-Work in progress- hypotensive effect of dietary proglandin precursor in hypertensive man

Dietary factors and hypertension

There is increasing evidence that nutritional factors are critical in the pathogenesis of essential hypertension typical for acculturated societies. These factors include sodium, potassium, calcium, alcohol, and type and level of fat in the diet. More research is needed, however, before the role of various nutrients in the prevention and treatment of hypertension will be ascertained.

Influence of dietary fats upon systolic blood pressure in the rat

Studies were performed to determine whether feeding diets with differing fatty acid content and composition had an influence on systolic blood pressure in the rat. Weanling male rats were fed standard laboratory chow (2.9% fat in total), or synthetic diets (10% fat in total) containing fish oil, butter, coconut oil or corn oil, for 5 weeks. Coconut oil and butter diets were rich in saturated fatty acids, whilst fish oil and corn oil were rich in the n-3 and n-6 unsaturated fatty acids respectively. Systolic blood pressure was measured using an indirect tail-cuff method at the end of the feeding period, and compared to a group of weanling rats. Feeding the different diets did not alter the growth of the rats, so all animals were of similar weights at the time of blood pressure determination. Control (chow fed) animals, at nine weeks of age, had higher systolic blood pressures than the weanling, baseline control group. Fish oil fed rats had similar pressures to the chow fed rats. Corn oil fed rats had significantly lower systolic pressures than the controls. The rats led the diets rich in saturated fatty acids (butter and coconut oil) had significantly higher blood pressures than all other groups. Systolic blood pressure was found to be significantly related to the dietary intakes of saturated and unsaturated fatty acids. The dietary intake of linoleic acid was significantly higher in corn oil fed rats than in other groups. Systolic blood pressure was inversely related to linoleic acid intake. Feeding a diet rich in saturated fatty acids significantly increases blood pressure in the rat. A high intake of n-6 fatty acids, and in particular linoleic acid, appears to have a hypotensive effect. Prenatal exposure of the rats to a maternal low protein diet, abolished the hypertensive effects of the coconut oil diet and the hypotensive effect of the corn oil diet upon young adult females. The intrauterine environment may, therefore, be an important determinant of the effects of these fatty acids on blood pressure in later life.

Dietary fat and blood pressure

Both animal and human data suggest that polyunsaturated fatty acids of n-6 and n-3 series may play a role in blood pressure regulation. The majority of dietary intervention studies have shown that changing from a high fat, low linoleic acid diet to a low fat, high linoleic acid diet lowers blood pressure. However, controlled, double-bind studies do not support the independent effect of linoleic acid. Polyunsaturated n-3 fish fatty acids lower blood pressure but only in pharmacological doses that cannot generally be recommended. The mechanisms of blood pressure regulation by n-6 and n-3 fatty acids seem to be related to prostaglandin metabolism.

Childhood prevention of essential hypertension

Childhood prevention of essential hypertension requires knowledge of alterable determinants of blood pressure in children; these include obesity and sodium intake and perhaps physical activity and intake of potassium and calcium. Altering these determinants may involve two general preventive strategies. The first is a population strategy, which attempts to lower blood pressure (or keep it from rising) among all children. Population strategies may require educating children to active participants in changing their behaviors (active approach) or may merely change their environment (passive approach). The second general strategy aims to focus on children at high risk of developing hypertension as adults. To determine the usefulness of this high-risk strategy, more information is needed about prediction of adult blood pressure from childhood values and about the efficacy of interventions to control blood pressure levels in high-risk children.

Dietary linoleic acid prevents the development of deoxycorticosterone acetate-salt hypertension

The aim of this study was to elucidate the effect of dietary variations of linoleic acid on the development of deoxycorticosterone acetate (DOCA)-salt hypertension in rats. All rats were divided into three groups and fed one of the following isocaloric diets with 8% NaCl: a high linoleic acid (HLA) (20% sunflower oil), a moderate linoleic acid (5% lard oil + 15% sunflower oil), or a low linoleic acid (DLA) (20% lard oil). After 4 weeks of feeding, we determined intraerythrocyte sodium, potassium, and magnesium concentrations, intra-aortic and lymphocyte magnesium content, and erythrocyte ouabain-sensitive 22Na efflux rate constant. Cytoplasmic free calcium concentration of lymphocytes from thymus was also determined with quin-2 as a fluorescent indicator. In the HLA group, the elevation of systolic blood pressure was significantly attenuated, and intraerythrocyte sodium concentration was significantly lower than in the DLA group. There were greater intraerythrocyte potassium and magnesium concentrations, intra-aortic and lymphocyte magnesium contents, and erythrocyte ouabain-sensitive 22Na efflux rate constant in the HLA group as compared with other groups. Cytoplasmic free calcium concentration in the HLA group was significantly lower than in other groups. Systolic blood pressure significantly correlated negatively with intraerythrocyte and intra-aortic magnesium concentrations and intraerythrocyte potassium concentration, and correlated positively with cytoplasmic free calcium concentration. Erythrocyte ouabain-sensitive 22Na efflux rate constant significantly correlated positively with intraerythrocyte magnesium concentration. These findings suggest that dietary linoleic acid can attenuate the development of DOCA-salt hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

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

The release of fatty acids from perfused mesenteries of spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY) was studied. The release of the prostaglandin precursors dihomogammalinolenic acid, arachidonic acid, and eicosapentaenoic acid was reduced in SHR when compared with age-matched WKY. The release of all other fatty acids detected in the effluent was also reduced. The differences in fatty acid release were evident even when tissue levels of the fatty acids were similar or higher in SHR than in controls. The addition of evening primrose oil and fish oil into the diet partially corrected these defects. Evening primrose oil and fish oil both attenuated increases in blood pressure, but fish oil was more potent than primrose oil. Although both diets reduced vascular reactivity, primrose oil was more effective with lower doses of norepinephrine whereas fish oil blunted the effects of both low and high doses of norepinephrine. The possible mechanisms for the effects of primrose oil and fish oil on vascular reactivity are briefly discussed.

Effect of dietary fats and carbohydrate on blood pressure of mildly hypertensive patients

The effect on blood pressure (BP) of replacing dietary saturated fat with either polyunsaturated fat (linoleic acid) or carbohydrate was studied in 21 untreated mildly hypertensive patients. In a randomized, double-blind, crossover protocol, all subjects received dietary supplements of cream, safflower oil, and carbohydrate in random sequence, each prepared in flavored yogurt or milk. Each supplement was administered for 6 weeks and followed by a 4-week washout period of no supplementation. Dietary linoleic acid increased from 4.6 to 13% of energy intake when the safflower oil replaced cream, while saturated fat decreased from 16 to 10%. Total fat intake was 37 to 38% during the cream and safflower oil periods but was 28% during the carbohydrate period. Compliance with the diets was demonstrated by significant changes in fasting plasma fatty acid measurements. Mean clinic BP was 135 +/- 9/93 +/- 6 mm Hg at baseline. There were no significant differences in BP measured in the clinic or at home among the three dietary periods. The protocol had more than 80% power to detect a mean effect of diet of 3 mm Hg systolic or 2 mm Hg diastolic BP. Therefore, replacing dietary saturated fat with carbohydrate or with linoleic acid does not affect BP in subjects with mild hypertension.

Effect of linoleic and oleic acids on blood pressure, blood viscosity, and erythrocyte cation transport

It has been proposed that dietary linoleic acid lowers blood pressure (BP) by being converted to arachidonic acid and prostanoids of the two-ene series. We tested the effects of linoleic acid on plasma arachidonic acid, blood pressure, blood viscosity, and RBC cation transport. Oleic acid, the major dietary monounsaturated fat and which is not a prostanoid precursor, was used as a control. Seventeen adults consumed 23 g/d of linoleic acid or oleic acid provided by genetic variants of safflower seed, each for 4 weeks in a double-blind crossover design. Linoleic and oleic acids were enriched significantly in the plasma cholesteryl esters, phospholipids and triglycerides during the respective periods of supplementation but there was no increase in arachidonate. Mean BP was 116.1/76.8 during ingestion of oleic and 113.6/74.6 during ingestion of linoleic acid (p = 0.09 systolic, p = 0.12 diastolic). The power of the study was over 75% for detecting a significant (p less than 0.05) effect of 4 mm Hg in systolic BP or diastolic BP. Whole blood and plasma viscosity, and RBC Li/Na countertransport, Na/K cotransport, and Na pump systems (Vmax) were unchanged during the protocol. Therefore, variations in dietary linoleic or oleic acids are unlikely to have major effects on BP or on several membrane-dependent erythrocyte functions related to hypertension.

Comparative study of the blood pressure effects of four different vegetable fats on young, spontaneously hypertensive rats

Following the suckling period, four groups of male four-week-old spontaneously hypertensive rats (SHR) were fed semisynthetic diets with 14% (by weight) of either sunflower seed oil [46% 18:2(n-6); linoleic acid (LA)-rich], linseed oil [62.5% 18:3(n-3) + 12.9% 18:2(n-6); alpha-linolenic acid (LNA)-rich], evening primrose oil [9.2% 18:3(n-6) + 71% 18:2(n-6); gamma-linolenic acid (LNA)-rich] or hydrogenated palm kernel fat [1.5% 18:2(n-6); polyunsaturated fatty acid (PUFA)-deficient], respectively, up to an age of 18 wk. All diets enriched with PUFA provoked an attenuation of hypertension development. The effect was lowest in the LA-rich group and highest in the gamma-LNA-rich group. Differences in fatty acid composition of renal phospholipids between groups reflect the fatty acids present in the respective dietary fats. Renomedullary production of PGF2 alpha was significantly reduced in alpha-LNA-rich and slightly diminished in gamma-LNA-rich fed rats. Aortic formation of 6-keto-PGF1 alpha and TXB2 was increased in animals fed the gamma-LNA-rich diet. Thus, the attenuation of hypertension development cannot be explained only by changes in prostanoid formation. Other mechanisms possibly involved should be pursued.

Slow desaturation and elongation of linoleic and alpha-linolenic acids as a rationale of eicosapentaenoic acid-rich diet to lower blood pressure and serum lipids in normal, hypertensive and hyperlipemic subjects

In normal, hypertensive and hyperlipemic subjects, diets supplemented with linoleic acid (LA) or alpha-linolenic acid (LNA) resulted in an increase of the corresponding fatty acids in serum lipids. However, their C20-derivatives, the prostaglandin precursors arachidonic acid (AA) and eicosapentaenoic acid (EPA), respectively, were not or only slightly augmented. On the other hand, an EPA-rich diet produced a marked increase of this fatty acid, especially in cholesterol esters. After this diet the decreases of blood pressure and serum lipids were more pronounced when compared with LA- and LNA-rich diets containing a 20-fold higher dose of the polyunsaturated fatty acids. The slow formation of AA and EPA from LA and LNA seems to be a characteristic finding in humans, being different from preferred laboratory animals, for instance, rats. This observation was independent of the presence of risk factors, like arterial hypertension or hyperlipoproteinemia (HLP).

Cardiovascular actions of dietary polyunsaturates and related mechanisms. A state-of-the-art-review

A survey of the effects of dietary polyunsaturates on the function of the cardiovascular system is given. In isolated hearts of rats dietary linoleate supply increases both coronary flow and heart muscle function. Hearts of rats fed high amounts of linoleic acid are protected against catecholamine (over)-stimulation. Polyunsaturate rich vegetable oils are effective in lowering blood pressure in several murine hypertension models. This effect seems to be closely related to antihypertensive changes in kidney function and in the function of the arterial vessel wall. Dietary polyunsaturates augment the hypotensive effect of antihypertensive drugs. Cardiovascular effects of dietary polyunsaturates are at least partly mediated via changes in the prostanoid metabolism as well as a reduction of the sympathetic activity. Evidence has been accumulated that cardiovascular effects of dietary polyunsaturates in animal and man are comparable. The observed effects are discussed against the background of a reduced risk of cardiovascular disease after a polyunsaturate rich diet in man.

Self-selected vs. controlled diet as a baseline for human studies: effects of nutrient intakes on blood pressure and on constituents of blood and urine

This study demonstrates that a three-week stabilization period, in which all subjects eat an identical diet, produced a more uniform but different baseline of metabolic parameters than the subject's self-selected or "habitual" diets. Subjects required more food energy to maintain initial body weights during the stabilization period than when they ate their reported self-selected diets; average intakes of almost all nutrients were higher from the stabilization than from the self-selected diet. The switch to the stabilization diet produced small but significant reductions in blood pressure, in some serum enzymes, urine volume, and sodium; and statistically significant increases in serum LDL cholesterol, potassium, aldosterone, protein, albumin, phosphorus, BUN, and in urine potassium. The findings indicate that results must be interpreted with caution from studies in which the baseline for measuring metabolic variables is established by feeding subjects a standardized diet that differed markedly from their regular, self-selected diets.

The effects of indomethacin and PGE2 on vascular reactivity in spontaneously hypertensive rats: possible role of prostaglandins in the pathogenesis of hypertension

Vascular reactivity was investigated in isolated perfused mesenteric vessels of young and adult SHR and age matched WKY. The primary objective was to investigate whether the difference in vascular reactivity between SHR and WKY would persist if endogenous prostaglandin synthesis was abolished and vascular reactivity restored with fixed exogenous quantities of PGE2. In young rats, when similar concentrations of PGE2 are infused in indomethacin blocked preparations, the difference in vascular reactivity between SHR and WKY is abolished. However, in adult rats the difference persists. It is concluded that enhanced prostaglandin synthesis in hypertension may participate in enhancing vascular reactivity.

Dietary fat and blood pressure: an intervention study on the effects of a low-fat diet with two levels of polyunsaturated fat

The role of dietary fat in human blood pressure control was studied among 84 middle-aged subjects (mainly couples) in two semirural communities in North Karelia, Finland. The families were randomly allocated into two groups that, after a baseline period of 2 weeks, changed their diet for a 12-week intervention period so that the proportion of energy derived from fats was similarly reduced in both groups, from 38 to 24%, but the polyunsaturated/saturated fatty acid (P/S) ratio was increased--from 0.2 to 0.9 in group I and to 0.4 in group II. After the intervention period, both groups switched back to their usual diet for a period of 5 weeks. During the intervention period, total serum cholesterol was reduced by 16% in group I and 14% in group II. Mean body weight and urinary sodium, potassium, calcium, and magnesium excretion changes were small or nonexistent. Mean systolic blood pressure decreased 4 mm Hg in group I (P less than 0.01) and 3 mm Hg in group II (P less than 0.01), and mean diastolic blood pressure decreased 5 mm Hg (P less than 0.001) and 4 mm Hg (P less than 0.01), respectively. The reductions were reversed during the switch-back period (P less than 0.01). These results confirm previous findings of the blood-pressure-reducing effect of a low-fat/high-P/S diet. Although a number of possible confounding factors can be ruled out, the dietary constituent accounting for the blood pressure change cannot be ascertained definitely. The results showed no significant further blood pressure reduction with more than a moderately increased P/S ratio when the saturated fat intake was markedly reduced.

Defective desaturation and elongation of n-6 and n-3 fatty acids in hypertensive patients

Hypertensive patients had higher levels of linoleic acid (LA) in serum lipids than normal controls. Administration of large doses of LA failed to raise the percentage of its metabolite arachidonic acid (AA) in serum lipids. Similarly, intake of large amounts of alpha-linolenic acid (alpha-LNA) failed to increase the amount of eicosapentaenoic acid (EPA). The percentage of EPA in serum lipids could readily be increased by direct administration of comparably low doses in a mackerel diet. Hypertensive subjects seem to desaturate and elongate LA and alpha-LNA only very slowly.

Changes of arachidonic acid in phosphatidylcholine different from other lipids in kidneys of spontaneously hypertensive rats after feeding a linoleic acid-rich diet

In spontaneously hypertensive rats (SHR) fed a linoleic acid-rich (LAR) diet over 22 weeks blood pressure could not be influenced when compared with SHR on linoleic acid-deficient (LAD) food. On the other hand, normotensive Wistar rats (WR) revealed a significantly lower blood pressure after feeding a LAR diet. The percentages of LA and AA were markedly increased in triglycerides and free fatty acids (FFA) in renal cortex and medulla of LAR-fed SHR and WR in comparison to LAD-fed animals. In renal phosphatidylethanolamine (PE) LA was also increased whereas AA remained unchanged. On the contrary, in phosphatidylcholine (PC) LA was only slightly augmented (in SHR) or even lowered (in WR), AA appearing decreased in SHR but increased in WR. These different changes in PE and PC indicate that individual phospholipids show a dissimilar behavior after dietary interventions, which can be masked by the evaluation of total phospholipids and might be of pathophysiological relevance.

Hormonal and nutritional enhancement of Na+-K+-ATPase activity may aid the prevention and treatment of essential hypertension

Subnormal activity of the Na+-K+-ATPase appears to be a common feature of essential hypertension, and may in fact play a pathogenic role in this disorder. If so, methods which relieve inhibition or enhance the activity of the sodium pump should have therapeutic or preventive value. Diuretics enhance the activity of the sodium pump in hypertensives, apparently by suppressing secretion of an inhibitory natriuretic factor, and it is likely that low-sodium diets have a similar effect. Activity of the Na+-K+-ATPase is also stimulated by thyroid hormone and insulin, and there are indications that thyroid therapy, as well as various measures which increase tissue insulin sensitivity, may have therapeutic value in essential hypertension. Nutritional measures which may enhance sodium pump activity include potassium supplementation, insurance of adequate magnesium intake, and consumption of rich sources of gamma-linolenic acid.

Lack of an effect of dietary saturated fat and cholesterol on blood pressure in normotensives

The effect on blood pressure (BP) levels of modifying the saturated fat and cholesterol content in the diet was studied in two separate protocols in normotensive volunteers. For 3 months, 19 men and women, aged 14 to 54 years, adhered to a diet that eliminated meat, poultry, eggs, and dairy fat from the subjects' customary nonvegetarian diet, which had included 71 g/day (35%) of dietary fat. The experimental diet reduced the consumption of saturated fat from 21 to 10 g, dietary cholesterol was lowered from 398 to 69 mg per day, but consumption of polyunsaturated fatty acids, carbohydrates, and dietary fiber was unchanged. Body weight and urinary sodium and potassium excretion were not significantly altered. Mean BP before and after the low fat diet was 116/74 and 115/74 mm Hg, respectively. A second double-blind study tested the effect on BP of dietary cholesterol at levels of 155 and 471 mg/day. Seventeen semivegetarian college students consumed one egg per day concealed in desserts for 3 weeks, and identical desserts containing no eggs for an additional 3 weeks. Mean BP at the end of the egg and eggless periods was 108/69 and 107/69 mm Hg, respectively. Thus, in short-term nutritional studies, dietary saturated fat and cholesterol at low-to-moderate levels of intake have no significant effects on BP in normotensive adults.

Serum fatty acids in Finnish men

The fatty acid compositions of 4 serum lipid fractions were analysed from 244 randomly selected 30-59-year-old Finnish men from 4 areas involved in a population survey ('Mini-Finland') in 1979-80. Men in eastern Finland had significantly lower mean percentages of linoleate (18:2) in CE, TG, FFA and PL (45.1, 10.3, 9.3 and 18.8%, respectively) than men in the western part of the country (48.4, 12.5, 10.6 and 20.2%, respectively). Very low values of 18:2 were encountered in the North Karelian community of Ilomantsi, especially in men aged 50-59 (40.9, 8.0, 7.5 and 16.8%, respectively). The percentage of alpha-linolenate tended also to be lower and those of saturated and monounsaturated fatty acids higher in the east, but there were no or only inconsistent differences in the contents of the prostaglandin precursors dihomo-gamma-linolenate, arachidonate and eicosapentaenoate. Eighteen men were studied in November and the following April. Only minor changes in the mean composition of serum fatty acids took place during this period and the correlation coefficients between the percentages of 18:2 recorded at the two time points ranged from 0.70 to 0.81. The low concentrations of 18:2 in serum lipids in Finnish men obviously reflect a low dietary P/S ratio and may contribute to the high prevalence of IHD in Finland and to its regional differences.

Effects of chronic arachidonate on blood pressure of spontaneously hypertensive rats

Three weeks of treatment with arachidonic acid (250 mg/kg/day, s.c.) produced an antihypertensive effect in 16 week-old spontaneously hypertensive rats (SHR) as compared with vehicle treated rats. Indomethacin (4 mg/kg, s.c. B.I.D.), given concurrently with arachidonate, abolished the antihypertensive effect. Plasma catecholamines were not altered by the arachidonate treatment, but blood pressure increments after spinal cord stimulation or after intravenous administration of norepinephrine and angiotensin II in the pithed rat were diminished. Increments in plasma catecholamines in response to spinal cord stimulation were similar in both groups of pithed rats. These data demonstrate the antihypertensive effect of arachidonic acid in SHR with established hypertension. This beneficial effect seems to be mediated through cyclooxygenase metabolites, and might be related to reduced responsiveness of peripheral blood vessels to pressor stimuli.

Inverse relationship between linoleic acid in serum and in adipose tissue of patients with essential hypertension

In patients with labile essential hypertension without and with overweight as well as in normotensive controls the fatty acid pattern of serum triglycerides and subcutaneous adipose tissue was estimated by gas liquid chromatography. In serum triglycerides of hypertensives linoleic acid was increased but appeared decreased in depot fat. This inverse relationship could not be found for arachidonic acid. Correspondingly, the C 18:2/C 20:4-ratio was higher in serum triglycerides than in adipose tissue. Only in depot fat of overweight hypertensives the percentage of arachidonic acid was decreased when compared to subjects with normal body weight. Linolenic acid remained unchanged in serum triglycerides but decreased significantly in adipose tissue of hypertensive patients. Eicosapentaenoic acid was increased in serum triglycerides and depot fat of patients with essential hypertension of normal body weight. The results are discussed with respect to the possible pathogenesis of essential hypertension and the hypotensive potency of dietary linoleic acid which has been described in patients with high blood pressure.

Fatty-acid composition of serum lipids predicts myocardial infarction

During a follow-up of five to seven years 33 out of 1222 middle-aged men initially free of coronary heart disease sustained fatal or non-fatal myocardial infarction or died suddenly. The fatty-acid composition of serum triglycerides, phospholipids, and cholesterol esters had been measured at the start of the surveillance in these men and in a control group of 64 men matched for age, serum cholesterol and triglyceride concentrations, blood pressure, obesity, smoking, and one-hour glucose tolerance. Palmitic and stearic acids of phospholipids were significantly higher and linoleic and most polyunsaturated fatty acids, including arachidonic acid and eicosapentaenoic acid, of phospholipids were lower in the subjects who sustained coronary events compared with the controls. Linoleic acid tended to correlate negatively with blood pressure while other polyunsaturated fatty acids, especially eicosapentaenoic acid, exhibited a negative correlation with blood pressure and relative body weight in the controls but not in the subjects who sustained coronary events. These findings suggest that the fatty-acid pattern of serum phospholipids is an independent risk factor for coronary heart disease.

Nutritional prevention of pre-eclampsia--a special role for 1 series prostaglandin precursors?

PGE1 appears to act as a physiological regulator of uteroplacental blood flow. Its vasodilatory, anti-vasopressor, and platelet stabilizing effects could be expected to counteract the placental ischemia, hypertension and excessive coagulation that are seen in pre-eclampsia. Supplementation with efficient essential fatty acid precursors of PGE1 reduces platelet aggregation, has been used with success in the treatment of hypertension and arterial vasospasm, and might offer a nutritional means of reducing the incidence and severity of pre-eclampsia. Assurance of adequate general nutrition also appears to be of importance in this regard.

Arachidonic acid metabolites, hypertension and arteriosclerosis

The level of arterial blood pressure is set by complete interactions of several mechanisms which influence both blood flow in and resistance of the vascular system. An imbalance favouring elevation of vascular resistance or extracellular volume will result in hypertension. Such alterations may include increased activity of the sympathetic nervous system, of the renin-angiotensin system, or excessive secretion of mineralocorticoids. Of equal importance may be a reduced activity of blood pressure-lowering factors such as prostaglandins and the kallikrein-kinin system. This paper describes the possible significance of prostaglandins in the pathophysiology of hypertension and in degenerative vascular disease, based on their involvement in the control of vascular resistance, renal regulation of extracellular volume and platelet-vessel wall interactions. An abnormality in the biosyn-thesis of certain prostaglandin endoperoxide metabolites may lead to hypertension even without an increase in the activity of the classic blood-pressure-elevating systems. The contribution of prostaglandins for the development of hypertension and degenerative vascular disease may be based on an inherent abnormality of the prostaglandin system, as well as on the effects of major risk factors such as dietary intake of sodium and fat on prostaglandin synthesis. Specific blockade or stimulation of distinct biosynthetic pathways leading to antagonistically acting prostaglandins and nutritional manipulation of precursor fatty acids should lead to a better understanding of the pathomechanisms involved and may offer new strategies for therapy or prevention of these cardiovascular disorders.

Augmented acute hypotensive effect of dihydralazine and clonidine after linoleic acid rich diet in normotensive conscious rats

The influence of dietary linoleic acid (LA) content on the cardiovascular effects of dihydralazine and clonidine was investigated in conscious rats. Male normotensive rats were fed either a diet rich in linoleic acid (LA) (13.3 cal-% LA) or a diet deficient in LA (0.5 cal-% LA) for a period of 5 months beginning in the pregnant mothers. Dihydralazine (1 mg/kg iv) or clonidine (10 micrograms/kg iv) were injected into conscious rats and blood pressure and heart rate were studied during a 20 min investigation period. The blood pressure lowering effects were higher in the rats fed the LA rich diet than in those fed the LA deficient diet 2, 5, 10 and 20 min after dihydralazine and 5 min after clonidine injection. The increase in heart rate per 10 mmHg blood pressure reduction after dihydralazine injection was lower in the rats fed on the diet rich in LA. We assume that the change in the cardiovascular effects of dihydralazine and clonidine by dietary LA may be caused by alterations of endogenous prostaglandin biosynthesis and sympathetic activity.

Evening primrose oil, a dietary prostaglandin precursor, diminishes vascular reactivity to renin and angiotensin II in rats

Polyunsaturated fatty acids (PUFA) are biosynthetic precursors of prostaglandins (PG). Endogenous biosynthesis of PG in vessel wall and kidney contributes to the regulation of arterial blood pressure. By increasing the fraction of PUFA in the diet systemic blood pressure can be lowered while PUFA deficient diet leads to an increase in blood pressure. To evaluate the effect of an enhanced PG biosynthesis by dietary PG precursors on vascular reactivity and vascular formation of prostacyclin-like activity, the pressor response to intravenous renin and angiotensin II in rats pretreated p.o. for 3 months with evening primrose oil (EPO, 1 ml/day) was determined and the antiaggregatory activity released by aortas of treated rats studied. EPO is unique in that it contains beside linoleic acid (72%), gamma-linolenic acid itself (9%). In contrast to olive oil treated rats EPO pretreatment diminished vascular reactivity to the vasopressor stimuli of renin and angiotensin II and increased the formation of vascular prostacyclin-like activity (p less than 0.05). These studies imply the possibility of a selective modulation of PG production by dietary maneuvers.

Attenuation of blood pressure increase in spontaneously hypertensive rats by diets enriched with polyunsaturated fatty acids

We investigated the influence of dietary polyunsaturated fatty acids (PUFA) on the blood pressure of spontaneously hypertensive rats (SHR). Feeding male adult SHR a linoleic acid (LA) rich or a PUFA poor diet did not alter the systolic blood pressure during a two months regimen. Feeding young male SHR an LA rich or a PUFA deficient diet beginning in the prehypertensive phase did not influence the development of hypertension. But when the regimen was begun in the pregnant mothers during the last week of pregnancy and continued in the offspring, the male offspring showed a significantly reduced increase in blood pressure when fed with an LA rich or a linolenic acid rich diet compared with PUFA deficient fed rats. This effect was not so markedly expressed in the female offspring.

Prospects for nutritional control of hypertension

Sodium restriction is not the only nutritional measure likely to prove valuable in the treatment and prevention of hypertension. The hypotensive effects of central adrenergic stimulation can be promoted by supplementary tyrosine, insulin potentiation (as with GTF), and (possibly) high-dose pyridoxine. Insulin potentiators (GTF) and prostaglandin precursors (essential fatty acids) should have direct relaxant effects on vascular muscle. A high potassium, low sodium diet, coenzyme Q, and prevention of cadmium toxicity (as with dietary selenium) may act to offset renally-mediated pressor influences. Functional combinations of these measures might prove to be substantially effective, in which case they would offer considerable advantages over potentially toxic drug therapies.

Effect of polyunsaturate-rich vegetable oils on blood pressure in essential hypertension

A group of essential hypertensives were treated for a period of six weeks with groundnut oil or safflower oil compared with a control group who were given a placebo medication. A significant drop in diastolic pressure occurred in the groups receiving the polyunsaturated fatty acid (PUFA) preparation. In another group of eight patients, who were already receiving traditional antihypertensive therapy, supplementation with PUFA rich oil resulted in a significant reduction in blood pressure. Further, after the end of the treatment period, an increase in diastolic pressure was found six to eight weeks later with return of pressures to approximately the pre-treatment level. These preliminary observations suggest that PUFA rich vegetable oils may be useful in the control of mild-to-moderate hypertension.

Prostaglandins, platelets, and atherosclerosis

Metabolism of arachidonic acid (AA) in blood platelets and in vascular endothelium does not lead to prostaglandins, but thromboxane A2 and prostacyclin are generated. These labile metabolites of AA antagonize each other: thromboxane A2 is a vasoconstrictor and proaggregatory agent, whereas prostacyclin dilates arteries, prevents platelets from aggregation, and dissipates the preformed platelet clumps. Prostacyclin is a powerful stimulator of adenylate cyclase in platelets and therefore its antiplatelet action is potentiated by phosphodiesterase inhibitors such as theophylline or dipyridamole. Cyclo-oxygenase of AA is inhibited by aspirin, thromboxane synthetase by analogues of prostaglandin endoperoxides, and prostacyclin synthetase by linear lipid peroxides. A hypothesis is put forward that atherosclerosis develops because of pathological, nonenzymic lipid peroxides. A hypothesis is put forward that atherosclerosis develops because of pathological, nonenzymic lipid peroxydation in the body and the subsequent molecular damage to prostacyclin synthetase in the rheologically determined areas of arterial walls. Endothelium deprived of prostacyclin is the basis for microthrombi formation, and follows a sequence of events described by Rokitansky and later by Ross. Prostacyclin is also a circulating hormone which is generated by the lungs. Thereby a damage of this "endocrine gland" by respiratory disorders, air pollution, or tobacco smoking are likely to contribute to pathogenesis of atherosclerosis, myocardial infarction, and arterial thromboembolism. Pharmacological treatment and prevention of these diseases should logically include antioxydants, prostacyclin and its analogues, thromboxane synthetase inhibitors and perhaps cyclooxygenase inhibitors (aspirin ?). Prostacyclin was already infused intravenously to men and its powerful antiaggregatory and deaggregatory actions were demonstrated. These properties of prostacyclin along with its vasodilator and positive inotropic actions destine this hormone to be a new type of antithrombotic drug in acute myocardial infarction.

Blood pressure and adipose tissue linoleic acid

In a natural, "free-living population" of 650 men, surveyed with the purpose of health assessment within an epidemiological design, a strongly significant negative correlation between the relative linoleic acid composition of adipose tissue and blood pressures was found (P less than 0.001). This correlation remained significant when age and weight were statistically controlled for. Thus, dietary, lipid-lowering linoleic acid seems to effect blood pressures as well in a favorable way.

[Prostaglandins in cardiovascular and renal function. Biochemical, physiological and clinical findings (author's transl)]

Prostaglandins (PG) are highly unsaturated, cyclic fatty acids with 20 carbon atoms which are biosynthesized from dihomo-gamma-linolenic, arachidonic and eicosapentaenoic acids. These fatty acids are either ingested or are biosynthesized from linoleic and linolenic acids, respectively. The PG-precursor fatty acids are liberated from membrane phospholipids by phospholipase A and are converted to prostaglandins by the multienzyme complex PG-synthetase. The activity of the PG-system is influenced by extracellular hormonal, neural and mechanical stimuli and by intracellular factors such as ion-concentration and activity of the enzymes adenyl- and guanylcyclase. Prostaglandins are tissue hormones or autacoids which act on their receptors near their site of synthesis and degradation. The prostaglandin family constitutes a group of more than 10 natural occurring compounds showing a variety of biological actions. In arteries and veins the different PG:s have vasodilating as well as vasoconstricting effects. In addition, they are involved in the regulation of vascular smooth muscle proliferation. Within the kidney PG:s have vascular and tubular actions. They antagonize the effect of ADH, mediate renin secretion and are involved in the control of electrolyte balance. In the regulation of platelet aggregation and platelet adhesion PG:s have opposite functions: Prostacyclin which is synthesized in the vascular wall antagonizes the aggregating action of Thromboxane A2 which is formed in the platelets. A defect or an imbalance in the production of PG:s in the vascular wall, in platelets or in the kidney is assumed to play a pathogenetic role in a variety of cardiovascular and renal diseases such as in hypertension, atherosclerosis, persistent ductus arteriosus and Bartter's syndrome.

The relationship of dietary fats to prostaglandin biosynthesis

The direct and indirect evidence that the fatty acid composition of dietary fat is involved in the regulation of prostaglandin biosynthesis was reviewed. Direct evidence included effects of essential fatty acid deficiencies and excesses on endogenous tissue levels and production rates of prostaglandins by several tissues. Indirect evidence included lipolytic, platelet aggregatory, hypertensive, inflammatory and immune responses. In general, composition of dietary fat did not affect prostaglandin biosynthesis unless a biochemical essential fatty acid deficiency was induced or the linoleate to saturated fatty acids ratio of the dietary fat was greater than 5. Most results were interpreted in light of changing fatty acid composition; however, very few direct measurements have been made.