Human erythroleukemia cells express functional thromboxane A2/prostaglandin H2 receptors

The human erythroleukemia (HEL) cell line is a cultured hematopoietic cell line reported to express platelet membrane glycoproteins and alpha-2 adrenergic receptors. The present studies were designed to determine if functional thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptors exist in HEL cells. Radioligand binding assays were performed using [125I]PTA-OH, a TXA2/PGH2 receptor antagonist. Scatchard analysis revealed one class of binding sites for 1-PTA-OH with a Kd = 122 +/- 18 nM and maximum binding = 1.7 +/- 0.3 x 10(5) sites/cell. Competition for [125I]PTA-OH binding with the TXA2/PGH2 receptor agonists SQ26655 and U46619 revealed one class of binding sites for SQ26655 with a Kd = 17 nM and two classes of binding sites for for U46619 with a Kd = 45 nM for the high-affinity site and a Kd = 450 nM for the low-affinity site. Competition for [125I]PTA-OH by the steroisomeric TXA2/PGH2 receptor antagonists L657925 and L657926 revealed two classes of binding sites for the more potent L657925 with a Kd = 8 nM for the high-affinity site and a Kd = 400 nM for the low-affinity site whereas L657926 bound to one class of sites with a Kd = 380 nM. Stimulation of the TXA2/PGH2 receptor by SQ26655 and U46619 resulted in concentration-dependent increases in [Ca++], as measured by FURA-2 fluorescence, with EC50 values of 28 +/- 2 and 149 +/- 32 nM, respectively. I-PTA-OH, L657925 and L657926 antagonized this response to U46619 with IC50 values similar in rank potency to that seen in the binding studies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endogenous vasoconstrictor prostanoids: role in serotonin and vasopressin-induced coronary vasoconstriction

A vasoconstrictor-induced prostacyclin (PGI2) production in a perfused rat heart was found, suggesting a mitigating role of PGI2 on coronary vasoconstriction. Treatment of the heart with cyclooxygenase inhibitors (aspirin or indomethacin) decreased PGI2 production by more than 90% and paradoxically reduced the vasoconstriction response. The attenuating effect of cyclooxygenase blockade suggested that endogenous prostanoids contribute to serotonin-, vasopressin- or U46619-induced vasoconstriction. Two prostaglandin (PG) H2/thromboxane A2 (TXA2) receptor antagonists, i.e., 13-azaprostanoic acid (13-APA) and SQ 29,548 were used to investigate putative endogenous vasoconstrictor prostanoids on the exogenously induced vasoconstriction. Retrogradely perfused (5-6 ml/min) rat hearts were rendered guiescent, yet responsive to stimuli, by local injection of lidocaine to the atrioventricular node. Changes in coronary vascular resistance (i.e., perfusion pressure at constant flow) were monitored and the cardiac effluent was collected for analysis of 6-keto PGF1 alpha (the stable metabolite of PGI2) as well as PGF2 alpha by radioimmunoassay. Three vasoconstrictors, i.e., serotonin, vasopressin and the TXA2/PGH2 analog U46619, as well as authentic PGD2, PGE2 and PGF2 alpha were infused. PGD2, PGE2 and PGF2 alpha exerted a dose-related coronary vasoconstriction, as did U46619, serotonin and vasopressin. Treatment with 13-APA (100 microM) or SQ 29,548 (100 nM) almost abolished U46619-induced vasoconstriction. The addition of PGH2/TXA2 receptor antagonists also significantly reduced the pressor effect of exogenously administered PGs, serotonin and vasopressin, with the exception that SQ 29,548 did not significantly antagonize PGE2-induced vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro characterization of a novel TXA2/PGH2 receptor ligand (S-145) in platelets and vascular and airway smooth muscle.

The stereoisomers of S-145, a novel thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor ligand, were compared to TXA2/PGH2 receptor antagonists, SQ29548 and BM13505 in guinea pig platelets, aortas and trachea. Equilibrium binding assays in platelets yielded Kd values (nanomolar) for (+)-S-145 (0.57 +/- 0.04), (-)-S-145 (9.2 +/- 1.3), SQ29548 (11.1 +/- 0.70) and BM13505 (118 +/- 16). In aortas, the corresponding Kb values (nanomolar) were (0.014 +/- 0.002), (1.90 +/- 0.31), (16.8 +/- 3.3) and (142 +/- 29), respectively, whereas in trachea, the Kd values (nanomolar) were (0.019 +/- 0.004), (1.12 +/- 0.18), (1.94 +/- 0.30) and (18.99 +/- 2.59), respectively. S-145 stereoisomers elicited platelet shape change stereoselectively that was characterized by EC50 values 8 to 16-fold higher than the EC50 values for these ligands to block aggregation induced by TXA2/PGH2 mimetic, U44069. S-145 (+)- and (-)-isomers stereoselectively induced transient aortic contraction at concentrations 214,000- and 16,000-fold higher, respectively, than the corresponding Kb values in this tissue. S-145-induced platelet shape change and aortic contraction were inhibitable by low concentrations of SQ29548. We postulate that S-145 may elicit partial agonist activity in platelets and aorta via lower affinity for the active than inactive state of the TXA2/PGH2 receptor in those tissues. S-145 had no agonist activity in isolated trachea possibly indicating different TXA2/PGH2 recognition sites in aorta and trachea or a smaller preligand ratio of active to inactive TXA2/PGH2 receptors in trachea than in aorta.     

Distinct platelet thromboxane A2/prostaglandin H2 receptor subtypes. A radioligand binding study of human platelets.

Thromboxane A2 (TXA2) and prostaglandin H2 (PGH2) may aggregate platelets via a common membrane receptor(s). To further characterize this receptor, binding of the radiolabeled TXA2/PGH2 mimetic [125I]BOP to washed human platelets (WP) was investigated. [125I]BOP was competitively displaced from its platelet binding site by stable TXA2/PGH2 analogues. Competition curves were shallow with Hill coefficients of -0.73 +/- 0.05 (P less than 0.001 different from unity) (90 +/- 1% specific binding). Scatchard plots were curvilinear and most consistent with two binding sites; a high-affinity site with Kd of 234 +/- 103 pM, Bmax of 0.7 +/- 0.3 pM/mg protein (180 +/- 87 sites/WP), and a lower affinity site with Kd of 2.31 +/- 0.86 nM, Bmax of 2.2 +/- 0.3 pM/mg protein (666 +/- 65 sites/WP). [125I]BOP association and dissociation kinetics gave a Kd of 157 pM without evidence of negative cooperativity. The EC50 for I-BOP-induced initial Ca2+ increase was 209 +/- 24 pM, shape change was 263 +/- 65 pM, and aggregation was 4.4 +/- 0.5 nM. Parallel binding studies using the TXA2/PGH2 receptor antagonist [125I]PTA-OH showed a single binding site. The rank order for TXA2/PGH2 analogues to displace [125I]PTA-OH was identical to that for [125I]BOP. These studies indicate that [125I]BOP binds to two distinct sites on human platelets that may represent platelet TXA2/PGH2 receptor subtypes. The close correlation of IC50 values for I-BOP-induced platelet shape change and aggregation with the two Kds for [125I]BOP binding suggests that these platelet responses may be independently mediated by the two putative receptors.     

Arachidonic acid-induced platelet aggregation is mediated by a thromboxane A2/prostaglandin H2 receptor interaction

The mechanism by which the active metabolites of arachidonic acid (AA), i.e., thromboxane A2 and/or prostaglandin H2 (TXA2/PGH2) induce platelet aggregation is not understood. Several reports have suggested that AA-stimulated aggregation is mediated by secreted ADP, whereas other studies have proposed that this response is ADP-independent. In the present report, we used the specific TXA2/PGH2 receptor antagonist, 13-azaprostanoic acid (13-APA), and the ADP antagonist, ATP, to examine the contribution of TXA2/PGH2 or secreted ADP to aggregation. We found that 13-APA, but not ATP, deaggregates platelets stimulated by AA or U46619 (a TXA2/PGH2 mimetic). In contrast, ADP-induced aggregation was reversed in response to ATP but not to 13-APA. These results suggest that TXA2/PGH2-stimulated aggregation is mediated through TXA2/PGH2 receptor occupation. Furthermore, secreted ADP does not appear to be required for maintenance of the AA-aggregation response.     

弥漫性脑损伤后低血压及高热对鼠脑血栓素 A_2 与前列环素代谢的变化

目的：探讨二次脑创伤（如低血压与高热）后大鼠脑血栓素Ａ２（ＴＸＡ２）与前列环素（ＰＧＩ２）的代谢变化及意义。方法：在Ｍａｒｍａｒｏｕ弥漫性脑损伤模型基础上，采用抽血造成低血压，及高热形成二次脑创伤。３２只ＳＤ大鼠随机分为假手术对照组、单纯脑损伤组、单纯二次脑创伤组及脑损伤合并二次脑创伤４组。所有动物均实施同步生理监护，伤后４小时检测脑内ＴＸＡ２与ＰＧＩ２的稳定代谢产物血栓素Ｂ２（ＴＸＢ２）及６酮前列腺素Ｆ１α（６ｋｅｔｏＰＧＦ１α）含量。结果：伤后４小时，与假手术组比较，脑损伤组ＴＸＢ２及６ｋｅｔｏＰＧＦ１α含量无明显变化；单纯二次脑创伤组仅６ｋｅｔｏＰＧＦ１α含量升高（Ｐ＜０．０５）；合并二次脑创伤组ＴＸＢ２及６ｋｅｔｏＰＧＦ１α含量均显著升高（Ｐ均＜０．０５），但ＴＸＢ２／６ｋｅｔｏＰＧＦ１α比值下降。结论：原发脑损伤后，合并低血压与高热可使ＴＸＡ２大量生成，通过引起脑血管痉挛及微血栓形成，增加脑微循环阻力，导致脑缺血、缺氧而加重原发性脑损伤。     

Pharmacologic characterization of human and canine thromboxane A2/prostaglandin H2 receptors in platelets and blood vessels: evidence for different receptors

The present study was undertaken to characterize thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors in platelets and blood vessels. Both human and canine platelet aggregation and saphenous vein contractions were induced by the stable TXA2/PGH2 mimetics (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z, 13E-dienoic acid (U46619) and 9,11-epithio-11,12-methano-TXA2 (ONO-11113). ONO-11113 was a more potent agonist than U46619 in the human saphenous vein but less potent in the platelet. These agonists were equipotent in the canine platelet but ONO-11113 was more potent in the saphenous vein. Platelet aggregation and saphenous vein contraction induced by U46619 were blocked in a dose-dependent manner by the TXA2/PGH2 receptor agonists 9,11-dimethylmethano-11,12-methano-16-phenyl-13,14-dehydro-13-aza- 15 alpha beta-omega-tetranor-TXA2 (ONO-11120), 9,11-dimethylmethano-11,12-methano-16-(4-hydroxyphenyl)-13,14-d ihy dro-13-aza-15 alpha beta-omega-tetranor-TXA2 (PTA-OH), 9,11-dimethylmethano-11,12-methano-16-(4-methoxyphenyl)-13,14-d ihy dro-13-aza-15 alpha beta-omega-tetranor-TXA2 (PTA-OM), 9,11-dimethylmethano-11,12-methano-16-(3-iodo-4-hydroxyphenyl-13,1 4-dihydro-13- aza-15 alpha beta-omega-tetranor-TXA2 (I-PTA-OH) and 9,11-dimethylmethano-11,12-methano-15-phenyl-13,14-dihydro-13-aza- 15 alpha beta-omega-pentanor-TXA2 [PTA-(omega-1)].(ABSTRACT TRUNCATED AT 250 WORDS)     

血浆血栓素A_2/前列腺素I_2值与骨骼肌无复流现象

背景：在骨骼肌无复流现象中血栓素A2及前列腺素I2是重要参与因子。目的：观察下肢动脉栓塞患者血浆血栓素A2/前列腺素I2值与骨骼肌发生无复流现象的关系。方法：选择经影像学及临床表现确诊为下肢动脉栓塞患者36例,行下肢动脉取栓,根据患者取栓后缺血肢体是否发生无复流现象分为无复流组（n=10）和对照组（n=26）。结果与结论：与对照组比较,无复流组取栓后0h无复流组前列腺素I2明显减少（P〈0.01）;取栓后24h,无复流组血栓素A2明显升高、前列腺素I2明显下降（P〈0.01）。与对照组相比,无复流组术后血栓素A2/前列腺素I2值升高（P〈0.05）。与术前相比,对照组术后血栓素A2/前列腺素I2值升高后然后下降,无复流组取栓后均维持较高的水平。而取栓前后两组血小板数量及血浆纤维蛋白原的水平差异均无显著性意义。同时术后24h点无复流组血栓素A2/前列腺素I2值与纤维蛋白原呈正相关（r=0.613,P=0.049）;而与血小板数量无相关性（r=0.199,P=0.543）。提示血栓素A2/前列腺素I2值可以作为判断动脉栓塞患者缺血再灌注后骨骼肌发生无复流现象的指标之一。     

Prostaglandin endoperoxides modulate the response to thromboxane synthase inhibition during coronary thrombosis.

Prostaglandin endoperoxides (PGG2/PGH2), precursors of thromboxane (TX) A2 and prostaglandins, may accumulate sufficiently in the presence of a TXA2 synthase inhibitor to exert biological activity. To address whether this modulates the response to TXA2 synthase inhibition in the setting of thrombosis in vivo, we examined the interaction of a TXA2 synthase inhibitor (U63,557a) and a TXA2/prostaglandin endoperoxide receptor antagonist (L636,499) in a canine model of coronary thrombosis after electrically induced endothelial injury. U63,557a exerted little inhibitory effect in this model despite a marked reduction in serum TXB2 and urinary 2,3-dinor-TXB2, an index of TXA2 biosynthesis. Combination of the two drugs was more effective than either drug alone. The enhanced effect achieved upon addition of the TXA2/prostaglandin endoperoxide receptor antagonist to the TXA2 synthase inhibitor suggests that the response to the latter compound was limited by the proaggregatory effects of prostaglandin endoperoxides. The increased effect of the combination over the receptor antagonist alone may reflect metabolism of PGG2/PGH2 to platelet inhibitory prostaglandins. This is supported by the following findings: (a) urinary 2,3-dinor-6-keto-PGF1 alpha, an index of prostacyclin biosynthesis, increased after administration of the synthase inhibitor, an effect that was exaggerated in the presence of thrombosis; (b) inhibition of arachidonate-induced platelet aggregation by U63,557a was dependent on the formation of a platelet-inhibitory prostaglandin; and (c) pretreatment with aspirin abolished the synergism between these compounds. These studies demonstrate that prostaglandin endoperoxides modulate the response to TXA2 synthase inhibition in vivo and identify a drug combination of potential therapeutic efficacy in the prevention of thrombosis.     

Cardiac and Renal Prostaglandin I2: BIOSYNTHESIS AND BIOLOGICAL EFFECTS IN ISOLATED PERFUSED RABBIT TISSUES

Both the isolated perfused rabbit heart and kidney are capable of synthesizing prostaglandin (PG) I(2). The evidence that supports this finding includes: (a) radiochemical identification of the stable end-product of PGI(2), 6-keto-PGF(1alpha), in the venous effluent after arachidonic acid administration; (b) biological identification of the labile product in the venous effluents which causes relaxation of the bovine coronary artery assay tissue and inhibition of platelet aggregation; and (c) confirmation that arachidonic acid and its endoperoxide PGH(2), but not dihomo-gamma-linolenic acid and its endoperoxide PGH(1), serve as the precursor for the coronary vasodilator and the inhibitor of platelet aggregation. The rabbit heart and kidney are both capable of converting exogenous arachidonate into PGI(2) but the normal perfused rabbit kidney apparently primarily converts endogenous arachidonate (e.g., generated by stimulation with bradykinin, angiotensin, ATP, or ischemia) into PGE(2); while the heart converts endogenous arachidonate primarily into PGI(2). Indomethacin inhibition of the cyclo-oxygenase unmasks the continuous basal synthesis of PGI(2) by the heart, and of PGE(2) by the kidney. Cardiac PGI(2) administration causes a sharp transient reduction in coronary perfusion pressure, whereas the intracardiac injection of the PGH(2) causes an increase in coronary resistance without apparent cardiac conversion to PGI(2). The perfused heart rapidly degrades most of the exogenous endoperoxide probably into PGE(2), while exogenous PGI(2) traverses the heart without being metabolized. The coronary vasoconstriction produced by PGH(2) in the normal perfused rabbit heart suggests that the endoperoxide did not reach the PGI(2) synthetase, whereas the more lipid soluble precursor arachidonic acid (exogenous or endogenous) penetrated to the cyclooxygenase, which apparently is tightly coupled to the PGI(2) synthetase.     

Antagonism of thromboxane A2/prostaglandin H2 by 13-azaprostanoic acid prevents platelet deposition to the de-endothelialized rabbit aorta in vivo

The present study evaluated the direct involvement of thromboxane A2/prostaglandin H2 (TXA2/PGH2) in the process of thrombus formation at a site of vascular damage. De-endothelialization of the rabbit aorta was performed by a balloon catheter technique. Platelet deposition to the injured vessel was measured using 111Indium-labeled autologous platelets. Studies using the radiolabeled TXA2/PGH2 antagonist, 13-azaprostanoic acid (13-APA), indicated that 13-APA has an in vivo half-life of approximately 35 min and is excreted by the kidney in the metabolized form. Addition of 13-APA to rabbit plasma samples in vitro produced a dose-dependent inhibition of arachidonic acid-induced platelet aggregation. When comparable plasma levels of 13-APA were achieved by infusion of 13-APA (300 micrograms/kg/min for 90 min), a similar dose-dependency of inhibition of ex vivo aggregation was observed. Furthermore, at a plasma concentration of 40 microM, 13-APA was found to inhibit platelet deposition to the de-endothelialized rabbit aorta by 45%. Because 13-APA does not interfere with arachidonic acid metabolism, the ability of 13-APA to suppress thrombus formation is presumably due to direct antagonism of TXA2/PGH2 at the platelet receptor level. These findings, therefore, provide evidence that TXA2 and/or PGH2 have a major role in platelet deposition at a site of vascular damage.     

Effects of nitroglycerin on human vascular prostacyclin and thromboxane A2 generation

We examined the effects of NTG on human saphenous and umbilical vein PGI2 and TXA2 generation. Vascular rings from both types of vessels generated TXA2 in addition to PGI2. The treatment of vascular rings with NTG in concentrations of 5 to 1000 ng/ml and subsequent incubation with AA caused a significant increase in PGI2 in the supernatants, as identified by bioassay (platelet aggregation inhibition) and by measurement of 6-keto-PGF1 alpha (stable hydrolysis product of PGI2). The maximum increase in PGI2 was observed with therapeutic concentrations of NTG, i.e., 5 to 10 ng/ml. The levels of vessel wall-generated TXB2 (stable metabolite of TXA2) were not affected by NTG treatment. A prior incubation of vascular rings with indomethacin abolished the increase in PGI2 after NTG treatment. In contrast, incubation of vascular rings with OKY 1581 (selective TXA2 inhibitor) resulted in a significant additional increase in PGI2 release but no change in TXB2 levels after NTG treatment. These studies indicate important effects of NTG on vascular PGI2 generation but not on TXA2 generation.     

次声对脑组织血栓素A_2、前列环素代谢的影响

目的　探讨次声作用后脑皮层组织血栓素A2 (TXA2 )、前列环素 (PGI2 )代谢改变及及代谢性谷氨酸受体拮抗剂MCPG的作用。方法　 40只SD大鼠随机分为正常对照、次声作用 1次、7次、14次及代谢性谷氨酸受体拮抗剂MCPG治疗 5组。采用第四军医大学研制的次声压力仓。用 8Hz、12 0dB的次声按规定次数 ,每次作用 2h。采用蛋白定量和放免法行脑TXA2 、PGI2 稳定代谢产物血栓素B2 (TXB2 )及 6 酮 PGF1α( 6 酮 )含量测定。结果　 7次与 14次组 ,TXB2 含量有显著意义升高 (P <0 .0 1) ,6 酮含量明显降低 (P <0 .0 1)。TXA2 /PGI2 值呈递增趋势 ;治疗组 ,TXB2 及 6 酮含量与TXA2 /PGI2 值恢复致正常水平。结论　次声可以通过引起脑TXA2 、PGI2 代谢改变造成脑损害 ,是次声导致脑损害的关键因素之一。MCPG可能通过影响脑TXA2 、PGI2 代谢改变而起脑保护作用。     

Prostaglandins in the kidney: developments since Y2K

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE(2), PGI(2) (prostacyclin), PGD(2), PGF(2alpha) and TXA(2) (thromboxane A(2)). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE(2) receptor), IP (PGI(2) receptor), DP (PGD(2) receptor), FP (PGF(2alpha) receptor) and TP (TXA(2) receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.     

Binding of a thromboxane A2/prostaglandin H2 receptor antagonist to washed human platelets

A binding site for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) antagonist [125I]9,11-dimethylmethano-11, 12-methano-16-(3-iodo-4-hydroxyphenyl)-13,14-dihydro-13-aza-15 alpha beta-omega-tetranor-TXA2 to washed human platelets was studied. 9,11-Dimethylmethano-11, 12-methano-16-(3-iodo-4-hydroxyphenyl)-13,14-dihydro-13-aza-15 alpha beta-omega-tetranor-TXA2 competitively antagonized aggregation of washed human platelets induced by the TXA2/PGH2 mimetic U46619. A Schild analysis of the pharmacologic study revealed a pA2 of 8.08 and a slope of -1.12. The pA2 value yielded a Kd of 8 nM. The association rate constant (k1) for [125I]PTA-OH was 6.6 X 10(6)M-1 min-1 and the dissociation rate constant (k-1) was 1.82 X 10(-1), yielding a kinetically determined Kd (k-1/k1) of 27 nM. Scatchard analysis of [125I]PTA-OH binding to washed human platelets revealed one class of binding sites with a Kd of 21 +/- 5 nM and maximum binding of 42 +/- 6.4 fmol/10(7) platelets (N = 5) (2530 +/- 380 binding sites/platelet). Several TXA2/PGH2 receptor agonists and antagonists competed with [125I]PTA-OH for binding. For the four antagonists used in this study, the rank order of potency for displacing the ligand from its binding site correlated (r = 0.93) with the rank order of potency for their ability to inhibit U46619-induced aggregation in human platelet-rich plasma. The antiaggregatory prostaglandins prostaglandin F2 alpha, prostaglandin D2, and Iloprost also displaced the ligand, but only at concentrations considerably higher than that required to produce their pharmacologic effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization and distribution of endothelin receptors in the pulmonary circulation: investigation of isolated, perfused, and ventilated rabbit lungs.

The aim of the study was to investigate the distribution of 2 subtypes of endothelin-receptors, mediating the effects of endothelin-1 (ET-1) in the pulmonary circulation. Until now, it is still unclear, whether ET(A) receptors or ET(B) receptors or even both are localized in pulmonary vessels. The experiments were performed on 72 isolated and ventilated rabbit lungs that were perfused with a cell- and plasma-free buffer solution. The arterial pressure and the lung weight gain were continuously registered. Intermittently perfusate samples were taken for determination of thromboxane A2 (TXA2) and prostacyclin (PGI2). The injection of ET-1 (10(-8) M, n = 6) resulted in a biphasic increase in pulmonary arterial pressure (PAP) that was accompanied by the generation of TXA2 and PGI2. Pretreatment with the ET(A)-receptor antagonist LU135252 (10(-6) M, n = 6) suppressed the pressure response after ET-1 application (P < 0.01 at 120 min) and reduced the generation of TXA2 (P < 0.05 at 120 min) and PGI2 (P < 0.05 at 120 min). Pretreatment with the cyclooxygenase inhibitor diclofenac (10 microg/mL; n = 6) also reduced the PAP increase after ET-1 injection. In contrast to this, the pulmonary vascular pressure reaction after ET-1 application was elevated, when ET(B)-receptor antagonist BQ788 (10(-6) M; n = 6) was given. Furthermore, the PGI2 to TXA2 ratio was shifted from 2.3 to 0.9, reflecting a predominance of vasoconstrictive TXA2. The simultaneous application of LU135252 and BQ788 significantly reduced the PAP increase after ET-1 application, but no beneficial effects were observed compared with the application of LU135252 solely. The injection of the ET(B)-receptor agonist sarafotoxin S6c (S6c; 10(-8) M, n = 6) also induced an increase in PAP that was not attenuated by pretreatment with the ET(B)-receptor antagonist BQ788 (10(-6) M, n = 6). LU135252 (n = 6) as well as the application of LU135252 in combination with BQ788 (n = 6) failed to suppress the pressure response after S6c, whereas the cyclooxygenase inhibitor diclofenac (10 microg/mL, n = 6) alone and in combination with LU135252 and BQ788 (n = 6) was able to prevent the PAP increase after S6c injection (P < 0.001). The results demonstrate that the ET-1-induced increase in pulmonary vascular resistance is mainly mediated via ET(A) receptors, whereas ET(B) receptors seem to mediate vasodilation, which was shown by an imbalance of TXA2 and PGI2 generation. On the other hand, the ET(B)-receptor agonist S6c induced vasoconstriction, which was only attenuated by the cyclooxygenase inhibitor diclofenac. From the current results we conclude that, apart from vasoconstrictor ET(A) receptors, at least 2 ET(B)-receptor subtypes are expressed in the pulmonary circulation, one mediating vasoconstriction, which was not blocked by BQ788, and one mediating vasodilation, which was influenced by BQ788.     

血浆血栓素A2/前列腺素I2值与骨骼肌无复流现象

背景:在骨骼肌无复流现象中血栓素A2及前列腺素I2是重要参与因子.目的:观察下肢动脉栓塞患者血浆血栓素A2/前列腺素I2值与骨骼肌发生无复流现象的关系.方法:选择经影像学及临床表现确诊为下肢动脉栓塞患者36例,行下肢动脉取栓,根据患者取栓后缺血肢体是否发生无复流现象分为无复流组(n=10)和对照组(n=26).结果与结论:与对照组比较,无复流组取栓后0 h无复流组前列腺素I2明显减少(P < 0.01);取栓后24 h,无复流组血栓素A2明显升高、前列腺素I2明显下降(P < 0.01).与对照组相比,无复流组术后血栓素A2/前列腺素I2值升高(P < 0.05).与术前相比,对照组术后血栓素A2/前列腺素I2值升高后然后下降,无复流组取栓后均维持较高的水平.而取栓前后两组血小板数量及血浆纤维蛋白原的水平差异均无显著性意义.同时术后24 h点无复流组血栓素A2/前列腺素I2值与纤维蛋白原呈正相关(r=0.613,P=0.049);而与血小板数量无相关性(r=0.199,P=0.543).提示血栓素A2/前列腺素I2值可以作为判断动脉栓塞患者缺血再灌注后骨骼肌发生无复流现象的指标之一.     

Desensitization of platelet thromboxane A2/prostaglandin H2 receptors by the mimetic U46619

Thromboxane A2 (TXA2) and prostaglandin H2 (PGH2) activate platelets through membrane receptors. This study sought to determine if changes occur in the TXA2/PGH2 receptor during its desensitization induced by exposure to its agonist 11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619). Washed human platelets were incubated for 30 min with U46619 in the presence of an antiaggregatory agent, Iloprost. The platelets were washed and the aggregation response to U46619 was determined. The EC50 increased from 372 +/- 94 nM in the control group to 826 +/- 143 nM for the U46619-pretreated group (n = 7). This desensitization was specific inasmuch as the aggregation responses to thrombin and the calcium ionophore A23187 were not affected by U46619 pretreatment. Desensitization was accompanied by a decrease in the number of binding sites for [3H]U46619 from 789 +/- 189 in the control to 386 +/- 120 sites per platelet in the U46619-treated group (n = 5) and a decrease in the number of binding sites for the TXA2/PGH2 receptor antagonist, [125I]9,11-dimethylmethano-11,12-methano-16(3-iodo-4-hydroxyphenyl )-13,14- dihydro-13-aza-15-alpha beta-omega-tetranor-TXA2 from 3988 +/- 957 to 2443 +/- 553 (n = 8). The Kd for U46619 was 37 +/- 10 nM in the control group and 23 +/- 11 nM for the U46619-treated group (n = 5). The Kd for I-9,11-dimethylmethano-11,12-methano-16(3-iodo-4-hydroxyphenyl)-13 ,14-dihydro- 13-aza-15-alpha beta-omega-tetranor-TXA2 changed from 58 +/- 12 nM in the control to 44 +/- 9 nM in the U46619-treated group (n = 8).(ABSTRACT TRUNCATED AT 250 WORDS)     

内皮素、前列环素与血栓素在妊娠高血压综合征发病中的作用

【目的】为探讨内皮素（ＥＴ－１）、前列环素（ＰＧＩ２）、血栓素（ＴＸＡ２）在妊娠高血压综合征（妊高征）发病中的作用。【方法】应用放射免疫法测定５５例妊高征患者,２３例正常妊娠妇女血浆ＥＴ－１,ＰＧＩ２,ＴＸＡ２浓度。【结果】①妊高征患者血浆ＥＴ－１浓度高于正常妊娠妇女,且随病情加重而上升。②中、重度妊高征患者血浆ＰＧＩ２较正常妊娠妇女低,中、重度妊高征患者血浆ＴＸＡ２较正常妊娠妇女高,两者随妊高征病情加重而下降或上升。③中、重度妊高征患者血浆ＥＴ－１与ＰＧＩ２呈负相关,与ＴＸＡ２呈正相关,ＰＧＩ２与ＴＸＡ２呈负相关。【结论】①ＥＴ－１,ＰＧＩ２,ＴＸＡ２可作为判断妊高征病情的指标。②ＥＴ－１可能是妊高征发病的主要原因。③ＰＧＩ２对ＥＴ－１具有拮抗作用,推测补充外源性ＰＧＩ２可能成为治疗妊高征的有效途径。     

强化胰岛素治疗对脓毒症大鼠肠道微循环的影响研究

目的 探讨强化胰岛素治疗对脓毒症时小肠微循环障碍的影响.方法 采用盲肠结扎穿孔术(CLP)制备脓毒症模型.将雄性SD大鼠随机分为对照组、脓毒症组、胰岛素组,每组16只.于给药后3、6、12、24 h各处死4只大鼠,取肠组织,采用放射免疫法检测血小板活化因子(PAF)、前列环素(PGI2)和血栓素A2(TXA2)含量.结果 脓毒症组大鼠制模后3 h PAF、PGI2、TXA2水平即明显升高,6 h达峰值,之后逐渐下降;不同时间点均较对照组明显升高(P均<0.05),且以TXA2升高明显,PGI2/TXA2比值降低.胰岛素组各时间点PAF、PGI2、TXA2水平均较脓毒症组明显降低,以TXA2降低较明显(P均<0.05),PGI2/TXA2比值升高.结论 胰岛素可通过改善PGI2/TXA2系统的失衡,对抗PAF过度分泌而减轻肠道微循环血管痉挛、抗血小板聚集、抑制血栓形成,从而起到保护脓毒症时肠道功能的作用.