15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and ifetroban

We tested the hypothesis that cyclooxygenase (COX), thromboxane A2 synthase (TxA2-S), thromboxane prostanoid receptors (TP-Rs), or superoxide anion (O2-) mediates enhanced contractions of renal afferent arterioles (Aff) of angiotensin II (Ang II)-infused rabbits. Rabbits were infused with vehicle (sham), Ang II 60 ng x kg(-1) x min(-1) (Ang II 60) or 200 ng x kg(-1) x min(-1) (Ang II 200). There was a selective enhanced vasoconstriction of Affs from Ang II 60 rabbits to Ang II (Deltadiameter-78+/-8% versus -43+/-9%; P<0.01) that was normalized by a TP-R antagonist but not by a superoxide dismutase (SOD) mimetic. Affs from Ang II 200 rabbits had increased (P<0.01) mRNA for COX-2 and enhanced vasoconstriction to Ang II, U-46 619 (TP-R mimetic), and endothelin-1 that was normalized by ifetroban plus tempol together. Endothelium removal enhanced Ang II responses of Affs from sham rabbits but blunted responses from Ang II 200 rabbits and abolished responses to ifetroban. Affs from Ang II 200 rabbits had an endothelium-dependent contraction factor (EDCF) response to that was blunted (P<0.001) by a SOD mimetic or antagonists of COX-1 or TxA2-S but normalized by antagonists of COX-2 or TP-R. Thus, enhanced Ang II responses in Affs from rabbits infused with slow pressor Ang II are mediated independently by O2- in the vascular smooth muscle cells and by an EDCF that is principally a vasoconstrictor prostaglandin generated by COX-2 >-1 activating TP-Rs, whereas enhanced responses in rabbits infused with a lower Ang II dose are dependent on TP-R but not O2-.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 8,11,14-Eicosatrienoic Acid; Angiotensin II; Animals; Arterioles; Bridged Bicyclo Compounds, Heterocyclic; Cyclic N-Oxides; Cyclooxygenase 2; Dose-Response Relationship, Drug; Endothelin-1; Endothelins; Endothelium, Vascular; Isoenzymes; Kidney; Male; Nitroarginine; Norepinephrine; Oxazoles; Oxidative Stress; Prostaglandin-Endoperoxide Synthases; Pyrazoles; Rabbits; Receptors, Thromboxane; RNA, Messenger; Spin Labels; Superoxides; Vascular Resistance; Vasoconstriction

These studies tested whether activation of central thromboxane (Tx)A2/prostaglandin (PG) H2 receptors raises blood pressure (BP). Messenger RNA for TxA2/PGH2 receptors was detected in normal Sprague-Dawley rat brain and in rat neuronal and astroglial brain cells in culture. The mean arterial blood pressure (MAP) was recorded in conscious rats during graded administration of the TxA2/PGH2 receptor agonist U-46,619 given intracerebroventricularly or intravenously. Because the pressor responses to intracerebroventricular (but not intravenous) U-46,619 were significantly greater in-high-salt compared with low-salt rats, high-salt rats were used for subsequent studies. The rise in MAP with intracerebroventricular administration of U-46,619 was greater than with intravenous administration and was more sustained. A comparison of plasma radioactivity after intracerebroventricular or intravenous injection of [3H]U-46,619 demonstrated that approximately 35% of the drug reached the systemic circulation by 5-15 min after intracerebroventricular administration. Coadministration of a TxA2/PGH2 antagonist, ifetroban, by intravenous or intracerebroventricular routes blocked the pressor responses induced by U-46,619. The half-maximal inhibition for blockade of responses was substantially lower for intracerebroventricular than for intravenous responses (intracerebroventricular: 0.03 +/- 0.01 vs. intravenous: 3.1 +/- 0.6 micrograms/kg; P < 0.001). The intravenous administration of ifetroban (10 micrograms/kg) caused a greater (P < 0.02) inhibition of pressor responses to U-46,619 (1 microgram/kg) given intravenously (81 +/- 3%) compared with U-46,619 given intracerebroventricularly (40 +/- 13%). In conclusion, TxA2/PGH2 receptor mRNA is expressed in neurons, glial, and brain stem of normal rats. The central administration of a TxA2/PGH2 mimetic raises blood pressure by interaction with specific central and peripheral receptors. This response is augmented in rats fed a high-salt compared with a low-salt diet.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Pressure; Brain Stem; Bridged Bicyclo Compounds, Heterocyclic; Gene Expression; Male; Oxazoles; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Sprague-Dawley; Receptors, Thromboxane; RNA, Messenger; Sodium Chloride, Dietary; Thromboxane A2

The thromboxane A2 (TxA2)/prostaglandin H2 (PGH2) receptor mimetic U-46619 (0.6 microgram.kg-1.min-1) was infused into conscious rats receiving a high-salt diet. U-46619 increased the mean arterial pressure (MAP) over 13 days by 25 +/- 2 mmHg, whereas the MAP of vehicle-infused controls did not change (-2 +/- 2 mmHg). In subgroups infused with U-46619, cardiac output was unchanged, whereas renal blood flow was reduced (before: 8.5 +/- 0.8; day 4: 5.7 +/- 0.7 ml/min; P < 0.01). Ifetroban (a specific TxA2/PGH2 receptor antagonist) reduced MAP to basal levels in the group receiving U-46619 when infused intravenously (1-100 micrograms/kg) but not intracerebroventricularly (1-100 ng/kg). Hexamethonium (10 mg/kg i.v., a ganglionic blocking agent) and prazosin (0.1 mg/kg, an alpha-adrenergic antagonist) decreased MAP significantly (P < 0.05) more in the experimental group (hexamethonium, U-46619: -55 +/- 3 vs. vehicle: -43 +/- 4 mmHg; and prazosin, U-46619: 28 +/- 3 vs. vehicle: 17 +/- 2 mmHg). In conclusion, hypertension during prolonged infusions of U-46619 into conscious, salt-loaded rats is accompanied by an increase in total and renal vascular resistance and is dependent on peripheral but not central TxA2/PGH2 receptors and on the autonomic and alpha 1-adrenergic peripheral sympathetic nervous systems.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Antihypertensive Agents; Blood Pressure; Bridged Bicyclo Compounds, Heterocyclic; Cardiac Output; Heart Rate; Hexamethonium; Hypertension; Male; Oxazoles; Prazosin; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Sprague-Dawley; Receptors, Prostaglandin; Receptors, Thromboxane; Receptors, Thromboxane A2, Prostaglandin H2; Renal Circulation; Sympathetic Nervous System; Thromboxane A2; Time Factors; Vasoconstrictor Agents

An experimental model of acute thrombosis was developed in pentobarbital- anesthetized ferrets. A 10-min anodal electrical stimulation of 1 mA was delivered to the external surface of the carotid artery while measuring carotid blood flow (CBF). This produced an occlusive thrombus in all vehicle-treated ferrets within 41 +/- 3 min with an average weight of 8 +/- 1 mg (n = 7). These thrombi were enriched in both platelets and fibrin and were adherent at the site of transmural vascular injury as determined by light and electron microscopy. To determine the model's sensitivity to antiplatelet drugs, aspirin or a thromboxane (TxA2) receptor antagonist (ifetroban) were administered 15 min before electrical stimulation. Thrombus weight was reduced 58% by aspirin (10 mg/kg, i.v.) and 74% by ifetroban (1 mg/kg + 1 mg/kg per hr, i.v.). Both drugs also improved CBF and decreased vascular occlusion. Ferrets were more sensitive than rats to aspirin's inhibition of collagen-induced platelet aggregation as determined ex vivo in whole blood. Separate in vitro platelet aggregation studies revealed species differences in reactivity to U-46619 (TxA2 receptor agonist) and collagen in the order of human > ferret > rat, with relatively lesser variations in ADP responses. These studies identify the ferret as a useful species for evaluating antithrombotic drugs in a model in which aspirin is efficacious.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aspirin; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Carotid Arteries; Carotid Artery Injuries; Collagen; Disease Models, Animal; Electric Stimulation; Ferrets; Fibrin; Humans; In Vitro Techniques; Male; Microscopy, Electron; Microscopy, Electron, Scanning; Oxazoles; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Prothrombin Time; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Species Specificity; Thrombosis; Thromboxane A2; Vasoconstrictor Agents

This study was designed to examine the impairment of endothelium-dependent relaxation in spontaneously hypertensive rats (SHR), to determine whether endothelial cell function is normalized by in vivo treatment with a thromboxane A2-prostaglandin endoperoxide (TP)-receptor blocker, and to establish whether endothelial dysfunction contributes to the elevated blood pressure. In isolated aortic rings from SHR, endothelium-dependent relaxations caused by acetylcholine, adenosine diphosphate, and alpha-thrombin were markedly impaired compared with those from Wistar-Kyoto (WKY) normotensive rats. Arachidonic acid-induced contractions were significantly enhanced in aorta from SHR. In contrast, relaxations caused by direct smooth muscle vasodilators, nitroprusside and cromakalim, and contractions caused by U-46619 were not different between SHR and WKY rats. Treatment of SHR with the oral TP-receptor antagonist, ifetroban, at 20 and 50 mg.kg-1.day-1 fully restored endothelium-dependent relaxation toward normal. However, ifetroban produced no effect on blood pressure in SHR. In vitro incubation of aortic rings from SHR with ifetroban also normalized relaxations to acetylcholine but had no effect in aorta from WKY. In contrast, the thromboxane A synthase inhibitor, dazoxiben, only partially improved abnormal acetylcholine-induced relaxations in aorta from SHR. The results demonstrate that endothelial cell dysfunction in hypertension can be restored to normal by selective TP-receptor blockade. Furthermore, endothelial cell dysfunction and TP-receptor activation may not significantly contribute to elevated systemic blood pressure in SHR.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aorta; Arachidonic Acid; Blood Pressure; Bridged Bicyclo Compounds, Heterocyclic; Endothelium, Vascular; Hypertension; Male; Oxazoles; Propionates; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Thromboxane; Thromboxane A2; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

180,291 1S-(1 alpha, 2 alpha, 3 alpha, 4 alpha)-2-[[3-[4- [(pentylamino)carbonyl]-2-oxazolyl]-7-oxabicyclo[2.2.1]hept- 2- yl]methyl]benzenepropanoic acid (BMS) is a potent and highly selective antagonist of thromboxane A2/prostaglandin endoperoxide (TP) receptors. In human platelet-rich plasma, BMS 180,291 inhibited platelet aggregation induced by arachidonate (800 microM) and U-46,619 (10 microM) with respective IC50 values of 7 +/- 1 (S.E.M.) and 21 +/- 2 nM. Inhibition of both the rate and full extent of 11,9-epoxymethano-prostaglandin H2 (U-46,619)-induced platelet aggregation were insurmountable at antagonist concentrations > 10 nM, but BMS 180,291 antagonized U-46,619-induced platelet shape change competitively with a KB of 11 +/- 2 nM. BMS 180,291 concentrations < or = 1 mM did not inhibit platelet aggregation induced by high concentrations of ADP (20 microM) or human alpha-thrombin (1 U/ml). BMS 180,291 inhibited binding of [3H]1S-[1 alpha,2 alpha(5Z),3 alpha,4 alpha]-7-[3-[[2- [(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]-hept-2- yl]-5-heptenoic acid to human platelet membranes with a kd of 4.0 +/- 1.0 nM and slope factor of 1.06 +/- 0.13. U-46,619-induced concentrations of rat aortae were competitively antagonized by BMS 180,291 with a KB of 0.6 +/- 0.1 nM. Aortic responses to norepinephrine, serotonin and angiotensin II were not inhibited by BMS 180,291 at 1 microM. U-46,619-induced contractions of guinea pig tracheal rings were antagonized in an almost all-or-none manner, with maximal blockade at > or = 1 nM BMS 180,291, but little effect at lower concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Administration, Oral; Animals; Aorta; Bridged Bicyclo Compounds, Heterocyclic; Cattle; Coronary Vessels; Dinoprostone; Fatty Acids, Unsaturated; Guinea Pigs; Humans; Hydrazines; In Vitro Techniques; Male; Mice; Muscle Contraction; Oxazoles; Platelet Aggregation; Propionates; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Sprague-Dawley; Receptors, Prostaglandin; Receptors, Thromboxane; Swine; Thromboxane B2; Trachea

The effects of the novel TxA2/prostaglandin endoperoxide (TP) receptor antagonist BMS 180,291 on platelet reactivity was determined ex vivo in conscious African green monkeys. Platelet aggregation responses to U-46,619 were decreased 50% and 100% at 23 to 24 hrs after BMS 180,291 oral doses of 1 and 3 mg/kg, respectively. In addition to inhibiting aggregation, a 3 mg/kg oral dose of BMS 180,291 also produced an 11 +/- 3-fold shift to the right in the U-46,619 concentration-response relationship for platelet shape change at 24 hrs after dosing. When the 3 mg/kg oral dose was continued for 11 days, the shift in this concentration-response relationship increased to 26 +/- 10- and 93 +/- 30-fold at 24 hrs after the 8th and 11th doses, respectively. This progressive inhibition corresponds to 93 +/- 3 and 99 +/- 1% blockade of platelet TP-receptors responsible for shape change, respectively. Comparable levels of TP-receptor blockade have been previously correlated with antithrombotic and antiischemic activities of TP-receptor antagonists in vivo. Platelet reactivity to U-46,619 had completely recovered on the 7th day after the final dose of BMS 180,291, indicating effective elimination from the circulation over this interval. In separate experiments, a 3-mg/kg i.v. dose of BMS 180,291 produced only marginal and transient hemodynamic effects in anesthetized African green monkeys. Overall, these data demonstrate that BMS 180,291 given orally once a day produces a sustained and therapeutically-relevant level of TP-receptor antagonism.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Chlorocebus aethiops; Dose-Response Relationship, Drug; Drug Administration Schedule; Oxazoles; Platelet Aggregation; Platelet Aggregation Inhibitors; Propionates; Prostaglandin Endoperoxides, Synthetic; Receptors, Thromboxane; Thromboxane A2