W. Förster

DIPYRIDAMOLE: A POTENT STIMULATOR OF PROSTACYCLIN (PGI2) BIOSYNTHESIS

1 Dipyridamole (0.01 to 0.75 mm) increased prostacyclin (PGI2) biosynthesis from tritiated arachidonic acid in rat stomach fundus homogenates by 21 to 350%. The transformation of prostaglandin H2 (PGH2) to PGI2 by a microsomal fraction of pig aorta was stimulated by dipyridamole at 0.1 m by 63% 2 In the isolated perfused heart of the rabbit dipyridamole at 1 and 5 μg/ml increased PGI2 release by 70% and 146% respectively. 3 Our results show a stimulation of the second step in PGI2 biosynthesis (from endoperoxides) by dipyridamole. This effect should be considered in relation to the therapeutic usage of the drug in myocardial infarction.

Influence of human low density and high density lipoprotein cholesterol on the in vitro prostaglandin I2 synthetase activity

We investigated in vitro the influence of low density lipoprotein (LDL) cholesterol and high density lioprotein (HDL) cholesterol separated from human serum on prostaglandin I2 synthetase activity studied by the conversion of prostaglandin H2 to prostaglandin I2 by the microsomal fraction of pig aorta. 6-Oxo-prostaglandin F1 alpha was analyzed by gas-liquid chromatography using prostaglandin F1 alpha as internal standard. We found a linear negative correlation (P less than 0.001) between the amount of LDL cholesterol in the incubation solution and prostaglandin I2 synthetase activity, whereas there was a positive correlation (P less than 0.01) between HDL cholesterol and prostaglandin I2 synthesis. A very low concentration of LDL cholesterol and a high concentration of HDL cholesterol stimulated prostaglandin I2 synthesis, whereas a high LDL cholesterol concentration inhibited prostaglandin I2 biosynthesis by 64%. The concentration range of LDL and HDL cholesterol was representative of physiologically low, normal or elevated levels of lipoproteins.

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

SummaryTen 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. Theα-linolenic, eicosapentaenoic and docosahexaenoic acids were increased (p<0.01), whereas linoleic and arachidonic acids were decreased (p<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.

Metabolism of [1-14C]-arachidonic acid by cultured calf aortic endothelial cells: evidence for the presence of a lipoxygenase pathway.

Intact cultured calf aortic endothelial cells from a 10th-14th subculture rapidly metabolize exogenous [1-14C]-arachidonic acid by three different routes: i) incorporation into triglycerides and phosphilipids in a ratio of about 2:1, ii) formation of lipoxygenase metabolites (12-hydroxy-5,8,10,14-eicosatetraenoic acid) and iii) formation of cyclooxygenase metabolites (6-keto-PG F1 alpha and PG F2 alpha). From analyses by thin-layer chromatography and high-pressure liquid chromatography it was established that the main lipoxygenase metabolites in intact cells are 12-hydroxy-5,8,10,14-eicosatetraenoic acid and a compound proposed to be (a) dihydroxyeicosatetraenoic acid(s). In frozen and thawed cells the incorporation of arachidonic acid into cellular lipids is abolished, whereas the lipoxygenase pathway is strongly enhanced. Under these conditions the cells produce predominantly 15-hydroxy-5,8,11,13-eicosatetraenoic acid in addition to 12-hydroxy-5,8,10,14-eicosatetraenoic acid. The formation of lipoxygenase products was inhibited by heating the cells or by preincubation with nordihydroguaiaretic acid or BW 755 degrees C, whereas indomethacin was without effect. The formation of 12-hydroxy-5,8,10,14-eicosatetraenoic acid by intact cells was inhibited by 5,8,11-eicosatriynoic acid. Indomethacin and acetylsalicylic acid inhibited the formation of cyclooxygenase metabolites. 15Ls-hydroxy-5,8,11,13-eicosatetraenoic acid was incorporated into cellular lipids, but not dihydroxyeicosatetraenoic acids. Exogenous [3H]-labelled prostacyclin and TxB2 were not incorporated but were metabolized to less polar products.

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); α-linolenic acid (LNA)-rich], evening primrose oil [9.2% 18∶3(n−6)+71% 18∶2(n−6); γ-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 γ-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 PGF2α was significantly reduced in α-LNA-rich and slightly diminished in γ-LNA-rich fed rats. Aortic formation of 6-keto-PGF1α and TXB2 was increased in animals fed the γ-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.

Anti-aggregatory effect of prostacyclin (PGI2) in vivo.

Prostacyclin (PGI2) when infused intravenously reduced the mortality of rabbits given high intravenous doses of arachidonic acid (AA). Prostaglandins E1 and D2 were ineffective. Indomethacin pretreatment abolished the toxic AA effect. Since the lethal effect of AA is partly due to the formation of platelet aggregates it is concluded that PGI2 is a most potent antiaggregatory prostaglandin in vivo.

Enhanced thromboxane production in the aorta of spontaneously hypertensive rats in vitro

Abstract TXB2 levels were measured in the media in which intact thorocic aortae from Okamoto spontaneously hypertensive rats (SHR) and from Wistar Kyota (WK) normotensive rats were incubated. TXB2 levels were significantly devated in the SHR rats.

Characterization of the adrenoceptors in coronary arteries of pigs

Abstract The effects of phenylephrine and norepinephrine and the influence of adrenoceptor blockers on them were investigated on isolated strips of pig coronary arteries of different diameter. Phenylephrine contracted large coronary arteries, an effect inhibited by phentolamine, but was ineffective on small coronary arteries. Norepinephrine either relaxed large coronary arteries or occasionally contracted them. Phentolamine potentiated the relaxing effect of norepinephrine and propranolol inhibited or even reversed it into a contraction. Small coronary arteries were without exception relaxed by norepinephrine. This effect was not influenced by phentolamine but was inhibited by propranolol. These findings prove the presence of α-adrenoceptors in pig coronary arteries with a large diameter although β-adrenoceptors predominate; α-adrenoceptors are not found in coronary arteries with a small diameter. The classification of β-adrenoceptors in the coronary musculature into one of the two β-types was determined by comparing the affinities of propranolol, practolol and H 35/25 on the β-adrenoceptors of isolated atrial preparation of guinea pigs and of strips of pig coronary arteries. While the affinities of propranolol were the same to both organs the affinity of practolol to the myocardium was 100 times higher than to the coronary arteries. On the other hand the affinity of H 35/25 to the coronary arteries was three times higher than to the myocardium. The selective effects of the β 1 -adrenoceptor blocker practolol on the myocardium and the β 2 -adrenoceptor blocker H 35/25 on the coronary arteries indicate that the β-adrenoceptors of the coronary arteries should be classified as β 2 -adrenoceptors.

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.

Differential influence of lipoproteins isolated from women and men on the activity of the PGI2 synthetase activity

We have found a correlation between the activity of the PGI2 synthetase in the microsomal fraction of pig aorta and the amount of high density lipoprotein (HDL) cholesterol in the incubation fluid. The reverse was true for low density lipoprotein (LDL) cholesterol. These correlations exist independently of whether the lipoproteins were isolated from men than from women as it is for HDL isolated from women than from men. This result may give an explanation for the differential risk against the incidence of cardiovascular disease between women and men at the same concentration of the individual lipoproteins in their blood.