Delay of the initiation of hypertension in spontaneously hypertensive rats by CV-4151, a specific thromboxane A2 synthetase inhibitor

When CV-4151, a specific thromboxane (TX) A2 synthetase inhibitor, was given orally to 4 week old (4w) spontaneously hypertensive rats (SHR) daily for 3 weeks, the initiation of hypertension was delayed by about one week. The agent increased urinary excretion of water, sodium and creatinine, reduced that of TXA2 (as TXB2), increased that of PGI2 (as 6-keto-PGF1 alpha) and enhanced urinary PGI2/TXA2. In 4w Wistar-Kyoto rats (WKY) and 18w SHR was established hypertension, the agent had little effect on blood pressure and renal function. In isolated, perfused kidneys of 6w SHR, CV-4151 markedly inhibited both arachidonic acid-induced pressor action and production of TXA2. TXA2 synthetase activity in renal cortical microsomes of 5w SHR was approximately 1.5 times higher than that in age-matched WKY. CV-4151 inhibited TXA2 synthetase activity of medullary and cortical microsomes more effectively in 5w SHR than in age-matched WKY. Thus, in young SHR, the TXA2 synthetase inhibitor seemed to improve renal function by altering the balance of renal TXA2 and PGI2 biosynthesis and subsequently caused a delay in the initiation of hypertension. The present findings lend support to the idea that an imbalance in the renal TXA2-PGI2 biosynthesis may be involved in the initiation of hypertension in SHR.     

丁基苯酞对大鼠局灶性脑缺血和重灌后脑内TXB2和6—keto—PGF1α…

目的：观察丁基苯酞（ＮＢＰ）对大鼠局灶性脑缺血及重灌后海马，纹状体和皮层中ＴＸＢ２及６－ｋｅｔｏ－ＰＧＦ１α含量的影响，方法：尼龙线栓塞法造成大鼠局灶性脑缺血模型，ＴＸＢ２和６－ｋｅｔｏ－ＰＧＦ１α用放免法测定。结果：ＮＢＰ１０ｍｇ．ｋｇ＾－１治疗对缺血重灌注后脑组织中ＴＸＢ２的产生具有抑制作用，但对６－ｋｅｔｏ－ＰＧＦ１α的产生无明显作用，ＮＢＰ２０ｍｇ．ｋｇ＾－１治疗后，重灌５ｍｉｎ缺血脑组织     

Routine measurement of thromboxane B2 and the prostacyclin metabolite 6-keto-prostaglandin F1 alpha in plasma

Thromboxane A2 (TXA2) is mainly formed in thrombocytes. It promotes thrombocyte aggregation and contracts the blood vessels. TXA2 appears to be a specific physiological thrombotic agent. Synthesis of TXA2 is elevated in patients with diabetes mellitus of types I and II and in hypertensive patients. TXA2 has a half-life of about 30 s under physiological conditions. Prostacyclin (PGI2) is formed in the vessel walls. Its action is antagonistic to TXA2, that is, it inhibits platelet aggregation and dilates the blood vessels. Synthesis of PGI2 is depressed in the presence of the classical 4 main risk factors for atherosclerosis: arterial hypertension, hyperlipoproteinaemia, smoking and diabetes mellitus. PGI2 has a half-life of about 3 min under physiological conditions. Since TXA2 and PGI2 are very labile and thus extremely difficult to measure, it is at present usual to measure their stable metabolites thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). Radioimmunological measurement (RIA) of TXB2 in plasma requires no preliminary work, but radioimmunological measurement of 6-keto-PGF1 alpha in plasma requires prior extraction and concentrating, since the concentration of 6-keto-PGF1 alpha in the plasma is usually below the detection limit of commercial RIA kits. This paper describes standardized conditions for drawing the blood sample, a simple method of extraction from plasma, and the reliability of two commercial RIA kits with 125I tracer in measuring TXB2 and 6-keto-PGF1 alpha in plasma.     

缺氧时TXA_2和PGI_2对心肌血流量变化的调节作用

目的本文旨在探讨TXA2和PGI2在缺氧时对心肌血流量的调节作用。方法大鼠随机分为平原组和急性缺氧组,用99mTc标记蟾蜍红细胞测定心肌血流量,用放免法分别测量血栓素A2、前列环素的含量。结果急性缺氧导致左、右心室心肌血流量、血浆TXB2含量、TXB2/6-keto-PGF1浕比值明显增高（P〈0.05）,左、右心室心肌血管阻力明显下降（P〈0.05）,6-keto-PGF1浕无明显变化？崧邸〖毙匀？氧时,左、右心室心肌血流量增加,TXA2和PGI2参与了急性缺氧时心肌血流量的调节,以TXA2的缩血管作用为主。     

Differential regulation of the cyclooxygenase pathway in starch elicited rat peritoneal macrophages by prostaglandin E2, U-44069, a stable endoperoxide analogue and dibutyryl-cyclic AMP

The basal and carrageenin-stimulated release of thromboxane (TX) B2, the stable product of TXA2, 6-ketoPGF1 alpha, the stable breakdown product of prostacyclin (PGI2) and prostaglandin (PG) E2 from 24 h starch elicited rat peritoneal macrophages was inhibited by dibutyryl-cyclic AMP (db-cAMP). PGE2 also inhibited the release of TXA2 and 6-keto-PGF1 alpha whereas the stable endoperoxide analogue, U-44069, stimulated PGE2 and 6-keto PGF1 alpha release but inhibited TXB2 release. The effects of all three mediators tested were related to an increase of M? intracellular cAMP content.     

Roles of endogenous prostacyclin and thromboxane A2 in the ischemic canine heart

The ability of the ischemic heart to release prostacyclin (PGI2) and thromboxane A2 (TXA2) was studied, together with the effects of these substances on the ischemic myocardium in open-chest dogs. We measured the plasma levels of 6-keto-PGF1 alpha and TXB2--which are stable metabolites of PGI2 and TXA2, respectively--as well as lactate and coronary venous blood flow. The dogs were divided into three groups of eight animals which received indomethacin (5 mg/kg), (E)-3-[4-l-imidazolylmethyl)phenyl]-2-propenoic acid hydrochloride monohydrate (OKY-046) (1 mg/kg), or the vehicle. A transient increase in 6-keto-PGF1 alpha was observed in the great cardiac vein 5 min after the ligation of the left anterior descending coronary artery (LAD). TXB2 and lactate increased 30 and 15 min, respectively, after the ligation. Indomethacin prevented significant increases in 6-keto-PGF1 alpha and TXB2, but accelerated the lactate release. OKY-046 prevented significant increases in TXB2 and lactate release, but did not counteract the increase in 6-keto-PGF1 alpha. Although coronary venous flow decreased significantly 5 min after the ligation in every group, the flow returned to the preligation level 15 min after the ligation in the OKY-046 and the vehicle groups. Thus, we have demonstrated the release of PGI2 and TXA2 from the ischemic heart and suggest beneficial effects of PGI2 and of a selective inhibitor of thromboxane synthetase on the ischemic myocardium.     

Evidence for vasoconstriction mediated by the endothelin-B receptor in domestic swine

Endothelin-1 (ET-1), a potent vasoactive and mitogenic peptide, has been implicated in a number of cardiovascular diseases, including congestive heart failure, neointimal hyperplasia associated with restenosis, and hypertension. The vasoconstriction induced by ET-1 is thought to be mediated mainly by its action on ET(A) receptors on vascular smooth muscle cells. Recent studies have indicated that vasoconstriction also may be mediated by stimulation of an ET(B)-receptor subtype. Increased use of the pig as a cardiovascular model prompted us to examine the receptor profile in this species using ABT-627, a potent, nonpeptide antagonist of the ET(A) receptor. The precursor to ET-1, big ET-1 (0.02 nmol/kg/min), was infused intravenously in domestic swine, resulting in a sustained increase in mean blood pressure of 38 +/- 3 mm Hg. After stabilization of the pressor response, ABT-627 (0.1-10 microg/kg/min) or vehicle was infused for 30 min. Whereas vehicle infusion had no appreciable effect, a dose-related reversal of the pressor response to big ET-1 (11-100%) was observed by the end of the ABT-627 infusion. Blood samples were assayed for plasma concentrations of ABT-627; peak levels ranged from 9 +/- 2 to 937 +/- 168 ng/ml. In a separate group of pigs, the highest dose of ABT-627 produced only a modest reversal of the hypertensive response to an infusion of angiotensin II (300 ng/kg/min). Additional results indicate that the vasoconstrictor effects produced by sarafotoxin 6C (0.03 and 0.3 nmol/kg), an agonist of the ET(B) receptor, are not blocked by treatment with ABT-627 (10 microg/kg/min). However, complete blockade of the S6C response could be achieved using the ET(B) antagonist, A-192621 (0.33 mg/kg/min). Our results define the dose-response relation for the ET(A)-receptor antagonist ABT-627 in the vasculature of the domestic pig and suggest the presence of an ET(B)-receptor subtype that mediates vasoconstriction in this species.     

Effects of phospholipases A2 from Vipera russelli snake venom on blood pressure, plasma prostacyclin level and renin activity in rats

Vipera russelli venom contains several isoenzymes of phospholipase A2 (PLA2) which were isolated by column chromatography. The effects of PLA2 fractions on blood pressure, plasma prostacyclin level and renin activity were studied in normotensive and renal hypertensive rats. PLA2 fractions II-5, II-7, III-3 and III-6 (0.1 mg/kg) injected i.v. into rats decreased the arterial blood pressure. The hypotensive action of PLA2 fractions was not affected by heat treatment (70-80 degrees C, 30 min, pH 6.8). After indomethacin (30 mg/kg, i.v.), the hypotensive response to PLA2 was markedly reduced. Plasma prostacyclin (PGI2) and thromboxane A2 (TXA2) levels were measured by radioimmunoassays of their degradation products, 6-keto-PGF1 alpha and TXB2, respectively. PLA2 fractions (0.1 mg/kg) induced an increase in plasma PGI2 and TXA2 levels. There was a positive linear correlation between the PLA2-induced hypotensive effect and the ratio of increased 6-keto-PGF1 alpha to TXB2 (r = 0.83) in normotensive rats. In renal hypertensive rats, the increase in PGI2 level was larger than in normotensive rats. Plasma renin activity was also measured by the radioimmunoassay. Plasma renin activity was reduced by PLA2 fractions in renal hypertensive rats, but not in normotensive rats. These results suggest that the hypotensive effect of PLA2 fractions in normotensive rats may be partly due to the increase in plasma prostacyclin and thromboxane A2 levels. In addition to the larger increase in plasma PGI2 level, the reduction in plasma renin activity may also contribute to the greater hypotensive effect of PLA2 fractions in renal hypertensive rats.     

去氢紫堇碱对兔血小板TXB2及主动脉6-keto-PGF1PGF1α含量的影响

Dehydrocorydaline (DHC) was shown to reduce the production of thromboxane B₂ (TXB₂)in platelets and 6-keto-prostaglandin F_1α (6-keto-PGF_1α in the aorta of rabbits in vitro. The effect of DHC increased with the increase of dose.DHC 0.41 mg was found to inhibit the formatiom of TXB₂ markedly while not reduce the content of 6-keto-FCF_1α. DHC also exhibited obvious inhibitory effect on the arachidonic acid (0.66mmol/L) induced formation of platelet malondialdehyde (MDA). These effects were similiar to the specific cycloxygenase inhibitor, aspirin (0.03 mg/ml). The results suggest that (1) DHC reduced both contents of TXA₂ and PGI₂ in vitro. (2) DHC markedly inhibited the system of cycloxygenase in cell microsomes. (3) As to whether TXA₂ synthetase or cycloxygenase was inhibited in these experiments is still to be elucidated.     

Prostacyclin and thromboxanes in carrageenan-induced pleurisy in the rat

The cellular origin and kinetics of TXB2 and 6-keto PGF1 alpha in carrageenan-induced pleurisy has been studied. Maximum levels of these prostanoids occurred 1 hour after induction of pleurisy. Mononuclear cells initially present in the pleural cavity synthesized TXB2 and 6-keto PGF1 alpha from (14C) arachidonic acid. By contrast, PMN cells harvested 6 hours after the induction of inflammation did not produce 6-keto-PGF1 alpha. Selective inhibition of thromboxane synthetase with drugs in vitro and in vivo increased the formation of 6-keto-PGF1 alpha, the stable breakdown product of PGI2. This metabolic effect was parallel to an increase in the volume of exudate and in PMN migration. These results suggest that TXA2 seems to be implicated not only as a chemotactic agent but also as an antagonist of PGI2 vasodilator effects.     

Prostaglandin endoperoxide-dependent vasospasm in bovine coronary arteries after nitration of prostacyclin synthase

In the present study we used a bioassay to study the effects of peroxynitrite (ONOO-) on angiotensin II (A-II)-triggered tension in isolated bovine coronary arteries in order to show the consequences of the previously reported PGI2-synthase inhibition by ONOO- in this model. The following results were obtained: 1. 1 micromol L(-1) ONOO- impaired A-II-induced vasorelaxation and caused a second long lasting constriction phase. Indomethacin (10(-5)M) prevented both effects. U51605, a dual blocker of PGI2-synthase and thromboxane (TX)A2-synthase mimicked the effects of ONOO-. 2. The selective TXA2/prostaglandin endoperoxide (PGH2) receptor antagonist SQ29548 antagonized the second vasoconstriction phase after ONOO- -treatment. Since a generation of TXA2 and 8-iso-prostaglandin F2alpha could be excluded a direct action of unmetabolized PGH2 on the TXA2/PGH2 receptor was postulated. 3. ONOO- dose-dependently inhibited the conversion of 14C-PGH2 into 6-keto-PGF1alpha in isolated bovine coronary arteries with an IC50-value of 100 nM. 4. Immunoprecipitation of 3-nitrotyrosine-containing proteins with a monoclonal antibody revealed PGI2-synthase as the only nitrated protein in bovine coronary arteries treated with 1 micromol 1(-1) ONOO-. 5. Using immunohistochemistry a co-localization of PGI2-synthase and nitrotyrosine-containing proteins was clearly visible in both endothelial and vascular smooth muscle cells. We concluded that ONOO- not only eliminated the vasodilatory, growth-inhibiting, antithrombotic and antiadhesive effects of PGI2 but also allowed and promoted an action of the potent vasoconstrictor, prothrombotic agent, growth promoter, and leukocyte adherer, PGH2.     

丹参酮Ⅱ-A对局灶性脑缺血大鼠COX-2、PGI2以及TXA2含量的影响

目的探讨丹参酮Ⅱ-A对局灶性脑缺血大鼠脑组织环氧化酶2(COX-2)及其下游产物含量的影响。方法 46只SD大鼠随机分为假手术(S)组(n=10)、缺血模型(I)组(n=11)和丹参酮Ⅱ-A低(T1)(n=12,丹参酮Ⅱ-A腹腔预注射1周,每日2mg/kg)、高(T2)(n=13,丹参酮Ⅱ-A腹腔预注射1周,每日4mg/kg)剂量预防组。采用持续性大脑中动脉线栓法制作局灶性脑缺血模型。持续栓塞3h后进行神经行为学评分,6h后断头取脑,干湿重法求出脑组织含水量,ELISA法测定脑组织中COX-2、6-酮前列腺素F1α(6-keto-PGF1α)、血栓素B2(TXB2)含量。结果与I组相比,T1、T2组神经功能损伤改善,脑组织含水量减少,COX-2、6-keto-PGF1α和TXB2的产生呈剂量依赖性的降低(P<0.01)。结论抑制COX-2及其下游产物TXA2、前列环素(PGI2)可能是丹参酮Ⅱ-A保护局灶性脑缺血大鼠神经功能的作用机制之一。     

短毛五加总甙对血小板聚集和PGI_2/TXA_2平衡的影响(英文)

短毛五加总甙(AGVPS)是中药短毛五加(Acanthopanax gracilistylus var. pubescens)的有效成份。本文发现短毛五加总甙能抑制正常家兔由多种诱导因素所致的血小板聚集。同时,它还抑制花生四稀酸所致血小板聚集时TXA_2的产生,增加离体家兔胸主动脉PGI_2产生。在高脂喂养的动脉粥样硬化的家兔模型上,能提高血浆PGI_2水平。     

Changes in prostacyclin, thromboxane A2 and F2-isoprostanes, and influence of eicosapentaenoic acid and antiplatelet agents in patients with hypertension and hyperlipidemia

Prostacyclin (PGI2), thromboxane A2 (TXA2) and F2-isoprostanes, prostaglandin F2-like compounds, have wide and contrasting spectrum of biological activities and may influence blood pressure and atherogenesis. To investigate the dynamics of PGI2, TXA2 and F2-isoprostanes in patients with hypertension and hyperlipidemia (HH group), we measured the major urinary metabolites of PGI2: 6-keto PGF1alpha (Keto) and 2,3-dinor-6-keto PGF1alpha, (Dinor), those of TXA2:TXB2 and 11-dehydro TXB2 (Dehydro), and urinary 8-isoprostane (Iso) in 34 patients. Urinary excretion of Dinor was significantly lower in patients than in controls and that of Dehydro was significantly higher in patients than in controls. Keto, TXB2 and Iso were not significantly different between them. Antiplatelet agents decreased not only TXA2 metabolites but also PGI2 metabolites. Urinary C-peptide immunoreactivity was correlated with Dinor and Dehydro. After administration of eicosapentaenoic acid (EPA), total cholesterol (T-cho) and triglycerides (TG) significantly decreased. Although prostanoids did not show significant change, changes in T-cho were correlated with changes in Dinor and changes in Iso. These results suggest that PGI2 and TXA2 of systemic origin might be related to the pathophysiology of hypertension and hyperlipidemia and that the dynamics of PGI2, TXA2 and F2-isoprostanes might be related to not only blood pressure regulation but also lipid and glucose metabolism.     

Release of slow reacting substance from the guinea-pig lung by phospholipases A2 of Vipera russelli snake venom

Phospholipases A2 (PLA2) of Vipera russelli venom were isolated by column chromatography. The ability of PLA2 fractions to release slow reacting substance (SRS) was studied in the guinea-pig lung perfused with Krebs' solution. The relationship between the perfusion pressure change produced by PLA2 and SRS release was also studied. Two PLA2 fractions (II-5 and III-3; 3-100 micrograms), injected into the lung increased the perfusion pressure and released SRS. Pretreatment of the lung with indomethacin (10 micrograms) reduced the pressure response induced by the PLA2 fractions. The SRS released in the lung effluent by PLA2 was identified by bioassay as a mixture of thromboxane A2 (TXA2), prostacyclin (PGI2) and leukotrienes. TXA2 and PGI2 release was also quantitated by radioimmunoassay of the degradation products TXB2 and 6-keto-PGF1 alpha, respectively. There was a positive linear correlation between the pressure increases and the ratios of TXB2 to 6-keto-PGF1 alpha (r = 0.87). It appears that the relative amounts of TXA2 and PGI2 released determine the effects of PLA2 fractions on the guinea-pig lung. The release of arachidonic acid metabolites, prostaglandins and leukotrienes may account for part of the hypotensive action of PLA2.     

Renal and systemic effects of chronic blockade of ET(A) or ET(B) receptors in normal rats and animals with experimental heart failure

Endothelin-1 (ET-1) is involved in the pathogenesis of cardiac and renal hemodynamic changes and impaired excretory function in congestive heart failure. It has previously been demonstrated that acute administration of ABT-627 (endothelin-A blocker) abolished systemic and renal vasoconstriction in controls and rats with congestive heart failure induced by a surgically created aortocaval fistula (Abassi et al. Clin Sci (Lond) 2002;103:S245-S248). In contrast, acute endothelin-B blockade by A-192621 exaggerated the ET-1 induced systemic and renal vasoconstriction. The present study examined the renal and systemic effects of chronically administered ABT-627 (24 mg/kg per day) or A-192621 (72 mg/kg per day) for 7 days via osmotic minipumps inserted intraperitoneally on the day of operation of sham controls and rats with congestive heart failure. Tailcuff measurements revealed that ABT- 627 significantly decreased mean arterial pressure from 108 +/- 2 mmHg to 87 +/- 2 mmHg (P < 0.05), whereas A-192621 significantly increased mean arterial pressure from 110 +/- 3 mmHg to 122 +/- 3 mmHg (P < 0.05) in controls. Despite the hypotensive effect of ABT-627, daily sodium excretion dramatically increased, but to a lesser extent in A-192621-treated controls. Furthermore, chronic administration of ABT-627 to controls attenuated the systemic and renal vasoconstriction induced by ET-1 (1 nmol/kg intravenous), whereas A-192621 augmented these effects. Similarly, chronic treatment with ABT-627 totally abolished the systemic and renal vasoconstriction caused by injected ET-1 in rats with congestive heart failure, whereas A192621 potentiated these effects. Chronic treatment of animals with congestive heart failure with ABT-627 did not influence daily sodium excretion, whereas treatment with A192621 significantly improved daily sodium excretion. Interestingly, treatment with either ABT-627 or A192621 significantly decreased cardiac hypertrophy in rats with congestive heart failure. In conclusion, in sham controls endothelin-B receptor mediated vasodilation and natriuresis, probably as a result of tubular action, whereas in congestive heart failure the excretory contribution of endothelin-B receptor was attenuated, resulting in Na+ retention.