Effects of highly purified eicosapentaenoic acid on vascular reactivity to angiotensin II and norepinephrine in the rabbit

Omega-3 fatty acids: a promising possible treatment for Meniere's disease and other inner ear disorders of unknown origin?

A consolidated therapy for "idiopathic" acute disorders of the inner ear, including Meniere's Disease (MD), does not exist despite the long-lasting and widespread attempts: this lack is strictly linked to pathogenic uncertainties. According to the theoretical model that our group developed and tested over the years, a possible cause of labyrinthine damage could be identified in systemic hemodynamic changes followed by an abnormal peripheral vasoconstriction: the latter could be responsible for a more or less prolonged ischemia able to threaten a highly energy-requiring and complicated organ as the inner ear. A possible way to treat MD attacks - as well as other inner ear disorders that possibly share the same origin - according to our model should be addressed to modulate the peripheral circulation and to maintain the balance of ion exchange, acting both on systemic hemodynamics and on cell and organelle membranes. Despite the absence of such a proposal in the English literature, a reliable solution could derive from the supplementation of the intake of a nutritional principle as Omega-3 (omega-3) polyunsaturated fatty acids (PUFAs) that seem to theoretically fulfil all the requirements necessary to achieve a homeostasis of the inner ear.

Omega-3 polyunsaturated fatty acid supplementation reduces hypertension in TGR(mRen-2)27 rats

To establish the effect of dietary omega-3 PUFA on angiotensin II (ANG II)-mediated hypertension, male TGR (mRen-2)27 (Ren-2) rats (animals with high ANG II activity) were maintained on a diet either deficient or sufficient in omega-3 PUFA from conception. Half the animals on each diet were treated with the angiotensin-converting enzyme inhibitor, perindopril, from birth. Ren-2 rats fed the omega-3 PUFA deficient diet were significantly more hypertensive than those fed the omega-3 PUFA sufficient diet. Perindopril reduced the blood pressure of both omega-3 PUFA-deficient and omega-3 PUFA-sufficient diet-fed Ren-2 rats. Body weight, body fat and plasma leptin were reduced by perindopril treatment but not affected by omega-3 PUFA supply. Given that the elevated blood pressure of the Ren-2 rat is mediated by ANG II, the data suggest that omega-3 PUFA may reduce hypertension via the renin-angiotensin system.

Concurrent treatment with an ACE inhibitor may amplify the utility of calcium supplementation for control of hypertension

Although supplemental calcium typically lowers blood pressure in subjects with salt-sensitive, low-renin hypertension - presumably by down-regulating increased production of parathyroid hormone (PTH) and/or parathyroid hypertensive factor (PHF) - its impact on the blood pressure of unselected hypertensive or normotensive subjects, as assessed by meta-analyses, appears to be trivial at best. This suggests that calcium may actually raise blood pressure a bit in some patients with high-renin hypertension, a prediction that is borne out in rodent models of this disorder. There is limited clinical evidence that long-term calcium supplementation tends to raise plasma renin activity; this finding, if valid, could evidently rationalize the equivocal clinical impact of calcium on blood pressure. Salt restriction likewise boosts renin production, and this effect tends to most notable in subjects whose blood pressure fails to decline during low-salt diets. Two clinical groups have demonstrated that salt restriction has a larger and more consistently beneficial impact on the blood pressure of hypertensives when they concurrently are treated with ACE inhibitors - evidently because the physiological impact of the associated rise in renin is blunted. Analogous logic suggests that calcium supplementation may be more beneficial for hypertensives in the context of ACE inhibition or blockade of angiotensin II receptors; this supposition that can readily be tested clinically. The imminent availability of safe nutraceutical ACE inhibitors may make it more feasible for the general public to benefit from these therapeutic/preventive possibilities.

Up-regulation of endothelial nitric oxide activity as a central strategy for prevention of ischemic stroke - just say NO to stroke!

Nitric oxide (NO) produced by the endothelium of cerebral arterioles is an important mediator of endothelium-dependent vasodilation (EDV), and also helps to prevent thrombosis and vascular remodeling. A number of risk factors for ischemic stroke are associated with impaired EDV, and this defect is usually at least partially attributable to a decrease in the production and/or stability of NO. These risk factors include hypertension, high-sodium diets, homocysteine, diabetes, visceral obesity, and aging. Conversely, many measures which may provide protection from ischemic stroke - such as ample dietary intakes of potassium, arginine, fish oil, and selenium - can have a favorable impact on EDV. Protection afforded by exercise training, estrogen replacement, statin drugs, green tea polyphenols, and cruciferous vegetables may reflect increased expression of the endothelial NO synthase. IGF-I activity stimulates endothelial NO production, and conceivably is a mediator of the protection associated with higher-protein diets in Japanese epidemiology and in hypertensive rats. These considerations prompt the conclusion that modulation of NO availability is a crucial determinant of risk for ischemic stroke. Multifactorial strategies for promoting effective cerebrovascular NO activity, complemented by measures that stabilize platelets and moderate blood viscosity, should minimize risk for ischemic stroke and help maintain vigorous cerebral perfusion into ripe old age. The possibility that such measures will also diminish risk for Alzheimer's disease, and slow the normal age-related decline in mental acuity, merits consideration. A limited amount of ecologic epidemiology suggests that both stroke and senile dementia may be extremely rare in cultures still consuming traditional unsalted whole-food diets. Other lines of evidence suggest that promotion of endothelial NO activity may decrease risk for age-related macular degeneration.

Influence of polyunsaturated fatty acids on vasoconstrictions induced by 8-iso-PGF(2alpha) and 8-iso-PGE(2)

8-iso-PGF(2alpha) and 8-iso-PGE(2), which are released in vivo by free radical catalyzed peroxidation of arachidonic acid, are equipotent vasoconstrictors in vivo and in vitro. It is assumed that they exert this effect via activation of the thromboxane A(2) (TP) receptor or a TP-receptor-like isoprostane receptor. Increased levels of 8-iso-PGF(2alpha) have been detected in human cardiovascular diseases. It has been found that polyunsaturated fatty acids (PUFAs) have many beneficial effects in cardiovascular diseases, including antivasoconstrictor actions. Therefore, we investigated the influence of perfusions with eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and dihomo-gamma-linolenic acid (DGLA) at final concentrations of 3 and 30 micromol/l on vasoconstriction induced by 8-iso-PGF(2alpha), 8-iso-PGE(2) and the thromboxane A(2) mimetic U 46619 in the vasculature of the isolated perfused rabbit ear. Additionally, the effect of indomethacin (final concentration 3 micromol/l) on the effects of the PUFAs was investigated. Our results show that the PUFAs at a concentration of 30 micromol/l caused a significant inhibition of the vasoconstrictions induced by 8-iso-PGF(2alpha), 8-iso-PGE(2) and U 46619. Furthermore, it can be assumed that a part of the inhibitory effect of DGLA is due to the effect of a cyclooxygenase product, probably PGE(1), because indomethacin reduced the inhibitory effect of DGLA.

Specificity and mechanism of fatty acid inhibition of aldosterone secretion

We have shown that unesterified, unsaturated long-chain fatty acids inhibit angiotensin II (AII) binding to receptors in adrenal glomerulosa cells. In this report, we show that oleic and arachidonic acids are specific inhibitors of the AT1 subtype of angiotensin receptor, and exert no effect on receptors of the AT2 subtype. By contrast, decanoic acid is a weak inhibitor of the AT2 subtype only. Our previous work on a post-receptor locus of inhibition by fatty acids of aldosterone biosynthesis showed that the 18-oxidase step is uniquely sensitive. In brief, the first and last steps involved in angiotensin-stimulated aldosterone secretion are particularly sensitive to inhibition by fatty acids. These results suggest a specific role for unesterified fatty acids in regulation of salt and water metabolism.

Dietary fats, fish, and blood pressure

In humans any effects of dietary saturated fats or omega-6 polyunsaturates on blood pressure appear to be mediated by changes in caloric intake and long-term weight changes. In contrast, omega-3 fatty acids have a mild antihypertensive effect which is seen most clearly in untreated subjects with higher blood pressures, in older people, and during sodium restriction. The mechanism may be due to a combination of effects consequent to incorporation of omega-3 fatty acids into vascular phospholipids, leading to reduced formation of endothelial contractile substances in larger vessels and impairment of sympathetic neuroeffector and other vasoconstrictor mechanisms in resistance vessels.

Fatty acids may regulate aldosterone secretion and mediate some of insulin's effects on blood pressure

Experiments in vitro and observation made in humans suggest that some unesterified fatty acids (FA) participate, as inhibitors, in the regulation of aldosterone secretion. Removal of FA from adrenal glomerulosa cells with albumin increases the responses to angiotensin II (AII) and dibutyryl cyclic AMP. Micromolar concentrations of some FA including arachidonic, oleic, linoleic, eicosapentaenoic, and docosahexaenoic inhibit aldosterone secretion by adrenal glomerulosa cells. Inhibition is specific--some acids like stearic are inactive, and the adrenal fasciculata is relatively resistant to inhibition. Oleic acid rapidly and reversibly inhibits aldosterone secretion by perfused dog adrenals. Observations in vivo suggest a reciprocal relationship between plasma levels of FA and aldosterone: insulin infusion into dogs lowers plasma FA and increases adrenal responsiveness to All; salt infusions into humans increase plasma FA as aldosterone falls; plasma FA are low in low-renin essential hypertension where adrenal responsiveness to All is high; plasma FA are inversely correlated with ratios of aldosterone to renin in black hypertensives; and plasma FA are high in some seriously ill patients whose aldosterone levels are inexplicably low. All receptors and the final step of aldosterone biosynthesis, oxidation at the 18 position, are the adrenal sites most sensitive to FA. Insulin's antinatriuresis may be mediated in part by its ability to lower plasma FA and thereby enhance adrenal response to secretagogues.

Effect of omega-3 fatty acids on the vascular response to angiotensin in normotensive men

There is a widespread interest in fish oil as a dietary supplement and possible nonpharmacologic adjunct in the treatment of hypertension. The effect of dietary fish oil on blood pressure is controversial and the effect on systemic hemodynamics and regional vascular reactivity in humans is unknown. To address these questions, a double-blind, placebo-controlled, crossover study on the effect of dietary fish oil substitution was performed during a carefully controlled diet in 8 normotensive men. Systemic hemodynamics and the forearm vascular response to intrabrachial artery infusions of norepinephrine, phentolamine and angiotensin II were obtained. Compared with a safflower oil placebo, dietary fish oil had no effect on cardiac output (6.42 +/- 0.38 vs 6.87 +/- 0.28 liters/min, p = not significant) or 24-hour blood pressure (122/68 +/- 3/3 vs 122/68 +/- 3/2 mm Hg, p = not significant). The vascular response to norepinephrine and phentolamine was unchanged. Fish oil, however, significantly (p < 0.05) reduced forearm vascular resistance responses to angiotensin II. These changes were associated with a reduction in plasma triglycerides (64 +/- 9 vs 39 +/- 4 mg/dl, p = 0.02) and an increase in plasma eicosapentaenoic acid levels (0.51 +/- 0.25 vs 1.72 +/- 0.35 microM, p < 0.05). Substitution of a moderate dose of fish oil for fat in a "Western diet" selectively attenuates the vascular response to angiotensin independently of changes in alpha-adrenergic vasoconstriction or systemic hemodynamics.

Blood pressure in spontaneously hypertensive rats fed butterfat, corn oil, or fish oil

Dietary fats have been shown to influence blood pressure in humans and animal models of hypertension. The ability of a particular fat to modulate arterial pressure appears to depend on its fatty acid profile rather than its degree of saturation or unsaturation. Little is known about the effects of specific dietary fats of animal origin on blood pressure. We tested the concurrent effects of both calcium and dietary fat on blood pressure development in the spontaneously hypertensive rat. Sixty animals were fed diets containing butterfat, fish oil, or corn oil from 3-26 weeks of age. Each diet among the three oils was further modified to contain either 0.25% or 2.0% of the diet as calcium. All six diets provided 18% of the diet (36% of the calories) as fat. The polyunsaturated-to-saturated fat ratio was 0.07, 0.84, and 4.54 for butterfat, fish oil, and corn oil, respectively. Fish oil consumption resulted in lower blood pressures compared with butterfat (p less than 0.036) or corn oil (p less than 0.0009). Similarly, butterfat feeding resulted in lower blood pressures when compared with corn oil (p less than 0.054). Supplementing the diet with calcium decreased blood pressure in both the butterfat and corn oil diets. When butterfat diets were supplemented with calcium, the resulting blood pressures did not differ significantly from those obtained with the two fish oil diets. It is concluded that butterfat, though highly saturated, is associated with less of an increase in the spontaneously hypertensive rat's blood pressure than is corn oil, which is highly unsaturated.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of eicosapentaenoic acid ethyl ester on proteinuria of streptozotocin-induced diabetes mellitus in rats

Streptozotocin (45 mg/kg) was intravenously administered to 7-week-old Wistar rats through their tail veins. After 11 days, the rats were divided into two groups. One group was fed a lipid-free diet (90%, w/w) plus lard (8%) and safflower oil (2%) for four weeks (Diet 1 group, n = 12). The other group was fed in the same way, except that safflower oil was replaced by 90% pure eicosapentaenoic acid (EPA) ethyl ester (Diet 2 group, n = 13). Twenty-four-hour urine was collected just before the diets started and during the experiment at 7-day intervals. In the second and third week, the levels of proteinuria were significantly lower in the Diet 2 group than they were in the Diet 1 group. There was no significant difference in the levels of creatinine, urea nitrogen, or lipids in plasma or in body weights between the two groups after four weeks on the diets. Because Diet 2 reduced proteinuria of diabetic rats compared to Diet 1, an EPA-rich diet may retard the development of diabetic nephropathy.

Eicosapentaenoic acid alters vascular reactivity and platelet adhesion in Watanabe heritable hyperlipidemic rabbits

Feeding a diet rich in eicosapentaenoic acid (EPA) to Watanabe heritable hyperlipidemic (WHHL) rabbits resulted in an attenuated aortic contractile response to the vasoconstrictor agent serotonin when compared to responses from WHHL rabbits fed normal rabbit chow. In contrast, only the maximal contractile response to norepinephrine was reduced in EPA-fed rabbit aortas. Additionally, methacholine-induced relaxations were potentiated in aortas obtained from the EPA-fed rabbits. When platelets obtained from EPA-fed rabbits were incubated with arachidonic acid, there was a reduced ability of the platelets to adhere to albumin-coated discs in comparison to control rabbit platelets. These data indicate a potentially beneficial effect of EPA in atherosclerotic WHHL rabbits.

Absorption and transport of fat in mammals with emphasis on n-3 polyunsaturated fatty acids

The current state of knowledge concerning the absorption and transport of dietary fat with emphasis on long-chain polyunsaturated n-3 fatty acids in mammals is reviewed. It is apparent that long-chain polyunsaturated n-3 fatty acids, either as free acids or as part of triglycerides, are readily absorbed in the gut and transported by the circulatory system. Indeed, it would appear that long-chain polyunsaturated n-3 fatty acids are digested, absorbed and transported similarly to other long-chain fatty acids with only minor variations, although there is much that is still not understood about these processes. The main unresolved issues in the area of the absorption and transport of long-chain polyunsaturated n-3 fatty acids appear to be: 1) If they, when located in the 2-position of triglycerides, have unique metabolic pathways; and 2) whether the unnatural forms, i.e., methyl or ethyl ester derivatives, are suitable vehicles for administration as dietary supplements. The effect in man of dietary, long-chain polyunsaturated n-3 fatty acids on blood serum lipid and lipoprotein levels, particularly the low density lipoproteins, remains controversial, except for the well-documented reduction in serum triglyceride levels. Also, there is uncertainty regarding their distribution and metabolism in tissues. Finally, if the consumption of long-chain polyunsaturated n-3 fatty acids has beneficial health consequences, what is the appropriate therapeutic dose? In view of these important, unresolved issues and uncertainties, it would seem prudent to direct additional research toward a better understanding of the overall process by which fat is digested, absorbed and transported.