laboratory animals, isolated heart preparations, and isolated heart cells (cardiomyocytes). The role of free radicals (reactive oxygen species) and antioxidants in disorders of cardiac rhythm also will be addressed within the perspective of reperfusion injury to the myocardium following ischemia. Emphasis will be placed on the cardioprotective role of nutritional factors and components and the possible cellular mechanisms by which such components may act.

Cilazapril and dietary gamma-linolenic acid prevent the deficit in sciatic nerve conduction velocity in the streptozotocin diabetic rat

Young adult male Hooded Wistar rats were rendered diabetic by administration of streptozotocin and maintained for 5 weeks on a diet containing either 6% olive oil as the total source of fat (OO diet), or purified gamma-linolenic acid (GLA) at a concentration of 0.5% with the remaining 5.5% provided by olive oil (GLA diet). Rats were treated with the angiotensin converting inhibitor, cilazapril, administered in the drinking water at a dose of 20 mg kg-1 body weight day-1. For the OO diet groups, sciatic nerve conduction velocity (NCV) in diabetic rats was reduced by 32% (p < 0.01) in comparison with nondiabetic (vehicle-treated) rats and 27.5% (p < 0.05) in comparison with diabetic rats treated with cilazapril. Diabetic, cilazapril-treated rats showed no reduction in NCV. For the nondiabetic, diabetic, and diabetic plus cilazapril groups fed GLA, the NCV was not significantly different, indicating that dietary GLA also prevented the deficit in the NCV induced by the diabetic state. Analysis of the sciatic nerve endoneurial phospholipid fatty acids revealed a significant reduction in the proportion of GLA and an elevation in the proportion of linoleic acid in the diabetic groups compared with the nondiabetic groups and this was independent of the cilazapril treatment or the dietary lipid supplement. Sciatic nerve myo-inositol content was unaltered while mannose, fructose, glucose, and sorbitol levels were elevated in the diabetic groups and these changes were independent of the cilazapril treatment or the dietary lipid supplement. These results indicate that in the rat, cilazapril treatment or dietary GLA, at the doses tested, are effective in preventing the deficit in the NCV induced by diabetes.

Genetic factors associated with altered sodium transport in human hypertension: a twin study

1. Na+/H+ antiporter/exchange activity (NHE) in human cheek epithelial cells was assessed in 288 female twins and siblings. The genetic contribution of factors to NHE activity was assessed in 128 matched twin pairs (76 monozygotic (MZ); 52 dizygotic (DZ)). 2. There was a small reduction in NHE with age and body mass index. The significant correlations (+/-their standard error (SE)) within MZ and DZ pairs of twins were 0.54 +/- 0.08 and 0.26 +/- 0.13, respectively, implying that genetic factors accounted for 54% of the variance in age-adjusted NHE. There was no cross-sectional relationship between NHE and measures of blood pressure. Based on within-pair differences, however, there was a weak negative association (r = 0.22; P < 0.05) between mean arterial pressure and NHE. 3. It remains to be determined whether NHE in cheek cells is associated with blood pressure tracking over time in young females.

Stimulation of human cheek cell Na+/H+ antiporter activity by saliva and salivary electrolytes: amplification by nigericin

Proton-dependent, ethylisopropylamiloride (EIPA)-sensitive Na+ uptake (Na+/H+ antiporter) studies were performed to examine if saliva, and ionophores which alter cellular electrolyte balance, could influence the activity of the cheek cell Na+/H+ antiporter. Using the standard conditions of 1 mmol/l Na+, and a 65:1 (inside:outside) proton gradient in the assay, the uniport ionophores valinomycin (K+) and gramicidin (Na+) increased EIPA-sensitive Na+ uptake by 177% (p < 0.01) and 227% (p < 0.01), respectively. The dual antiporter ionophore nigericin (K(+)-H+) increased EIPA-sensitive Na+ uptake by 654% (p < 0.01), with maximal Na+ uptake achieved by 1 min and at an ionophore concentration of 50 mumol/l, with an EC50 value 6.4 mumol/l. Pre-incubation of cheek cells with saliva or the low molecular weight (MW) components of saliva (saliva activating factors, SAF) for 2 h at 37 degrees C, also significantly stimulated EIPA-sensitive Na+ uptake. This stimulation could be mimicked by pre-incubation with 25 mmol/l KCl or K(+)-phosphate buffer. Pre-incubating cheek cells with SAF and the inclusion of 20 mumol/l nigericin in the assay, produced maximum EIPA-sensitive Na+ uptake. After pre-incubation with water, 25 mmol/l K(+)-phosphate or SAF, with nigericin in all assays, the initial rate of proton-gradient dependent, EIPA-sensitive Na+ uptake was saturable with respect to external Na+, with Km values of 0.9, 1.7, and 1.8 mmol/l, and Vmax values of 13.4, 25.8, and 31.1 nmol/mg protein/30 sec, respectively. With 20 mumol/l nigericin in the assay, Na+ uptake was inhibited by either increasing the [K+]o in the assay, with an ID50 of 3 mmol/l. These results indicate that nigericin can facilitate K+i exchange for H+o and the attending re-acidification of the cheek cell amplifies 22Na+ uptake via the Na+/H+ antiporter. The degree of stimulation of proton-dependent, EIPA-sensitive Na+ uptake is therefore dependent, in part, on the intracellular [K+]i.

Human buccal epithelial cells as a potential biochemical predictor of essential hypertension: identification of key cellular processes

1. Human cheek cell Na+/H+ antiporter activity (measured as the rate of proton-dependent 22Na+ uptake) was determined in seven normotensive (NT) and four hypertensive (HT) subjects following preincubation of cheek cells with a low molecular weight fraction isolated from NT saliva together with the ionophore, nigericin. 2. Cheek cells preincubated in this manner exhibited greater Na+/H+ antiporter activity with the mean values being 4.2 nmol Na+.mg protein.5 min for the NT group and 1.7 for the HT group. 3. It is possible that stimulation of Na+ transport is due to cellular accumulation of K+ ions during preincubation which, in the presence of the K+/H+ selective ionophore, nigericin, can cause cellular reacidification promoting further 22Na+ uptake via the Na+/H+ antiporter.

Fish oils modulate blood pressure and vascular contractility in the rat and vascular contractility in the primate

The effect of dietary fish oils on development of hypertension and vascular response in vitro were studied in rats and a primate. Dietary fish oils (MaxEPA and an n-3 ethyl ester concentrate of higher EPA and DHA content) were administered to spontaneously hypertensive (SHR), stroke-prone spontaneously hypertensive (SHR-SP) and a backcross of SHR and Wistar Kyoto (SHR/WKY) rats from 4-16 weeks of age. Blood pressure was monitored during the feeding period and vascular responses measured in the aorta and mesenteric vascular bed in vitro. Depending on the strain of rat used and the composition of the fish oil the attenuation in blood pressure was 10-26 mmHg. Fish oils attenuated the response mediated by sympathetic nerve stimulation or intralumenal norepinephrine in the perfused mesenteric vascular bed preparation from the SHR. This attenuation was more pronounced for fish oils enriched with eicosapentaenoic acid and docosahexaenoic acid and was more prominent in the SHR and SHR/WKY backcross than it was in the SHR-SP. Prostanoid synthesis or nitric oxide modulation of alpha-adrenoceptor responses were shown not to be involved in the attenuation of vascular responses produced by fish oil. The maximum contraction of aortic ring preparations in response to norepinephrine (NE) was significantly smaller in SHR than WKY rats fed olive oil and for SHR rats maintained on fish oils the contraction was close to WKY olive oil values. Evidence was obtained also for a modulation of vasoconstrictor responses by dietary fish oils in the perfused mesenteric bed of the marmoset monkey.

Depressed cheek cell sodium transport in human hypertension

Na+ transport activity was measured in cheek cells from untreated hypertensive subjects and age-matched normotensive controls identified from a blood pressure screening program. Cheek cells were isolated by a simple mouth wash procedure and Na+ transport activity was measured as the proton-dependent uptake of 22Na+ using a rapid filtration assay. The rate of Na+ uptake was about 45% lower in hypertensive subjects and this difference persisted in a follow up study 2 years later involving those subjects who remained untreated for their hypertension. The proton independent Na+ uptake was also reduced by about 46% in the hypertensive group. The increase in the rate of cheek cell Na+ transport with increasing transcellular proton gradient values was also significantly lower in hypertensive subjects. The reduced cheek cell Na+ transport observed in hypertensive subjects may indicate decreased activity of the Na+/H+ antiporter and/or changes in the ion permeability properties of the cheek cell plasma membrane in the hypertensive state. This novel assay provides a biochemically based method for discriminating between normotensive and hypertensive subjects and makes use of tissue which can be obtained in a relatively non-invasive manner.

Osmotic and other properties of isolated human cheek epithelial cells

This study describes some biological properties of human cheek (buccal epithelial) cells, isolated by mouth wash. Yields ranged from 6.5 to 20.6 x 10(6) cells, with a mean (+/- SE) of 12.2 +/- 4.2 x 10(6) cells, which gave 0.55 +/- 0.01 x 10(6) cells/mg protein. Vital stain exclusion was similar in cells isolated in either water (89 +/- 2%) or 250 mM sucrose (87 +/- 3%). From our measurements of cell volume and electrolyte content, we estimated intracellular Na+ and K+ concentrations to be between 0.3-0.5 and 7.4-13.0 mM, respectively. In 22 adult subjects, basal, prickle, intermediate, and superficial cells represented 0.3 +/- 1.4, 51 +/- 2.4, 26 +/- 0.9, and 22.7 +/- 1.8%, respectively, of the total sample. Cheek cells exhibited a low endogenous rate of oxygen consumption, which was stimulated by glucose or succinate and inhibited by KCN or NaF. Cheek cells were osmotically stable in a wide range of media, including water. However, they exhibited shrinkage and collapse in hypertonic media, particularly polyethylene glycol.

Characterization of Na(+)-H+ antiporter activity associated with human cheek epithelial cells

Na+ transport activity was characterized in human cheek epithelial cells obtained from normotensive adult subjects. The cells were isolated using a mouth-wash procedure and assayed for Na+ uptake using a radioactive (22Na+) rapid filtration assay. Cheek cells displayed proton-dependent Na+ uptake activity that was dependent on the magnitude of the externally directed proton gradient measured using the fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to determine intracellular pH. Amiloride, ethylisopropylamiloride (EIPA), 5-(N,N-dimethyl)-amiloride, 5-(N-methyl-N-isobutyl)-amiloride (MIA), and 5-(N,N-hexamethylene)-amiloride (NNHA) all inhibited proton-dependent Na+ uptake, with MIA, EIPA, and NNHA being the most potent. The Michaelis constant (Km) for extracellular Na+ was 5.7 mM, while the maximum velocity for Na(+)-H+ antiporter activity was 4.3 nmol Na+.mg protein-1.30s-1. The Km for intracellular H+ was 0.17 microM, with a Hill coefficient of 0.7. Stimulation by ouabain and inhibition by bumetanide of cheek cell proton-dependent Na+ uptake indicated only relatively low activities of Na(+)-K(+)-ATPase and Na(+)-K(+)-2Cl- cotransport, respectively. These results are consistent with the presence of Na(+)-H+ antiporter activity in cheek cells. Cheek cells therefore provide a convenient, relatively noninvasive source of tissue for examining Na(+)-H+ antiporter activity in human subjects.

Sodium transport activity in cheek epithelial cells from adolescents at increased risk of hypertension

Sodium transport including amiloride-sensitive Na+/H+ antiporter activity was measured in cheek epithelial cells of adolescents displaying either high or low BP tracking characteristics and in a subgroup of high BP tracking adolescents exhibiting a positive family history of hypertension. From the BP tracking behaviour of over 500 adolescents measured over a period of three years, 24 low BP tracking and 29 high BP tracking adolescents were recruited for the study. Cheek cells were collected from these subjects and proton-dependent, amiloride-sensitive Na+/H+ antiporter activity and the response of this antiporter to a proton gradient were measured. Cheek cell Na+/H+ antiporter activity was 50% lower (P = 0.0004) in the high BP tracking group (1.02 +/- 0.15 nmol Na+/mg protein/5 min (mean +/- SEM) compared with the activity in the low BP tracking group (2.05 +/- 0.24). A significantly lower Na+/H+ antiporter activity (69%; P < 0.01) was also apparent in the high BP tracking adolescents with family history of hypertension (n = 7) compared with the low BP tracking group. The graded response of cheek cell Na+/H+ antiporter activity to the proton gradient was 58% lower (P = 0.0039) for adolescents in the high BP tracking group compared with the low BP tracking group. Passive Na+ influx was also significantly lower in the cheek cells of the high BP tracking group. Our results therefore show that the activity of the Na+/H+ antiporter in cheek cells and the passive Na+ transport activity are lower in those adolescents considered at greatest risk of future development of essential hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between salivary growth factors, electrolytes and abnormal sodium transport in human hypertension

We have previously shown cheek cell Na+/H+ antiporter activity to be reduced in human hypertensives. We have now examined the relationship between abnormal antiporter activity and a variety of salivary factors. Total protein concentration and amylase activity were higher in hypertensives, but salivary flow rate and epidermal growth factor, transforming growth factor-alpha, calcium, and magnesium concentrations were not significantly different between hypertensives and normotensives. The lowered cheek cell Na+/H+ antiporter activity in those hypertensives with diastolic BP greater than 95 mmHg was accompanied by lowered salivary Na+/H+ ratios. In borderline hypertensives (diastolic BP between 90 and 95 mmHg), the Na+/H+ ratio was reduced to a similar extent to that seen in those hypertensives with a diastolic BP above 95 mmHg, however the cheek cell antiporter activity was not reduced, suggesting that these two differences are not related in a simple fashion in all hypertensives. It is concluded that it is unlikely that differences in salivary growth factors explain the lowered cheek cell Na+/H+ antiporter activity observed in human hypertension. Our findings indicate that salivary electrolyte composition may be related to cheek cell Na+/H+ antiporter activity and these parameters may be altered in hypertension.

The effect of dietary supplementation with eicosapentaenoic acid on the phospholipid and fatty acid composition of erythrocytes of marmoset

Adult male marmoset monkeys were fed eicosapentaenoic acid (20:5n-3) as the ethyl ester in diets containing either 32% (reference diet, no added cholesterol) or 7% (atherogenic diet with 0.2% added cholesterol) linoleic acid (18:2n-6) for 30 wk. No changes were seen in the level of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) but minor changes were observed in both the sphingomyelin (SPM) and phosphatidylinositol plus phosphatidylserine (PI+PS) fractions of erythrocyte lipids. The extent of total n-3 fatty acid incorporation into membrane lipids was higher in atherogenic diets (polyunsaturated/monounsaturated/saturated (P/M/S) ratio 0.2:0.6:1.0) than reference diets (P/M/S ratio 1:1:1) and this was true for both PE (33.4 +/- 1.0% vs 24.3 +/- 1.1%) and PC (9.3 +/- 0.5% vs 4.9 +/- 0.3%). Although suitable controls for cholesterol effects were not included in the study, earlier results obtained with marmosets lead us to believe such effects were probably small. Regardless of basic diet (atherogenic, reference), 20:5n-3 was preferentially incorporated into PE (10.8 +/- 0.2%, 6.0 +/- 0.02%) while smaller amounts were incorporated into PC (6.9 +/- 0.4%, 3.2 +/- 0.2%). The major n-3 polyunsaturated fatty acid found in PE in response to dietary 20:5n-3 was the elongation metabolite 22:5n-3 in both the atherogenic (17.7 +/- 0.7%) and reference (14.3 +/- 1.0%) dietary groups; 22:6n-3 levels were less affected by diet (4.7 +/- 0.3% and 3.9 +/- 0.2%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation and effects of dietary eicosapentaenoate (20:5(n-3)) on plasma and erythrocyte lipids of the marmoset following dietary supplementation with differing levels of linoleic acid

The effect of dietary eicosapentaenoic acid (EPA, 20:5(n-3), as the ethyl ester) on plasma lipid levels and the incorporation of EPA into erythrocyte and plasma lipids were investigated in the marmoset monkey. Marmosets were fed high mixed-fat diets (14.5% total fat) supplemented with or without 0.8% EPA for 30 weeks. Markedly elevated plasma cholesterol (16.4 mmol/l) was induced by an atherogenic-type diet but with EPA supplementation, plasma cholesterol increased to only 6.6 mmol/l. Plasma triacylglycerol levels were not elevated with an atherogenic type diet. Substantial EPA incorporation was evident for plasma phospholipid, triacylglycerol and cholesterol ester fractions. The proportion of docosapentaenoic acid (22:5(n-3)) but not docosahexaenoic acid (22:6(n-3)) was also elevated in these plasma lipid fractions. Greatest incorporation of EPA occurred when it was administered with an atherogenic type diet having a P:M:S (polyunsaturated:monounsaturated:saturated) fatty acid ratio of about 0.2:0.6:1.0 in comparison to the control diet of 1.0:1.0:1.0. Incorporation of EPA and 22:5(n-3)) into erythrocyte phospholipids was also apparent and this was at the expense of linoleic acid (18:2(n-6)). These results in the marmoset highlight both the cholesterol-lowering properties of EPA and the extent of its incorporation into plasma lipids and erythrocyte membrane phospholipids with far greater incorporation occurring when the level of dietary linoleic acid was reduced.

Effect of a high fat/cholesterol diet with or without eicosapentaenoic acid on plasma lipids, lipoproteins and lipid transfer protein activity in the marmoset

Marmosets fed a diet supplemented with 0.2% cholesterol and 10% sheep fat (by weight) developed hypercholesterolemia with a 4-fold increase in plasma cholesterol (4.28 +/- 0.57-16.38 +/- 4.22 mmol/l, mean +/- SD, P less than 0.001). This was due mainly to a 5-fold increase in the intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) fraction (d = 1.006-1.063 g/ml). The proportion of plasma cholesterol in high density lipoproteins (HDL) decreased from 56% to 25% although HDL cholesterol increased from 2.40 +/- 0.42 to 4.09 +/- 0.92 mmol/l (P less than 0.001), and HDL particle radius increased from 5.10 +/- 0.18 nm to 6.06 +/- 0.73 nm (P less than 0.05). Plasma lipid transfer protein (LTP) activity increased 2.5-fold in whole plasma and 2-fold in lipoprotein-deficient plasma. The atherogenic lipoprotein profile was attenuated by adding 0.8% eicosapentaenoic acid (EPA, 20:5 n - 3, as the ethyl ester) to the atherogenic diet. Plasma cholesterol increased only 55% to 6.64 +/- 2.55 mmol/l with only an 80% increase in lipoproteins in the d = 1.006-1.063 g/ml fraction and a more favourable proportion of plasma cholesterol in HDL (44%) than without EPA. LTP activity was reduced to 1.7-fold above control in whole plasma by addition of EPA to the atherogenic diet. There was a positive correlation between plasma cholesterol and LTP activity in whole plasma (r = 0.89, P less than 0.001) and in lipoprotein-deficient plasma (r = 0.67, P less than 0.001). EPA therefore attenuated some of the adverse effects of a 0.2% cholesterol, 10% sheep fat diet on plasma lipids and lipoproteins and induced a less atherogenic profile.

A comparison of lung lamellar body phospholipids from premature and term infants: is sphingomyelin a contaminant of surfactant?

Lamellar bodies were isolated from homogenates of lungs obtained at autopsy from premature infants (n = 9), and compared to lamellar bodies from three full term reference groups including 55 infants with sudden infant death syndrome (SIDS), 14 control infants, and 3 who succumbed to intra-uterine death (IUD) at term. Analysis of the phospholipids was expected to reveal a high proportion of sphingomyelin (Spm) in the lamellar bodies isolated from the lungs of premature infants (24 to 33 weeks gestational age) since at this stage of their development the percentage of Spm in the amniotic fluid is high. However, Spm was either absent or a small proportion of the total phospholipid in lamellar body surfactant from these premature infants. Spm was also a small percentage of phospholipid in the lamellar body surfactant of infants with SIDS and from control and IUD specimens. It is suggested that Spm may not be a normal constituent of lamellar body surfactant but rather a contaminant from membranes.

Effects of dietary eicosapentaenoate (20:5 n-3) on cardiac beta-adrenergic receptor activity in the marmoset monkey

Eicosapentaenoic acid (EPA; 20:5 n-3; ethyl ester) in combination with atherogenic or non-atherogenic high fat diets was fed to young adult male marmoset monkeys for a period of 30 weeks. EPA markedly reduced the raised plasma cholesterol level evident when feeding an atherogenic diet but did not influence the cardiac membrane cholesterol-to-phospholipid ratio. EPA and its elongation product 22:5 n-3 was incorporated into cardiac membrane phospholipids at the expense of linoleic and arachidonic acids. Dietary EPA increased cardiac beta-AR affinity and reversed the decreased beta-AR affinity evident when feeding an atherogenic diet.

The development of pulmonary surfactant lipids in a neonatal marsupial and the rat

The composition of pulmonary surfactant during development was compared in a marsupial, the tammar wallaby, and the rat. For both species phospholipid fatty acid and neutral lipid fatty acid composition is similar, and phosphatidylcholine was the principal phospholipid at each age group. The relative amount of each phospholipid class significantly changed with time in both species but the extent of these changes did not vary between species. The neutral lipid component of surfactant varied significantly between the marsupial and eutherian, with higher levels of free cholesterol observed in the former. Overall the lipid composition of pulmonary surfactant in the developing wallaby is similar to that seen in eutherians with the exception being the level of free cholesterol.

The effect of temperature on isolated perfused hearts of heterothermic marsupials

1. The thermal response of isolated perfused hearts of four dasyurid marsupials was determined and compared with that of two rodents. 2. Heart beat rate was strongly temperature dependent in all species. 3. The temperature of cardiac arrest in the species investigated in the present study and of others collected from the literature occurred at a mean of about 13 degrees C in homeotherms, 7 degrees C in daily heterotherms, and 1 degrees C in hibernators. 4. For both marsupials and placentals the temperature of cardiac arrest in hibernators and daily heterotherms correlated with the minimum body temperature during torpor.

Decreased lung surfactant disaturated phosphatidylcholine in sudden infant death syndrome

The lipid composition of lung surfactant obtained by lung lavage at autopsy in 40 infants dying from the sudden infant death syndrome (SIDS), was compared to that obtained from 12 infants dying from other causes (control group). Analysis of the lipids from the two groups showed no major difference in the proportions of the various phospholipid classes particularly the predominant component, phosphatidylcholine (PC), which was present at 60.7 +/- 0.9% (mean +/- S.E.) of the total phospholipids in the SIDS group and 57.9 +/- 2.9% in the control group. However the proportion of the PC present as the disaturated form (DSPC), was significantly (P less than 0.01) reduced in the SIDS group (65.8 +/- 1.6%) in comparison to the control group (77.4 +/- 3.5%). The proportion of DSPC present in the PC fraction of SIDS infants in the high-risk age range of 1-26 weeks (63.9 +/- 1.9%) was also significantly reduced (P less than 0.01) in comparison to the total control group of infants. For infants older than 26 weeks, significant differences in the proportion of DSPC in PC were not observed between SIDS and control groups. A functional consequence of the observed reduction in the DSPC content of lung surfactant of SIDS infants could be a greater degree of fluidity of the surfactant, particularly at exhalation. Such a biophysical change in surfactant properties could have a profound influence on lung function and be a causative factor in sudden infant death.

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.

Dietary lipid modulation of myocardial beta-adrenergic mechanisms, Ca2+-dependent automaticity, and arrhythmogenesis in the marmoset

Dietary lipid supplements high in either saturated fatty acids derived from sheep perirenal fat or polyunsaturated fatty acids (65% linoleic acid) derived from sunflower seed oil were fed to marmoset monkeys (Callithrix jacchus) for 20 months. The effect of these long-term dietary lipid supplements on myocardial contractile function and their influence on responses to isoprenaline and external calcium concentration were examined using isolated papillary muscles and atria. Isoprenaline potency was increased by the sheep fat-supplemented diet, which induced significant three- to eightfold leftward parallel shifts of isoprenaline dose-response curves for papillary muscle and left atrial inotropy and right atrial chronotropy. The antagonist potency of propranolol was not influenced by diet. The incidence of isoprenaline-induced spontaneous tachyarrhythmias in electrically driven papillary muscles and left atria was reduced by the sunflower seed oil-supplemented diet and increased by the sheep fat diet, as were the spontaneous beat rate and calcium-dependent automaticity of right atria. These results show that dietary lipids can significantly modify stimulus-response coupling and alter the susceptibility to arrhythmogenesis in the heart of the nonhuman primate, and indicate that nutritional interventions may modify responses to cardioactive drugs as well as influence the development of cardiac disease.

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

Diets supplemented with high levels of saturated or unsaturated fatty acids supplied by addition of sheep kidney fat or sunflower seed oil, respectively, were fed to rats with or without dietary cholesterol. The effects of these diets on cardiac membrane lipid composition, catecholamine-stimulated adenylate cyclase and beta-adrenergic receptor activity associated with cardiac membranes, were determined. The fatty acid-supplemented diets, either with or without cholesterol, resulted in alterations in the proportion of the (n-6) to (n-3) series of unsaturated fatty acids, with the sunflower seed oil increasing and the sheep kidney fat decreasing this ratio, but did not by themselves significantly alter the ratio of saturated to unsaturated fatty acids. However, cholesterol supplementation resulted in a decrease in the proportion of saturated and polyunsaturated fatty acids and a dramatic increase in oleic acid in cardiac membrane phospholipids irrespective of the nature of the dietary fatty acid supplement. The cholesterol/phospholipid ratio of cardiac membrane lipids was also markedly increased with dietary cholesterol supplementation. Although relatively unaffected by the nature of the dietary fatty acid supplement, catecholamine-stimulated adenylate cyclase activity was significantly increased with dietary cholesterol supplementation and was positively correlated with the value of the membrane cholesterol/phospholipid ratio. Although the dissociation constant for the beta-adrenergic receptor, determined by [125I](-)-iodocyanopindolol binding, was unaffected by the nature of the dietary lipid supplement, the number of beta-adrenergic receptors was dramatically reduced by dietary cholesterol and negatively correlated with the value of the membrane cholesterol/phospholipid ratio. These results indicate that the activity of the membrane-associated beta-adrenergic/adenylate cyclase system of the heart can be influenced by dietary lipids particularly those altering the membrane cholesterol/phospholipid ratio and presumably membrane physico-chemical properties. In the face of these dietary-induced changes, a degree of homeostasis was apparent both with regard to membrane fatty acid composition in response to an altered membrane cholesterol/phospholipid ratio, and to down regulation of the beta-adrenergic receptor in response to enhanced catecholamine-stimulated adenylate cyclase activity.

Influence of dietary fats on blood coagulation and prostaglandin production in the common marmoset

Common marmosets were fed a standard marmoset diet (REF) or diets supplemented with 12% (wt/wt) sunflower seed oil (SSO) or sheep fat (SF) for a period of 90 weeks. The values for coagulation indices, clotting time, and Russel viper venom time were consistent with decreased thrombotic tendency of platelets from animals on the SSO diet relative to the low fat, REF diet animals, while an increased tendency to thrombosis was observed with SF-fed marmosets. The SSO- and SF-supplemented marmosets showed a significantly reduced thromboxane (TXB2) generation from platelets aggregating to collagen (ASC) relative to the REF group, while at 50 micrograms/ml ASC this difference was maintained only by the SSO group. The SF diet-fed marmosets showed a reduced prostacyclin (measured as 6-keto-PGF1 alpha) generation from incubated aorta relative to the REF or SSO-fed groups, which were not different from each other. A reduced proportion of platelet phospholipid arachidonic acid (20:4, n-6) and increased alpha-tocopherol concentration was consistent with the decreased aggregability and thromboxane generation of platelets from SSO-fed marmosets relative to the REF and SF groups. The SF diet-fed marmosets, on the other hand, showed minimal change in arachidonic acid, alpha-tocopherol or platelet reactivity from the REF group. These differing responses to dietary fats are discussed in relation to the potential for the development of thrombosis and atherosclerosis.

A comparison of the properties of the cardiac beta-adrenergic receptor adenylyl cyclase system in the rat and the marmoset monkey

1. A comparison was made between adrenergic receptor binding properties and catecholamine-stimulated adenylyl cyclase activity in cardiac membrane fractions from the rat and the marmoset monkey. 2. [125I]HEAT and [125I]ICYP were used to determine respectively, the alpha- and beta-adrenergic receptor binding in cardiac membrane fractions. 3. Greatest adrenergic receptor density and degree of specific binding was evident using membranes sedimenting between 6000 and 46,000 g. 4. In rat heart, the ratio of beta- to alpha-adrenergic receptors was 57:43, while for the marmoset this ratio was 92:8. 5. Basal, isoproterenol, sodium fluoride and forskolin-stimulated adenylyl cyclase activities in the rat and marmoset monkey were investigated in several different cardiac membrane fractions. 6. The highest-fold stimulation of adenylyl cyclase activity was present in membranes sedimenting between 0 and 500 g. 7. Adenylyl cyclase activities were higher in the marmoset heart membrane preparations, however the rat heart adenylyl cyclase exhibited greater sensitivity to isoproterenol; ED50 3.8 X 10(-7) M compared with 7.5 X 10(-7) M for the marmoset. 8. Differences between rat and marmoset catecholamine-sensitive adenylyl cyclase activity were apparent when a variety of adrenergic agonists and antagonists were tested. 9. In the marmoset but not the rat, adrenergic antagonists alone stimulated basal adenylyl cyclase activity. 10. Differences in the activation of cardiac adenylyl cyclase by GTP and GMP-PNP were also evident between the rat and the marmoset monkey, particularly with regard to basal and isoproterenol-stimulated activity.

Thermotropic interaction of vitamin E with dimyristoyl and dipalmitoyl phosphatidylcholine liposomes

The effect of vitamin E on the thermal behavior of two saturated phosphatidylcholines was investigated by differential scanning calorimetry. For dimyristoyl and dipalmitoyl phosphatidylcholines, the addition of vitamin E at concentrations of 1, 5 and 10 mol% vitamin E, resulted in a lowering of the phase transition temperature and a broadening of the temperature range of the phase transition indicating an increase in the fluidity of the phospholipids. Taken together with other physical studies on the effect of vitamin E on (unsaturated) phospholipids, these results indicate that vitamin E could influence the physical properties of membrane phospholipids in addition to its known antioxidant role. The likelihood of this interaction would be enhanced if vitamin E was not randomly distributed in biological membranes but rather was located in domains where its local concentration, relative to phospholipids, was elevated.

Mitochondrial membrane fatty acid composition in the marmoset monkey following dietary lipid supplementation

Diets supplemented with high levels of saturated fatty acids derived from sheep kidney (perirenal) fat or unsaturated fatty acids derived from sunflowerseed oil were fed to marmoset monkeys for 22 wk. The effect of such diets on plasma, red blood cell phospholipids, and liver, heart, kidney and brain mitochondrial phospholipid fatty acids was determined. Despite large differences in the level and type of lipid present in the experimental diets, there was little effect on the proportion of saturated to unsaturated fatty acids in the phospholipids of the membranes examined. The diets did, however, alter the proportion of the various classes of polyunsaturated fatty acids in the membrane phospholipids, with the sunflowerseed oil diet elevating and the sheep kidney fat diet reducing the n-6/n-3 unsaturated fatty acid ratio, relative to a low (mixed fat) reference diet. This change occurred in all membranes except brain, in which only a small response to altered dietary lipid intake was observed. Elevation of dietary linoleic acid led to an increase in membrane linoleic acid and a marked decrease in membrane arachidonic acid, such that the membranes from animals fed the sunflowerseed oil diet exhibited the lowest proportion of arachidonic acid. In this latter respect, the response of the marmoset monkey to dietary lipid supplementation differs markedly from the rat. Our inability to alter significantly membrane lipid saturation/unsaturation supports the notion that a homeostatic mechanism is in some way responsible for buffering membranes from the effects of significant changes in the nature of the dietary lipid intake.

Membrane homeostasis: thermotropic behaviour of microsomal membrane lipids isolated from livers of rats fed cholesterol-supplemented diets

Differential scanning colorimetry (DSC) has been applied to study the phase transition properties of isolated lipids from liver microsomal membranes of rats fed high cholesterol diets with or without high levels of either saturated (coconut oil) or unsaturated (sunflower seed oil) fat. DSC of aqueous buffer dispersions of liver microsomal lipids exhibited two independent, reversible phase transitions. The dietary cholesterol treatments had their major effect on the temperature at which the lower phase transition (T1) occurred. This transition occurred at a lower temperature when cholesterol was added to the diet, irrespective of the nature of the fatty acid supplement. However the magnitude of decrease was more when cholesterol was fed with sunflower seed oil. Inclusion of cholesterol into the rat diets also lowered the enthalpy values for the lower phase transition (T1). No appreciable effect on the temperature of the higher phase transition (T2) was observed, however the enthalpy values were slightly decreased by cholesterol feeding. These results suggest that certain domains of microsomal lipids, probably containing some relatively higher melting-point lipids, independently undergo solidus or gel formation and this transition (T2) is not greatly affected by dietary cholesterol. On the other hand, domains representing the bulk of the microsomal lipids undergo a phase change (T1) at temperatures which are dependent on cholesterol content and fatty acid profiles of the membrane, which are in turn, modified by dietary cholesterol intake.

Blood pressure and dietary polyunsaturated and saturated fats: a controlled trial

Fifty-four healthy, omnivore normotensive volunteers aged 20-59 years were randomly allocated either to a control group eating a low polyunsaturated to saturated fat ratio (P/S ratio) diet (0.3) throughout, or to one of two experimental groups eating a high P/S ratio diet (1.0) for one of two 6-week experimental periods. Changes in other components were avoided. Twenty-four hour diet records showed substantial changes in the P/S ratio for experimental groups when on the high P/S ratio diet (0.3 to 1.0). There were significant increases in relative concentrations of linoleic acid in plasma phospholipids when on the high P/S ratio diet. There was no consistent effect of dietary P/S ratio elevation from 0.3 to 1.0 on group mean systolic and diastolic blood pressures. Adjustment of blood pressure changes for changes in electrolytes, other dietary components, plasma lipids, weight and other lifestyle variables did not alter this result. It was concluded that the blood pressure lowering effect of a vegetarian diet reported previously was unlikely to have been due to changes in dietary P/S ratio.

Arrhenius parameters of mitochondrial membrane respiratory enzymes in relation to thermoregulation in endotherms

The relationship between the body temperature (Tb), the Arrhenius critical temperature (T*), and the apparent activation energy above T* (Ea1), of liver and heart mitochondrial respiratory enzymes from eleven homeothermic and eight heterothermic species was determined using a linear regression analysis. An inverse relation was observed between T* and Ea1 during torpor and hibernation. In all thermoregulatory states, T* decreased with Tb and T* was equal to or below Tb. During torpor Ea1 increased in a linear manner as Tb was lowered. It appears that the above Arrhenius parameters are closely linked to the thermoregulatory state of endotherms and thus may represent an adaptation for function at low Tb's.

Homeostatic control of membrane fatty acid composition in the rat after dietary lipid treatment

Diets in which both the lipid content and composition (polyunsaturated to saturated fatty acid ratio) were varied were fed to rats for 20 weeks, and the effects on the tissue lipid profiles were determined. The fatty acid profile of the plasma lipids, and the phospholipid fatty acids of the mitochondrial and microsomal fractions of liver, heart, kidney and brain, as well as erythrocyte membranes were determined. Despite large differences in the level and type of lipid present in the experimental diets and in the proportion of saturated fatty acids in the plasma lipids in response to the various diets, there was little effect on the proportion of saturated to unsaturated fatty acids in the phospholipids of the various membranes examined. The major effect of altering the dietary level of polyunsaturated to saturated fatty acids was on the ratio of the omega 6/omega 3 series of unsaturated fatty acids in the membrane lipids. This change occurred in all tissues except the brain, in which only a small response to altered dietary lipid intake was observed. The omega 6/omega 3 ratio was elevated upon feeding a diet rich in omega 6 polyunsaturated fatty acids, but decreased when a diet rich in saturated fatty acids was fed. The failure to significantly alter membrane lipid saturation/unsaturation in the tissues examined would suggest that a homeostatic mechanism is operative in biological membranes and may act to buffer membranes from the effects of changes in the nature of the dietary lipid intake.

Species variation in the ouabain sensitivity of cardiac Na+/K+-ATPase. A possible role for membrane lipids

The role of membrane lipid composition on the modulation of ouabain sensitivity of cardiac Na+/K+-ATPase has been studied in vitro using several animal species. The animals can be grouped as ouabain-sensitive and ouabain-insensitive species. Ouabain-sensitive species (I50; 0.5-2.2 microM) include sheep, marmoset, pig and the guinea pig, whilst rat and mouse form the ouabain-insensitive group (I50; 100-105 microM). Although no species variation in the distribution of major phospholipid classes was observed, significant differences were apparent in the proportions of certain saturated and unsaturated phospholipid fatty acids. Thus, there was a marked increase in the relative proportion of docosahexaenoic (22:6, omega-3) acid in the Na+/K+-ATPase preparations from the rat and mouse compared to ouabain-sensitive species. Despite these differences, all animals had similar proportions of total saturated (sigma SAT) and total unsaturated (sigma Unsat) fatty acids. On the other hand, a good correlation between the unsaturation index of membrane lipids and I50 value for ouabain was observed. It is proposed that acyl chain characteristics (unsaturation and/or chain length) rather than the head group of the phospholipid molecule play a major role in the modulation of Na+/K+-ATPase to inhibition by ouabain.

Response of rat heart membranes and associated ion-transporting ATPases to dietary lipid

The effects of different dietary fat intake on the lipid composition and enzyme behaviour of sarcolemmal (Na+ + K+)ATPase and sarcoplasmic reticulum Ca2+-ATPase from rat heart were investigated. Rat diets were supplemented with either sunflower seed oil (unsatd./satd. 5.6) or sheep kidney fat (unsatd./satd. 0.8). Significant changes in the phospholipid fatty acid composition were observed in both membranes after 9 weeks dietary lipid treatment. For both membranes, the total saturated/unsaturated fatty acid levels were unaffected by the dietary lipid treatment, however the proportions of the major unsaturated fatty acids were altered. Animals fed the sunflower seed oil diet exhibited an increase in n-6 fatty acids, including linoleic (18:2(n-6] and arachidonic (20:4(n-6] while the sheep kidney fat dietary rats were higher in n-3 fatty acids, principally docosahexaenoic (22:6), with the net result being a higher n-6/n-3 ratio in the sunflower seed oil group compared to sheep kidney fat dietary animals. Fluorescence polarization indicated that the fluidity of sarcoplasmic reticular membrane was greater than that of sarcolemmal membrane, with a dietary lipid-induced decrease in fluidity being observed in the sarcoplasmic reticular membrane from sheep kidney fat dietary animals. Despite these significant changes in membrane composition and physical properties, neither the specific activity nor the temperature-activity relationship (Arrhenius profile) of the associated ATPases were altered. These results suggest that with regard to the parameters measured in this study, the two ion-transporting ATPases are not modulated by changes which occur in the membrane lipid composition as a result of the diet.

Dietary-induced changes in the fatty acid composition of human cheek cell phospholipids: correlation with changes in the dietary polyunsaturated/saturated fat ratio

Healthy normotensive volunteers aged 20 to 59 yr were randomly allocated either to a control group or to one of two experimental groups. The control group ate a low P/S ratio diet for 12 wk while the first experimental group ate a high P/S ratio diet for 6 wk followed by a low P/S ratio diet for the next 6 wk. The second experimental group ate a low P/S ratio diet in the first 6 wk followed by a high P/S ratio diet for the next 6 wk. Dietary P/S ratio, plasma linoleic acid (18:2), and cheek cell phospholipid 18:2 levels were compared in each dietary group at the end of the 1st and 2nd 6 wk. On change from a low to a high P/S ratio diet, there was a 36% increase in the proportion of 18:2 in the cheek cell phospholipids in comparison with the proportion existing before the change. This was associated with an increase in the proportion of 18:2 in the plasma lipids of this group. No reduction in the proportion of 18:2 in the cheek cell phospholipids was apparent in the control group or the group which changed from a high to a low P/S ratio diet, although in the latter group there was a reduction in the proportion of 18:2 in the plasma lipids. As the phospholipid fatty acid composition of human cheek cells reflects dietary lipid status under certain conditions, this observation may be useful in dietary and nutritional studies, particularly as human cheek cells can be obtained in a noninvasive manner.

The composition of cardiac phospholipids in rats fed different lipid supplements

Changes in dietary lipid intake are known to alter the fatty acid composition of cardiac muscle of various animals. Because changes in cardiac muscle membrane structure and function may be involved in the pathogenesis of arrhythmia and ischemia, we have examined the effects of dietary lipid supplements on the phospholipid distribution and fatty acid composition of rat atria and ventricle following 20 weeks feeding of diets supplemented with either 12% sunflower-seed oil or sheep fat. Neither lipid supplement produced significant changes in the proportions of cholesterol, total phospholipids or phosphatidylcholine, phosphatidylethanolamine or diphosphatidylglycerol,--the phospholipid classes that together account for more than 90% of the total phospholipids of rat cardiac muscle. Significant changes were found in the profiles of the unsaturated fatty acids of all 3 phospholipid components of both atria and ventricle. Although similar, the changes between these tissues were not identical. However, in general, feeding a linoleic acid-rich sunflower seed oil supplement resulted in an increase in the omega-6 family of fatty acids, whereas feeding the relatively linoleic acid-poor sheep fat supplement decreased the level of omega-6 fatty acids but increased the levels of the omega-3 family, resulting in major shifts in the proportions of these families of acids. In particular, the ratio of arachidonic acid: docosahexaenoic acid (20:4,omega-6/22:6,omega-3), which is higher in all phospholipids of atria than ventricle, is increased by feeding linoleic acid, primarily by increasing the level of arachidonic acid in the muscle membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of mitochondrial respiration and membrane lipid composition in the rat and marmoset following dietary lipid supplementation

Rats and marmosets were fed different lipid supplemented diets and the phospholipid fatty acid composition and the respiration rate of liver and heart mitochondria were determined. For both species, diets of differing lipid saturation had little effect on the ratio of saturated to unsaturated fatty acids in the mitochondrial membranes, however the omega 6/omega 3 unsaturated fatty acid ratio was significantly altered by diets of different lipid saturation. In comparison to animals fed low fat diets, mitochondrial respiration in the marmoset was reduced by high fat diets irrespective of the dietary level of lipid saturation. This effect of high fat diets on mitochondrial respiration was not observed for the rat.

Differential modulation of rat heart mitochondrial membrane-associated enzymes by dietary lipid

Diets supplemented with high levels of saturated fatty acids derived from sheep kidney (perirenal) fat or unsaturated fatty acids derived from sunflower seed oil were fed to rats and the effect on heart mitochondrial lipid composition and membrane-associated enzyme behaviour was determined. The dietary lipid treatments did not change the overall level of membrane lipid unsaturation but did alter the proportion of various unsaturated fatty acids. This led to a change in the omega 6/omega 3 unsaturated fatty acid ratio, which was highest in the sunflower seed oil fed rats. Arrhenius plots of the mitochondrial membrane associated enzymes succinate-cytochrome c reductase and oligomycin-sensitive adenosinetriphosphatase (ATPase) after dietary lipid treatment revealed different responses in their critical temperature. For succinate-cytochrome c reductase, the critical temperature was 29 degrees C for rats fed the sheep kidney fat diet and 20 degrees C for rats fed the sunflower seed oil diet. In contrast, no shift in the critical temperature for the mitochondrial ATPase was apparent as a result of the differing dietary lipid treatments. The results suggest that the discontinuity in the Arrhenius plot of succinate-cytochrome c reductase is induced by some change in the physical properties of the membrane lipids. In contrast, mitochondrial ATPase appears insensitive, in terms of its thermal behaviour, to changes occurring in the composition of the membrane lipids. However, the specific activity of the mitochondrial ATPase was affected by the dietary lipid treatment being highest for the rats fed the sheep kidney fat diet. No dietary lipid effect was observed for the specific activity of succinate-cytochrome c reductase. This differential response of the two mitochondrial membrane enzymes to dietary-induced changes in membrane lipid composition may affect mitochondrial oxidative phosphorylation.

The effect of dietary lipids on the thermotropic behaviour of rat liver and heart mitochondrial membrane lipids

Diets supplemented with relatively high levels of either saturated fatty acids derived from sheep kidney fat (sheep kidney fat diet) or unsaturated fatty acids derived from sunflower seed oil (sunflower seed oil diet) were fed to rats for a period of 16 weeks and changes in the thermotropic behaviour of liver and heart mitochondrial lipids were determined by differential scanning calorimetry (DSC). The diets induced similar changes in the fatty acid composition in both liver and heart mitochondrial lipids, the major change being the omega 6 to omega 3 unsaturated fatty acid ratio, which was elevated in mitochondria from animals on the sunflower seed oil diet and lowered with the mitochondria from the sheep kidney fat dietary animals. When examined by DSC, aqueous buffer dispersions of liver and heart mitochondrial lipids exhibited two independent, reversible phase transitions and in some instances a third highly unstable transition. The dietary lipid treatments had their major effect of the temperature at which the lower phase transition occurred, there being an inverse relationship between the transition temperature and the omega 6 to omega 3 unsaturated fatty acid ratio. No significant effect was observed for the temperature of the higher phase transition. These results indicate that certain domains of mitochondrial lipids, probably containing some relatively higher melting-point lipids, independently undergo formation of the solidus or gel phase and this phenomenon is not greatly influenced by the lipid composition of the mitochondrial membranes. Conversely, other domains, representing the bulk of the membrane lipids and which probably contain the relatively lower melting point lipids, undergo solidus phase formation at temperatures which reflect changes in the membrane lipid composition which are in turn, a reflection of the nature of the dietary lipid intake. These lipid phase transitions do not appear to correlate directly with those events considered responsible for the altered Arrhenius kinetics of various mitochondrial membrane-associated enzymes.

The influence of water on the phase transition of sheep lung surfactant. A possible mechanism for surfactant phase transitions in vivo

The effect of water on the thermal properties of sheep lung surfactant lipids was determined by differential scanning calorimetry. Dry surfactant exhibited a phase transition with an upper limit of about 54 degrees C, whereas that of the fully hydrated surfactant was about 30 degrees C. The effect of water was confined to a range of hydration values from 0 to 25%. The results indicate that pulmonary surfactant lipids are capable of undergoing both thermotropic and lyotropic mesomorphism in vitro. The degree of hydration of the surfactant could influence its in vivo biophysical role in alveolar dynamics. Indeed, small changes in the surfactant to water ratio induced by regional differences in the surfactant concentration at the alveolar surface during alveolar expansion and contraction could be sufficient to trigger isothermal phase transitions in the surfactant lipids. This would allow changes to occur in the equilibrium between solidus and fluidus surfactant during the respiratory cycle.

Dietary lipid modulation of rat liver mitochondrial succinate: cytochrome c reductase

Diets supplemented with high levels of either saturated fatty acids or unsaturated fatty acids were fed to adult rats for a period of 9 weeks and changes in the liver mitochondrial membrane phospholipid fatty acid composition and thermal behaviour of succinate: cytochrome c reductase were determined. The dietary treatment induced a change in the omega 6 to omega 3 unsaturated fatty acid ratio in the membrane lipids, with the ratio being highest with the unsaturated fatty acid and lowest with the saturated fatty acid diet. Arrhenius plots of succinate: cytochrome c reductase activity exhibited differences in both critical temperature (Tf) and Arrhenius activation energy (Ea) depending on the type of dietary treatment. The Tf was elevated from 23 degrees C in control to 32 degrees C in the saturated fatty acid-supplemented group. No significant effect on the Tf was observed in the unsaturated fatty acid-supplemented group however higher Ea values were observed due to the unsaturated fatty acid diet. The changes in succinate: cytochrome c reductase are probably due to changes in the lipid-protein interactions in the membrane, induced by the dietary lipid supplementation.

Differences in the fatty acid composition of atrial and ventricular phospholipids of rat heart following standard and lipid-supplemented diets

1. The major saturated fatty acids of the phospholipids of rat heart atria and ventricles are similar and are not greatly altered by supplementing the diet with widely different types of lipid. 2. There are important differences in the relative proportions of the major unsaturated fatty acids of the phospholipids of these anatomically and functionally distinct regions of the heart. 3. The proportions of linoleic (C18:2, eta-6) and docosahexaenoic (C22:6, eta-3) acid are significantly higher in the ventricles than in the atria; the proportions of oleic (C18:1, eta-9) arachidonic (C20:4, eta-6) and docosatetraenoic acids (22:4, eta-6) are higher in atria. 4. The differences in unsaturated fatty acid profiles persist even after twelve months of feeding lipid supplements of sunflower seed oil (SSO) or sheep kidney (perirenal) fat (SKF). 5. However, the ratios of arachidonic to docosahexaenoic acid in both tissues are changed by decreasing the intake of linoleic acid, which apparently favours the conversion of dietary linolenic (C18:3, eta-3) to docosahexaenoic acid. The level of docosahexaenoic acid is greater in the ventricles than in the atria, and greatest when the animals were fed SKF diet. 6. The physiological and pharmacological differences in ventricles and atria may arise from differences as fundamental as the phospholipid fatty acid composition of cardiac membranes.

Thermal phase transitions in sheep, rat and rabbit surfactant lipids detected by differential scanning calorimetry

1. The thermal behaviour of sheep, rat and rabbit pulmonary surfactant lipids was investigated using high sensitivity differential scanning calorimetry (DSC). 2. Phase transitions were evident in the surfactant lipids from all three animals, with the upper limit of the phase transition being 30.1 C in the sheep, 36.8 C in the rat and 36.3 C in the rabbit. 3. The relatively greater fluidity of the sheep surfactant lipids in comparison to those of the rat and rabbit was due primarily to differences in their palmitic acid content.