Influences of fatty acids and lipids from biological sources on the in vitro biosynthesis of prostaglandin I2 (PGI2)

Influence of a plasma fraction of human blood, rich in high density lipoprotein, on in vitro formation of prostaglandin I2 (PGI2) and thromboxane A2 (TXA2)

The influence of a plasma fraction of human blood, rich in high density lipoprotein (HDL), was investigated on the "in vitro" formation of PGI2 and TXA2. The addition of 1 mg HDL-cholesterol per ml incubation fluid stimulated significantly the biotransformation of prostaglandin H2 into PGI2 by the microsomal fraction of pig aorta. The TXB2 formation capacity of whole clotted blood was inhibited by administration of HDL in a dose dependent manner. These results suggest that added HDL is able to enhance the ratio PGI2:TXA2. This did not depend on the preparation of HDL either by ultracentrifugation or by precipitation.

Reevaluation of circulating prostacyclin and thromboxane in diabetes

Although several investigators have attempted to measure the plasma levels of prostacyclin (PGI2) and thromboxane A2 (TXA2) in diabetes and normal subjects, their results have been controversial. In this study, we measured plasma PGI2 and TXA2 levels in diabetic patients and normal subjects. The plasma PGI2 and TXA2 were determined by RIA as 6-keto-PGF1 alpha and TXB2, respectively. The plasma levels of 6-keto-PGF1 alpha were significantly reduced in diabetics with microangiopathy (52.5 +/- 18.9 pg/ml, mean +/- SE, p less than 0.05) compared with those of normal subjects. Diabetics as a whole also showed lower levels of 6-keto-PGF1 alpha than normal subjects (57.8 +/- 26.1 vs. 70.2 +/- 20.7 pg/ml), though this was not significant statistically. The plasma 6-keto-PGF1 alpha levels did not significantly correlate with either age of the patients or duration of diabetes in diabetics. Interestingly, however, hemoglobin A1c significantly correlated inversely with 6-keto-PGF1 alpha levels in diabetics without microangiopathy (r = -0.60, p less than 0.05). The plasma levels of TXB2 in diabetics were significantly higher than those of normal subjects (155.2 +/- 69.5 vs. 108.0 +/- 30.0 pg/ml, p less than 0.05). These data suggest that an imbalance of circulating PGI2 and TXA2 may contribute to the development of diabetic microangiopathy.

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.

Thromboxane A2 (TXA2) formation by washed human platelets under the influence of low and high density lipoproteins from healthy donors

Low density lipoprotein (LDL) stimulates TXA2 formation (measured as malondialdehyde) in washed human platelets with active cyclooxygenase, whereas high density lipoprotein (HDL) does not show any influence on TXA2 formation in this system. These results support the hypothesis that the proaggregatory action of a high plasma LDL concentration may be mediated by modification in the biosynthesis of eicosanoids. The mode of action of lipoproteins is discussed.

Effect of HDL and LDL from pre and post menopausal women on prostacyclin synthesis

Earlier we found LDL and HDL to differentially affect the synthesis of PGI2 from PGH2 by pig aorta microsomes and that this depended on the gender of the lipoprotein donors. Here we report there are also differences in the effects of LDL and HDL from pre- and postmenopausal women. The influence of the lipoproteins from postmenopausal women on the PGI2 formation is similar to the action of lipoproteins from men. We suggest that endogenous PGI2 formation is regulated by the sex related composition of the lipoproteins.

Inhibition of prostaglandin I2 (PGI2) formation by LDL-cholesterol or LDL-peroxides?

A hypothesis of Gryglewski et al. explains the correlation between increased level of LDL and development of atherosclerosis by inhibition of PGI2 synthesis by increased peroxide content of LDL. The aim of the present paper was to examine this hypothesis. The major results are: 1) Preparation of LDL in the presence of .02% butylated hydroxytoluene did not reduce the lipid peroxide content of LDL from men and women and not change the inhibition or stimulation of the in vitro biosynthesis of PGI2 by LDL isolated from blood of men or women, respectively. 2) In the LDL and HDL, respectively, of healthy men we found nearly the same lipid peroxide levels (nmole malondialdehyde (MDA)/mg lipoprotein-cholesterol) as in the lipoproteins of male patients with hyperlipidemia type IIa or IV, but the peroxide concentration is three times higher in HDL as in LDL. 3) LDL isolated from healthy men inhibited in dose dependent fashion the generation of PGI2 from PGH2 by aortic microsomes whereas LDL from premenopausal women stimulated PGI2 formation even calculated as LDL lipid peroxides (in nM MDA/ml). The results call into question the hypothesis that diminished PGI2 formation by atherosclerotic vessels is related to inhibition of PGI2 synthetase by lipid peroxides present in LDL in the lesions. A new working hypothesis is presented that also the fatty acid pattern and the lipid class composition in the LDL are important for their influence on the PGI2 formation.

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.

Low density lipoprotein (LDL) from male volunteers stimulated the thromboxane formation by human platelets

LDL (0.5 - 2.0 mg LDL-cholesterol/ml) isolated from venous blood of healthy male volunteers stimulated dose-dependently the malondialdehyde (MDA) formation by frozen human platelets, used as a marker for the activity of the thromboxane synthetase. HDL (0.25 - 1.0 mg HDL-cholesterol/ml) and human serum albumin (1 - 10 mg/ml) had no concentration-dependent influence on the MDA formation. If these results can be extended to in vivo they suggested the strong connection between the prostaglandin and lipoprotein hypothesis of pathogenesis of atherosclerosis.

The influence of linseed oil diet on fatty acid pattern in phospholipids and thromboxane formation in platelets in man

Ten healthy volunteers daily received 30 ml linseed oil for 4 weeks in addition to the "normal" diet. The influence of linseed oil diet on the fatty acid pattern of plasma phospholipids and thromboxane formation in platelets was investigated. The fatty acid pattern was analysed by gas liquid chromatography. The alpha-linolenic, eicosapentaenoic and docosahexaenoic acids were increased (p less than 0.01), whereas linoleic and arachidonic acids were decreased (p less than 0.05) after 4 weeks of the linseed oil diet. The thromboxane formation of platelets were unchanged. Additionally the influence of HDL and LDL on PGI2 biosynthesis in pig aortic microsomes (PAM) was investigated. HDL taken from serum before and after 3 weeks of linseed oil diet and LDL taken after 3 weeks of diet stimulated the PGI2 formation in PAM, whereas LDL taken from serum before the diet period inhibited the PGI2 formation in PAM.