Release of fatty acids by perfused vascular tissue in normotensive and hypertensive rats

Effect of omega-3 fatty acid-containing phospholipids on blood catecholamine concentrations in healthy volunteers: a randomized, placebo-controlled, double-blind trial

OBJECTIVE

We previously reported that administration of fish oil rich in docosahexaenoic acid (DHA) increased the plasma ratio of epinephrine to norepinephrine (NE) at rest in young adults who were under chronic stress and that this effect was achieved mainly through depression of NE. However, not many reports have documented the effects of eicosapentaenoic acid (EPA) and DHA on blood catecholamine levels in healthy humans. Therefore, we performed another intervention study to test their effect on catecholamines with healthy subjects under no chronic stress.

METHODS

Twenty-one healthy young adults (15 men and 6 women) were randomly assigned to an omega-3 group (n = 9) or a control group (n = 12) in a double-blind manner. Twenty capsules of shellfish-derived lipids containing 762 mg of EPA plus DHA per day were administered to the omega-3 group for 2 mo. The controls took the same amount of placebo capsules. Fasting blood samples after a 30-min rest with a catheter in a forearm vein were obtained at the start and the end of the study for catecholamine measurements.

RESULTS

EPA but not DHA concentrations in red blood cells significantly increased in the omega-3 group compared with the control group (P < 0.001). Plasma NE concentrations were significantly decreased in the omega-3 group (from 1.49 +/- 0.39 nmol/L to 1.05 +/- 0.14 nmol/L) compared with the control group (from 1.12 +/- 0.24 nmol/L to 1.39 +/- 0.32 nmol/L) with analysis of covariance (P < 0.001). The differences remained significant (P = 0.01) even after deletion of three subjects in the omega-3 group who had the highest baseline NE values and one in the control group who had the lowest baseline NE value to nullify a significant baseline differences in NE between groups.

CONCLUSION

This study demonstrated that EPA plus DHA supplementation lowered plasma NE concentrations in normal volunteers even at the small dose of 762 mg of EPA plus DHA per day. This effect of EPA plus DHA to lower plasma NE concentrations may be important to understand some of the effects of fish oils on diseases.

Effects of docosahexaenoic acid on vascular pathology and reactivity in hypertension

Previous studies have shown that docosahexaenoic acid (DHA) has an antihypertensive effect in spontaneously hypertensive rats (SHR). To investigate possible mechanisms for this effect, vascular pathology and reactivity were determined in SHR treated with dietary DHA. SHR (7 weeks) were fed a purified diet with either a combination of corn/soybean oils or a DHA-enriched oil for 6 weeks. Histological evaluation of heart tissue, aorta, coronary, and renal arteries was performed. Vascular responses were determined in isolated aortic rings. Contractile responses to agonists, including norepinephrine (10(-9) to 10(-4) M), potassium chloride (5-55 mM), and angiotensin II (5 x 10(-7) M) were assessed. Vasorelaxant responses to acetylcholine (10(-9) to 10 (-4) M), sodium nitroprusside (10(-9) to 10(-6) M), papaverine (10(-5) to 10(-4) M), and methoxyverapamil (D600, 1-100 microM) were determined. DHA-fed SHR had significantly reduced blood pressure (P < 0.001) and vascular wall thicknesses in the coronary, thoracic, and abdominal aorta compared with controls (P < 0.05) Contractile responses to agonists mediated by receptor stimulation and potassium depolarization were not altered in DHA-fed SHR. Endothelial-dependent relaxations to acetylcholine were not altered which suggests endothelial-derived nitric oxide production/release is not affected by dietary DHA. Other mechanisms of vascular relaxation, including intracellular cyclic nucleotides, cGMP, and cAMP were not altered by dietary DHA because aortic relaxant responses to sodium nitroprusside and papaverine were similar in control and DHA-fed SHR. No significant differences were seen in relaxant responses to the calcium channel blocker, D600, or contractile responses to norepinephrine in the absence of extracellular calcium. These results suggest that dietary DHA does not affect mechanisms related to extracellular calcium channels or intracellular calcium mobilization. Moreover, the contractile and vasorelaxant responses are not differentially altered with dietary DHA in this in vivo SHR model. The findings demonstrate that dietary DHA reduces systolic blood pressure and vascular wall thickness in SHR. This may contribute to decrease arterial stiffness and pulse pressure, in addition to the antihypertensive properties of DHA. The antihypertensive properties of DHA are not related to alterations in vascular responses.

Docosahexaenoic acid--induced vasorelaxation in hypertensive rats: mechanisms of action

The authors investigated the vasorelaxant properties of the omega-3 fatty acid, docosahexaenoic (DHA, 22:6n-3), and the possible involvement of endothelium-derived nitric oxide, prostanoids, opening of K+ channels, and/or modulation of calcium-mediated events. Isolated aorta from male spontaneously hypertensive rats (SHR) (age 16-17 weeks) were used to measure isometric tension. DHA-induced (1-100 mumol/l) relaxation was examined following contraction to norepinephrine (NE) (10(-6) mol/l) or high-K+ (80 mmol/l) solution in the presence and absence of various inhibitors and calcium-containing solution. DHA acid induced a significant vasorelaxant effect in both NE and high-K(+)-induced contracted SHR aortic rings, although DHA relaxations were greater in high-K(+)-induced contracted rings. In the absence of extracellular calcium, DHA (5-30 mumol/l) inhibited the initial phasic and sustained components of NE-induced contraction under different conditions. Inhibition of nitric oxide synthesis by N omega-nitro-L-arginine methyl ester hydrochloride (100 mumol/l) had no effect on DHA relaxations; however, indomethacin or nifedipine caused significant inhibition at > or = 30 mumol/l DHA. The K+ channel blocker, glibenclamide, but not tetraethyl-ammonium, also had an inhibitory effect on DHA-induced relaxation. These results indicate that DHA's vasorelaxant actions in SHR aorta are independent of endothelium-derived nitric oxide; however, at DHA concentrations > or = 30 mumol/l, vasodilatory prostanoids that activate ATP-sensitive K+ channels (KATP) may be involved. At lower concentrations, DHA-induced relaxation appears to be attributed to modulation of intracellular Ca2+ release and L-type Ca2+ channels in vascular smooth muscle cells. The vasorelaxant properties of DHA may contribute, in part, to the blood pressure-lowering effect of dietary fish oil in this hypertensive model.

Depression and bipolar disorder: relationships to impaired fatty acid and phospholipid metabolism and to diabetes, cardiovascular disease, immunological abnormalities, cancer, ageing and osteoporosis. Possible candidate genes

Depression and bipolar disorder are two of the commonest illnesses in the developed world. While some patients can be treated effectively with available drugs, many do not respond, especially in the depression related to bipolar disorder. Depression is associated with diabetes, cardiovascular disease, immunological abnormalities, multiple sclerosis, cancer, osteoporosis and ageing: in each case depressed individuals have a worse outcome than non-depressed individuals. In all of these conditions there is now evidence of impaired phospholipid metabolism and impaired fatty acid-related signal transduction processes. Impaired fatty acid and phospholipid metabolism may be a primary cause of depression in many patients and may explain the interactions with other diseases. Several novel gene candidates for involvement in depression and bipolar disorder are proposed.

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

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

Calcium metabolism, osteoporosis and essential fatty acids: a review

Essential fatty acid (EFA)-deficient animals develop severe osteoporosis coupled with increased renal and arterial calcification. This picture is similar to that seen in osteoporosis in the elderly, where the loss of bone calcium is associated with ectopic calcification of other tissues, particularly the arteries and the kidneys. Recent mortality studies indicate that the ectopic calcification may be considerably more dangerous than the osteoporosis itself, since the great majority of excess deaths in women with osteoporosis are vascular and unrelated to fractures or other bone abnormalities. EFAs have now been shown to increase calcium absorption from the gut, in part by enhancing the effects of vitamin D, to reduce urinary excretion of calcium, to increase calcium deposition in bone and improve bone strength and to enhance the synthesis of bone collagen. These desirable actions are associated with reduced ectopic calcification. The interaction between EFA and calcium metabolism deserves further investigation since it may offer novel approaches to osteoporosis and also to the ectopic calcification associated with osteoporosis which seems to be responsible for so many deaths.

The cardiovascular protective role of docosahexaenoic acid

Dietary fish oils rich in n-3 polyunsaturated fatty acids can modulate a diverse range of factors contributing to cardiovascular disease. This study examined the relative roles of eicosapentaenoic acid (20:5 n-3; EPA) and docosahexaenoic acid (22:6 n-3; DHA) which are the principal n-3 polyunsaturated fatty acids regarded as candidates for cardioprotective actions. At low dietary intakes (0.4-1.1% of energy (%en)), docosahexaenoic acid but not eicosapentaenoic acid inhibited ischaemia-induced cardiac arrhythmias. At intakes of 3.9-10.0%en, docosahexaenoic acid was more effective than eicosapentaenoic acid at retarding hypertension development in spontaneously hypertensive rats (SHR) and inhibiting thromboxane-like vasoconstrictor responses in aortas from SHR. In stroke-prone SHR with established hypertension, docosahexaenoic acid (3.9-10.0%en) retarded the development of salt-loading induced proteinuria but eicosapentaenoic acid alone was ineffective. The results demonstrate that purified n-3 polyunsaturated fatty acids mimic the cardiovascular actions of fish oils and imply that docosahexaenoic acid may be the principal active component conferring cardiovascular protection.

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.

High fish oil diet increases oxidative stress potential in mammary gland of spontaneously hypertensive rats

1. The purpose of this study was to determine whether high omega-3 (19% menhaden oil, 1% corn oil) or high omega-6 (20% corn oil) fatty acid diets would decrease expression of hypertension in the female spontaneously hypertensive rat (SHR), promote tumourigenesis in the rat 7,12-dimethylbenz[a]anthracene (DMBA) model of mammary cancer or increase the susceptibility of the mammary gland to lipid peroxidation. A group of rats on a 5% corn oil diet served as the low fat control group. 2. We found that the high omega-3 and high omega-6 fatty acid diets did not significantly decrease mean arterial pressure. Marked differences occurred between the effects of omega-3 and omega-6 high fatty acid diets on baseline oxidation, auto-oxidation and iron-ascorbate catalyzed oxidation. The omega-3 diet showed 675% increase in basal oxidation, a 2624% increase in auto-oxidation and a 4244% increase in iron-ascorbate catalyzed oxidation compared to the omega-6 diet in mammary tissue homogenates. Although all rats were given 5 mg DMBA (i.g.), no mammary tumours were observed in any of the dietary groups. 3. We conclude that: (i) high polyunsaturated fatty acid diets do not decrease blood pressure in the female SHR; (ii) high fish oil diet markedly increases oxidative potential in the mammary gland; and (iii) the female SHR is resistant to DMBA-induced tumourigenesis.

Dietary fish oil administration retards blood pressure development and influences vascular properties in the spontaneously hypertensive rat (SHR) but not in the stroke prone-spontaneously hypertensive rat (SHR-SP)

In the present study, we compared the blood pressure in the SHR-SP and in the spontaneously hypertensive rat (SHR) after dietary administration of fish oil from 4 to 17 weeks of age. The retarding influence of dietary fish oils on the development of hypertension was prominent in the SHR (26 mmHg) and not evident in the SHR-SP (8 mmHg). The enhanced development of blood pressure in both the SHR and the SHR-SP is characterised by an elevated maximum contraction in the mesenteric vascular bed to sympathetic nerve stimulation and to injected noradrenaline. In SHR, but not SHR-SP, this maximum contraction was significantly attenuated by dietary fish oil. Likewise, acetylcholine mediated relaxation of the isolated aorta was enhanced in preparations from the SHR but not the SHR-SP. These physiological changes were also associated with a change in the total n-3 polyunsaturated fatty acids (PUFAs) content in vascular tissue, which were inversely proportional to the prevailing blood pressure values seen in all three strains of rat receiving dietary fish oils. Platelet activated thromboxane production was equally depressed in WKY (Wistar Kyoto), SHR and SHR-SP rats. The results indicate that the blood pressure lowering effect of fish oil when administered during the period of development of hypertension is much greater in the SHR than it is in the SHR-SP. Furthermore the lowering of blood pressure by fish oil administration is related to a restoration of normal vascular contraction and normal vascular relaxation, but not related to a suppression of serum thromboxane production.

Comparative study of diets enriched with evening primrose, black currant, borage or fungal oils on blood pressure and pressor responses in spontaneously hypertensive rats

The effects of oils enriched with gamma-linolenic acid (GLA) on blood pressure and pressor responses were examined in spontaneously hypertensive rats (SHR). Rats were fed purified diets containing evening primrose (EPO), black currant (BCO), borage (BOR) or fungal (FGO) oils for 7 weeks. Significant reductions in blood pressure were obtained in SHR rats maintained on diets enriched with GLA oils. The antihypertensive effect was not associated with enhanced pressor responsiveness to norepinephrine or angiotensin II. Moreover, no differences were found in blood pressure responses to the calcium channel blocker, verapamil. The results suggest that GLA-enriched oils inhibit the development of hypertension in the SHR rat. The blood pressure lowering effect is not mediated by altered pressor responses to vasoconstrictor hormones or intracellular calcium mechanisms.

Blood pressure reduction by fish oil in adult rats with established hypertension--dependence on sodium intake

The effects of fish oil combined with dietary sodium restriction on blood pressure and mesenteric vascular resistance were examined in a series of experiments with adult normotensive (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Rats were fed normal or low sodium diets containing fish oil, olive oil or safflower oil. Small but significant reductions of blood pressure (measured directly in conscious rats) were seen in SHRSP but not in WKY after 8 weeks on a fish oil/low sodium diet, compared with rats fed olive or safflower oil diets with normal sodium content. This antihypertensive effect was not dependent on neurally mediated vasoconstriction but was associated with a reduction of basal resistance in the blood-perfused mesenteric artery. Subcutaneous injection of fish oil reduced blood pressure in adult SHRSP on a normal sodium diet. However, there was a further fall in blood pressure when sodium intake was reduced. The results indicate the antihypertensive effect of fish oil can be enhanced by restricting sodium intake.