In vivo effects of a novel thromboxane A2/prostaglandin H2 (TXA2/PGH2) partial agonist, (+)5(Z)-7-[3-endo-phenylsulfonylamino[2.2.1]- bicyclohept-2-exo-yl]-heptenoic acid [(+)-S-145], on vascular, platelet and cardiac function.

A novel thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor ligand, (+)5(Z)-7-[3-endo-phenylsulfonylamino[2.2.1]-bicyclohept-2-e xo- yl]-heptenoic acid [(+)-S-145], was evaluated in guinea pigs to assess the in vivo pharmacodynamic profile of this compound at vascular, cardiac and platelet TXA2/PGH2 receptors. Comparison was made to the TXA2/PGH2 receptor antagonist SQ29548. Upon i.v. injection, (+)-S-145, but not SQ29548, elicited transient (approximately 1 min) increases in mean arterial blood pressure (ED50 +/- 95% confidence limit = 6.1 + 4.0, -2.2 micrograms/kg). The potency of i.v. (+)-S-145 (ID50 = 6.3 + 2.3, -2.3 micrograms/kg) against the pressor response to subsequent i.v. TXA2/PGH2 mimetic, U44069, was 9.5-fold greater than that of SQ29548 (ID50 = 59.1 + 52.9, - 52.9 micrograms/kg). Intravenous (+)-S-145 inhibited U44069-induced decreases in circulating platelet count (ID50 = 4.2 + 4.1, - 2.0 micrograms/kg). In thoracotomized guinea pigs, i.v. (+)-S-145 (31.6 micrograms/kg) and increasing i.v. doses of U44069 increased mean arterial blood pressure, total peripheral resistance, left ventricular end-diastolic pressure and left ventricular peak positive dP/dt (LV + dP/dt) and depressed cardiac output (P < .05). Pretreatment with i.v. (+)-S-145 (31.6 micrograms/kg) abolished these U44069-induced effects. In thoracotomized guinea pigs in which left ventricular end-diastolic pressure and HR were held constant, U44069 again increased LV + dP/dt (P < .05), but (+)-S-145 decreased LV + dP/dt (P < .05), which indicates the lack of an (+)-S-145 direct inotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of thromboxane A2/prostaglandin H2 binding sites in guinea pig cardiac membrane preparations.

Thromboxane A2 (TXA2) and prostaglandin H2 (PGH2) induce platelet aggregation and are potent vasoconstrictors, and they have been implicated in coronary vasospasm and myocardial infarction. The TXA2 mimetic [1S-(1 alpha, 2 beta (5Z), 3 alpha (1E,3S*), 4 alpha)]-7-[3-(3-hydroxy-4-(4'- iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1]heptan-2-yl]-5-h eptenoic acid (IBOP) was used to characterize binding to microsomal membrane preparations from saline-perfused guinea pig atria (GPA) and ventricles (GPV). [125I]IBOP bound to GPA and GPV in a protein-dependent and saturable manner, although total binding was two-fold greater and non-specific binding was proportionately less in GPA compared to GPV. Analysis of equilibrium binding data indicated one class of binding sites in both GPA and GPV with Kd values of 333 +/- 117 and 645 +/- 187 pM, respectively, which were in close agreement with kinetically determined Kd values of 226 and 882 pM, respectively. Bmax values of GPA and GPV of 57 +/- 5.6 and 24 +/- 4.3 fmol/mg protein were significantly different (P < 0.01). Ki values (from IC50s) were determined for various TXA2/PGH2 analogues and prostaglandins in competition binding assays with [125I]IBOP. The rank order for ability to inhibit binding in GPA was U46619 = SQ29548 > I-PTA-OH > PGF2 alpha = PGE2. In GPV, the rank order was U46619 = SQ29548 > PGF2 alpha = I-PTA-OH = PGE2. [125I]IBOP binding to GPA and GPV was completely displaced by the TXA2/PGH2 agonist U46619 and by the TXA2/PGH2 antagonist SQ29548.(ABSTRACT TRUNCATED AT 250 WORDS)

Dipyridamole directly inhibits vascular smooth muscle cell proliferation in vitro and in vivo: implications in the treatment of restenosis after angioplasty.

OBJECTIVES: The effect of dipyridamole on smooth muscle cell proliferation and prevention of intimal thickening after arterial injury was investigated. BACKGROUND: In addition to antiplatelet activity, dipyridamole also inhibits cell proliferation. We examined whether the antiproliferative action of dipyridamole on smooth muscle cells, as demonstrated here, has a direct effect on intimal thickening after vascular injury. METHODS: Cell proliferation was determined by measuring deoxyribonucleic acid (DNA) synthesis and by cell counting. The in vivo effect of locally delivered dipyridamole was determined in a rabbit model with carotid or femoral artery injury. RESULTS: Dipyridamole produced a dose-dependent inhibition of smooth muscle cell proliferation, producing 50% inhibition at 7 micrograms/ml. Structural analogues SH-869 and mopamidol were 10 to 100 times less effective than dipyridamole, suggesting that cell growth inhibition may be unrelated to the antiplatelet activity of dipyridamole. Inhibition of cell proliferation by dipyridamole was attenuated by increasing the serum concentration in the culture medium. Bypassing serum by local delivery of dipyridamole at the periadventitial site produced 63% inhibition (p < 0.05) of cell replication in balloon-injured arteries. Locally delivered dipyridamole also inhibited intimal thickening (20%, p < 0.05) after balloon injury. CONCLUSIONS: Dipyridamole inhibited smooth muscle cell proliferation in vitro. This activity was attenuated by serum proteins. Locally delivered dipyridamole inhibited cell replication in arteries and intimal thickening after balloon injury. These results suggest that although systemic treatment with dipyridamole may not be efficacious because of inadequate serum levels, its antiproliferative action on smooth muscle cells may reduce restenosis when the drug is delivered locally after coronary angioplasty.

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.

Characterization of a thromboxane A2/prostaglandin H2 receptor in guinea pig lung membranes using a radioiodinated thromboxane mimetic.

Thromboxane A2 (TXA2) and prostaglandin H2 (PGH2) are potent constrictors of airway smooth muscle and may mediate some of the pulmonary effects of leukotrienes. To date, the TXA2/PGH2 receptor in lung has not been well characterized. In this report, we describe the evaluation of the TXA2/PGH2 receptor in guinea pig lung membranes using the new radiolabeled TXA2 mimetic [1S(1 alpha,2 beta(5Z),3 alpha(1E,3S*),4 alpha)]-7-[3-(3-hydroxy-4-(4'- iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1]heptan-2-yl]-5-h eptenoic acid (IBOP). IBOP elicited a dose-dependent contraction of guinea pig lung parenchymal strips (EC50 = 3.03 +/- 0.97 nM, three experiments), which was blocked by the TXA2/PGH2 antagonists SQ29548 (pKB = 7.44 +/- 0.2, three experiments), BM13505 (pKB = 6.29 +/- 0.26, three experiments), and I-PTA-OH (pKB = 5.82 +/- 0.36, three experiments). In radioligand binding studies, the binding of [125I]IBOP to guinea pig lung membranes prepared from perfused lungs was saturable, displaceable, and dependent upon protein concentration. Binding was optimal at pH 6.5 and was enhanced by the addition of mono- and divalent cations. The standard assay buffer was 25 mM 3-(N-morpholino)propanesulfonic acid, pH 6.5, 100 mM NaCl, 5 mM MgCl2. Binding was inhibited by pretreatment with dithiothreitol, N-ethylmaleimide, or beta-mercaptoethanol. Binding was unaffected by the addition of guanine nucleotide analogs at concentrations up to 300 microM. Analysis of the time course of binding of [125]IBOP at 30 degrees yielded k-1 = 0.0447 min-1, k1 = 2.49 x 10(8) M-1 min-1, and Kd = k-1/k1 = 180 pM. Computer analysis of equilibrium binding studies using nonlinear methods (LUNDON-1) revealed a single class of noninteracting binding sites with a Kd of 86.9 +/- 11.9 pM and a Bmax of 81.8 +/- 7.7 fmol/mg of protein (three experiments). [125I]IBOP binding to guinea pig lung membranes was inhibited by a series of TXA2/PGH2 receptor agonists and antagonists, with a rank order different from that previously determined for washed guinea pig platelets (Spearman's r = 0.686, p greater than 0.05). [125I]IBOP binding to guinea pig lung membranes was also inhibited by the prostanoids prostaglandin D2, prostaglandin E2, prostaglandin F2 alpha, and 9 alpha,11 beta-prostaglandin F2, all of which have been proposed to act at the TXA2/PGH2 receptor in lung.

Effect of l-propoxyphene on plasma levels and analgesic activity of d-propoxyphene in the rat.

Oral administration of l-propoxyphene with d-propoxyphene enhances the analgesic activity of d-propoxyphene as expressed in the rat tail heat test. The combination of d- and l-propoxyphene at a dose of 10 mg/kg each was found to have activity in the analgesic assay equivalent to that observed with d-propoxyphene at a dose of 20 mg/kg. In the same test, l-propoxyphene at a dose of 40 mg/kg had no activity. Co-administration of equal amounts of l-propoxyphene with d-propoxyphene (10 mg/kg p.o.) results in an increase in circulating plasma levels of d-propoxyphene from 9 +/- 2 to 114 +/- 39 ng/ml 15 minutes after administration. The increase in plasma levels is accompanied by a proportional increase in the brain and lung levels with no significant change in the liver levels. When d-propoxyphene (4 mug/ml) was infused in the isolated perfused rat liver, over 98% of the drug was extracted in a single pass through the liver. When l-propoxyphene was added to the perfusate (4 mug/ml), the extraction of d-propoxyphene was decreased to less than 90%. These results indicate that l-propoxyphene increases the systemic availability of d-propoxyphene by altering the amount of d-propoxyphene extracted by the liver.