Reduction of blood pressure associated with dietary polyunsaturated fat

Impact of Dietary Lipids on the Reverse Cholesterol Transport: What We Learned from Animal Studies

Reverse cholesterol transport (RCT) is a physiological mechanism protecting cells from an excessive accumulation of cholesterol. When this process begins in vascular macrophages, it acquires antiatherogenic properties, as has been widely demonstrated in animal models. Dietary lipids, despite representing a fundamental source of energy and exerting multiple biological functions, may induce detrimental effects on cardiovascular health. In the present review we summarize the current knowledge on the mechanisms of action of the most relevant classes of dietary lipids, such as fatty acids, sterols and liposoluble vitamins, with effects on different steps of RCT. We also provide a critical analysis of data obtained from experimental models which can serve as a valuable tool to clarify the effects of dietary lipids on cardiovascular disease.

Dietary linoleic acid and human health: Focus on cardiovascular and cardiometabolic effects

This narrative review aims to discuss the more relevant evidence on the role of linoleic acid (LA), a n-6 essential fatty acid that constitutes the predominant proportion of dietary polyunsaturated fatty acids (PUFA), in cardiovascular health. Although LA can be metabolized into Arachidonic Acid (AA), a 20 carbon PUFA which is the precursor of eicosanoids, including some with proinflammatory or prothrombotic-vasoconstrictor action, the large majority of experimental and clinical studies have assessed the potential benefit of increasing dietary intake of LA. Overall, data from clinical studies and meta-analyses suggest an association between high dietary intakes or tissue levels of n-6 PUFA, and specifically LA, and the improvement of cardiovascular risk (mainly of the plasma lipid profile), as well as long-term glycaemic control and insulin resistance. Most observational data show that elevated/increased dietary intake or tissue levels of LA is associated with a reduced incidence of cardiovascular diseases (mainly coronary artery diseases) and of new onset metabolic syndrome or type 2 diabetes. The effects of LA (or n-6 PUFA) in other physio-pathological areas are less clear. High quality clinical trials are needed to assess both the actual amplitude and the underlying mechanisms of the health effects related to dietary intake of this essential fatty acid.

[N-6 fatty acids and cardiovascular health: dietary intake recommendations]

Omega-6 polyunsaturated fatty acids (n-6 PUFA) are well known for their critical role in many physiological functions and reduce risks of cardiovascular disease (CVD). However, some argue that excessive consumption of n-6 PUFA may lead to adverse effects on health and therefore recommend reducing dietary n-6 PUFA intake or fixing an upper limit. Epidemiological studies show that n-6 PUFA dietary intake significantly lowers blood LDL-cholesterol levels. In addition, n-6 PUFA intake lower several cardiovascular risk factors such as blood pressure, inflammatory markers, haemostatic parameters and obesity. Data from prospective cohort and interventional studies converge towards a specific protective role of dietary n-6 PUFA intake, in particular linoleic acid, against CVD. In regards to studies examined in this narrative review, recommendation for n-6 PUFA intake above 5%, and ideally about 10% of total energy appears justified for the prevention of ischemic heart disease.

n-6 Fatty acids and cardiovascular health: a review of the evidence for dietary intake recommendations

n-6 PUFA are well known for their critical role in many physiological functions and seem to reduce risks of CHD. However, some argue that excessive consumption of n-6 PUFA may lead to adverse effects on health and therefore recommend reducing dietary n-6 PUFA intake or fixing an upper limit. In this context, the present work aimed to review evidence on the link between n-6 PUFA and risks of CVD. Epidemiological studies show that n-6 PUFA dietary intake significantly lowers blood LDL-cholesterol levels. In addition, n-6 PUFA intake does not increase several CVD risk factors such as blood pressure, inflammatory markers, haemostatic parameters and obesity. Data from prospective cohort and interventional studies converge towards a specific protective role of dietary n-6 PUFA intake, in particular linoleic acid, against CVD. n-6 PUFA benefits are even increased when SFA intake is also reduced. In regards to studies examined in this narrative review, recommendation for n-6 PUFA intake above 5 %, and ideally about 10 %, of total energy appears justified.

Linoleic acid induces relaxation and hyperpolarization of the pig coronary artery

Linoleic acid, a polyunsaturated C18 fatty acid, is one of the major fatty acids in the coronary arterial wall. Although diets rich in linoleic acid reduce blood pressure and prevent coronary artery disease in both humans and animals, very little is known about its mechanism of action. We believed that its beneficial effects might be mediated by changes in vascular tone. We investigated whether linoleic acid induces relaxation of porcine coronary artery rings and the mechanism involved in this process. Linoleic acid and two of its metabolites, 13-hydroxyoctadecadienoic acid (13-HODE) and 13-hydroperoxyoctadecadienoic acid (13-HPODE), induced dose-dependent relaxation of prostaglandin (PG) F2alpha-precontracted rings that was not affected by indomethacin (10[-5] mol/L), a cyclooxygenase inhibitor, or cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (CDC; 10[-5] mol/L), a lipoxygenase inhibitor. Removal of endothelial cells had no effect on vasorelaxation, suggesting a direct effect on the vascular smooth muscle cells (VSMC). When rings were contracted with KCl, linoleic acid failed to induce relaxation. Although tetrabutylammonium (5 x 10[-3] mol/L), a nonselective K+ channel blocker, slightly inhibited the relaxation caused by linoleic acid, glibenclamide (10[-6] mol/L), an ATP-sensitive K+ channel blocker, and charybdotoxin (7.5x10[-8] mol/L) or tetraethylammonium (5x10[-3] mol/L), two different Ca2+-activated K+ channel blockers, had no effect. However, relaxation was completely blocked by ouabain (5x10[-7] mol/L), a Na+/K+-ATPase inhibitor, or by a K+-free solution. In addition, linoleic acid (10[-6] mol/L) caused sustained hyperpolarization of porcine coronary VSMC (from -49.5+/-2.0 to -60.7+/-4.2 mV), which was also abolished by ouabain. We concluded that linoleic acid induces relaxation and hyperpolarization of porcine coronary VSMC via a mechanism that involves activation of the Na+/K+-ATPase pump.

The effects of omega-3 polyunsaturated fatty acids on blood pressure: a methodologic analysis of the evidence

The potentially beneficial blood pressure (BP)-lowering effects of marine omega-3 polyunsaturated fatty acids (omega-3-PUFAs) remain controversial. The objective of this qualitative and quantitative (meta-analysis) analysis was to evaluate the results of all available randomized controlled trials that studied the effect of omega-3-PUFAs on BP response. A comprehensive search of the English literature from 1970 to 1988 disclosed only six randomized controlled investigations out of 22 published reports. Four of these were evaluable and therefore eligible for this analysis. Of these, only one evaluated hypertensive subjects. In two trials, there were statistically significant reductions in BP; the one reporting an investigation of hypertensive subjects showed the greatest reduction. Using established methodologic criteria, the quality of each report was evaluated by independent observers. Following this appraisal, the outcomes of each investigation were reanalyzed and pooled using a meta-analysis. There was no statistically significant difference between the omega-3-PUFA groups and the control groups, possibly because of failure to include hypertensive subjects in all but one trial. Despite the positive effects in two studies, little scientifically valid evidence is available to demonstrate a significant BP-lowering effect of omega-3-PUFAs. Areas needing more attention in future research are identified and methods to improve study designs are suggested.

Relation between vegetarian/nonvegetarian diets and blood pressure in black and white adults

We examined the possible interaction of race and diet on blood pressure (BP) in volunteer Black Seventh Day Adventists compared to volunteer White church members. Height, weight, waist and hip circumference, and resting seated BP were recorded in Black vegetarians (n = 55; age: 54.7 +/- 16.9 yrs), Black nonvegetarians (n = 59; 56.1 +/- 14.1 yrs), White vegetarians (n = 164; 52.2 +/- 16.7 yrs), and White nonvegetarians (n = 100; 52.6 +/- 15.6 yrs) attending a regional conference. Forty-four percent of the Black nonvegetarians were medicated hypertensives, compared to only 18 percent of the Black vegetarians, 7 percent of the White vegetarians, and 22 percent of the White nonvegetarians. Black vegetarians exhibited lower age and sex-adjusted systolic BP (means = 122.9/74.4 mm Hg) than Black nonvegetarians (means = 132.2/75.9 mm Hg). After further adjusting BP for body mass index and waist/hip ratio, the systolic BP among Black vegetarians remained lower (122.8) than Black nonvegetarians (129.7) but higher than that of the Whites who showed no diet-related BP differences.

The antihypertensive effects of fish oil. A controlled study of polyunsaturated fatty acid supplements in essential hypertension

Both n-3 and n-6 polyunsaturated fats have been suggested to lower blood pressure, an effect ascribed to altered biosynthesis of eicosanoids. To test these hypotheses, we studied blood pressure and eicosanoid production during supplementation of dietary fat for four weeks in 32 men with mild essential hypertension. Supplementation was preceded and followed by four-week run-in and recovery periods. Groups of eight subjects received either 10 ml or 50 ml of fish oil (3 or 15 g of n-3 fatty acids) daily, 50 ml of safflower oil (39 g of n-6 fatty acids), or 50 ml of a mixture of oils that approximated the types of fat present in the American diet. The biosynthesis of eicosanoids was assessed by the measurement of urinary metabolites. Blood pressure decreased in the men who received the high dose of fish oil (systolic pressure by a mean of 6.5 mm Hg [P less than 0.03] and diastolic pressure by 4.4 mm Hg [P less than 0.015]), but not in the other groups. Although the formation of vasodilatory prostacyclins (prostaglandins I2 and I3) increased initially, this increase was not maintained as blood pressure fell. The level of thromboxane A2 metabolites fell; metabolites of thromboxane A3 were detected in the groups receiving fish oil. The formation of prostaglandin E2 increased during supplementation with safflower oil and tended to decrease with fish oil; no prostaglandin E3 metabolite was detected. Our data indicate that high doses of fish oil can reduce blood pressure in men with essential hypertension. However, the clinical usefulness and safety of fish oil in the treatment of hypertension will require further study.

New insights and new approaches for the treatment of essential hypertension: selection of therapy based on coronary heart disease risk factor analysis, hemodynamic profiles, quality of life, and subsets of hypertension

The pharmacologic therapy of mild primary hypertension (diastolic blood pressure less than 105 mm Hg) has effectively reduced hypertensive arteriolar end organ disease such as cerebrovascular accidents, congestive heart failure, and nephropathy, but there has been no convincing evidence that coronary heart disease (CHD) or its complications, acute myocardial infarction or angina, have been reduced. The risks of therapy with certain antihypertensive drugs may outweigh their treatment benefits as it relates to CHD. The optimal treatment strategy should be to reduce all CHD risk factors, reverse the hemodynamic abnormalities present by lowering the systemic vascular resistance (SVR), preserving cardiac output (CO) and perfusion, and to select the best antihypertensive drug for concomitant medical diseases or problems while maintaining a good quality of life. Antihypertensive drugs that have favorable or neutral effects on CHD risk factors include alpha blockers, calcium channel blockers, central alpha agonists, and angiotensin-converting enzyme inhibitors. On the other hand, diuretics and beta blockers without intrinsic sympathomimetic activity have unfavorable effects on many CHD risk factors. Baseline and serial evaluation of the effects of these drugs on serum lipids, lipid subfractions, glucose, uric acid, electrolytes, exercise tolerance, left ventricular hypertrophy, blood pressure, SVR, CO, perfusion, concomitant diseases, and side effects is necessary to evaluate overall cardiovascular risk.

Papillary collecting tubule synthesis of prostaglandin E2 in Dahl rats

Isolated kidneys of Dahl salt-sensitive rats (DS) excrete sodium less readily than those of Dahl salt-resistant rats (DR). The collecting tubule is an important source of papillary prostaglandin E2 and is a site of significant sodium reabsorption. We cultured renal papillary collecting tubule cells from 5-week-old, prehypertensive DS and DR on a low salt diet and also after 14 weeks of high salt feeding, and we measured prostaglandin E2 synthetic capacity. Unstimulated renal papillary collecting tubule cells from 5-week-old DS produced 62 +/- 5% less prostaglandin E2 than did comparable cells from DR (p less than 0.001). The cells from DS also synthesized less prostaglandin E2 after stimulation with the calcium ionophore A23187 (67 +/- 6% of control; p less than 0.001) or the addition of exogenous arachidonate (74 +/- 7% of control; p less than 0.01). Urinary prostaglandin E2 excretion was also diminished in the 5-week-old DS compared with their salt-resistant counterparts (18.1 +/- 1.3 vs 23.9 +/- 1.7 ng/24 hr; p less than 0.025). After high salt feeding, the DS became hypertensive but the DR remained normotensive. Renal papillary collecting tubule cells cultured from these DS continued to produce less prostaglandin E2 than those from control rats, both in the basal state (60 +/- 12% of control; p less than 0.09) and after stimulation with ionophore (62 +/- 2% of control; p less than 0.002). In these older animals, the DS continued to underexcrete prostaglandin E2 compared with the DR (29.7 +/- 3.2 vs 42.2 +/- 6.1 ng/24 hr; p less than 0.08). The underproduction of prostaglandin E2 in the papillary collecting tubule of DS may play a role in their inadequate renal natriuretic capacity and contribute to the onset and maintenance of salt-induced hypertension in this strain.

The effect of dietary polyunsaturated fat on cation transport and hypertension in the rat

1. Essential hypertension is associated with increased intracellular sodium in both erythrocytes and leucocytes. Reports in the literature indicate that increasing the level of polyunsaturated fat in the diet reduces hypertension. In the present study, spontaneously hypertensive rats (Wistar-Kyoto, which develop systolic blood pressures in excess of 140 mmHg by 8 weeks of age) were fed on high-fat diets (40% energy derived from fat), the fat being maize oil (high in polyunsaturated fatty acids, PUFA) and coconut oil (low in PUFA). 2. Significantly higher blood pressures developed by 110 d of age in the rats fed on a high-PUFA diet, compared with those fed on the low-PUFA diet. 3. In thymocytes, ouabain-sensitive efflux rate constants were significantly lower in the group fed on the high-PUFA diet. Ouabain-insensitive efflux rate constants were unaffected by diet.

The relative contribution of body fat and fat pattern to blood pressure level

Although the association between body weight and blood pressure is irrefutable, body fat mass and blood pressure level may not necessarily be directly related. To clarify the relative contribution of fat mass to blood pressure level, we analyzed data on 399 adults consecutively entering a weight control program. Although most subjects were notably overweight (mean ideal body weight 177%), the population represented a wide spectrum of body weights and blood pressure levels. Study parameters included body fat mass (by total body water, 40K, and Steinkamp formula), lean body mass, body build (chest to height ratio), fat cell number and size from bilateral buttock biopsy specimens, upper fat pattern by arm to thigh circumference ratio, and central fat pattern by subscapular to triceps skinfold ratio. Our results concurred with previously noted correlations between obesity and blood pressure (as mean arterial pressure): weight (r = 0.44), percentage of body fat (r = 0.19), and absolute fat mass (r = 0.38; all p less than 0.01); however, lean body mass, age, and body build correlated highly with both fat mass and mean arterial pressure, thereby confounding this relationship. Multivariate analysis was performed to evaluate the relative contribution of fat mass to mean arterial pressure in the presence of these and other potentially confounding variables. Lean body mass, age, body build, and an upper body fat pattern were found to contribute significantly to the variation in mean arterial pressure (p less than 0.01). In their presence, percentage of body fat, absolute fat mass, central fat pattern, fat cell characteristics, and age of onset of obesity did not significantly improve the predictability of mean arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet, blood pressure, and multicollinearity

Recent reports of an inverse association between dietary calcium intake and hypertension stimulated this analysis of the relationship of blood pressure to more than 20 dietary factors among a group of 8000 Japanese men in Hawaii. Reported intakes of potassium, calcium, protein, and milk were all inversely associated with blood pressure levels when examined one at a time while controlling for other risk factors. Alcohol intake was directly associated with blood pressure, and was treated as a confounding variable in the analysis. The association of potassium intake with blood pressure was relatively stronger than the associations for other nutrients, but the intake of potassium was so highly correlated with intakes of calcium, milk, and protein that it was not statistically possible to identify the independent association of potassium and blood pressure. Calcium intake was strongly correlated with milk and potassium intakes, and only calcium from dairy sources was associated with blood pressure. These data thus indicate that several dietary factors are inversely related to blood pressure levels independently of other risk factors such as age, body mass, and alcohol intake. The high degree of intercorrelation (multicollinearity) among these dietary factors, however, indicates that the independent role of any specific nutrient cannot be conclusively separated from the possible effects of other nutrients in this type of study.

Exercise and hypertension

Hypertension is a major risk factor for atherosclerosis. In this article the authors review the use of physical activity as therapy for elevated blood pressure and explore the hemodynamic effects of exercise among patients with treated and untreated hypertension. Recommendations concerning the use of exercise in the management of hypertension are outlined.