Influence of dietary linoleic acid content on blood pressure regulation in salt-loaded rats (with special reference to the prostaglandin system)

Fatty acids increase hepatitis B virus X protein stabilization and HBx-induced inflammatory gene expression

The protein level of human hepatitis B virus (HBV) in infection is variable, depending on patient context. We previously reported that HBV X protein (HBx) induces hepatic lipid accumulation and inflammation. Here, we show that abnormal levels of hepatic fatty acids increase HBx protein stability during HBV expression, resulting in the potentiation of HBx-induced inflammation. Reactive oxygen species, Ca(2+) signaling and expression levels of various lipid metabolic genes were investigated in HBx-expressing cells and in HBx transgenic mice. Fatty acids, including palmitate, stearate and oleate, increased HBx protein stability by preventing proteasome-dependent degradation. Hepatic inflammation induced by a high fat diet (HFD) and HBx was measured based on the expression of interleukin-6 and tumor necrosis factor α. In addition, the protein level of HBx increased in HFD-HBx transgenic mice. Reactive oxygen species production and intracellular Ca(2+) signal activation play critical roles in fatty-acid-induced HBx stabilization. Abnormal levels of hepatic fatty acids resulted in synergistic induction of HBx protein and liver inflammatory gene expression through HBx protein stabilization. These results indicate that different fatty acid levels in the liver might affect HBV-induced pathogenesis.

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.

A cross-sectional ecological analysis of blood pressure and its determinants in eleven Pacific populations

A cross-sectional interpopulation analysis of blood pressure and its determinants was conducted with the data collected during epidemiologic surveys in 11 Pacific island populations from 1975 to 1981. In each of these populations, the mean arterial blood pressure increased with age; the overall blood pressure levels differed among the populations. The multivariate analyses suggest that dietary factors that result in differences in body mass, plasma cholesterol, and glucose intolerance contribute considerably to interpopulation differences in blood pressure. The impact of these differences in effects of dietary factors on interpopulation blood pressure seemed to be uniform, even though the overall levels of each of these three variables differed significantly among the populations. This study of blood pressure data, accrued from 6224 men and 7029 women aged 20-79 years, supports the hypothesis that dietary factors strongly contribute to high blood pressure as well as to interpopulation differences in the prevalence of hypertension. We propose using these data in planning programs for prevention and control of hypertension in the Pacific countries.

Dietary N-6 and N-3 fatty acids and salt-induced hypertension in the borderline hypertensive rat

This study examined the effects of salt-loading on blood pressure (BP) development in the borderline hypertensive rat (BHR) and its modification by dietary n-3 and n-6 fatty acids. In experiment 1, 4 groups (n = 10/group) of male BHR receiving 1% NaCl as a replacement for tap water were placed on chow enriched with either olive oil (OL), sunflower oil (SUN), evening primrose oil (EPO) or fish oil for 6 weeks. BP, heart rate, body weight, water, Na+ and K+ intake and urinary output were measured weekly. SUN and fish oil reduced the pressor response to salt seen vs the OL group by 50%, and EPO abolished the pressor response, reducing BP below control levels. The BP response was unrelated to either food intake or water and electrolyte intake and excretion. In experiment 2, male BHR received water +/- 18:3n-6 (0.04 mg/hr in OL via ip pump) or 1% NaCl +/- 18:3n-6 (n = 12/group) for 12 weeks, followed by 2 weeks recovery on tap water. Salt increased BP, and 18:3n-6 decreased this response, but had no effect on animals receiving tap water. In experiment 3, effects of 3 doses of 18:3n-6 (0.04, 0.08, and 0.12 mg/hr) on the pressor response to 1% NaCl were examined. All doses reduced the BP response to salt vs controls with no dose-response. These data suggest that the BHR is genetically salt-sensitive, and that dietary n-3 and n-6 fatty acids can attenuate the cardiovascular response to salt in this model.

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.

Impaired catecholamine inactivation. A prohypertensive stimulus after dietary linoleate deficiency in salt-loaded rats?

Experiments were carried out on salt-loaded rats (1.5% NaCl as drinking fluid) to further explore the mechanisms by which blood pressure increases after a linoleic acid-deficient (LAd) diet. In 4-week-old LAd rats (0.5 cal% LA, hydrogenated palm kernel fat) compared to linoleic acid-rich rats (LAr, 13.3 cal% LA, sunflower oil), we observed, from the base of a reduced content of omega-6-polyunsaturated fatty acids in the tissues, an increase in blood pressure by 12 mm Hg (p less than 0.001), a diminished formation of prostaglandin E (PGE), and an unchanged formation of PGF in the aorta as well as a reduction in the in vitro uptake of 14C-norepinephrine into cardiac, aortic, and renal tissues, and a reduced degradation rate of 14C-norepinephrine in cardiac tissue. These differences in LAr vs LAd rats were not exaggerated. With respect to aortic PGE formation, 14C-norepinephrine uptake into aortic and renal tissues and 14C-norepinephrine degradation even lessened when the diet was begun prenatally, although the reduction of omega 6-polyunsaturated fatty acids in the tissues was aggravated. Our conclusion is that a fault in catecholamine inactivation may be involved in the pathogenesis of increased sympathetic activity and blood pressure elevation in LAd-fed, salt-loaded rats, possibly via alterations of endogenous prostanoid formation.

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.