Increased permeability of bovine aortic endothelial cell monolayers in response to a thromboxane A2-mimetic.

The present study was designed to investigate the ability of thromboxane to modulate the clearance rate of 125I-albumin through bovine aortic endothelial cell (BAEC) monolayer grown on polycarbonate micropore membrane. Stimulation of BAEC with the TXA2 mimetic U44069 (10(-8), 10(-7) and 10(-6) M) elicited a dose-dependent increase of labeled albumin passage across BAEC monolayers. This effect was markedly reduced by the TXA2 antagonist L655240 (10(-7) and 10(-6) M). Our results suggest that TXA2 may modulate the permeability of endothelial cells directly through activation of specific receptors.

The effects and molar potency of iloprost, U46619 and sodium nitroprusside on capsular and vascular smooth muscle of the isolated perfused canine spleen.

The isolated canine spleen was perfused at constant flow with continuous recording of splenic arterial perfusion pressure (SAPP) and spleen weight. Intra-arterial injections of the thromboxane A2 (TXA2) mimetic U46619 caused dose-related increases in splenic arterial perfusion pressure (SAPP) of short duration (ED50 0.31 nmol). There were very small changes in spleen weight accompanying any of the vasoconstrictor responses to U46619. The stable analogue of prostacyclin, iloprost, caused dose-dependent reductions in SAPP (ED50 1.3 nmol) indicating vasodilation. There were no changes in spleen weight to any doses of iloprost indicating a lack of action on capsular smooth muscle. Similarly, the nitric oxide (NO) mimetic sodium nitroprusside caused dose-related reductions in SAPP of short duration (ED50 5.8 nmol). No changes in spleen weight accompanied splenic vasodilator responses to any dose of sodium nitroprusside (SNP). The results indicate the potential actions and intrinsic potency of three endogenous vasoactive substances and provide information about their relative roles in the control of the splenic microcirculation in situations when they are released.

Effects of U46619 and of inhibitors of the synthesis of TXA2 on insulin action on the metabolism of labelled glucose in uteri isolated from ovariectomized-diabetic rats.

The production of 14CO2 from labelled glucose by isolated uterine strips from ovariectomized-diabetic rats has been studied. U46619, an analogue of TXA2 did not affect basal glucose metabolism; however, insulin-induced increment in CO2 production was completely blocked, both in ovariectomized (OVD) or ovariectomized-estrogenized (OVED) diabetic uterus. OKY064 as well as UK38485, both inhibitors of TXA2 synthesis, stimulated glucose metabolism (p < 0.05) similar to that of insulin in uterine tissue from OVD and OVED rats. Inhibition in the synthesis and release of TXB2 was detected (p < 0.01) by uterine radioconversion of 14C-arachidonic acid when adding OKY38485 to the incubation medium, and the production of other prostanoids such as 6-keto-PGF1 alpha, PGF2 alpha and PGE2 was enhanced. In summary, TXA2 inhibited insulin-induced glucose metabolism in diabetic animals.

Mechanisms involved in the contractile responses of kinins in rat portal vein rings: mediation by B1 and B2 receptors.

This study investigates the mechanisms involved in kinin-induced contractions in rings of rat portal vein (RPV). Bradykinin (BK), Lys-BK, Met-Lys-BK, Tyr8-BK (TBK) and des-Arg9-BK (DABK) all caused graded contractions in RPV, with the following order of potency (EC50, nanomolar): Met-Lys-BK (0.3) > Lys-BK (0.5) > BK (0.9) > TBK (2.3) >> DABK (46.0). The potency of DABK and maximal contractions for DABK and BK, but not for TBK or NE, increased as a function of in vitro incubation period, reaching the maximum at 4.5 hr. Cycloheximide (a protein synthesis inhibitor, 70 microM), incubated for 4.5 hr, inhibited almost completely the CRCs for DABK and blocked the latter phase of CRCs for BK, not altering contractions induced by U46619 (9,11-dideoxy-9 alpha, 11 alpha-methano-epoxy prostaglandin F2 alpha) (a thromboxane A2/prostaglandin H2-mimetic). Incubation of RPV with D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK (HOE 140, a selective B2 receptor antagonist, 0.01-100 nM), caused a parallel rightward displacement of the BK and TBK concentration-response curves (CRCs). Schild plots were linear, yielding pA2 values of 11.4 and 9.3, respectively. The slope for HOE 140 against TBK-induced contractions did not differ from unity (1.23 +/- 0.21), whereas against BK was significantly lesser than unity (0.72 +/- 0.20). The CRCs induced by DABK were not affected by HOE 140 (100 nM). In addition, the CRCs for DABK at 4.5 hr were shifted to the right in a parallel form in the presence of des-Arg9-[Leu8]-BK (a selective B1-receptor antagonist, 1 microM), yielding a pA2 value of 6.7.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of bradykinin mediating pertussis toxin-insensitive biphasic response in circular muscle of the isolated guinea pig ileum.

The mechanisms underlying the biphasic response (BR) of the circular muscle of the guinea pig ileum (CMGPI) to bradykinin (BK) have been examined. Both BK and lysyl-BK (1 nM to 1 microM) caused graded contractions followed by relaxations of the CMGPI, yielding EC50 of 21 and 92 nM for contraction and of 10 and 27 nM for relaxation, respectively. The selective B1 receptor agonist Des-Arg9-BK was without effect up to 3 microM. The potencies of BK and lysyl-BK to evoke BR were markedly increased by enalapril (3 microM) and decreased by raising the preparation tone with the thromboxane A2/prostaglandin H2-mimetic U46619 (30 ng/ml). The BR of CMGPI to BK was unaffected by atropine, yohimbine, pyrilamine, propranolol, prazosin, phorbol ester, des-Arg9-[leu8]-BK (1 microM, each), tetrodotoxin (0.3 microM), [3,4,5-trimethoxybenzoic acid-8-(diethylamino) octyl ester (10 microM), [N-6-(aminohexyl)-5-chloro-1-naphthalenosulfonamide (10 microM), glibenclamide (0.3 microM), nordihydroguaiaretic acid (50 microM), phenidone (30 microM) or dexamethasone (0.1 microM). However, indomethacin (3 microM), ibuprofen (30 microM) and 3-amino, 1-(m-[trifluoromethyl] phenyl)2-pyrazoline (10 microM) each abolished the relaxant and increased the contractile response to BK, suggesting that a cyclo-oxygenase-derived eicosanoid mediates relaxation and limits contraction. Prostaglandin (PG) E2 (up to 100 nM) caused only graded relaxations, PGF2 alpha (up to 3 microM) and 9,11-dideoxy-9 alpha,11 alpha-methanoepoxy prostaglandin F2 alpha (up to 300 ng/ml) caused only contractions and the PGI2 analog iloprost was without effect up to 1 micrograms/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

New approach to the mechanism of antiasthmatic action of Tranilast.

The mechanism proposed to explain the antiasthmatic antiallergic action of Tranilast is the inhibition of chemical mediator release from mast cells and leukocytes as well as the antagonism of smooth muscle contracting activity of leukotrienes. It has been shown that this drug inhibits platelet aggregation induced "in vitro" by different stimuli. We investigated the effect of Tranilast on the release of thromboxane from guinea pig isolated lungs stimulated by the calcium ionophore A 23187 and the contraction of smooth muscle induced by this eicosanoid. Tranilast did not inhibit the release of arachidonic acid metabolites from the lungs but it prevented the contraction of the rat aorta induced by thromboxane released from lungs. Moreover, the drug antagonized the contraction of rat and rabbit isolated aortas stimulated by the thromboxane/endoperoxide mimetic U 46619. These effects might be mediated by a blockade of calcium uptake, since the drug was able to induce the relaxation of rabbit aortas previously contracted by potassium. Calcium ions are involved in the activation of mast cells, leukocytes, platelets and smooth muscle; therefore, the inhibition of calcium uptake might mediate the pharmacological properties of Tranilast.

TXB2: cardiostimulant effect that involves beta-adrenoceptor and Na+ + K+-ATPase activity.

The biological properties of Thromboxane B2 (TXB2) on isolated rat heart were studied. Its actions were compared with U-46619 a Thromboxane A2 mimetic compound and with isoproterenol. TXB2 induced a concentration-dependent increase in contractility, that was non-competitively antagonized by propranolol. In addition TXB2 inhibited Na+ + K+-ATPase activity at the same concentrations that influenced the mechanical activity. Inhibition of beta-adrenoceptors efficiently blocked the inhibitory action of TXB2 upon Na+ + K+-ATPase-activity. Isoproterenol simulated the positive inotropic effect and the inhibitory action of TXB2 on Na+ + K+-ATPase-activity. In contrast, U-46619 did not alter the basal dF/dt, neither the enzyme activity. The foregoing results suggest that TXB2 resembles the biological effect of catecholamines-inducing stimulation of myocardial contractility and inhibition of Na+ + K+-ATPase activity.

Protective effects of the thromboxane receptor antagonists BM 13.177 and BM 13.505 against U 46619-induced sudden death in rats.

The purpose of this study was to evaluate the pharmacology and pharmacodynamics of the thromboxane receptor antagonists, BM 13.177 and BM 13.505, for prevention of U 46619-induced sudden death in anesthetized male Sprague-Dawley rats. The injection of U 46619 (100 micrograms/kg i.v.) produced sudden death typically between 5 and 15 min. Administration of 0.01 mg/kg BM 13.505 (i.v.) 0.1 h prior to the U 46619 challenge did not protect against sudden death, while doses of 0.03 mg/kg or greater protected completely (100% survival). A dose of 1 mg/kg BM 13.505 afforded protection to 2 h but not to 24 h, while a single dose of 30 mg/kg administered 24 h prior to the U 46619 challenge provided complete protection against the lethal event. Administration of BM 13.177 (30 mg/kg, i.v. or i.p.) blocked the effects of U 46619 when administered 0.1 h before the challenge, but not when given 2 or 3 h prior to the challenge with U 46619. Pretreatment with indomethacin did not block the effects of U 46619, indicating that formation of endogenous thromboxane does not play a major role in the lethal effects of U 46619, and that blockade of the lethal effects of U 46619 was specific for thromboxane receptor antagonists. These data demonstrate that BM 13.177 and BM 13.505 prevented sudden death produced by the injection of U 46619. At comparable doses of 30 mg/kg, the duration of action for BM 13.505 was was significantly greater than for BM 13.177. These data suggest that BM 13.177 and BM 13.505 may be useful for the investigation of diseases where thromboxane is involved.