The thromboxane A2/prostaglandin endoperoxide receptor antagonist activity of CV-4151, a thromboxane A2 synthetase inhibitor

The thromboxane A2/prostaglandin endoperoxide (TXA2/PGH2) receptor antagonist activity of CV-4151, a potent TXA2 synthetase inhibitor, was examined. CV-4151 inhibited guinea pig and human platelet aggregation induced by U-44069 with IC50 values of 1.2 +/- 0.3 X 10(-5) and 1.9 +/- 0.4 X 10(-5) M, respectively, and inhibited the specific binding of [3H]U-46619 to washed guinea pig and human platelets with IC50 values of 1.2 +/- 0.3 X 10(-6) and 5.1 +/- 1.0 X 10(-6) M, respectively. CV-4151 competitively inhibited the contraction of rabbit aortic strips induced by U-44069 with a pA2 value of 5.90. In experiments in mice in vivo, CV-4151 (1 and 10 mg/kg i.v.) significantly inhibited the thrombocytopenia induced by U-44069 in a dose-dependent manner. These results show that CV-4151 has a distinct TXA2/PGH2 receptor antagonist effect, and that this effect together with its inhibition of TXA2 synthetase could be important for the pharmacological action of this compound.     

Pharmacology of L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpro pan oic acid); a potent, selective thromboxane/prostaglandin endoperoxide antagonist

L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpropa noic acid) has been studied in vitro on the guinea-pig tracheal chain, pulmonary artery and thoracic aorta ring and shown to be a potent, competitive antagonist of contractions induced by the prostaglandin endoperoxide analogue, U-44069 (pA2 values 8.0, 8.4 and 8.0 respectively). Selectivity on the guinea-pig trachea was indicated by non-competitive antagonism of contractions induced by prostaglandin D2 and minimal activity against contractions induced by leukotriene D4, prostaglandin F2 alpha, serotonin, histamine and acetylcholine. L-655,240 was a potent inhibitor of the aggregation of washed human platelets induced by U-44069 (IC50 value 7 X 10(-9) M) and inhibited aggregation of human platelet rich plasma induced by U-44069, U-46619, thromboxane A2 and collagen but not ADP or platelet activating factor. In vivo i.v. L-655,240 administered to guinea-pigs inhibited bronchoconstriction induced by i.v. U-44069 and arachidonic acid (ED50 values 0.09 and 0.23 mg kg-1) but not histamine, acetylcholine or serotonin. When administered to rhesus monkeys (3 and 10 mg/kg p.o.), L-655,240 inhibited ex vivo platelet aggregation induced by U-44069 but not ADP. It is concluded that L-655,240 is a potent, selective, orally active thromboxane/prostaglandin endoperoxide antagonist.     

Effects of ONO-3708, an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on blood vessels

The pharmacological properties of a novel thromboxane A2/prostaglandin endoperoxide receptor antagonist, ONO-3708, on blood vessels were examined in vitro and in vivo. ONO-3708, 10 microM, inhibited the rabbit aorta contractions induced by thromboxane A2, prostaglandin H2, 11,9-epoxymethano-prostaglandin H2 (U-46619) or prostaglandin F2 alpha without affecting the contractions induced by angiotensin II, serotonin or norepinephrine. ONO-3708, at a concentration of 1 to 100 nM, appeared to be a competitive inhibitor of the contractile responses of the canine basilar artery to 9,11-epithio-11,12-methano-thromboxane A2 (STA2), U-46619 and PGF2 alpha, and a non-competitive inhibitor of the contractile responses to 15-hydroperoxy-eicosatetraenoic acid (15-HPETE). In in vivo studies, ONO-3708 (10 and 100 micrograms/kg per min i.v.) ameliorated the decrease in diameter of the basilar artery induced by the i.v. infusion of STA2 (0.1 microgram/kg per min) in cats. Furthermore, infusion of ONO-3708 (10 and 30 micrograms/kg per min i.v.) prevented the cerebral vasospasm in an experimental subarachnoid hemorrhage model in dogs. These results indicate that ONO-3708 is a potent antagonist of the thromboxane A2/prostaglandin endoperoxide receptor in vitro and in vivo and may be of therapeutic use in preventing cerebral vasospasm.     

Effects of ONO-3708, an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on platelet aggregation and thrombosis

The beneficial effects of an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, 7-[2 alpha,4 alpha-(dimethylmethano)-6 beta-(2-cyclopentyl-2 beta- hydroxyacetamido)-1 alpha-cyclohexyl]-5(Z)-heptenoic acid (ONO-3708) on thrombosis were examined. ONO-3708 at 0.1-3 microM inhibited the human platelet aggregation induced by thromboxane A2, prostaglandin H2, collagen, ADP (secondary phase) and epinephrine (secondary phase) without affecting prostanoid synthesis and the content of cyclic AMP in platelets. The in vivo effects, on coronary thrombosis in this case, were examined in two canine models. ONO-3708, 3 to 300 micrograms/kg i.v., prevented dose dependently the coronary thrombosis induced by partial obstruction of the coronary artery. ONO-3708, 3 micrograms/kg per min i.v., significantly prevented electrically stimulated coronary thrombosis without affecting systemic blood pressure and heart rate. These results indicate that the thromboxane A2/prostaglandin endoperoxide receptor could play an important role in the pathogenesis of thrombosis and that ONO-3708 may have therapeutic advantages in preventing thrombosis.     

Anesthetized rabbit as a model for ischemia- and reperfusion-induced arrhythmias: Effects of quinidine and bretylium

Experiments were performed to assess the feasibility of using anesthetizes rabbits for the study of ischemia- and reperfusion-induced arrhythmias. Initial studies indicated that occulusion of the left anterior descending coronary artery produced ectopic activity in only one out of eight rabbits. All rabbits subject to occlusion of the left circumflex artery below where it emerges from under the left atrial appendage had ECG changes (ST-segment elevation, Lead II), 80% had arrhythmias, and 50% died in ventricular fibrillation during the first 20 min of coronary artery occulusion. Subsequent reperfusion in the survivors produced further arrhythmias in the majority of rabbits, and one fibrillated. Although a high incidence of ectopic activity was also observed in rabbits subject to occlusion of the left circumflex artery close to its origin, or both the left anterior descending and circumflex arteries, this was accompanied by marked reductions in arterial blood pressure. Thus, occlusion of the left circumflex artery at the lower site was chosen for all further studies. Quinidine hydrochloride 10 mg kg⁻¹ (n = 1) or bretylium tosylate 20 mg kg⁻¹ (n = 10) administered 15 min prior to coronary artery occlusion reduced the incidence of ischemia-induced ventricular fibrillation to 10% compared with 60% in controls (n = 15). Although bretylium reduced arterial blood pressure and heart rate, neither drug altered the hemodynamic consequences of coronary artery occulusion (e.g., increased left ventricular end diastolic pressure). Bretylium at doses of 5 and 20 mg kg⁻¹, but not quinidine, reduced the ST-segment elevation that developed during the ischemic period. The ability to detect the antifibrillatory activity of quinidine and bretylium suggests that the anesthetized rabbit may provide a useful alternative or additional model for the study of arrhythmias induced by acute myocardial ischemia.     

Diversion of prostaglandin endoperoxide metabolism by selective inhibition of thromboxane A2 biosynthesis in lung, spleen or platelets.

Infusion of arachidonic acid through the guinea pig lung or the cat spleen causes a release of thromboxane A2 and prostaglandins, as measured by bioassay. After incubation of human platelets with arachidonate similar metabolites are formed, as demonstrated chromatographically. Infusion of imidazole (50-75 microgram/ml) through the lung or spleen specifically inhibits thromboxane A2 production and diverts the pathway to the prostaglandins, mainly prostaglandin F2alpha. In human platelets imidazole causes a dose-dependent inhibition of thromboxane A2 formation (ID50 5.5 X 10(-4) M). This inhibition is accompanied by a dose-dependent increase in prostaglandin F2alpha. Since thromboxane A2 induces platelet aggregation and is a potent vasoconstrictor, diversion of pathways to prostaglandins with opposite or less potent action might be of relevance in the treatment of cardiovascular diseases.     

Effect of (+)-S-145 calcium salt dihydrate, an orally active antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on platelet aggregation

The effect of (+)-S-145, (1R, 2S, 3S, 4S)-(5Z)-7-(3-phenylsulfonylaminobicyclo [2.2.1] hept-2-yl) heptenoic acid on human and guinea pig platelet aggregation was examined. (+)-S-145 sodium salt inhibited human platelet aggregation induced by arachidonic acid (AA), 9,11-methanoepoxy-PGH2 (U 46619), collagen, ADP or epinephrine with the IC50 being 0.047-0.146 microM in an in vitro system. When (+)-S-145 calcium salt dihydrate was administered orally to guinea pigs, it inhibited AA-, U-46619- or collagen-induced platelet aggregation dose-dependently with the minimum effective dose being 0.03 mg/kg, and the effective duration being maximally 3 hr. The inhibiting potency and effective duration of (+)-S-145 calcium salt dihydrate after multiple administrations, once a day (0.5 mg/kg) for 7 days, were almost the same as those after a single administration. Although (+)-S-145 sodium salt showed a partial agonist effect (shape change) on platelets in vitro, the effect diminished after pretreatment of the platelets with a lower dose of this compound. These data suggest that (+)-S-145 calcium salt dihydrate is an orally effective potent platelet aggregation inhibitor.     

The effect of the thromboxane A2/prostaglandin endoperoxide receptor antagonist SQ 30,741 on myocardial infarct size and blood flow during myocardial ischemia and reperfusion

The effect of the thromboxane A2 (TXA2) receptor antagonist SQ 30,741 on infarct size and myocardial blood flow during coronary occlusion and reperfusion was determined. In anesthetized dogs, the left circumflex coronary artery (LCX) was occluded and after 10 min a continuous infusion of SQ 30,741 (1 mg/kg + 1 mg/kg/h, i.v.) or saline was begun. After 90 min of LCX occlusion, the LCX was reperfused for 5 h and infarct size was then determined. Myocardial blood flows before, during, and after occlusion were determined using radioactive microspheres. SQ 30,741 resulted in a significant decrease in infarct size (34% +/- 6% of left ventricular area at risk) compared to controls (60% +/- 9%). Cardioprotection was also found with SQ 30,741 when infarct size was normalized for both area at risk and predrug collateral flow. The protective effect of SQ 30,741 occurred without an increase in collateral flow. At 1 h postreperfusion, subendocardial flow was significantly higher in SQ 30,741-treated animals (109 +/- 15 ml/min/100 g) compared to controls (71 +/- 16 ml/min/100 g). SQ 30,741, in the dose resulting in infarct size reduction, produced a 95% inhibition of platelet TXA2 receptors throughout the experiment as measured by dose-dependent inhibition of the ex vivo platelet shape change response to U-46,619, a TXA2 mimetic. Thus, a dose of SQ 30,741 that results in TXA2 blockade also results in myocardial salvage without changes in collateral flow.     

ICI 180080, a novel selective thromboxane receptor antagonist: synthesis and relative activity

The preparation of a novel potent thromboxane receptor antagonist ICI 180080, 5(Z)-7-[2,2-dimethyl-4-(2-hydroxyphenyl)-1,3-dioxan-cis-5-yl] heptenoic acid, is described together with its methyl ether and methyl ester. Thromboxane antagonist pA2 data against U 46619 is presented for rabbit thoracic aorta in-vitro (ICI 180080, pA2 = 7.5). The relative antagonist pA2 values obtained are discussed in terms of the chemical structure of the molecules. The potent activity of ICI 180080 is attributed to a specific orientation of the phenolic oxygen, due to an intramolecular hydrogen bond.     

Effects of nicotine on cardiac prostaglandin and platelet thromboxane synthesis.

1 Rabbit hearts were perfused with a solution containing [14C]-arachidonic acid (AA) and various concentrations of nicotine (3 x 10(-8) to 3 x 10(-5) M). The venous effluent was collected and extracted for lipid acid material, which was subsequently subjected to thin layer radiochromatography. 2 Human platelets were incubated with nicotine (10(-8) to 10(-4) M), in the absence or presence of unlabelled AA. The amount of smooth muscle stimulating activity resulting from 30s of incubation was tested on a rabbit aortic strip. 3 In hearts perfused with [14C]-AA; nicotine induced a dose-related depression of the release of [14C]-6-keto-prostaglandin F1alpha, and a parallel increase of [14C]-prostaglandin E2. 4 Nicotine neither induced synthesis of thromboxane in human platelets, nor affected the platelet synthesis of thromboxane induced by AA. 5 It is suggested that nicotine affects the metabolism of prostaglandin endoperoxides in the heart by inhibiting their conversion to prostacyclin and facilitating, directly or indirectly, the formation of prostaglandin E2.     

Responsiveness of platelets and coronary arteries from different species to synthetic thromboxane and prostaglandin endoperoxide analogues

1--Platelet-rich plasma (PRP) from humans, cats, dogs (after addition of 10 microM adrenaline), rabbits and guinea-pigs aggregated in response to sodium arachidonate or 9,11-azo-prostaglandin H2, while PRP obtained from sheep was unresponsive to either agent. 2--The stable thromboxane (Tx) analogues, carbocyclic TxA2 (CTA2) and pinane TxA2 (PTA2) significantly inhibited these aggregatory responses in platelets from humans, dogs and guinea-pigs, while PTA2 but not CTA2 produced significant inhibition in cat platelets. The aggregatory response of PRP from rabbits was not significantly blocked by either analogue. 3--CTA2 and the endoperoxide analogue 9,11-methanoepoxy PGH2 (U-46619) constricted coronary arteries from cats, dogs, rabbits and guinea-pigs, while sheep vessels were unresponsive to either analogue. 4--Vasoconstrictor responses to U-46619 were significantly attenuated by PTA2 in vessels from all species. However, constriction produced by CTA2 was blocked significantly only in vessels from cats, dogs and guinea-pigs. 5--These results demonstrate the species differences which exist in the responsiveness of platelets and coronary arteries to thromboxane and endoperoxide analogues. Furthermore, the results illustrate the importance of species selection in the study of thromboxane antagonists for potential therapeutic use.     

小檗碱对大鼠再灌心律失常及钙调节的作用

小檗碱（Ｂｅｒ，１０ｍｇ·ｋｇ－１）使缺血／再灌后ＶＴ发生率明显降低，持续时间明显缩短，无１例发生ＶＦ及死亡，与对照组比较差异有显著性。离体实验表明：小檗碱（３０μｍｏｌ·Ｌ－１），能抑制高钙条件下Ｃａ２＋内流，而增加低钙条件下的Ｃａ２＋内流。结果表明：小檗碱具有预防再灌心律失常作用；不同Ｃａ２＋浓度能够影响心肌４５Ｃａ内流；小檗碱对心肌Ｃａ２＋内流有双向调节作用，尤其在高Ｃａ２＋条件下，降低４５Ｃａ内流可能是其抗心律失常作用机制之一。     

The protective effects of CP-060S on ischaemia- and reperfusion-induced arrhythmias in anaesthetized rats

1. CP-060S is a novel sodium and calcium overload inhibitor, and is also characterized as a calcium channel blocker. As these activities have each been shown independently to ameliorate ischaemia damage in the myocardium, the combination may synergistically exert cardioprotection. In this study, therefore, the protective effect of CP-060S against ischaemia- and reperfusion-induced arrhythmia was evaluated in anesthetized rats.
2. Rats were anaesthetized with pentobarbitone, and the left anterior descending coronary artery was occluded for either 5 min with subsequent reperfusion (a reperfusion-induced arrhythmia model) or 30 min without (an ischaemia-induced arrhythmia model). All drugs were intravenously administered 1 min before the onset of occlusion.
3. In the reperfusion-induced arrhythmia model, the animals in the vehicle-treated group exhibited ventricular tachycardia (VT) in 100%, ventricular fibrillation (VF) in 89%, and death caused by sustained VF in 56%. CP-060S (30–300 μg kg⁻¹) dose-dependently suppressed the incidences of arrhythmias. Significant decreases occurred at 100 μg kg⁻¹ in VF (incidence: 42%) and mortality (8%), and at 300 μg kg⁻¹ in VT (50%), VF (33%) and mortality (8%). This protective effect of CP-060S was 10 times more potent than that of a pure calcium channel blocker, diltiazem (30–1000 μg kg⁻¹) we tested, in terms of effective dose ranges. As both drugs decreased myocardial oxygen consumption estimated by rate-pressure product to a similar extent, the calcium channel blocking activity of CP-060S would not seem to be sufficient to explain its potency.
4. In the same model, co-administration of ineffective doses of diltiazem (300 μg kg⁻¹) and a sodium and calcium overload inhibitor, {"type":"entrez-nucleotide","attrs":{"text":"R56865","term_id":"826971","term_text":"R56865"}}R56865 (100 μg kg⁻¹), produced significant suppression of VT (incidence: 62%), VF (46%) and mortality (8%). By contrast, co-administration of {"type":"entrez-nucleotide","attrs":{"text":"R56865","term_id":"826971","term_text":"R56865"}}R56865 at the same dose with CP-060S (300 μg kg⁻¹) did not add to the effect of a single treatment of CP-060S.
5. In the ischaemia-induced arrhythmia model, CP-060S (300 μg kg⁻¹) significantly decreased the incidence of VF from 75% to 29%, whereas diltiazem (1 mg kg⁻¹) was ineffective.
6. These results suggest that CP-060S inhibits both ischaemia- and reperfusion-induced arrhythmia. The combination of the calcium channel blocking effect and the calcium overload inhibition was hypothesized to contribute to these potently protective effects.

     

Effects of sotalol, (-)-propranolol and prazosin on reperfusion-induced arrhythmias and increased cardiac norepinephrine release

The pharmacological actions of sotalol, (-)-propranolol and prazosin on norepinephrine (NE) concentration and creatine kinase (CK) activity in the coronary sinus blood of the ischemic heart were studied in open-chest dogs. A 60 min occlusion of the left anterior descending coronary artery was followed by a reperfusion period of 30 min. In saline-treated dogs, a significant increase in coronary sinus NE concentration occurring 30 s after the onset of reperfusion was followed by a rapid decrease to the initial value within 15 min. CK activity increased gradually and continuously starting 5 min after the beginning of reperfusion. A good correlation (r = 0.9, n = 8, P less than 0.05) was obtained in saline-treated dogs when the calculated slope of the time-activity curves for CK release was plotted against the corresponding peak concentration of NE. The increase in coronary sinus NE concentration upon reperfusion was accompanied by an increased arrhythmic ratio. Sotalol (5 mg/kg i.v.) diminished the increase in coronary sinus NE concentration along with a significant decrease in the arrhythmic ratio. The administration of either (-)-propranolol (0.1 mg/kg i.v.) or prazosin (1 mg/kg i.v.) did not significantly affect the increase in coronary sinus NE concentration. The arrhythmic ratio was significantly reduced by prazosin but not by (-)-propranolol. The rise in coronary sinus CK activity was significantly diminished in the presence of either sotalol, (-)-propranolol or prazosin. These results suggest that the occurrence of severe ventricular arrhythmias upon reperfusion may be related to the action of the increased myocardial NE on the cardiac alpha-adrenoceptors. The increased coronary sinus CK activity suggests that increased cardiac sympathetic activation may accelerate or aggravate the myocardial damage. We conclude that the antiarrythmic effect of sotalol may be due at least in part to its inhibitory action on the release of cardiac NE upon reperfusion.     

Antagonistic action of AA-2414 on thromboxane A2/prostaglandin endoperoxide receptor in platelets and blood vessels

AA-2414, (+/-)-7-(3,5,6-trimethyl-1,4-benzoquinon-2-yl)-7-phenylheptanoi c acid, inhibited the aggregation of guinea pig platelets induced by a prostaglandin endoperoxide (PGH2) analogue, U-44069 and the specific binding of another analogue, [3H]U-46619 to washed guinea pig platelets with IC50 values of 3.1 x 10(-7) and 8.2 x 10(-9) M, respectively. AA-2414 competitively inhibited the contraction of rabbit aorta and pig coronary arteries induced by U-44069 with pA2 values of 8.3 and 9.0, respectively. AA-2414 also inhibited the contraction of rabbit aorta induced by PGF2 alpha (pA2: 7.8) and the contraction of pig coronary arteries induced by PGF2 alpha, PGD2 and 9 alpha,11 beta-PGF2 with pA2 values of 7.8, 8.6 and 7.8, respectively. But, AA-2414 had no effect on the antiaggregatory effect of PGD2 on the aggregation of guinea pig platelets. In experiments with guinea pigs ex vivo, AA-2414 (0.1-1 mg/kg, p.o.) dose-dependently inhibited the platelet aggregation induced by U-44069; the inhibition at a dose of 1 mg/kg was 100% at 1 hr and was 89% even at 24 hr after the administration. The thromboxane (TX) A2/PGH2 receptor antagonistic action of AA-2414 was stereospecific. These results show that AA-2414 is a potent, orally active and long acting TXA2/PGH2 receptor antagonist. In addition, AA-2414 has PGF2 alpha, PGD2 and 9 alpha,11 beta-PGF2 antagonistic effects.     

Suppression of reperfusion-induced arrhythmias with combined administration of 5-HT2 and thromboxane A2 antagonists.

1. The effects of the 5-HT2 antagonist, ICI 170,809 and the thromboxane A2 antagonist, ICI 192,605, given alone and in combination (n = 12 per group), were examined in anaesthetized rats. Haemodynamics and arrhythmias induced by permanent coronary artery occlusion or by reperfusion after 5 min of ischaemia were monitored. 2. In a study on reperfusion-induced arrhythmias, the only significant effect of ICI 170,809 (1 mg kg-1, i.v.) was a reduction in the number of ventricular premature beats (VPBs). ICI 192,605 (1 mg kg-1 min-1, i.v.) did not alter reperfusion-induced arrhythmias. However, in combination, when compared with controls, these drugs caused significant reductions in the incidence of ventricular tachycardia (VT), 100% to 58%; ventricular fibrillation (VF), 92% to 33%; and the mortality due to sustained VF, 67% to 17%. There was also a significant reduction in the number of VPBs following reperfusion. 3. In a second study with lower doses of drugs, ICI 170,809 (0.3 mg kg-1) and ICI 192,605 (0.3 mg kg-1 min-1) had no significant effects on reperfusion-induced arrhythmias either alone or in combination. 4. A third study examined the effects of the higher doses of the drugs on ischaemia-induced arrhythmias. Neither drug alone, nor in combination, altered the incidence of ischaemia-induced VT, VF, the mortality, or the number of VPBs. 5. These results indicate that, in contrast to the administration of either drug alone, combined administration of a 5-HT2 antagonist and a thromboxane A2 antagonist caused marked suppression of reperfusion-induced but not ischaemia-induced arrhythmias.     

Protective effects of trans-13-APT, a thromboxane receptor antagonist, in endotoxemia

The effect of the thromboxane A2/prostaglandin H2 (TxA2/PGH2) receptor antagonist trans-7[2-(p-hydroxyphenethylamino)-cyclopentyl]-heptanoic acid (trans-13-APT) on certain pathogenic sequelae of endotoxic shock and associated changes in arachidonic acid metabolism in the rat was investigated. trans-13-APT, an analog of 13-azaprostanoic acid, was synthesized and found to block human platelet aggregation induced by the thromboxane mimetic U46619. Pretreatment with trans-13-APT did not significantly alter the elevations in plasma immunoreactive (i) TxB2 or iPGE, 0.5 or 4 h after the intravenous administration of Salmonella enteritidis endotoxin. However, in the trans-13-APT-pretreated group, 4 h after administration of the endotoxin, plasma i6-keto-PGF1 alpha was significantly (p less than 0.05) reduced to 1.2 +/- 0.3 ng/ml (n = 17) compared with vehicle-treated rats (2.4 +/- 0.5 ng/ml; n = 18). The elevation in plasma i6-keto-PGF1 alpha seen 0.5 h (n = 17/group) after endotoxin infusion was not altered by trans-13-APT. trans-13-APT also significantly (p less than 0.05) attenuated the endotoxin-induced fall in platelet count (135 +/- 27 X 10(3)/mm3 vs. 350 +/- 65 X 10(3)/mm3 and hypoglycemia (73 +/- 9 vs. 97 +/- 7 mg/dl), but not the leukopenia. Since the reticuloendothelial system may be an important source of iTxB2 and i6-keto-PGF1 alpha during endotoxemia, in vitro studies were conducted with adherent peritoneal cells. High concentrations of trans-13-APT (50 and 100 microM) significantly reduced (p less than 0.05) basal but not endotoxin-induced synthesis of iTxB2 and i6-keto-PGF1 alpha by isolated adherent rat peritoneal cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a thromboxane receptor antagonist on prostaglandin D2 and histamine induced bronchoconstriction in man.

Many prostanoids including are prostaglandin (PG) F2 alpha and PGD2 are potent bronchoconstrictor agents. There is evidence to suggest that airway thromboxane (TP) receptor may act as a common receptor for their bronchoconstrictor actions. We tested the hypothesis that inhaled prostaglandin (PG) D2-induced bronchoconstriction is mediated by interacting with the TP receptor antagonist, ICI 192605, on the bronchoconstrictor response to inhaled PGD2 in a double-blind, placebo-controlled and crossed-over trial in normal subjects. The effect of ICI 192605 on histamine induced bronchoconstriction served as control for non-specific bronchodilatory actions. The study had two phases; the first consisted of two inhaled PGD2 challenge study days, and the second phase was that of inhaled histamine. Each study day was separated by at least a week. On each study day, the challenge tests were carried out 30 min after ingestion of 100 mg ICI 192605 or placebo. Doubling concentrations of agonist were given till more than 35% fall in post-diluent specific airway conductance (sGaw) occurred. The concentration needed to cause a fall in a sGaw of 35% post-diluent value (PC35sGaw) was then determined from linear interpolation of the log dose-response. Eight male subjects (median age 26, range 20-35 years) completed the study. ICI 192605 did not change baseline airway calibre 30 min after ingestion on either PGD2 or histamine study days. ICI 192605 significantly shifted the dose-response curve to inhaled PGD2 to the right by a median of 3.4 fold (Wilcoxon rank sign test, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding of a thromboxane A2/prostaglandin H2 receptor antagonist to guinea-pig platelets

The binding of [125I]9,11-dimethylmethano-11,12-methano-16-(3-iodo-4-hydroxypheny l)-13,14- dihydro-13-aza-15 alpha beta-omega-tetranor-TXA2 [( 125I]PTA-OH), a thromboxane A2/prostaglandin H2 receptor antagonist, to washed guinea-pig platelets was studied. [125I]PTA-OH bound to guinea-pig platelets in a saturable and displaceable manner. The Kd for [125I]PTA-OH was 14.5 +/- 2 nM (n = 4) and the Bmax was 32 +/- 7 fmol/10(7) platelets or 1,927 +/- 422 binding sites/platelet. The IC50 value for a series of 13-azapinane TXA2 analogs to antagonize the TXA2/PGH2 mimetic U46619-induced platelet aggregation and displace [125I]PTA-OH from its binding site was determined. The IC50 values for the series of five antagonists were highly correlated (r = 0.99) in the binding assays and aggregation studies. The ability of a series of five agonists to displace [125I]PTA-OH from its binding site was compared to their ability to induce platelet aggregation. All the agonists completely displaced the ligand from its binding site but their rank order did not correlate well with their ability to induce aggregation (r = 0.37). Collectively, the data are consistent with the notion that [125I]PTA-OH binds to a putative TXA2/PGH2 receptor in guinea-pig platelets.     

Effect of the opiate antagonist naloxone on digitalis induced cardiac arrhythmias

To test the hypothesis that the endogenous opioid system is operative in digitalis arrhythmias, guinea pigs anesthetized with pentothal and breathing spontaneously were allocated to a control group or four naloxone groups: 0.1 mg/kg i.v., 1.0 mg/kg i.v., 2 mg/kg i.v. or 4 mg/kg i.v. after the induction of arrhythmias by digoxin 100 micrograms/kg i.v. every 15 min. Naloxone at higher doses resulted in a rapid development of fatal arrhythmias with high degree AV block being more frequent than ventricular tachycardiac or fibrillation. Survival was significantly and inversely related to naloxone dose. The role of the autonomic nervous system was studied using cervical cord transection at the C7 level or bilateral cervical vagotomy, or atropine 1.2 mg/kg pretreatment. Cord transection, but not vagotomy, was associated with a significantly higher digoxin dose to produce arrhythmias. Naloxone 4 mg/kg i.v. shortened survival in cord transected animals, but less than in intact animals. Naloxone did not alter survival in vagotomized animals or animals that were pretreated with atropine. Thus, naloxone accelerates the development of fatal cardiac arrhythmias suggesting that endogenous opioids are involved in digitalis toxic arrhythmias an effect interrelated to the autonomic, mainly parasympathetic, nervous system.